Dopamine deficiency in the substantia nigra causes Parkinson’s disease.

GABA-A receptors are ligand-gated chloride channels; activation increases Cl⁻ influx causing hyperpolarization and inhibition.

Nicotinic Nm receptors are located at the neuromuscular junction and mediate skeletal muscle contraction.

Glutamate is the main excitatory neurotransmitter in the CNS, acting on NMDA and AMPA receptors.

Local anaesthetics block voltage-gated sodium channels, preventing depolarization and nerve impulse conduction.

Tryptophan is converted to 5-hydroxytryptophan, then to serotonin.

Beta-1 receptors in the heart increase heart rate and contractility when stimulated by norepinephrine.

GPCRs activate G-proteins that modulate adenylyl cyclase (cAMP) or phospholipase C (IP3/DAG).

Benzodiazepines increase the frequency of Cl⁻ channel opening when GABA binds.

Lorazepam is preferred because it has rapid onset and longer duration of action in the brain (less redistribution).

Flumazenil competitively antagonizes benzodiazepines at GABA-A receptors.

Midazolam has a short half-life (~2 hours), rapid onset, and causes anterograde amnesia, making it ideal for procedures.

Barbiturates prolong the duration that chloride channels stay open when GABA binds.

Thiopental (ultra-short-acting) causes rapid induction due to high lipid solubility.

Phenobarbital is a potent inducer of CYP3A4 (and CYP2C9), increasing metabolism of many drugs including warfarin and oral contraceptives.

Lorazepam (also oxazepam, temazepam) undergoes glucuronidation only–”LOT” drugs.

Abrupt benzodiazepine withdrawal can cause rebound anxiety, tremors, and seizures due to CNS hyperexcitability.

Zolpidem selectively binds alpha-1 subunits, providing hypnotic effect with less anxiolytic/muscle relaxant action.

Caffeine competitively blocks adenosine receptors, preventing adenosine’s sedative effects.

Caffeine (as caffeine citrate) is preferred for neonatal apnoea due to wider therapeutic index, longer half-life, and less toxicity than theophylline.

Doxapram stimulates peripheral chemoreceptors and medullary respiratory centres, increasing ventilation.

Theophylline toxicity causes seizures, arrhythmias, nausea, and vomiting.

Sibutramine (serotonin-norepinephrine reuptake inhibitor for obesity) increased risk of heart attacks and strokes, leading to withdrawal.

Theophylline has the most potent cardiac effects (arrhythmias, tachycardia) among methylxanthines.

Theobromine is abundant in cocoa/chocolate products.

Modafinil inhibits dopamine reuptake, increasing dopaminergic transmission, promoting wakefulness with lower abuse potential than amphetamines.

SSRIs (Selective Serotonin Reuptake Inhibitors) like fluoxetine specifically block serotonin transporter.

Fluoxetine and its active metabolite (norfluoxetine) have half-lives of 4-6 days, minimizing withdrawal.

Amitriptyline has the highest anticholinergic and cardiotoxic effects (arrhythmias, QT prolongation) among TCAs.

MAOIs prevent tyramine breakdown; tyramine in aged cheese/wine causes norepinephrine release, leading to hypertensive crisis.

Aged cheese contains high tyramine levels, which can precipitate hypertensive crisis in MAOI users.

Serotonin syndrome triad: mental status changes (agitation/confusion), autonomic instability (hyperthermia, tachycardia), and neuromuscular abnormalities (rigidity, clonus, hyperreflexia).

Combining MAOIs with SSRIs dramatically increases serotonin, causing serotonin syndrome.

Bupropion (dopamine-norepinephrine reuptake inhibitor) is FDA-approved for smoking cessation (as Zyban) and depression (as Wellbutrin).

John’s Wort induces CYP3A4 (and P-glycoprotein), reducing effectiveness of oral contraceptives, warfarin, cyclosporine, and HIV medications.

Anticholinergic effects include urinary retention, dry mouth, constipation, blurred vision, and tachycardia.

Lithium, atypical antipsychotics (aripiprazole, quetiapine), or thyroid hormone (T3) are added to augment antidepressant response in treatment-resistant depression.

Bupropion lowers seizure threshold dose-dependently, especially in high doses or eating disorders.

ECT is highly effective for severe/treatment-resistant depression, especially with psychotic features, catatonia, or suicidality.

Duloxetine (SNRI) is approved for depression, generalized anxiety, diabetic neuropathy, and fibromyalgia.

Typical antipsychotics (haloperidol) cause high EPS (dystonia, akathisia, parkinsonism, tardive dyskinesia) due to D2 blockade.

Clozapine causes agranulocytosis (1-2%), requiring weekly-to-monthly WBC/ANC monitoring.

Olanzapine and clozapine cause the most weight gain/metabolic effects.

Dopamine normally inhibits prolactin release; D2 blockade in tuberoinfundibular pathway removes this inhibition, causing hyperprolactinaemia (galactorrhoea, amenorrhoea).

NMS presents with hyperthermia, severe muscle rigidity (“lead pipe”), altered consciousness, and autonomic instability.

Aripiprazole is a D2 partial agonist (“dopamine system stabilizer”), reducing EPS and prolactin elevation.

Benztropine (anticholinergic) or diphenhydramine rapidly reverses acute dystonia by restoring dopamine-acetylcholine balance.

Clozapine is the only antipsychotic proven effective for treatment-resistant schizophrenia (after 2 adequate trials fail).

Lithium has a narrow therapeutic index (0.6-1.2 mEq/L) and causes hypothyroidism and nephrogenic diabetes insipidus, requiring regular monitoring.

Thiazides increase lithium reabsorption in proximal tubule (compensating for sodium loss), raising lithium levels.

Lithium toxicity causes coarse tremor (fine tremor is therapeutic side effect), ataxia, confusion, seizures, and arrhythmias.

Valproate causes neural tube defects (spina bifida) in 1-2% of exposures – highest among anti-seizure drugs.

