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Here are complete answers for every question on your pharmacology paper:

MCQ Answers

Q9. A Type 1 Diabetes patient taking insulin for 6 months - preferred route? Answer: C. SC (Subcutaneous)

Reason: Insulin is a polypeptide - it gets destroyed in the GI tract (so oral is not possible). IV is reserved for emergencies (e.g., DKA management). IM gives erratic absorption. SC is the standard long-term route: it provides predictable, sustained absorption and allows self-administration. The subcutaneous tissue (abdomen, thigh, arm) creates a depot for gradual release.

Q10. A boy traveling by bus - drug to prevent motion sickness? Answer: A. Promethazine

Reason: Motion sickness involves the vestibular system and requires drugs that cross the blood-brain barrier (BBB) to act centrally. Promethazine is a first-generation H1 antihistamine with strong anticholinergic and antiemetic properties - it crosses the BBB and blocks muscarinic receptors in the vomiting center/labyrinth. Cetirizine, Loratadine, and Fexofenadine are 2nd/3rd generation antihistamines that do NOT significantly cross the BBB and are therefore ineffective for motion sickness.

Section 2 - Long Answer (10 marks)

Classification of Beta Blockers; Side Effects and Therapeutic Uses

Classification

A. Based on Cardioselectivity (beta-1 selectivity):

Category	Drugs	Beta-1 : Beta-2 Selectivity
Non-selective	Propranolol, Timolol, Nadolol, Pindolol, Sotalol	Block both β1 and β2
Cardioselective (β1-selective)	Metoprolol, Atenolol, Bisoprolol, Acebutolol, Esmolol	Preferentially block β1

B. Based on Intrinsic Sympathomimetic Activity (ISA / Partial Agonist Activity):

Category	Drugs
With ISA	Pindolol, Acebutolol, Oxprenolol
Without ISA	Propranolol, Metoprolol, Atenolol, Timolol

ISA drugs cause less bradycardia and less lipid disturbance at rest.

C. Based on Membrane-Stabilizing Activity (MSA / quinidine-like):

With MSA: Propranolol, Acebutolol, Oxprenolol
Without MSA: Atenolol, Nadolol, Timolol

D. With additional alpha-blocking property:

Labetalol, Carvedilol (block α1 + β1 + β2) - used in hypertension and heart failure

E. Based on lipid solubility (affects CNS penetration):

Lipid soluble	Water soluble
Propranolol, Metoprolol, Labetalol	Atenolol, Nadolol, Sotalol
Cross BBB - more CNS effects	Less CNS effects, renally excreted

Therapeutic Uses

Hypertension - reduce cardiac output and renin release (Atenolol, Metoprolol)
Angina pectoris - reduce heart rate and oxygen demand (Propranolol, Metoprolol)
Cardiac arrhythmias - Class II antiarrhythmic; useful in SVT, AF rate control, VT (Propranolol, Esmolol, Sotalol)
Myocardial infarction - reduce mortality, prevent reinfarction (Metoprolol, Atenolol)
Heart failure - paradoxically beneficial in chronic HF; reduce sympathetic overdrive (Carvedilol, Metoprolol succinate, Bisoprolol)
Thyrotoxicosis - control tachycardia and sympathomimetic symptoms (Propranolol)
Glaucoma - reduce aqueous humor production (Timolol eye drops)
Migraine prophylaxis - Propranolol, Metoprolol
Essential tremor - Propranolol
Anxiety / situational phobia - Propranolol (blocks peripheral tremor, palpitations)
Pheochromocytoma - after adequate alpha-blockade, beta blockers control tachycardia
Portal hypertension - Propranolol reduces variceal bleeding risk

Side Effects

Cardiovascular:

Bradycardia, heart block (AV block)
Worsening of heart failure (acute decompensation if started abruptly)
Cold extremities, Raynaud's phenomenon (beta-2 block reduces peripheral vasodilation)
Rebound hypertension/angina on abrupt withdrawal

Respiratory:

Bronchoconstriction (beta-2 block) - dangerous in asthmatics and COPD; cardioselective drugs are relatively safer

