Antipsychotics
Standard Answer:
(2023 Main, 2023 Resit, 2022 Main, 2021 Main, 2021 Resit, 2012 — recurs every year) Classification: 1. Typical (first-generation) antipsychotics: Chlorpromazine (low potency), Haloperidol, Fluphenazine (high potency) — primarily D2 receptor antagonists. 2. Atypical (second-generation) antipsychotics: Clozapine, Olanzapine, Risperidone, Quetiapine, Aripiprazole (partial D2 agonist) — antagonize D2 and, notably, 5-HT2A receptors (and other receptors). Basic differences between typical and atypical neuroleptics: • Receptor profile: Typical agents primarily block D2 receptors; atypical agents block D2 and 5-HT2A receptors (with varying additional affinity for other receptors), and some (aripiprazole) act as D2 partial agonists. • Extrapyramidal side effects (EPS): Typical agents cause significantly more EPS (dose-dependent D2 blockade in the nigrostriatal pathway); atypical agents cause substantially less EPS, partly because 5-HT2A blockade increases dopamine release in the striatum, offsetting D2 blockade there. • Negative symptoms: Atypical agents show greater efficacy against negative symptoms (apathy, social withdrawal, flat affect) of schizophrenia, whereas typical agents mainly address positive symptoms (hallucinations, delusions). • Metabolic effects: Atypical agents (especially olanzapine, clozapine) are more strongly associated with weight gain, dyslipidemia, and new-onset diabetes. • Prolactin: Typical agents (and risperidone among atypicals) cause more hyperprolactinaemia; most other atypicals cause less due to weaker/faster-dissociating D2 blockade or partial agonism. • Clozapine specifically is reserved for treatment-resistant schizophrenia due to the risk of agranulocytosis (requiring regular blood count monitoring), but has the lowest EPS liability and no prolactin elevation. Advantages of atypical agents (explicitly asked, 2023 Resit, 2021 Resit): Reduced EPS (less parkinsonism, dystonia, akathisia, tardive dyskinesia), efficacy against negative and cognitive symptoms in addition to positive symptoms, lower risk of hyperprolactinaemia (except risperidone), improved subjective tolerability/adherence — traded off against greater metabolic risk (weight gain, diabetes, dyslipidemia). Three extrapyramidal side effects of antipsychotics (D2-receptor blockade in the nigrostriatal pathway): 1. Acute dystonia – sustained, involuntary muscle contraction/spasm (e.g., torticollis, oculogyric crisis), occurring within hours to days of starting treatment. 2. Akathisia – subjective and objective motor restlessness, an inability to sit still, occurring days to weeks into treatment. 3. Parkinsonism (drug-induced) – bradykinesia, rigidity, tremor, resembling idiopathic Parkinson’s disease, occurring weeks into treatment. 4. Tardive dyskinesia – involuntary, repetitive orofacial/limb movements developing after months to years of treatment, thought due to dopamine receptor supersensitivity/ upregulation; often irreversible even after drug withdrawal. Pharmacodynamics and side effect profile of dopamine receptor agents in psychosis, galactorrhoea, and Parkinsonism (2022 Main): • In psychosis, D2 receptor antagonists (antipsychotics) reduce excess mesolimbic dopaminergic activity, controlling positive symptoms, but their D2 blockade in the tuberoinfundibular pathway removes dopamine’s normal inhibitory control on prolactin secretion, causing hyperprolactinaemia and galactorrhoea as an adverse effect. • In galactorrhoea due to hyperprolactinaemia (e.g., from a prolactinoma), D2 receptor agonists (bromocriptine, cabergoline) are used therapeutically to suppress prolactin release. • In Parkinsonism, D2 receptor agonists (pramipexole, ropinirole, bromocriptine) or the dopamine precursor levodopa are used to restore striatal dopaminergic tone lost through nigrostriatal degeneration. This demonstrates the same pharmacological axis (dopamine receptor modulation) being exploited in opposite directions depending on the clinical context. Classify antipsychotic agents (Loxapine) (2012): Loxapine is a typical/first-generation antipsychotic (dibenzoxazepine class) with mixed D2 and 5-HT2A antagonism (has some “atypical-like” properties); used for acute agitation in schizophrenia; adverse effects: EPS, sedation, orthostatic hypotension, anticholinergic effects; inhaled formulation used for rapid control of agitation.