Lamotrigine causes SJS/TEN, especially with rapid titration or valproate co-administration (which doubles lamotrigine levels).

Carbamazepine induces CYP3A4, increasing its own metabolism (autoinduction), requiring dose adjustments after 2-4 weeks.

Disulfiram blocks aldehyde dehydrogenase, causing acetaldehyde accumulation with alcohol → flushing, nausea, tachycardia.

Long-acting benzodiazepines (diazepam, chlordiazepoxide) prevent withdrawal seizures via GABA enhancement.

Naloxone is a competitive opioid receptor antagonist, rapidly reversing respiratory depression.

Mu receptors (MOR) mediate analgesia, euphoria, respiratory depression, and dependence.

Buprenorphine is a partial mu agonist with a ceiling effect on respiratory depression, making it safer for chronic use and opioid use disorder treatment.

Methadone has a long half-life (24-36 hours), good oral bioavailability, and prevents withdrawal without significant euphoria at stable doses, enabling once-daily dosing.

Opioid overdose triad: miosis (pinpoint pupils), respiratory depression, and CNS depression.

Suboxone contains buprenorphine + naloxone.

Cocaine blocks dopamine reuptake in the mesolimbic pathway, causing euphoria and addiction.

MDMA releases serotonin massively, causing hyperthermia, bruxism (jaw clenching), empathy, and potentially serotonin syndrome.

THC in cannabis activates CB1 receptors in the CNS, causing euphoria, altered perception, and appetite stimulation.

PCP is an NMDA receptor antagonist, causing dissociation, hallucinations, and agitation.

IV benzodiazepines (lorazepam preferred, diazepam alternative) are first-line for status epilepticus, followed by phenytoin/fosphenytoin if seizures persist.

Purkinje cells and hippocampal pyramidal neurons (CA1) are most vulnerable to hypoxia due to high metabolic demands.

Red neurons (eosinophilic, shrunken neurons with pyknotic nuclei) represent early coagulative necrosis occurring 12–24 hours post-ischemia.

CA1 (Sommer sector) is most vulnerable to global ischemia due to high glutamate receptor density causing excitotoxicity.

Watershed (border zone) infarcts occur at junctions between arterial territories (e.g., ACA-MCA, MCA-PCA) during global hypoperfusion.

Layers 3 and 5 (pyramidal cell layers) are most vulnerable to hypoxia due to high metabolic activity.

Hypertension causes 50–60% of spontaneous intracerebral hemorrhages, typically in basal ganglia, thalamus, pons, and cerebellum.

Charcot-Bouchard microaneurysms form in small penetrating arteries (lenticulostriate) due to chronic hypertension and rupture causes deep hemorrhage.

Putamen/basal ganglia (60%) is the most common site, followed by thalamus, pons, and cerebellum.

Middle meningeal artery rupture (usually from temporal bone fracture) causes epidural hematoma with characteristic lens-shaped appearance.

Bridging veins cross subdural space and tear with head trauma, especially in elderly with brain atrophy.

Epidural hematoma appears biconvex/lens-shaped because dura is tightly attached to skull, limiting spread.

Epidural hematoma classically presents with initial loss of consciousness, lucid interval, then rapid deterioration as hematoma expands.

MCA supplies lateral cerebral cortex (face/arm motor area), causing contralateral face and arm weakness with relative leg sparing.

ACA supplies medial frontal cortex including leg motor area on medial surface.

Basilar artery occlusion affecting ventral pons destroys corticospinal and corticobulbar tracts, causing quadriplegia and anarthria with preserved consciousness and vertical eye movements.

PICA occlusion causes lateral medullary infarction presenting with ipsilateral facial sensory loss, Horner syndrome, ataxia, and contralateral body pain/temperature loss.

Lacunar infarcts (<15mm) occur in territories of small penetrating arteries, commonly in basal ganglia, thalamus, internal capsule, and pons due to lipohyalinosis from hypertension/diabetes.

Atherothromboembolism (from carotid, aortic, or cardiac sources) causes ~85% of ischemic strokes.

Ruptured berry (saccular) aneurysms cause ~85% of non-traumatic SAH, typically at Circle of Willis branch points.

Anterior communicating artery (30–35%) is the most common site, followed by posterior communicating artery and MCA bifurcation.

ADPKD has strong association with berry aneurysms (10–30% of patients) due to defective extracellular matrix proteins.

SAH presents with sudden “worst headache of my life” reaching maximum intensity within seconds (thunderclap).

Xanthochromia (yellow CSF) results from bilirubin released during RBC breakdown, appearing >12 hours after SAH and persisting 2–4 weeks.

Cerebral vasospasm (days 4–14) is the leading cause of morbidity/mortality after initial SAH, causing delayed ischemic deficits.

Alzheimer’s shows extracellular amyloid (Aβ) plaques and intracellular neurofibrillary tangles (hyperphosphorylated tau).

Neurofibrillary tangles contain hyperphosphorylated tau forming paired helical filaments inside neurons.

Amyloid plaques contain Aβ peptide (especially Aβ42) derived from amyloid precursor protein (APP) cleavage.

PSEN1 mutations cause ~70% of familial early-onset AD.

APOE ε4 is the strongest genetic risk factor for sporadic late-onset AD, increasing risk 3-fold (heterozygous) to 15-fold (homozygous).

Entorhinal cortex and hippocampus show earliest pathology, explaining initial memory impairment.

Lewy bodies (eosinophilic intracytoplasmic inclusions with halo) in substantia nigra are pathognomonic of Parkinson’s.

Lewy bodies contain aggregated alpha-synuclein (hence “synucleinopathy”).

Substantia nigra shows depigmentation due to loss of neuromelanin-containing dopaminergic neurons.

Dopamine deficiency in nigrostriatal pathway causes motor symptoms (tremor, rigidity, bradykinesia).

Clinical symptoms manifest when 70–80% of striatal dopamine is lost, reflecting significant compensatory reserve.