Metabolic:

Masking of hypoglycemia symptoms (tachycardia masked) - important in diabetics on insulin
Impaired glycogenolysis - prolonged hypoglycemia
Raised triglycerides, reduced HDL (except ISA drugs and Carvedilol)

CNS (lipid-soluble drugs):

Fatigue, sleep disturbances, nightmares, depression (Propranolol > Atenolol)

Others:

Erectile dysfunction
Increased risk of developing type 2 diabetes (when combined with thiazides)
Sotalol: QT prolongation, Torsades de Pointes

Section 3 - Reasoning Questions (3 x 5)

A. Urine is alkalinized in barbiturate and salicylate poisoning

Both barbiturates and salicylates are weak acids (pKa ~3-8). The principle used is ion trapping. In alkaline urine (pH 7.5-8.5), these weak acids are predominantly in their ionized form (A⁻). Ionized molecules cannot cross lipid membranes, so they cannot be reabsorbed from the renal tubule back into the blood. This "traps" the drug in the urine and significantly increases its renal excretion. Sodium bicarbonate IV is given to achieve urinary alkalinization. This is an application of the Henderson-Hasselbalch principle to enhance elimination.

B. Folinic acid is given along with Methotrexate

Methotrexate (MTX) is a folate antagonist - it inhibits dihydrofolate reductase (DHFR), preventing conversion of dihydrofolate to tetrahydrofolate (THF, active form). This depletes active folate co-factors needed for purine and thymidylate synthesis, killing rapidly dividing cells. However, this also causes toxicity to normal tissues (mucositis, myelosuppression). Folinic acid (Leucovorin = 5-formyl-THF) is the active reduced form of folate that bypasses DHFR entirely - it does not need to be reduced by DHFR to become active. It rescues normal cells from MTX toxicity ("Leucovorin rescue") without significantly protecting the tumor cells (which are exposed to higher drug concentrations). This is given 24 hours after high-dose MTX.

C. Atropine is contraindicated in narrow angle glaucoma

Atropine is an antimuscarinic drug. It blocks M3 muscarinic receptors in the iris sphincter muscle (causing mydriasis - pupil dilation) and in the ciliary muscle (causing cycloplegia). In narrow-angle (closed-angle) glaucoma, the anterior chamber angle is already narrowed. Mydriasis (pupil dilation) causes the iris to bunch up at the periphery, mechanically blocking the trabecular meshwork at the iridocorneal angle. This obstructs drainage of aqueous humor, causing a sudden and dangerous rise in intraocular pressure (acute angle-closure crisis), which can lead to blindness if untreated.

D. Glycopyrrolate is given before anaesthesia as a preanesthetic medication

Glycopyrrolate is a quaternary ammonium antimuscarinic drug given as a preanesthetic agent for the following reasons:

Antisialagogue effect: Blocks M3 receptors in salivary/bronchial glands - reduces secretions in the airway, preventing aspiration and improving intubation conditions.
Prevents bradycardia: Halogenated anesthetics and manipulation of the airway can trigger vagal (M2) reflexes causing severe bradycardia; glycopyrrolate blocks this.
Reduces gastric secretions: Decreases gastric acid and motility.
Advantage over Atropine: Being a quaternary compound, glycopyrrolate does NOT cross the BBB - so it avoids CNS effects like sedation, confusion, and does not cause tachycardia as strongly as atropine. It also does not cross the placenta, making it safer.

E. Aspirin should be avoided in patients with peptic ulcer disease

Aspirin (acetylsalicylic acid) causes gastric damage by two mechanisms:

Direct irritation: Being a weak acid, aspirin in the acidic gastric environment remains in its un-ionized (lipid-soluble) form, which penetrates the gastric mucosal cells and causes direct injury.
Inhibition of COX-1: Aspirin irreversibly inhibits COX-1, which normally produces prostaglandins (PGE2, PGI2). These prostaglandins are cytoprotective - they stimulate mucus and bicarbonate secretion, maintain mucosal blood flow, and reduce acid secretion. Without this protective prostaglandin production, the stomach lining becomes vulnerable to acid damage - worsening existing ulcers and predisposing to bleeding.