Antidepressants
Standard Answer:
(2018 Paper II, 2017, 2015, 2014, 2013, 2010) Theories of depression and general mechanisms of action of antidepressants: • Monoamine hypothesis – depression results from a functional deficiency of monoamine neurotransmitters (serotonin, norepinephrine, and to a lesser extent dopamine) in the CNS; most antidepressants act by increasing synaptic availability of these monoamines. • Neurotrophic/neuroplasticity hypothesis – chronic stress/depression is associated with reduced hippocampal BDNF (brain-derived neurotrophic factor) and neuronal atrophy; antidepressants, through prolonged use, upregulate BDNF signalling and promote neurogenesis, which may better explain the delayed onset of clinical antidepressant effect (weeks) despite immediate monoamine elevation. • HPA axis dysregulation hypothesis – depression associated with hypercortisolism/HPA axis hyperactivity. Classification with mechanisms: 1. SSRIs (Selective Serotonin Reuptake Inhibitors): Fluoxetine, Sertraline, Paroxetine, Citalopram — block the serotonin transporter (SERT), increasing synaptic serotonin. 2. SNRIs: Venlafaxine, Duloxetine — block both serotonin and norepinephrine transporters. 3. Tricyclic antidepressants (TCAs): Imipramine, Amitriptyline — block serotonin and norepinephrine reuptake; also have antimuscarinic, antihistaminic, and alpha-blocking activity (accounting for their broader side effect profile). 4. Monoamine oxidase inhibitors (MAOIs): Phenelzine, Tranylcypromine (non-selective); Selegiline (MAO-B selective) — inhibit intraneuronal breakdown of monoamines. 5. Atypical antidepressants: Bupropion (dopamine/norepinephrine reuptake inhibitor), Mirtazapine (α2-antagonist, increases NE/5-HT release; also antihistaminic — sedating, appetite-stimulating), Trazodone (5-HT2A antagonist/weak reuptake inhibitor, sedating). Pharmacology of Imipramine (TCA): Blocks reuptake of both serotonin and norepinephrine at presynaptic transporters, increasing their synaptic availability. Also has antimuscarinic (dry mouth, blurred vision, constipation, urinary retention), antihistaminic (sedation, weight gain), and α1-blocking (postural hypotension) properties. Cardiotoxic in overdose (quinidine-like Na⁺ channel blockade causing arrhythmias — a major cause of TCA overdose mortality). Used for depression, neuropathic pain, enuresis (historically, imipramine specifically). Pharmacology of Bupropion: Inhibits reuptake of dopamine and norepinephrine (minimal serotonergic activity — hence low sexual dysfunction risk compared to SSRIs); lowers seizure threshold (contraindicated in seizure disorders/eating disorders with electrolyte disturbance, e.g., bulimia); also used for smoking cessation. Lithium (mechanism of action, pharmacokinetics, adverse effects): • Mechanism: Not fully elucidated; proposed mechanisms include inhibition of inositol monophosphatase (disrupting the phosphoinositide second-messenger pathway) and inhibition of glycogen synthase kinase-3 (GSK-3), affecting neuronal signalling and gene expression relevant to mood stabilization. • Pharmacokinetics: Narrow therapeutic index requiring regular plasma level monitoring; excreted almost entirely unchanged by the kidney, handled similarly to sodium (reabsorbed in the proximal tubule) — hence sodium depletion (diuretics, dehydration, low-salt diet) increases lithium reabsorption and risk of toxicity; renal clearance reduced in renal impairment, NSAID use, and ACE inhibitor/ARB use. • Adverse effects: Tremor, polyuria/polydipsia (nephrogenic diabetes insipidus — lithium antagonizes ADH action on the collecting duct), hypothyroidism, weight gain, teratogenicity (Ebstein’s anomaly — a cardiac malformation), and at toxic levels: ataxia, confusion, seizures, cardiac arrhythmias. • Used as first-line mood stabilizer for bipolar disorder (both acute mania and maintenance/relapse prevention).
