Pharmacology
MBBS Pharmacology — high-yield long questions and short notes from K.D. Tripathi, covering general pharmacology, autonomic and cardiovascular drugs, CNS, autacoids, chemotherapy, endocrine and more, written to the marks with mechanisms, classification, clinical uses, adverse effects and pearls.
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Definition
Neurohumoral transmission is the transfer of impulses across synapses by chemical transmitters acting on autonomic receptors.
Transmitters
- Acetylcholine — all preganglionic, parasympathetic postganglionic
- Noradrenaline — sympathetic postganglionic
- Adrenaline — adrenal medulla
Cholinergic Receptors
- Muscarinic (M1–M5) — heart, glands, smooth muscle
- Nicotinic — ganglia, skeletal muscle
Adrenergic Receptors
- α1 — vasoconstriction; α2 — ↓ transmitter release
- β1 — heart (↑ rate, force)
- β2 — bronchodilation, vasodilation
Transmitters cross the synapse to activate specific autonomic receptors. Receptor Main effect M (muscarinic) ↓ heart rate, secretions α1 Vasoconstriction β1 ↑ Heart rate β2 Bronchodilation Applied
- β1 blockers in hypertension
- β2 agonists in asthma
🔑KEY POINTS TO REMEMBER- ACh: all preganglionic + parasympathetic postganglionic; NA: sympathetic.
- Cholinergic: muscarinic & nicotinic.
- Adrenergic: α1 (vasoconstriction), β1 (heart), β2 (bronchodilation).
📚SOURCES: Essentials of Medical Pharmacology (K.D. Tripathi); Goodman & Gilman’s The Pharmacological Basis of Therapeutics; Katzung’s Basic & Clinical Pharmacology.Definition
Cholinergic drugs (cholinomimetics) mimic acetylcholine, acting directly on receptors or indirectly by inhibiting cholinesterase.
Classification
- Direct-acting — pilocarpine, bethanechol, carbachol
- Indirect (reversible) — neostigmine, physostigmine, edrophonium
- Indirect (irreversible) — organophosphates
Actions
- ↓ Heart rate, ↓ BP
- ↑ Secretions (salivary, gastric)
- Bronchoconstriction, ↑ gut motility
- Miosis, ↓ intraocular pressure
These drugs boost acetylcholine action, producing parasympathetic effects. Drug Use Pilocarpine Glaucoma Neostigmine Myasthenia gravis Bethanechol Urinary retention Applied
- Myasthenia gravis, glaucoma
- Post-operative urinary retention
🔑KEY POINTS TO REMEMBER- Direct (pilocarpine) vs indirect (neostigmine) cholinomimetics.
- Effects: ↓ HR, ↑ secretions, miosis, ↑ gut motility.
- Used in myasthenia gravis and glaucoma.
📚SOURCES: Essentials of Medical Pharmacology (K.D. Tripathi); Goodman & Gilman’s The Pharmacological Basis of Therapeutics; Katzung’s Basic & Clinical Pharmacology.Definition
Anticholinergic (antimuscarinic) drugs block muscarinic receptors, opposing parasympathetic actions.
Drugs
- Atropine, hyoscine (natural)
- Ipratropium (inhaled), tiotropium
- Dicyclomine (antispasmodic)
- Tropicamide (eye)
Actions
- ↑ Heart rate (blocks vagus)
- ↓ Secretions (dry mouth)
- Bronchodilation, ↓ gut motility
- Mydriasis, cycloplegia; urinary retention
Blocking muscarinic receptors reverses parasympathetic activity. Drug Use Atropine Bradycardia, poisoning Ipratropium COPD, asthma Tropicamide Eye examination Applied
- Organophosphate poisoning (atropine)
- Preanaesthetic medication
🔑KEY POINTS TO REMEMBER- Block muscarinic receptors → ↑ HR, dry mouth, mydriasis, bronchodilation.
- Atropine, ipratropium, tropicamide.
- Atropine is the antidote in organophosphate poisoning.
📚SOURCES: Essentials of Medical Pharmacology (K.D. Tripathi); Goodman & Gilman’s The Pharmacological Basis of Therapeutics; Katzung’s Basic & Clinical Pharmacology.Definition
Adrenergic drugs (sympathomimetics) mimic the actions of noradrenaline and adrenaline at adrenergic receptors.
Classification
- Direct-acting — adrenaline, noradrenaline, phenylephrine, salbutamol
- Indirect-acting — tyramine, amphetamine
- Mixed — ephedrine
Receptor Effects
- α1 → vasoconstriction (↑ BP)
- β1 → ↑ heart rate and force
- β2 → bronchodilation, uterine relaxation
These drugs reproduce sympathetic fight-or-flight responses. Drug Receptor Use Adrenaline α + β Anaphylaxis Phenylephrine α1 Nasal decongestant Salbutamol β2 Asthma Applied
- Anaphylaxis, shock, cardiac arrest
- Asthma (β2 agonists)
🔑KEY POINTS TO REMEMBER- Direct (adrenaline, salbutamol), indirect (amphetamine), mixed (ephedrine).