Section 4 - Short Notes / Applied Aspect (4 x 5)

A. Adrenaline in acute anaphylactic shock

Anaphylaxis causes: massive vasodilation (hypotension), bronchoconstriction, angioedema, and increased vascular permeability. Adrenaline (epinephrine) acts on:

α1 receptors: Causes vasoconstriction - raises blood pressure, reduces mucosal edema/angioedema
β1 receptors: Increases heart rate and cardiac output - reverses hypotension/cardiac collapse
β2 receptors: Causes bronchodilation - relieves bronchoconstriction; also inhibits mast cell degranulation (reducing histamine/mediator release)

Route: IM into the lateral thigh (vastus lateralis) is preferred - faster absorption than SC, avoids IV complications. Dose: 0.5 mg (0.5 mL of 1:1000) IM in adults. Adrenaline is the ONLY drug that addresses all life-threatening components of anaphylaxis simultaneously - no antihistamine or corticosteroid can substitute for it in the acute phase.

B. Pharmacological basis of N-acetylcysteine (NAC) in Paracetamol poisoning

Normal paracetamol metabolism: ~90% conjugated with glucuronide/sulfate (non-toxic). ~5-10% oxidized by CYP2E1 to a toxic reactive metabolite called NAPQI (N-acetyl-p-benzoquinone imine). Normally, NAPQI is rapidly detoxified by conjugation with glutathione (GSH).

In overdose: The glucuronide/sulfate pathways are saturated. More drug is shunted to CYP2E1, producing excess NAPQI. Hepatic glutathione stores are depleted. Unbound NAPQI covalently binds to hepatic cell proteins causing centrilobular hepatic necrosis (can be fatal).

NAC mechanism: NAC acts by:

Directly replenishing glutathione (GSH) - NAC is a GSH precursor (it provides cysteine)
Acting as a direct antioxidant/scavenger of NAPQI
Providing sulfate groups (alternative detoxification pathway)

Most effective within 8-10 hours of overdose; still beneficial up to 24 hours. NAC is the specific antidote for paracetamol poisoning.

C. Sublingual route - advantages and disadvantages

Advantages	Disadvantages
Drug absorbed directly into systemic circulation via sublingual veins - bypasses portal circulation (no first-pass metabolism)	Only small doses can be given
Rapid onset of action (e.g., GTN in 1-2 min)	Drug must be lipid-soluble and potent
Avoids gastric acid degradation	Unpleasant taste
Patient can spit out drug and stop absorption if needed	Irritation of oral mucosa with repeated use
No need for water/swallowing	Short duration of action
Useful when oral absorption is poor	Not suitable for drugs that cause mucosal irritation

Classic examples: Glyceryl trinitrate (GTN) for acute angina, Buprenorphine, Nifedipine (used sublingually in emergencies).

D. Drugs used for treatment of migraine

Acute/Abortive treatment:

Triptans (5-HT1B/1D agonists): Sumatriptan (drug of choice), Rizatriptan, Zolmitriptan - cause vasoconstriction of dilated meningeal vessels and inhibit trigeminal nerve transmission
NSAIDs: Ibuprofen, Naproxen, Aspirin - for mild-moderate attacks
Ergot alkaloids: Ergotamine, Dihydroergotamine (DHE) - 5-HT and alpha agonist; vasoconstriction
Antiemetics: Metoclopramide, Domperidone (also improve gastric motility, aiding drug absorption)
Gepants (CGRP receptor antagonists): Rimegepant, Ubrogepant - newer agents

Prophylactic treatment (given daily):

Beta blockers: Propranolol, Metoprolol (first line)
TCAs: Amitriptyline
Anticonvulsants: Sodium valproate, Topiramate
CCBs: Flunarizine, Verapamil
Anti-CGRP monoclonal antibodies: Erenumab, Fremanezumab (newer biologics)

E. Plasma half-life (t½) of drugs

Definition: Plasma half-life (t½) is the time required for the plasma concentration of a drug to fall to half its original value after distribution equilibrium has been achieved.