Parkinson’s Disease — Classification of Drugs and Role of Antimuscarinics
Standard Answer:
(2023 Resit, 2021 Resit, 2011, “Pharmacology 1”) Classification (based on Neuroprotective vs Symptomatic strategies): A. Symptomatic (dopaminergic) therapy: 1. Dopamine precursor: Levodopa (usually combined with a peripheral decarboxylase inhibitor — Carbidopa or Benserazide — to prevent peripheral conversion to dopamine, reducing peripheral side effects like nausea and allowing more levodopa to cross the blood-brain barrier). 2. Dopamine agonists: Bromocriptine (ergot-derived), Pramipexole, Ropinirole (non-ergot) — directly stimulate dopamine receptors, often used early in younger patients or as adjuncts to reduce levodopa dose/motor fluctuations. 3. MAO-B inhibitors: Selegiline, Rasagiline — inhibit central breakdown of dopamine, prolonging its action (selegiline has also been proposed to have neuroprotective properties). 4. COMT inhibitors: Entacapone, Tolcapone — block peripheral (and central, tolcapone) breakdown of levodopa/dopamine, prolonging levodopa’s effect and smoothing “on-off” fluctuations. 5. Antimuscarinic agents: Trihexyphenidyl, Benztropine — restore the dopamine-acetylcholine balance in the striatum. 6. Amantadine: enhances dopamine release, blocks NMDA glutamate receptors; useful early and for levodopa-induced dyskinesias. B. Neuroprotective strategies (proposed, evidence limited): MAO-B inhibitors (selegiline, rasagiline) — reduce oxidative dopamine metabolism-related neuronal damage; evidence for true disease-modifying effect remains inconclusive. Role of antimuscarinic agents: In Parkinson’s disease, loss of nigrostriatal dopaminergic neurons leads to a relative excess of striatal cholinergic activity (normally dopamine inhibits ACh release in the striatum). Antimuscarinics (trihexyphenidyl, benztropine) restore the dopamine-acetylcholine balance, particularly improving tremor and rigidity (less effect on bradykinesia). They are especially useful in younger patients (less tolerant of anticholinergic CNS side effects than the elderly) and for drug-induced Parkinsonism from antipsychotics. Limited by anticholinergic adverse effects: dry mouth, blurred vision, urinary retention, constipation, confusion/memory impairment (particularly problematic in elderly patients, where they may worsen cognitive decline). Detailed pharmacology of Levodopa (a commonly examined single-drug answer): Levodopa crosses the blood-brain barrier (unlike dopamine) via the large neutral amino acid transporter and is converted to dopamine by dopa decarboxylase in surviving nigrostriatal neurons, replenishing striatal dopamine. Given with carbidopa to inhibit peripheral decarboxylation (reducing required dose, nausea, and peripheral cardiovascular effects). Adverse effects: nausea/vomiting, postural hypotension, psychiatric effects (hallucinations, confusion — especially in elderly), and with long-term use, motor fluctuations (“wearing-off,” “on-off” phenomenon) and dyskinesias.
Anaesthesia — Stages, General Anaesthetics, Benzodiazepines vs Barbiturates
Standard Answer:
(2023 Main, 2022 Main, 2021 Main, 2016, 2013 — recurs heavily) Stages of anaesthesia (Guedel’s classification, classically with ether): 1. Stage I – Analgesia – from onset of anaesthetic administration to loss of consciousness; patient retains some ability to feel pain but is drowsy. 2. Stage II – Excitement (delirium) – loss of consciousness to onset of regular breathing; characterized by excitement, delirium, irregular respiration, potential for laryngospasm, vomiting — the most dangerous stage, minimized by rapid induction agents (IV agents) to move quickly through it. 3. Stage III – Surgical anaesthesia – from onset of regular respiration to respiratory paralysis; subdivided into 4 planes of progressively deeper anaesthesia (loss of eye reflexes, muscle relaxation) — surgery is performed in this stage. 4. Stage IV – Medullary paralysis (overdose) – severe depression of the vasomotor and respiratory centres, leading to circulatory and respiratory failure and death if not managed — represents anaesthetic overdose. “Balanced anaesthesia”: the combined use of multiple agents (IV induction agent, inhalational maintenance agent, neuromuscular blocker, opioid analgesic) each contributing a specific desired component (hypnosis, analgesia, muscle relaxation, amnesia) at lower individual doses, reducing the toxicity/side effects of any single high-dose agent while achieving all requirements of surgical anaesthesia. Properties of an ideal general anaesthetic agent: • Smooth, rapid induction and recovery • Adequate muscle relaxation • Wide margin of safety (high therapeutic index) • Minimal cardiovascular/respiratory depression • Non-irritant, non-flammable, non-explosive • Potent analgesic and amnestic properties • Minimal metabolism/toxic metabolites, rapid elimination Comparison of Benzodiazepines and Barbiturates: Feature Benzodiazepines Barbiturates Mechanism Bind a specific site on the GABA-A Bind a distinct site on the GABA-A receptor (distinct from the GABA and receptor, prolonging the duration of barbiturate sites), enhancing the channel opening; at high frequency of chloride channel opening concentrations, can directly open in response to GABA — requires the the channel independent of GABA presence of GABA (allosteric (less receptor-selective, hence more potentiator) dangerous) Respiratory Milder, safer at high doses (ceiling effect Marked, dose-dependent, can depression on chloride channel frequency) cause fatal respiratory/CNS depression especially in overdose Therapeutic Wide margin of safety Narrow margin of safety index Antagonism Specific antagonist available: No specific antagonist Flumazenil (competitive antagonist at (management is supportive) the benzodiazepine site) Use in Used for sedation, premedication, Ultra-short-acting agents anaesthesia induction (e.g., midazolam) — provides (thiopental) used for rapid IV amnesia and anxiolysis induction of anaesthesia Use in Diazepam/lorazepam are first-line for Phenobarbital used as second/third-seizure acute seizures/status epilepticus line antiepileptic, particularly in disorder neonates Tolerance/ Can develop with chronic use Enzyme induction (CYP450) leads dependence to tolerance and significant drug interactions Enzyme Minimal Marked hepatic CYP450 induction induction (many drug interactions) Muscle relaxant, anticonvulsant, and sedative effects of benzodiazepines (specifically asked): Benzodiazepines produce sedation/hypnosis at low doses (useful for insomnia, pre-anaesthetic anxiolysis), anticonvulsant effect by enhancing GABAergic inhibition throughout the CNS (terminating seizure activity — diazepam/lorazepam are first-line for status epilepticus), and muscle relaxation via enhancement of GABAergic inhibitory transmission at spinal interneurons (useful for spasticity, muscle spasm). Pharmacological antagonism of benzodiazepines and barbiturates: Flumazenil competitively antagonizes benzodiazepines at the benzodiazepine binding site — clinically used to reverse benzodiazepine-induced sedation/overdose, though it carries a risk of precipitating seizures in benzodiazepine-dependent patients. No specific pharmacological antagonist exists for barbiturates; management of barbiturate overdose is supportive (airway/ventilatory support, and urinary alkalinization with sodium bicarbonate can enhance elimination of phenobarbital specifically, via ion trapping, since it is a weak acid). Named ultra-short-acting barbiturate (e.g., Thiopental): Highly lipid-soluble, rapidly crosses the blood-brain barrier producing anaesthesia within seconds (“arm-to-brain” circulation time); action terminated rapidly by redistribution from brain to less well-perfused tissues (muscle, then fat), not by metabolism — hence very short duration despite a long elimination half-life; used for rapid IV induction of anaesthesia; risk of laryngospasm, respiratory depression, hypotension; contraindicated in porphyria. Ketamine, Methoxyflurane, Thiopental, Diazepam (short notes): • Ketamine – NMDA receptor antagonist; produces “dissociative anaesthesia” (profound analgesia and amnesia with retained but disconnected consciousness — eyes may remain open); causes sympathetic stimulation (↑ HR, BP — useful in hypotensive/shock patients, contraindicated in hypertension/raised ICP); associated with emergence delirium/hallucinations (mitigated by co-administered benzodiazepines); bronchodilator effect useful in asthmatic patients requiring anaesthesia; also used sub-anaesthetically as an antidepressant (esketamine). • Methoxyflurane – volatile inhalational anaesthetic, largely obsolete due to nephrotoxicity from fluoride ion metabolites (dose-dependent renal impairment); low-dose formulations still used in some countries for emergency analgesia (e.g., ambulance settings). • Thiopental – see above. • Diazepam – long-acting benzodiazepine; used for anxiolysis, sedation, seizure/status epilepticus management, alcohol withdrawal, muscle spasm; has active metabolites (desmethyldiazepam) prolonging its effective duration; accumulates with repeated dosing, especially in elderly/hepatic impairment. Local anaesthetics — mechanism, factors modulating action: • Mechanism: Local anaesthetics (e.g., lidocaine, bupivacaine) block voltage-gated Na⁺ channels from the intracellular side of the neuronal membrane (must first cross the membrane in the uncharged/lipid-soluble form, then bind the channel in the charged form), preventing the rising phase of the action potential and thus blocking nerve impulse conduction. Smaller, unmyelinated fibres (pain, temperature, autonomic) are blocked before larger myelinated fibres (touch, motor) — a clinically useful differential block. • Factors modulating action: lipid solubility (potency, faster onset), pKa (proportion of ionized vs unionized drug at tissue pH — affects onset; inflamed/acidic tissue impairs efficacy since more drug remains ionized and cannot cross the membrane), protein binding (duration of action), addition of vasoconstrictors (e.g., epinephrine) — reduces systemic absorption, prolongs local action, reduces systemic toxicity, and reduces bleeding at the injection site; fibre diameter/myelination (differential blockade); dose and concentration used. Opioid antagonists: Naloxone (short-acting, IV/IM, used for acute opioid overdose reversal), Naltrexone (long-acting, oral, used for relapse prevention in opioid/alcohol use disorder) — both competitive antagonists at µ-opioid receptors.