- α1 vasoconstriction, β1 cardiac, β2 bronchodilation.
- Adrenaline is first-line in anaphylaxis.
📚SOURCES: Essentials of Medical Pharmacology (K.D. Tripathi); Goodman & Gilman’s The Pharmacological Basis of Therapeutics; Katzung’s Basic & Clinical Pharmacology.Definition
Adrenergic blocking drugs antagonise α or β adrenergic receptors, opposing sympathetic effects.
Alpha Blockers
- Non-selective — phenoxybenzamine, phentolamine
- α1-selective — prazosin, tamsulosin
- Effect: vasodilation, ↓ BP
Beta Blockers
- Non-selective — propranolol
- Cardioselective (β1) — atenolol, metoprolol
- Effect: ↓ heart rate, ↓ BP, ↓ renin
Alpha blockers dilate vessels; beta blockers slow and weaken the heart. Drug Type Use Prazosin α1 blocker Hypertension, BPH Propranolol Non-selective β Angina, arrhythmia Atenolol β1 selective Hypertension Applied
- Avoid non-selective β blockers in asthma
- Phaeochromocytoma (α block before β)
🔑KEY POINTS TO REMEMBER- α blockers (prazosin) → vasodilation; β blockers → ↓ HR, ↓ BP.
- Cardioselective β1 (atenolol) safer in asthma.
- In phaeochromocytoma block α before β.
📚SOURCES: Essentials of Medical Pharmacology (K.D. Tripathi); Goodman & Gilman’s The Pharmacological Basis of Therapeutics; Katzung’s Basic & Clinical Pharmacology.Definition
Organophosphate poisoning results from irreversible inhibition of cholinesterase, causing accumulation of acetylcholine.
Features (cholinergic crisis)
- Muscarinic — salivation, lacrimation, urination, defaecation, miosis, bronchorrhoea
- Nicotinic — fasciculations, muscle weakness, paralysis
- CNS — confusion, convulsions, coma
Treatment
- Atropine — blocks muscarinic effects
- Pralidoxime (2-PAM) — reactivates cholinesterase (give early)
- Decontamination, airway support, diazepam for fits
Blocking cholinesterase floods synapses with acetylcholine. Drug Action Atropine Blocks muscarinic effects Pralidoxime Reactivates enzyme Applied
- Common poisoning (insecticides)
- Pralidoxime ineffective after ‘ageing’
🔑KEY POINTS TO REMEMBER- Organophosphates irreversibly inhibit cholinesterase.
- Muscarinic + nicotinic + CNS features.
- Treat with atropine + pralidoxime (early).
📚SOURCES: Essentials of Medical Pharmacology (K.D. Tripathi); Goodman & Gilman’s The Pharmacological Basis of Therapeutics; Katzung’s Basic & Clinical Pharmacology.Definition
Neostigmine is a reversible anticholinesterase that increases acetylcholine at synapses, mainly acting peripherally.
Features
- Quaternary compound — does not cross the blood-brain barrier
- Reversible cholinesterase inhibition
- Also direct action on nicotinic receptors
Uses
- Myasthenia gravis
- Reversal of non-depolarising muscle relaxants
- Post-operative paralytic ileus, urinary retention
By sparing acetylcholine, neostigmine strengthens neuromuscular transmission. Feature Detail CNS entry No (quaternary) Main use Myasthenia gravis Applied
- Given with atropine (limits muscarinic effects)
- Physostigmine crosses into CNS (unlike neostigmine)
🔑KEY POINTS TO REMEMBER- Neostigmine = reversible anticholinesterase (peripheral only).
- Used in myasthenia gravis, reversal of relaxants.
- Combined with atropine (blocks muscarinic effects).
📚SOURCES: Essentials of Medical Pharmacology (K.D. Tripathi); Goodman & Gilman’s The Pharmacological Basis of Therapeutics; Katzung’s Basic & Clinical Pharmacology.Definition
Adrenaline (epinephrine) is a direct-acting sympathomimetic stimulating both α and β adrenergic receptors.
Actions
- α1 → vasoconstriction (↑ BP)
- β1 → ↑ heart rate and force
- β2 → bronchodilation
- Metabolic — ↑ glucose, ↑ lipolysis
Uses
- Anaphylaxis (drug of choice)
- Cardiac arrest
- With local anaesthetics (prolongs action)
- Control of superficial bleeding
Adrenaline raises blood pressure and opens airways — ideal in anaphylaxis. Receptor Effect α1 Vasoconstriction β1 ↑ Cardiac output β2 Bronchodilation Applied
- Anaphylaxis — 0.5 mg IM (adult)
- Adverse: palpitations, hypertension, arrhythmia
🔑KEY POINTS TO REMEMBER- Adrenaline acts on α + β receptors.