Huntington’s is caused by CAG trinucleotide repeat expansion (>40 repeats) in huntingtin gene on chromosome 4, encoding polyglutamine.

Caudate nucleus atrophy with loss of medium spiny neurons is characteristic, causing “box-car” ventricles on imaging.

Huntington’s is autosomal dominant with complete penetrance if >40 CAG repeats.

Anticipation occurs due to CAG repeat expansion during transmission (especially paternal), causing earlier onset in offspring.

Friedreich ataxia results from GAA repeat expansion in frataxin gene (chromosome 9), causing mitochondrial iron accumulation.

SCAs affect cerebellum, spinocerebellar tracts, and brainstem, causing progressive ataxia.

ALS affects both UMNs (corticospinal tracts) and LMNs (anterior horn cells), causing combined spasticity/hyperreflexia and muscle wasting/fasciculations.

C9orf72 hexanucleotide repeat expansion is the most common cause of familial ALS (~40%) and frontotemporal dementia.

Extraocular muscles are spared in ALS, differentiating it from myasthenia gravis.

Werdnig-Hoffmann (SMA type 1) is the most severe spinal muscular atrophy with LMN degeneration presenting in infancy with hypotonia (“floppy baby”).

Bunina bodies (small eosinophilic inclusions in motor neurons) are characteristic of ALS.

Group B Streptococcus (Streptococcus agalactiae) and E. coli are most common in neonates (acquired from birth canal).

Streptococcus pneumoniae is the most common cause in adults, followed by N. meningitidis.

Bacterial meningitis shows elevated protein (>100 mg/dL), decreased glucose (<40 mg/dL or <50% serum), and neutrophilic pleocytosis.

Viral meningitis shows lymphocytic pleocytosis, mildly elevated protein, and normal glucose (viruses don’t consume glucose like bacteria).

Neisseria meningitidis causes fulminant meningococcemia with DIC, bilateral adrenal hemorrhage, and shock (Waterhouse-Friderichsen syndrome).

TB meningitis shows lymphocytic pleocytosis, elevated protein, and characteristically low glucose (similar to bacterial).

HSV-1 causes most sporadic viral encephalitis, characteristically affecting temporal lobes.

HSV-1 has tropism for temporal lobes (especially inferomedial), causing hemorrhagic necrotizing encephalitis.

Negri bodies (eosinophilic cytoplasmic inclusions in hippocampal pyramidal neurons and Purkinje cells) are pathognomonic of rabies.

Cowdry type A inclusions (eosinophilic intranuclear inclusions with halo) occur in HSV and VZV infections.

Direct extension from sinusitis, otitis media, or mastoiditis is most common (~40–50%), followed by hematogenous spread.

Otogenic abscesses spread to adjacent temporal lobe or cerebellum.

Streptococci (especially viridans and microaerophilic) are most common, often in mixed infections.

Brain abscess shows ring enhancement (contrast uptake by capsule) with central hypodensity (necrosis/pus).

Toxoplasma encephalitis is an AIDS-defining illness, occurring when CD4 <100 cells/μL due to reactivation of latent infection.

Toxoplasmosis shows multiple ring-enhancing lesions, commonly in basal ganglia and corticomedullary junction.

Cats are definitive hosts where sexual reproduction occurs; oocysts shed in feces infect humans.

Glioblastoma (WHO grade IV) is the most common malignant primary brain tumor in adults, followed by meningioma (most common benign).

Pilocytic astrocytoma (WHO grade I) is the most common pediatric brain tumor, typically in cerebellum.

Pseudopalisading necrosis (tumor cells arranged around necrotic areas) is a histologic hallmark of glioblastoma along with microvascular proliferation.

Oligodendroglioma shows round cells with clear cytoplasm and central nucleus (“fried egg” artifact from formalin fixation).

Psammoma bodies (laminated calcifications) are characteristic of meningiomas, also seen in papillary thyroid carcinoma and serous ovarian tumors.

Meningiomas arise from arachnoid cap (meningothelial) cells of arachnoid villi.

Medulloblastoma arises in cerebellar vermis (midline) in children, can spread via CSF.

Homer Wright rosettes (tumor cells around neuropil core, no central lumen) are characteristic of medulloblastoma and neuroblastoma.

MS is characterized by inflammatory demyelination with relative axonal preservation initially (though axonal loss occurs later).

Relapsing-remitting MS (RRMS) accounts for ~85% of initial presentations, with discrete attacks followed by recovery.

Oligoclonal IgG bands in CSF (absent in serum) indicate intrathecal antibody synthesis, present in >90% of MS patients.

Dawson fingers are periventricular demyelinating lesions oriented perpendicular to ventricles (along medullary veins), characteristic of MS on MRI.

Wallerian degeneration is degeneration of the axon and myelin distal to injury site, occurring within days.

Seddon classification includes neurapraxia (conduction block, best prognosis), axonotmesis (axon disrupted, endoneurium intact), and neurotmesis (complete transection, worst prognosis).

Neurapraxia is focal demyelination/conduction block with intact axon, allowing rapid recovery (weeks) once myelin repairs.

GBS presents with acute ascending flaccid paralysis, areflexia, and albumino-cytologic dissociation in CSF.

Albumino-cytologic dissociation (elevated protein >45 mg/dL with <10 cells/μL) is classic CSF finding in GBS due to blood-nerve barrier disruption without inflammation in CSF space.

MG is caused by autoantibodies against nicotinic acetylcholine receptors at neuromuscular junction, causing fatigable weakness.

10–15% of MG patients have thymoma; thymectomy can be beneficial.

Fatigable weakness (improves with rest, worsens with use) is the hallmark of MG due to progressive ACh receptor blockade.

NF1 results from NF1 gene mutation on chromosome 17 encoding neurofibromin (tumor suppressor).

≥6 café-au-lait spots (>5mm prepubertal, >15mm postpubertal) are diagnostic criterion for NF1.

Bilateral vestibular (acoustic) schwannomas are diagnostic of NF2 (chromosome 22, NF2/merlin gene).