Epilepsy / Antiepileptic Drugs
Standard Answer:
(2023 Main, 2021 Main, 2016, 2015, 2013, 2012, 2011) Classification of antiepileptic drugs (by mechanism): 1. Sodium channel blockers: Phenytoin, Carbamazepine, Lamotrigine, Valproate (partially) — stabilize the inactivated state of voltage-gated Na⁺ channels, reducing high-frequency neuronal firing. 2. GABA-enhancing agents: Benzodiazepines (diazepam, lorazepam, clonazepam), Phenobarbital, Vigabatrin (blocks GABA transaminase, ↑ GABA), Tiagabine (blocks GABA reuptake). 3. Calcium channel blockers (T-type): Ethosuximide, Valproate — block T-type Ca²⁺ channels in thalamic neurons, the mechanism underlying efficacy specifically in absence seizures. 4. Multiple mechanism/broad-spectrum agents: Valproate (Na⁺ channel blockade + T-type Ca²⁺ channel blockade + ↑ GABA via inhibition of GABA transaminase/succinic semialdehyde dehydrogenase), Topiramate, Levetiracetam (binds synaptic vesicle protein SV2A, modulating neurotransmitter release). Mechanism of action of Valproate (specifically asked, 2021 Main): Multiple proposed mechanisms — (1) blockade of voltage-gated Na⁺ channels (use-dependent, similar to phenytoin/carbamazepine), (2) inhibition of GABA transaminase and succinic semialdehyde dehydrogenase, increasing GABA levels, and (3) blockade of T-type Ca²⁺ channels — this broad mechanism explains its efficacy across multiple seizure types (generalized tonic-clonic, absence, myoclonic). Adverse effects: hepatotoxicity, teratogenicity (neural tube defects — highest teratogenic risk among AEDs), pancreatitis, weight gain, tremor, hair loss, thrombocytopenia. Classification of clinical seizure types treatable pharmacologically: Generalized seizures (tonic-clonic, absence, myoclonic, atonic) and focal (partial) seizures (simple partial, complex partial, focal with secondary generalization); status epilepticus as an emergency subtype. GABA receptor agonists in epilepsy treatment (pharmacological basis): GABA is the principal inhibitory neurotransmitter in the CNS, acting on GABA-A receptors (ligand-gated Cl⁻ channels) to hyperpolarize neurons and raise seizure threshold. Benzodiazepines and barbiturates, as positive allosteric modulators of the GABA-A receptor, enhance this inhibitory tone, explaining their broad anticonvulsant efficacy, particularly for terminating acute seizure activity (status epilepticus). Carbamazepine (detailed pharmacology): Blocks voltage-gated Na⁺ channels in a use-dependent manner (preferentially binds the inactivated state, stabilizing it and reducing high-frequency repetitive firing characteristic of seizure activity). Used for focal seizures, generalized tonic-clonic seizures, trigeminal neuralgia, and as a mood stabilizer in bipolar disorder. Adverse effects: sedation, diplopia/ataxia, hyponatremia (SIADH-like effect), aplastic anaemia/agranulocytosis (rare, serious), Stevens-Johnson syndrome (particularly associated with HLA-B*1502 allele, more common in some Asian populations), strong CYP450 inducer (including autoinduction of its own metabolism), teratogenic (neural tube defects). Phenytoin (detailed pharmacology): Blocks voltage-gated Na⁺ channels (similar use-dependent mechanism as carbamazepine). Exhibits zero-order kinetics at therapeutic/toxic doses (saturable hepatic metabolism), making dose titration challenging and small dose increases producing disproportionate rises in plasma concentration. Adverse effects: gingival hyperplasia, hirsutism, cerebellar signs (nystagmus, ataxia) at toxic levels, megaloblastic anaemia (interferes with folate metabolism), teratogenic (fetal hydantoin syndrome), osteomalacia (interferes with vitamin D metabolism), Stevens-Johnson syndrome, strong CYP450 inducer. Classify antiepileptics, three general mechanisms, three general side effects (Part II Resit): Mechanisms as above (Na+ channel blockade, GABA enhancement, Ca2+ channel blockade). General side effects across the class: sedation/drowsiness, ataxia/dizziness, cognitive slowing, and (for many agents) idiosyncratic hypersensitivity reactions (rash, Stevens-Johnson syndrome) and teratogenicity. Absence seizures (explanation, and Carbamazepine pharmacology as paired question): Absence seizures are generalized, non-convulsive seizures characterized by brief (~10-second) lapses in awareness with no post-ictal confusion, associated with 3 Hz spike-and-wave discharges on EEG, arising from abnormal oscillatory activity in thalamocortical circuits mediated by T-type calcium channels. (Note: carbamazepine is not effective for and can actually worsen absence seizures — the drug of choice for absence seizures is ethosuximide or valproate, both T-type Ca²⁺ channel blockers.) Drug of choice for absence seizures: Ethosuximide — selectively blocks T-type (low-threshold) calcium channels in thalamic neurons, which generate the abnormal rhythmic burst firing underlying the 3 Hz spike-wave discharges of absence seizures, without significant Na+ channel-blocking activity. Valproate is an alternative (preferred when the patient also has coexisting generalized tonic-clonic seizures, since ethosuximide covers absence seizures only). Status epilepticus (2012): A neurological emergency defined as continuous seizure activity (or repetitive seizures without recovery of consciousness between them) lasting more than 5 minutes, requiring immediate treatment because prolonged seizure activity causes excitotoxic neuronal injury, metabolic derangement (hypoxia, acidosis, hyperthermia, rhabdomyolysis), and increasing pharmacoresistance the longer it continues. First-line treatment: IV benzodiazepine (lorazepam or diazepam) for rapid termination, followed by a loading dose of a longer-acting agent (phenytoin/fosphenytoin or valproate) to prevent recurrence; refractory status epilepticus may require anaesthetic doses of midazolam, propofol, or barbiturates with airway control.