- ↑ BP, ↑ HR, bronchodilation.
- Drug of choice in anaphylaxis (IM).
📚SOURCES: Essentials of Medical Pharmacology (K.D. Tripathi); Goodman & Gilman’s The Pharmacological Basis of Therapeutics; Katzung’s Basic & Clinical Pharmacology.Definition
Atropine is a naturally occurring antimuscarinic (anticholinergic) drug that blocks muscarinic receptors competitively.
Actions
- ↑ Heart rate (blocks vagal tone)
- ↓ Secretions (dry mouth, ↓ sweating)
- Mydriasis + cycloplegia
- Bronchodilation, ↓ gut motility
Uses
- Organophosphate / mushroom poisoning
- Bradycardia
- Preanaesthetic medication (↓ secretions)
- With neostigmine for reversal
Atropine blocks muscarinic effects, reversing cholinergic excess. System Effect Heart ↑ rate Eye Mydriasis, cycloplegia Glands ↓ secretion Applied
- Atropine poisoning: hot, dry, red, mad, blind
- Contraindicated in glaucoma, BPH
🔑KEY POINTS TO REMEMBER- Atropine = competitive muscarinic blocker.
- ↑ HR, dry mouth, mydriasis, bronchodilation.
- Antidote for organophosphate poisoning.
📚SOURCES: Essentials of Medical Pharmacology (K.D. Tripathi); Goodman & Gilman’s The Pharmacological Basis of Therapeutics; Katzung’s Basic & Clinical Pharmacology.Definition
Selective β₂ agonists such as salbutamol stimulate β₂ receptors, causing bronchodilation with fewer cardiac effects.
Actions
- Bronchodilation (main effect)
- Uterine relaxation (tocolysis)
- Skeletal muscle tremor
- Minimal β1 (cardiac) effect at usual dose
Uses
- Bronchial asthma (inhaled, reliever)
- COPD
- Premature labour (tocolysis)
- Hyperkalaemia (drives K⁺ into cells)
Selective β₂ stimulation opens airways without much cardiac effect. Drug Duration Salbutamol Short-acting Salmeterol Long-acting Applied
- Inhaled route → fewer systemic effects
- Adverse: tremor, tachycardia, hypokalaemia
🔑KEY POINTS TO REMEMBER- β₂ agonists → bronchodilation (salbutamol short, salmeterol long).
- Also used for tocolysis and hyperkalaemia.
- Adverse: tremor, tachycardia, hypokalaemia.
📚SOURCES: Essentials of Medical Pharmacology (K.D. Tripathi); Goodman & Gilman’s The Pharmacological Basis of Therapeutics; Katzung’s Basic & Clinical Pharmacology.Definition
Alpha-adrenergic blockers antagonise α receptors; prazosin is a selective α1 blocker causing vasodilation.
Actions
- α1 blockade → arteriolar + venous dilation
- ↓ Blood pressure
- Relaxes bladder neck and prostatic smooth muscle
Uses
- Hypertension
- Benign prostatic hyperplasia (tamsulosin)
- Phaeochromocytoma (phenoxybenzamine)
- Raynaud’s phenomenon
Blocking α1 receptors relaxes vessels and prostatic smooth muscle. Drug Selectivity Prazosin α1 Tamsulosin α1A (prostate) Phenoxybenzamine Non-selective Applied
- First-dose postural hypotension (give at night)
- α block before β in phaeochromocytoma
🔑KEY POINTS TO REMEMBER- α1 blockers → vasodilation, ↓ BP.
- Prazosin (hypertension), tamsulosin (BPH).
- First-dose postural hypotension is characteristic.
📚SOURCES: Essentials of Medical Pharmacology (K.D. Tripathi); Goodman & Gilman’s The Pharmacological Basis of Therapeutics; Katzung’s Basic & Clinical Pharmacology.Definition
Dopamine is a catecholamine and sympathomimetic whose effects are dose-dependent, used in shock.
Dose-Dependent Actions
- Low dose — dopaminergic (renal vasodilation, ↑ urine output)
- Moderate dose — β1 (↑ cardiac output)
- High dose — α1 (vasoconstriction, ↑ BP)
Uses
- Cardiogenic and septic shock
- Acute heart failure
- Given as IV infusion (short half-life)
The receptor targeted — and so the effect — changes with infusion rate. Dose Receptor Effect Low Dopaminergic Renal blood flow Moderate β1 ↑ Contractility High α1 Vasoconstriction Applied
- Shock with oliguria
- Adverse: tachycardia, arrhythmia
🔑KEY POINTS TO REMEMBER- Dopamine effects are dose-dependent.
- Low = renal, moderate = β1 cardiac, high = α1 vasoconstriction.
- Used in shock as IV infusion.
📚SOURCES: Essentials of Medical Pharmacology (K.D. Tripathi); Goodman & Gilman’s The Pharmacological Basis of Therapeutics; Katzung’s Basic & Clinical Pharmacology.