Lisch nodules are pigmented iris hamartomas, present in >90% of adult NF1 patients, useful for diagnosis.

NF1 gene encodes neurofibromin, a GTPase-activating protein that inactivates RAS.

Vestibular schwannomas are the hallmark of NF2, followed by meningiomas (multiple) and spinal ependymomas.

Plexiform neurofibromas (diffuse, “bag of worms”) are pathognomonic of NF1 and can undergo malignant transformation (5–10%).

Carbon monoxide (CO) is the classic cerebral poison.

Carboxyhemoglobin gives the characteristic cherry-red or bright pink color to blood, skin, and viscera in CO poisoning.

In Pakistan, being an Islamic country, alcohol consumption is prohibited for Muslims.

Alcohol dehydrogenase (ADH) is the primary enzyme metabolizing ethyl alcohol in the liver, converting it to acetaldehyde.

Ethyl alcohol follows zero-order kinetics and is eliminated at a constant rate of approximately 15-20 mg% (average 15 mg%) per hour, regardless of blood concentration.

Respiratory depression and respiratory arrest is the primary cause of death in acute alcohol intoxication.

Alcohol causes mydriasis (dilated pupils), not miosis.

Blindness is the hallmark of methyl alcohol (methanol) poisoning.

Formic acid (and formaldehyde) are the toxic metabolites of methanol.

Ethyl alcohol (ethanol) is the classic antidote for methanol poisoning.

Thiopental is an ultra-short acting barbiturate (duration <30 minutes), used for induction of anesthesia.

Barbiturate blisters (bullous skin lesions) are pathognomonic of barbiturate poisoning, found at pressure points.

Diazepam has a long half-life of 20-100 hours, with active metabolites extending duration further.

Flumazenil is the specific competitive antagonist at GABA-A benzodiazepine receptors.

Suicidal ingestion is the most common manner of organophosphate poisoning in Pakistan and other developing countries due to easy availability of agricultural pesticides.

Organophosphates irreversibly inhibit acetylcholinesterase, causing accumulation of acetylcholine at muscarinic and nicotinic receptors.

DUMBELS represents muscarinic effects: Diarrhea, Urination, Miosis, Bradycardia/Bronchospasm/Bronchorrhea, Emesis, Lacrimation, Salivation.

Atropine + Pralidoxime (2-PAM) is the standard treatment.

Intermediate syndrome occurs 24-96 hours after acute cholinergic crisis resolution.

Carbamates cause reversible (temporary) acetylcholinesterase inhibition, unlike the irreversible binding of organophosphates.

Aluminum phosphide (celphos/wheat pill) releases phosphine gas which causes severe myocardial toxicity and refractory cardiogenic shock.

Phosphine gas has a characteristic garlic-like or decaying fish odor.

Accidental ingestion is the most common route of kerosene poisoning in children, often due to storage in soft drink bottles and attractive color.

Chemical pneumonitis (aspiration pneumonia) is the main cause of morbidity and mortality.

Induced vomiting dramatically increases aspiration risk.

LSD is a potent serotonin 5-HT2A receptor agonist, producing its characteristic hallucinogenic effects.

Flashbacks (HPPD – Hallucinogen Persisting Perception Disorder) are spontaneous recurrence of perceptual disturbances weeks to months after last LSD use, without taking the drug.

Conjunctival injection (red/bloodshot eyes) is a classic sign of cannabis use.

Delta-9-THC is the primary psychoactive compound responsible for the “high” in cannabis.

Amphetamines cause tachycardia, NOT bradycardia.

“Ice” or “Crystal meth” are street names for methamphetamine.

Meth mouth describes the severe, rapid dental decay seen in chronic methamphetamine users.

Physical dependence is defined by the appearance of withdrawal (abstinence) syndrome when the drug is stopped or reduced.

Tolerance is the need to progressively increase the dose to achieve the same effect, due to neuroadaptation.

Miosis (pinpoint pupils) is a sign of opioid INTOXICATION, not withdrawal.

A delusion is a fixed, false belief that is firmly maintained despite clear evidence to the contrary and is not accepted by other members of the person’s culture.

A hallucination is a perception experienced in the absence of any external stimulus – seeing, hearing, or feeling something that isn’t there.

“Unsound mind” is a legal (not medical) term indicating mental illness severe enough to impair judgment, understanding, or responsibility for actions.

Involuntary admission requires certification by a psychiatrist that the patient has mental illness AND poses danger to self or others OR is incapable of self-care.

Initial involuntary admission is for up to 30 days (1 month).

Testamentary capacity (sound disposing mind) is essential for a valid will.

The will is invalid if the paranoid delusions directly affected the testamentary dispositions (e.g., disinheriting family due to delusional beliefs about them).

Section 84 PPC (similar to M’Naghten rules) states: “Nothing is an offence if done by a person who, at the time, was incapable of knowing the nature of the act or that it was wrong/contrary to law, by reason of unsoundness of mind.” Self-proclaimed insanity or any mental illness is insufficient.

The irresistible impulse test (not part of M’Naghten but recognized in some jurisdictions) provides defense if a person couldn’t control their conduct despite knowing it was wrong.

Classic anticholinergic toxidrome: “Dry as a bone (anhidrosis), Red as a beet (flushing), Blind as a bat (mydriasis, cycloplegia), Hot as a hare (hyperthermia), Mad as a hatter (delirium).” SLUDGE describes cholinergic excess (opposite). “Fight or flight” is sympathetic activation.

Dhatura (Datura stramonium) contains tropane alkaloids – atropine, hyoscine (scopolamine), and hyoscyamine.

Extradural (epidural) hematoma classically presents with a lucid interval – initial unconsciousness from concussion, recovery, then deterioration as the hematoma expands.

Contre-coup injury occurs opposite (contralateral) to the impact site, due to the brain striking the skull on the opposite side during deceleration.

CSF rhinorrhea (nose) or otorrhea (ear) is pathognomonic of skull base fracture with dural tear.