Morphine — Mechanism, Effects, Toxicity, Clinical Indications
Standard Answer:
(2023 Main, 2023 Resit, 2021 Main, 2013, 2012 — recurs heavily) Mechanism of action: Morphine is a full agonist at µ (mu)-opioid receptors (also acts at κ and δ receptors), which are Gi-protein coupled — activation inhibits adenylate cyclase (↓cAMP), opens G-protein-coupled inwardly rectifying K⁺ channels (hyperpolarization), and closes voltage-gated Ca²⁺ channels, reducing neurotransmitter release (particularly substance P) at spinal and supraspinal sites involved in pain transmission, and activating descending inhibitory pain pathways (periaqueductal grey). Pharmacological effects: • Analgesia – for both somatic and visceral pain, altering both perception and emotional response to pain. • Euphoria (also basis of abuse potential) and sedation. • Respiratory depression – ↓ sensitivity of the medullary respiratory centre to CO2 (the major cause of death in overdose). • Miosis (pinpoint pupils — via Edinger-Westphal nucleus stimulation) — a classic diagnostic sign. • Antitussive effect – suppression of the medullary cough centre. • GI effects – constipation (↓ propulsive motility, ↑ sphincter tone — does not develop tolerance, unlike other effects). • Nausea/vomiting (stimulation of chemoreceptor trigger zone). • Biliary spasm, urinary retention, histamine release (flushing, itching), hypotension. Symptoms/signs of morphine toxicity (overdose triad): Respiratory depression, pinpoint pupils (miosis), and coma/CNS depression. Also: hypotension, bradycardia, hypothermia, pulmonary oedema in severe overdose. Treatment of acute morphine poisoning: Airway/ventilatory support, naloxone (competitive opioid antagonist, reverses respiratory depression and coma — may need repeated dosing due to naloxone’s shorter half-life than morphine), supportive care, gastric decontamination if recent oral ingestion. Clinical indications: Moderate-severe acute and chronic pain (including cancer pain, post-surgical pain), acute pulmonary oedema (reduces preload/anxiety), acute myocardial infarction pain, palliative care/end-of-life dyspnoea management.
Organophosphate Poisoning
Standard Answer:
(See Section 1, Q3 — cross-referenced; also 2021 Main, 2023 Main) Refer to full answer under General/Autonomic Pharmacology (Section 1). Summary: muscarinic (DUMBELS), nicotinic (fasciculation/weakness), and CNS effects (seizures, coma); treatment with atropine (titrated to drying of secretions), pralidoxime (before enzyme “aging”), diazepam for seizures, and supportive ventilation. Approach to management of a child who ingested Dichlorvos (organophosphate insecticide) (specific paediatric scenario, Pharmacology 2): 1. ABCs – secure airway, assist ventilation if depressed, give supplemental oxygen. 2. Decontamination – remove contaminated clothing, wash skin thoroughly (dichlorvos is well absorbed dermally); gastric lavage/activated charcoal only if ingestion was recent and airway is protected. 3. Atropine – titrate to effect (drying secretions, resolution of bronchospasm/bradycardia), doses may need to be much higher and more frequent than in adults, weight-based. 4. Pralidoxime – early administration (before enzyme aging occurs) to reactivate acetylcholinesterase, particularly important for reversing nicotinic (neuromuscular) effects. 5. Seizure control – benzodiazepines (diazepam) if seizures occur. 6. Supportive care – monitor for respiratory failure (leading cause of death), electrolytes, continuous cardiorespiratory monitoring given delayed/prolonged toxicity risk (some organophosphates cause intermediate syndrome with delayed neuromuscular weakness). 7. Avoid – morphine, succinylcholine, and other drugs that may worsen cholinergic toxicity or interact adversely with pseudocholinesterase inhibition.
Attention Deficit Disorder (ADD)
Standard Answer:
(2012 CNS Assessment) Definition: A neurodevelopmental disorder characterized by persistent, developmentally inappropriate patterns of inattention and/or hyperactivity-impulsivity that impair functioning across multiple settings (school, home, work). Drug management: 1. Stimulants (first-line): Methylphenidate, Amphetamine salts — block dopamine and norepinephrine reuptake transporters (and promote release), increasing catecholaminergic tone in the prefrontal cortex, improving attention/impulse control. Adverse effects: appetite suppression, insomnia, growth suppression (with long-term use in children), increased heart rate/blood pressure, potential for abuse/dependence. 2. Non-stimulants: Atomoxetine (selective norepinephrine reuptake inhibitor — no abuse potential, alternative when stimulants are contraindicated or poorly tolerated), Guanfacine/Clonidine (α2-agonists, useful particularly for hyperactivity/impulsivity and comorbid tics).