Formula: t½ = 0.693 × Vd / CL (where Vd = volume of distribution, CL = clearance)

Significance:

Determines dosing interval - drugs with short t½ need frequent dosing; long t½ allows once-daily dosing
Determines time to reach steady state - approximately 4-5 half-lives to reach steady state
Determines time for drug to be eliminated - ~5 half-lives for complete elimination (~97%)
Helps in predicting duration of drug action
Useful in loading dose calculations and adjusting dose in renal/hepatic impairment

t½ category	Example
Very short (minutes)	Adenosine, Esmolol
Short (hours)	Penicillin, Aspirin
Medium (6-12 h)	Metformin
Long (>24 h)	Amiodarone, Digoxin
Very long (weeks)	Chloroquine

Section 5 - Differentiate Between (5 x 3)

A. First Generation vs Second Generation Antihistamines

Feature	1st Generation	2nd Generation
Examples	Diphenhydramine, Promethazine, Chlorpheniramine, Cyclizine	Cetirizine, Loratadine, Fexofenadine, Desloratadine
CNS penetration	Yes (lipid-soluble)	Minimal/No
Sedation	Marked	Little to none
Anticholinergic effects	Present (dry mouth, urinary retention, blurred vision)	Absent
Duration of action	Short (4-6 hrs)	Long (12-24 hrs)
Dosing	3-4 times/day	Once daily
Motion sickness use	Yes (Promethazine, Dimenhydrinate)	No
Antiemetic use	Yes	No
Use in allergic rhinitis	Less preferred (sedation)	Preferred

B. Drug Synergism vs Drug Antagonism

Feature	Synergism	Antagonism
Definition	Two drugs produce an effect greater than or equal to the sum of individual effects	One drug reduces or abolishes the effect of another
Types	Additive (1+1=2), Potentiation (1+0=2)	Competitive, Non-competitive, Chemical, Physiological
Example (Additive)	Aspirin + Codeine for pain	--
Example (Potentiation)	Alcohol + Benzodiazepine (CNS depression)	--
Example (Competitive)	--	Naloxone blocks morphine (opioid receptor)
Example (Non-competitive)	--	Phenoxybenzamine (irreversible α-blocker) vs adrenaline
Example (Physiological)	--	Insulin vs Glucagon
Example (Chemical)	--	Dimercaprol chelates heavy metals
Clinical use	Combination therapy (e.g., anti-TB drugs, cancer)	Antidotes, managing overdose

C. First Order vs Zero Order Kinetics of Drug Elimination

Feature	First Order Kinetics	Zero Order Kinetics
Definition	A constant fraction of drug is eliminated per unit time	A constant amount of drug is eliminated per unit time
Rate of elimination	Proportional to plasma concentration	Independent of plasma concentration (saturated)
Half-life	Constant, independent of dose	Not constant - increases with dose
Plasma concentration-time curve	Exponential (linear on log scale)	Linear (non-linear/straight line on arithmetic scale)
Dose-response	Predictable, proportional	Unpredictable, small dose increase → large effect
Examples	Most drugs (Aspirin at low doses, most antibiotics)	Phenytoin, Ethanol, Aspirin (at high doses), Warfarin (at high doses)
Clinical importance	Safe, predictable	Dangerous: small overdose → toxicity; need therapeutic drug monitoring
Mechanism	Elimination pathways not saturated	Elimination pathways (enzymes/transporters) are saturated (Michaelis-Menten kinetics)

Section 6 - Short Notes (5 x 4)

A. Enterohepatic Circulation of Drugs

Definition: The process by which a drug (or its metabolite) excreted in bile into the intestine is reabsorbed from the intestine back into the portal blood, returned to the liver, and re-excreted - forming a cycle.