Hangman’s fracture is a bilateral fracture through the pars interarticularis of C2 (axis) vertebra, classically from judicial hanging with submental knot causing hyperextension.

Russell’s viper (Daboia russelii) causes maximum snakebite mortality in Pakistan and the Indian subcontinent.

Neurotoxic venoms (Cobra, Krait) cause descending paralysis – ptosis (first sign), bulbar palsy, and respiratory muscle paralysis leading to death.

The 20WBCT is a bedside test for venom-induced coagulopathy.

ASV is polyvalent (against common venomous species in the region) or monovalent (specific species).

Clostridium botulinum toxin blocks acetylcholine release from presynaptic terminals at the neuromuscular junction by cleaving SNARE proteins.

Botulism triad: symmetric descending flaccid paralysis (starting with cranial nerves), afebrile (no fever), and clear sensorium (patient alert).

Home-canned, fermented, or improperly preserved foods (low acid content, anaerobic conditions) are classic sources.

Infant botulism occurs when infants ingest spores (classically from honey) that germinate in the immature gut and produce toxin in vivo.

All differentiate them: Botulism has descending paralysis (starts cranially), no sensory involvement, and normal CSF.

Treatment: botulinum antitoxin (neutralizes circulating toxin, doesn’t reverse bound toxin) and intensive supportive care, especially mechanical ventilation for respiratory failure.

Local anaesthetics like lidocaine block voltage-gated sodium channels, preventing action potential generation and propagation.

GABA-A receptors are ligand-gated chloride channels; activation causes chloride influx and hyperpolarization.

Beta-1 receptors couple to Gs proteins, activating adenylyl cyclase and increasing cAMP.

Alpha-2 receptors are presynaptic autoreceptors on sympathetic neurons; their activation inhibits norepinephrine release (negative feedback).

Lorazepam, oxazepam, and temazepam undergo direct glucuronidation (phase II) only, making them safer in liver disease.

Flumazenil is a competitive antagonist at the benzodiazepine binding site on GABA-A receptors, reversing sedation without affecting GABA itself.

Abrupt benzodiazepine discontinuation after chronic use causes withdrawal syndrome including rebound anxiety, tremors, insomnia, and seizures due to reduced GABAergic inhibition.

Diazepam has a long half-life (20-100 hours) with active metabolites (desmethyldiazepam, oxazepam), causing next-day hangover effects.

At high doses, barbiturates can directly open GABA-A chloride channels even without GABA (GABA-mimetic action), causing profound CNS and respiratory depression.

Thiopental is an ultra-short-acting IV barbiturate ideal for rapid anaesthesia induction.

Phenobarbital is a potent CYP450 inducer, increasing warfarin metabolism and reducing its anticoagulant effect.

Methylphenidate is a first-line ADHD treatment that blocks DAT and NET, increasing synaptic dopamine and norepinephrine in prefrontal cortex.

Doxapram is a respiratory analeptic that stimulates peripheral carotid chemoreceptors and medullary respiratory centers, increasing tidal volume and respiratory rate.

Caffeine blocks adenosine A1 and A2A receptors.

Theophylline exhibits saturable (zero-order) metabolism at higher concentrations, meaning small dose increases cause disproportionate rises in plasma levels.

Ciprofloxacin inhibits CYP1A2, the primary enzyme metabolizing theophylline, increasing theophylline levels and toxicity risk.

Theophylline has the strongest bronchodilator and significant cardiac effects, making it useful for asthma but risky for arrhythmias.

Sibutramine was withdrawn due to increased risk of myocardial infarction and stroke in the SCOUT trial, especially in patients with cardiovascular risk factors.

SSRIs selectively block SERT (serotonin transporter) with minimal effect on muscarinic, histaminic, and alpha-adrenergic receptors, reducing anticholinergic effects, sedation, and orthostatic hypotension seen with TCAs.

Serotonin stored in platelets is released during injury, promoting platelet aggregation.

Sertraline and citalopram/escitalopram have the lowest CYP450 inhibition, causing fewer drug interactions.

SSRI discontinuation syndrome occurs with abrupt cessation, especially with short half-life SSRIs like paroxetine.

TCAs block muscarinic receptors causing anticholinergic effects: dry mouth, constipation, urinary retention, blurred vision, and confusion (especially in elderly).

TCAs block cardiac fast sodium channels, causing QRS widening.

Sodium bicarbonate is first-line for TCA-induced cardiac toxicity; it increases serum pH, reducing drug binding to sodium channels and narrowing QRS.

Tyramine in aged cheese is normally metabolized by MAO-A in the gut.

Meperidine with MAOIs causes two dangerous interactions: hypertensive crisis (sympathomimetic effect) and serotonin syndrome (serotonergic effect).

Transdermal selegiline delivers drug directly to systemic circulation, bypassing gut where MAO-A metabolizes tyramine.

Serotonin syndrome results from excessive serotonergic activity, often from combining SSRIs with other serotonergic drugs (tramadol, MAOIs, triptans, linezolid).

Serotonin syndrome features hyperreflexia, clonus, and myoclonus with rapid onset (hours).

John’s Wort induces CYP3A4 and P-glycoprotein, increasing metabolism of oral contraceptives, antiretrovirals, warfarin, cyclosporine, and many other drugs, reducing their efficacy.

Lithium augmentation is evidence-based for partial responders to antidepressants.

Aripiprazole is a partial D2 agonist and 5-HT1A agonist, stabilizing dopamine activity.

ECT produces rapid antidepressant effects within days, crucial for severely depressed patients with suicidal ideation or catatonia.

Anticholinergics (glycopyrrolate, atropine) are given pre-ECT to prevent vagally-mediated bradycardia and reduce secretions during the seizure.

Acute dystonia results from D2 receptor blockade in the nigrostriatal pathway, causing dopamine-acetylcholine imbalance.

D2 blockade in the tuberoinfundibular pathway removes dopamine’s inhibition of prolactin release, causing hyperprolactinemia with amenorrhea, galactorrhea, gynecomastia, and sexual dysfunction.