Toxicology — Heavy Metals, Gases, and Testing Methods
Standard Answer:
9a. Carbon Monoxide, Sulphur Dioxide, Nitrogen Dioxide, Particulates (2018 Paper II, 2017, 2016 — recurs) • Carbon monoxide (CO): ◦ Properties: colourless, odourless gas, produced by incomplete combustion. ◦ Mechanism of toxicity: binds haemoglobin with ~200–250 times the affinity of oxygen, forming carboxyhaemoglobin (COHb), reducing oxygen-carrying capacity; also shifts the oxygen-haemoglobin dissociation curve to the left, impairing oxygen release to tissues; directly inhibits cytochrome oxidase, impairing cellular respiration. ◦ Clinical features: headache, dizziness, confusion, cherry-red skin discolouration (classic but often absent), seizures, coma, cardiac ischaemia. ◦ Treatment: remove from exposure, 100% oxygen (accelerates dissociation of CO from haemoglobin, reducing COHb half-life from ~4–6 hours in room air to ~40–80 minutes), hyperbaric oxygen therapy for severe poisoning (further reduces COHb half-life, may reduce delayed neurological sequelae). • Sulphur dioxide (SO2): ◦ Properties: pungent, water-soluble gas, produced by burning sulphur-containing fuels. ◦ Mechanism of toxicity: high water solubility causes it to react with moisture in the upper respiratory tract, forming sulfurous acid, causing immediate irritation of the eyes, nose, and upper airway (bronchoconstriction, especially in asthmatics). ◦ Treatment: remove from exposure, bronchodilators, supportive respiratory care, corticosteroids for severe airway inflammation. • Nitrogen dioxide (NO2): ◦ Properties: less water-soluble than SO2, allowing deeper penetration into the lower respiratory tract before causing irritation. ◦ Mechanism of toxicity: causes delayed pulmonary oedema (may present hours after exposure with minimal initial symptoms — “silo-filler’s disease” in agricultural exposure), free radical-mediated lipid peroxidation of alveolar membranes. ◦ Treatment: supportive respiratory care, corticosteroids, monitoring for delayed pulmonary oedema even if initially asymptomatic. • Particulates (PM10 — particulate matter <10 microns): ◦ Definition: airborne particles small enough to be inhaled into the lower respiratory tract and deposited in the alveoli. ◦ Toxicology: causes chronic inflammation, oxidative stress, exacerbation of asthma/ COPD, associated with increased cardiovascular and respiratory morbidity/mortality with chronic exposure. 9b. Asbestos Dust (2016, 2011, “THEORY”) Fibrous silicate mineral; inhaled fibres deposit in the distal airways/alveoli, resisting clearance due to their fibre geometry, causing chronic inflammation, fibrosis, and oxidative DNA damage. Long latency (20–40 years) toxicological consequences: asbestosis (progressive pulmonary fibrosis), pleural plaques, mesothelioma (a signature, near-pathognomonic malignancy of asbestos exposure), and bronchogenic carcinoma (markedly potentiated by concurrent smoking — synergistic, not merely additive, risk). 9c. Lead and Cadmium (2018 Paper II [via heavy metals], Part II Resit, “Pharmacology 2”) • Lead: ◦ Target organs/effects: CNS (encephalopathy, especially in children — irreversible cognitive impairment even at low levels), peripheral nervous system (wrist/foot drop from motor neuropathy), haematological (inhibits ALA dehydratase and ferrochelatase in haem synthesis, causing microcytic anaemia with basophilic stippling), renal (proximal tubular damage, “lead nephropathy”), reproductive toxicity. ◦ Treatment/chelation: EDTA (calcium disodium edetate), Dimercaprol (BAL) for severe/encephalopathic cases, Succimer (DMSA) for oral chelation in less severe/ paediatric cases. • Cadmium: ◦ Target organs/effects: kidney (proximal tubular dysfunction — proteinuria, “Itai-itai disease” with bone pain/osteomalacia in severe chronic exposure), lung (emphysema with inhalational exposure), bone (osteoporosis/osteomalacia via interference with vitamin D metabolism and calcium handling). ◦ Treatment: primarily supportive; chelation therapy is generally ineffective/of limited benefit for cadmium (unlike lead) and may worsen renal toxicity; prevention of further exposure is key. 9d. Acute vs Chronic Toxicity; Critical vs Sub-critical Effects (using Lead as example) (2017 Paper II) • Acute toxicity – adverse effects resulting from a single or short-term high-level exposure, appearing rapidly (e.g., acute lead encephalopathy from massive ingestion). • Chronic toxicity – adverse effects resulting from repeated, low-level exposure over a prolonged period, often insidious in onset (e.g., chronic low-level lead exposure causing cumulative neurodevelopmental impairment in children, detectable only through biomonitoring). • Critical effect – the specific adverse effect that occurs at the lowest exposure level/dose