Clozapine causes agranulocytosis (1-2% risk), requiring weekly WBC monitoring initially, then biweekly after 6 months, then monthly.

Tardive dyskinesia (TD) involves involuntary choreoathetoid movements of orofacial muscles after prolonged antipsychotic use.

Neuroleptic malignant syndrome (NMS) features hyperthermia, lead-pipe rigidity, autonomic instability, and elevated CK due to D2 receptor blockade.

Valproate enhances GABA by inhibiting GABA transaminase, blocking sodium channels, and affecting intracellular signaling.

Valproate has the highest teratogenic risk (neural tube defects 1-2%, spina bifida).

Lithium inhibits ADH action on collecting ducts (interferes with aquaporin-2 expression), causing nephrogenic diabetes insipidus with polyuria and compensatory polydipsia.

Thiazide diuretics increase lithium levels by reducing sodium and water, causing compensatory proximal tubule lithium reabsorption.

Lithium inhibits thyroid hormone synthesis and release, causing hypothyroidism in up to 20% of patients.

Hemodialysis is indicated for severe lithium toxicity (levels >2.5 mEq/L or severe symptoms) as lithium is water-soluble with small molecular weight and no protein binding.

Benzodiazepines (diazepam, chlordiazepoxide, lorazepam) are first-line for alcohol withdrawal, preventing seizures and delirium tremens by enhancing GABA transmission (cross-tolerance with alcohol).

Disulfiram inhibits aldehyde dehydrogenase, causing acetaldehyde accumulation when alcohol is consumed, producing unpleasant symptoms (disulfiram-ethanol reaction).

Wernicke encephalopathy (confusion, ataxia, ophthalmoplegia) results from thiamine deficiency.

Mu receptors mediate analgesia, euphoria, respiratory depression, miosis, constipation, and physical dependence.

Methadone is a full mu agonist with long half-life (24-36 hours), used for opioid maintenance therapy.

Buprenorphine is a partial mu agonist with high receptor affinity.

Naloxone is a competitive mu antagonist with short half-life (30-90 minutes), requiring repeated dosing for long-acting opioids.

MDMA (ecstasy) causes massive serotonin, dopamine, and norepinephrine release.

Cocaine blocks monoamine reuptake, causing sympathetic overstimulation. “Formication” (bugs crawling sensation) is characteristic of cocaine psychosis.

Phencyclidine (PCP) is an NMDA receptor antagonist causing dissociative anesthesia, violent behavior, nystagmus (horizontal, vertical, rotatory), and analgesia.

Phenytoin and carbamazepine block voltage-gated sodium channels by prolonging inactivation, reducing sustained high-frequency firing without affecting normal neuronal function.

Ethosuximide specifically blocks T-type (low-threshold) calcium channels in thalamic neurons, which generate the 3-Hz oscillations of absence seizures.

Phenytoin causes gingival hyperplasia (altered fibroblast metabolism), hirsutism, coarsening of facial features, and acne–limiting its use in young women.

Lamotrigine can cause severe rashes including Stevens-Johnson syndrome and toxic epidermal necrolysis, especially with rapid titration or concurrent valproate (which inhibits lamotrigine metabolism).

IV benzodiazepines (lorazepam preferred over diazepam due to longer anticonvulsant effect) are first-line for status epilepticus.

Refractory status epilepticus requires pharmacological coma with propofol, midazolam infusion, or pentobarbital.

MAC is the minimum alveolar concentration at which 50% of patients don’t respond to surgical incision (ED50 for immobility).

Low blood-gas partition coefficient means the gas is poorly soluble in blood, so alveolar concentration rises rapidly, equilibrating quickly with brain (rapid induction).

Malignant hyperthermia is triggered by volatile anesthetics (halothane, sevoflurane) and succinylcholine in genetically susceptible individuals (RYR1 mutation).

Nitrous oxide oxidizes cobalt in vitamin B12, irreversibly inhibiting methionine synthase required for myelin synthesis and DNA synthesis (thymidine production).

Ketamine (NMDA antagonist) produces dissociative anesthesia with analgesia, maintains airway reflexes, and causes sympathetic stimulation (cardiovascular stability or increase).

Remifentanil is an ultra-short-acting opioid metabolized by plasma esterases (not hepatic CYP), with context-insensitive half-life–no accumulation with prolonged infusion.

Barbiturates (thiopental) induce hepatic ALA synthase, increasing porphyrin synthesis and precipitating acute porphyric attacks.

Glycopyrrolate is a quaternary ammonium compound that doesn’t cross the blood-brain barrier, causing fewer CNS effects (confusion, sedation) compared to atropine and scopolamine.

Fentanyl is commonly added to epidural bupivacaine for labor analgesia.

Meperidine is metabolized to normeperidine, which has a long half-life (15-40 hours) and causes CNS excitation and seizures in mothers, but in neonates (immature metabolism) causes prolonged respiratory depression.

Carbidopa inhibits peripheral dopa decarboxylase, preventing levodopa conversion to dopamine peripherally.

Peak-dose dyskinesia (chorea, dystonia) occurs at maximum levodopa plasma concentrations due to pulsatile dopamine stimulation. “Wearing-off” is loss of effect before next dose. “On-off” is unpredictable fluctuations.

Quetiapine and clozapine have low D2 affinity and can treat psychosis in Parkinson’s without significantly worsening motor symptoms.

Metoclopramide is a D2 antagonist that crosses the BBB, causing extrapyramidal symptoms including drug-induced parkinsonism, especially with prolonged use in elderly women.

Triptans are 5-HT1B/1D agonists.

Beta-blockers (propranolol, metoprolol, timolol) prevent migraine by inhibiting cortical spreading depression, modulating serotonergic systems, and stabilizing neuronal membranes.

High-flow 100% oxygen (12-15 L/min for 15-20 minutes) is first-line abortive treatment for cluster headaches, relieving pain in most patients within 15 minutes.

Local anesthetics exhibit “use-dependent” (phasic) block–they preferentially bind to open (activated) and inactivated sodium channels.

Organophosphate compounds cause irreversible inhibition of acetylcholinesterase, leading to accumulation of acetylcholine at synapses.

Strychnine competitively blocks glycine receptors in the spinal cord, removing inhibition on motor neurons.

Tetanospasmin (tetanus toxin) is transported retrogradely to the spinal cord where it blocks release of inhibitory neurotransmitters (glycine and GABA) from Renshaw cells.

Blood alcohol levels of 300-400 mg/dL correspond to the stupor stage characterized by marked muscular incoordination, inability to stand, and approaching unconsciousness.

Ethyl alcohol imparts a characteristic spirituous or fermented odor to stomach contents and body fluids during autopsy.

Blood alcohol concentrations of 400-500 mg/dL are generally considered fatal in non-tolerant individuals due to respiratory depression and cardiovascular collapse.

In India, under the Motor Vehicles Act, the legal limit for blood alcohol concentration while driving is 30 mg/dL (0.03%).

Wernicke’s encephalopathy results from thiamine (Vitamin B1) deficiency, common in chronic alcoholics due to poor nutrition and impaired absorption.

Methanol is metabolized by alcohol dehydrogenase to formaldehyde, which is rapidly converted to formic acid by aldehyde dehydrogenase.

Ethanol has a 20-fold higher affinity for alcohol dehydrogenase compared to methanol.

Methanol poisoning causes congestion, edema, and degeneration of the optic disc and retina due to formic acid toxicity to the visual pathway.

The minimum lethal dose of methanol is approximately 30-60 mL (1-2 oz) in adults.

Barbiturate overdose produces coma, miosis, hypotension, hypothermia, and depressed reflexes.

Flumazenil is a competitive antagonist at the benzodiazepine binding site on the GABA-A receptor.

Barbiturate blisters are bullous lesions occurring at pressure points and dependent areas (buttocks, heels, knees) in deeply comatose patients.

Barbiturate withdrawal is a medical emergency featuring anxiety, tremors, seizures (potentially fatal), delirium, and hyperthermia.

This presentation describes organophosphate poisoning with cholinergic crisis (SLUDGE syndrome + miosis).

Aluminum phosphide (common suicide agent in India) releases phosphine gas on contact with moisture, producing a characteristic garlic-like/decaying fish odor.

Superwarfarins (brodifacoum, bromadiolone) are long-acting vitamin K antagonists that inhibit clotting factor synthesis, causing severe hemorrhagic manifestations.

Organophosphate poisoning causes miosis (pinpoint pupils) due to excessive acetylcholine stimulation of the muscarinic receptors in the iris sphincter muscle.

The most dangerous complication of kerosene ingestion is aspiration pneumonitis.

Gastric lavage and induced emesis are contraindicated in kerosene ingestion because they dramatically increase aspiration risk.

Chemical pneumonitis following kerosene aspiration presents with rapid-onset respiratory distress and bilateral infiltrates, often worse on the right due to anatomical bronchial angles.

LSD is a potent hallucinogen causing vivid visual hallucinations, synesthesia, mydriasis, tachycardia, and hyperthermia.

Flashbacks (Hallucinogen Persisting Perception Disorder) are spontaneous recurrences of LSD-like perceptual disturbances occurring weeks to months after last use, without re-ingestion.

Psilocybin is converted to psilocin in the body, which acts as an agonist at serotonin 5-HT2A receptors, similar to LSD.

Amphetamines enter nerve terminals and displace stored catecholamines (dopamine, norepinephrine) causing massive release.

Amphetamine psychosis closely mimics paranoid schizophrenia with persecutory delusions, auditory hallucinations, ideas of reference, and bizarre behavior.

Beta-blockers alone (like propranolol) are contraindicated in stimulant toxicity because blocking beta-2 vasodilatory effects leaves alpha-mediated vasoconstriction unopposed, potentially worsening hypertension and causing coronary vasospasm.

Opioid withdrawal produces a flu-like syndrome: rhinorrhea, lacrimation, yawning, piloerection (“cold turkey”), diarrhea, muscle cramps, and drug craving.

Tolerance is the need for progressively higher doses to achieve the same pharmacological effect, resulting from neuroadaptive changes (receptor downregulation, enzyme induction).

Physical dependence is a physiological state where the body requires the drug to maintain normal function, and withdrawal symptoms occur upon discontinuation.

The McNaughten rule (1843) states that for an insanity defense, the accused must prove that due to mental disease, he did not know the nature and quality of his act, OR did not know it was wrong.

Fitness to stand trial requires that the accused can understand the nature of charges, understand court proceedings, and meaningfully assist in their own defense.

Automatism refers to involuntary actions performed without conscious awareness or control, such as during sleepwalking, epileptic seizures, or hypoglycemia.

An advance directive under the Mental Healthcare Act 2017 allows a person to document their treatment preferences, which come into effect when they lose the capacity to make decisions due to mental illness.

Involuntary admission under MHCA 2017 requires: 1) severe mental illness requiring treatment, 2) lack of capacity to make decisions, and 3) risk of harm to self/others without treatment.

Supported admission involves consent from a nominated representative appointed by the person themselves (in advance) OR, if none exists, a family member or caregiver.

Testamentary capacity (sound disposing mind) requires: 1) understanding the nature of making a will, 2) knowing the extent of property, 3) knowing the claims of potential beneficiaries, and 4) ability to express intentions clearly.

A person with mental illness can make a valid will during a lucid interval (clear period) OR if the illness/delusions don’t affect the specific decisions in the will.

Simply having a diagnosis doesn’t exempt responsibility.

Under the Indian Contract Act, contracts by persons of unsound mind are voidable, meaning the mentally ill person (or their representative) can choose to void or ratify it.

Datura contains tropane alkaloids (atropine, scopolamine, hyoscyamine) causing classic anticholinergic syndrome: “Hot as a hare, blind as a bat, dry as a bone, red as a beet, mad as a hatter.” This includes hyperthermia, mydriasis, tachycardia, dry skin, urinary retention, and delirium.