in the most sensitive population, used to set exposure limits (for lead, this is neurodevelopmental toxicity in children, occurring at blood lead levels once considered “safe”). • Sub-critical effects – biological changes that occur at exposure levels below the critical effect threshold, representing early/subtle biomarkers of exposure without overt clinical toxicity (e.g., mild inhibition of ALA dehydratase activity at blood lead levels below those causing anaemia or encephalopathy). • Methods used in toxicity testing and risk assessment: ◦ Acute toxicity testing – LD50 determination. ◦ Sub-acute/sub-chronic and chronic toxicity studies – repeated-dose animal studies over weeks to the animal’s lifespan, assessing organ toxicity, carcinogenicity, and establishing the No Observed Adverse Effect Level (NOAEL). ◦ Genotoxicity testing – e.g., the Ames test (bacterial reverse mutation assay), assessing mutagenic potential as a surrogate for carcinogenic risk. ◦ Teratogenicity/reproductive toxicity studies. ◦ Risk assessment process: hazard identification → dose-response assessment (deriving NOAEL/reference dose) → exposure assessment (estimating actual human exposure) → risk characterization (combining hazard and exposure data to estimate population risk), often applying uncertainty/safety factors to extrapolate from animal data to humans. 9e. Ames Test (2011) A bacterial reverse-mutation assay using histidine-dependent Salmonella typhimurium strains; the test substance (with and without metabolic activation via liver S9 fraction, simulating human hepatic biotransformation) is applied to bacteria that cannot synthesize histidine; if the substance is mutagenic, it induces reverse mutations restoring histidine synthesis, allowing bacterial colony growth on histidine-deficient media. Colony counts (compared to control) provide a measure of mutagenic potential, used as a rapid, inexpensive screening test correlating (imperfectly) with carcinogenic potential, since many carcinogens act via genotoxic/mutagenic mechanisms. 9f. Methyl Mercury and Cadmium — Target Organs, Effects, Mechanisms, Removal (2010 Paper II) • Methyl mercury: ◦ Target organ: primarily the CNS (crosses blood-brain barrier readily due to lipid solubility) — causes paraesthesia, ataxia, visual field constriction, hearing impairment, and in severe cases (Minamata disease), profound neurological disability; crosses the placenta causing severe fetal neurotoxicity (methylmercury is more dangerous to the developing fetus than to adults at equivalent exposure). ◦ Mechanism: binds sulfhydryl groups on proteins/enzymes, disrupting cellular function, generates oxidative stress, disrupts microtubule function impairing neuronal migration in the developing brain. ◦ Removal/treatment: chelation with agents such as DMSA/DMPS (dimercaprol is less effective and can worsen CNS mercury redistribution); primary strategy is avoidance of further exposure (e.g., limiting consumption of large predatory fish). • Cadmium: See 9c above.
Toxin/Toxicant Mechanism Comparisons
Standard Answer:
(2018 Paper II) Tetrodotoxin vs Tetanus neurotoxin: • Tetrodotoxin (from pufferfish) blocks voltage-gated Na⁺ channels on the extracellular side of excitable membranes (nerve and muscle), preventing action potential generation, causing progressive flaccid paralysis and potentially fatal respiratory failure, while consciousness is typically preserved. • Tetanus neurotoxin (from Clostridium tetani) is taken up at the neuromuscular junction and transported retrogradely to the spinal cord, where it cleaves synaptobrevin (VAMP), blocking release of the inhibitory neurotransmitters glycine and GABA from inhibitory interneurons (Renshaw cells), causing disinhibition of motor neurons and spastic paralysis (rigidity, spasms — trismus/lockjaw, opisthotonus) — mechanistically opposite in effect to tetrodotoxin despite both being neurotoxins. Botulinum toxin A — indications and contraindications: • Mechanism: cleaves SNARE proteins (SNAP-25) at the presynaptic neuromuscular junction, preventing ACh vesicle fusion/release, causing flaccid paralysis. • Indications: cervical dystonia, blepharospasm, spasticity (post-stroke, cerebral palsy), chronic migraine prophylaxis, hyperhidrosis, cosmetic use (facial wrinkles), strabismus, achalasia (injected into lower oesophageal sphincter). • Contraindications: neuromuscular junction disorders (myasthenia gravis, Eaton-Lambert syndrome — risk of severe/generalized weakness), infection at injection site, pregnancy/breastfeeding (limited safety data), known hypersensitivity.
Local Anaesthetics and Stages of Anaesthesia (short notes)
Standard Answer:
(2010 Paper II, “THEORY”) See Section 4 Q4 above for full detail on local anaesthetic mechanism and stages of anaesthesia.