Physostigmine is a reversible acetylcholinesterase inhibitor that crosses the blood-brain barrier, making it effective for both central and peripheral anticholinergic effects.

Datura seeds are characteristic: kidney-shaped or flat, brownish to black, with a rough or pitted surface.

The classic “lucid interval” (talk and die phenomenon) is characteristic of epidural hematoma, typically from rupture of the middle meningeal artery following temporal bone fracture.

Subdural hematoma appears as a crescent-shaped (concave) collection that can spread across the brain surface, as blood accumulates between dura and arachnoid.

Dementia pugilistica (“punch-drunk syndrome”) is chronic traumatic encephalopathy (CTE) from repeated head injuries.

C4-C5 injury causes quadriplegia (paralysis of all four limbs) with intact diaphragm function (phrenic nerve C3-5).

L1 (and T12) is the most commonly injured vertebra in axial loading injuries (falls landing on buttocks/feet) because it’s at the thoracolumbar junction where the rigid thoracic spine meets the mobile lumbar spine.

Krait venom is predominantly neurotoxic, causing flaccid paralysis by blocking acetylcholine release at neuromuscular junctions.

Hemotoxic venoms (Russell’s viper, saw-scaled viper) contain procoagulants and anticoagulants that cause consumption coagulopathy (venom-induced consumption coagulopathy – VICC).

Botulinum toxin is produced by *Clostridium botulinum* in anaerobic conditions (improperly canned foods).

Botulism characteristically causes descending paralysis (cranial nerves → limbs) with dilated, poorly reactive pupils (parasympathetic block).

This is a case-control study because it starts with the outcome (lung cancer cases and controls) and looks backward at exposure (smoking history).

This is a prospective cohort study as it starts with an exposed group and follows them forward in time for disease development.

Cross-sectional studies measure exposure and outcome simultaneously at one point in time, making them useful for prevalence estimation.

Ecological studies analyze data at the population or group level rather than individual level.

Double-blind means both the participant and the investigator are unaware of treatment allocation, minimizing bias in assessment and reporting.

Incidence rate = (New cases / Population at risk) × 100,000 = (250/50,000) × 100,000 = 500 per 100,000.

Point prevalence = (Existing cases at a point in time / Total population) × 100 = (1,000/100,000) × 100 = 1%.

Cause-specific mortality rate = (Deaths from specific cause / Total population) × 100,000 = (50/500,000) × 100,000 = 10 per 100,000.

When crude rates differ but age-specific rates are similar, the difference is due to age structure.

Proportional mortality rate represents the proportion of deaths due to a specific cause out of total deaths, not population.

Case fatality rate (CFR) = (Deaths from disease / Total cases of disease) × 100 = (50/200) × 100 = 25%.

Sensitivity = True Positives / (True Positives + False Negatives) × 100 = 90/100 × 100 = 90%.

Positive predictive value (PPV) decreases dramatically with low prevalence, as false positives outnumber true positives.

Specificity = 90% means 90% of healthy people test negative.

Wilson and Jungner criteria require treatable conditions, not 100% curability.

There is an inverse relationship between sensitivity and specificity when adjusting cutoff values.

WHO defines mental health as well-being where individuals realize abilities, cope with stress, work productively, AND contribute to community.

DALY = YLL + YLD, measuring total burden of disease as years of healthy life lost.

Treatment gap refers to the percentage of individuals with mental disorders who need but do not receive treatment.

Primary prevention aims to prevent disease onset through health promotion and risk reduction.

Mean is most sensitive to outliers as it includes all values in calculation.

In positive skew, the tail extends toward higher values, pulling the mean rightward.

Mode is the most frequently occurring value in a dataset.

Median is the middle value when data is arranged in order.

Range = Maximum – Minimum.

Standard deviation (SD) is the square root of variance, returning the measure to original units (e.g., kg, cm).

In normal distribution: 68% within ±1 SD, 95% within ±2 SD, 99.7% within ±3 SD (Empirical Rule/68-95-99.7 rule).

CV = (SD/Mean) × 100, expressing variability as a percentage of the mean.

Normal distribution is perfectly symmetric: mean = median = mode at the center.

Standard normal distribution (Z-distribution) is a special normal distribution with mean = 0 and SD = 1.

A 95% CI means if we repeated the study many times, 95% of calculated intervals would contain the true population mean.

Standard Error (SE) = SD/√n.

Higher confidence requires a wider interval to be more certain of capturing the true value.

When p-value (0.03) < alpha (0.05), we reject the null hypothesis; results are statistically significant.

Type I error (α error, false positive) = rejecting null hypothesis when it’s actually true (finding effect when none exists).

Power = 1 – β, representing probability of correctly rejecting a false null hypothesis (detecting true effect). β is Type II error rate.

Lowering alpha (0.05 → 0.01) reduces Type I error but increases Type II error (inverse relationship).

Z-test requires known population standard deviation.

When calculated Z (2.5) > critical Z (1.96), the result falls in the rejection region, so we reject the null hypothesis.

T-test uses sample standard deviation when population SD is unknown (most real-world situations).

Paired t-test compares two related measurements from the same subjects (before-after design).

Chi-square test analyzes association between categorical variables by comparing observed versus expected frequencies in a contingency table.

Both variables are categorical (binary): smoking status and disease status.

Chi-square assumptions require expected frequencies ≥5 in at least 80% of cells.

Correlation coefficient ranges from -1 to +1.

R² represents proportion of variance in dependent variable explained by independent variable.

In Y = a + bX, “b” (here 3) is the slope/regression coefficient, indicating for each unit increase in X, Y increases by 3 units. “a” (here 2) is the Y-intercept (Y value when X = 0).

FAST is a public education tool: Face drooping, Arm weakness, Speech difficulty, Time to call emergency services.

Age is a non-modifiable risk factor – it cannot be changed through intervention.