Mechanism:

Drug absorbed from intestine → reaches liver via portal vein
Liver conjugates drug (glucuronide/sulfate) → excreted into bile → enters intestine
Intestinal bacteria (β-glucuronidase) deconjugate the drug → releasing the free (active) drug
Lipid-soluble free drug is reabsorbed from the intestine → portal vein → liver → cycle continues

Consequences:

Prolongs drug half-life and duration of action
Increases drug exposure (higher AUC)
Interrupting the cycle (e.g., with activated charcoal or antibiotics) speeds elimination

Examples: Morphine, Chloramphenicol, Oral contraceptives (ethinylestradiol - important: broad-spectrum antibiotics can reduce OCP efficacy by disrupting enterohepatic circulation), Rifampicin, Digoxin, Warfarin.

B. Classification of Alpha Adrenergic Blockers

I. Non-selective (block α1 and α2):

Reversible/Competitive: Phentolamine, Tolazoline
Irreversible/Non-competitive: Phenoxybenzamine

II. Selective α1 blockers:

Prazosin (short-acting, prototype)
Terazosin, Doxazosin (long-acting)
Tamsulosin, Alfuzosin (selective for α1A in prostate - used for BPH)

III. Selective α2 blockers:

Yohimbine (research use, ED)

IV. Alpha blockers with additional properties:

Labetalol, Carvedilol (also β-blockers)
Urapidil (also central 5-HT1A agonist)

Therapeutic Uses of Alpha blockers:

Hypertension (Prazosin, Doxazosin)
Benign Prostatic Hyperplasia/BPH (Tamsulosin, Alfuzosin - relax smooth muscle of bladder neck and prostate)
Pheochromocytoma (Phenoxybenzamine - preoperative management)
Raynaud's phenomenon (Prazosin)
Erectile dysfunction (Yohimbine)

Side effects: Postural hypotension ("first-dose phenomenon" with Prazosin), reflex tachycardia (with non-selective), nasal stuffiness, fluid retention.

C. Therapeutic Uses of Atropine

Atropine is a competitive, reversible antagonist at muscarinic (M1, M2, M3) receptors.

Preanaesthetic medication: Reduces secretions (antisialagogue), prevents reflex bradycardia
Organophosphate poisoning: Reverses SLUDGE effects (Salivation, Lacrimation, Urination, Defecation, GI cramps, Emesis) - given in large doses until secretions dry up
Bradycardia / Heart block: Blocks M2 receptors in SA/AV nodes - increases heart rate
Ophthalmic uses:
- Mydriasis (pupil dilation) for fundus examination
- Cycloplegia (ciliary muscle paralysis) for refraction testing in children
Antispasmodic: Reduces GI and ureteric colic (blocks M3 in smooth muscle)
Peptic ulcer disease: Reduces gastric acid secretion (M1 blockade) - largely replaced by H2 blockers/PPIs
Motion sickness: Hyoscine (scopolamine) - related anticholinergic
COPD/Asthma: Ipratropium (inhaled antimuscarinic) - related drug, not atropine itself
Antidote for physostigmine/neostigmine overdose

D. Bioavailability of Drugs

Definition: Bioavailability (F) is the fraction (proportion) of an administered drug that reaches the systemic circulation in an unchanged (active) form, and the rate at which it does so.

For IV administration, F = 1 (100%) by definition.

Formula: F = (AUC oral / AUC IV) × 100%

Factors affecting bioavailability:

First-pass metabolism (hepatic): Major cause of low oral bioavailability - drug absorbed from intestine passes through liver via portal vein and is extensively metabolized before reaching systemic circulation. Examples: Propranolol (F ~25%), Morphine (F ~30%), Lignocaine (F ~3% - not given orally), GTN (F <1% - given sublingually/transdermally)
Solubility: Lipid-soluble drugs better absorbed; water-soluble poorly absorbed orally
Particle size and formulation: Affects dissolution rate
GI motility: Rapid motility reduces absorption
Gut wall metabolism (CYP3A4 in enterocytes)
P-glycoprotein (efflux pump): Pumps drug back into gut lumen
Drug interactions: Enzyme inducers (Rifampicin) reduce bioavailability; enzyme inhibitors (Grapefruit juice/CYP3A4) increase it
Food effects: May increase or decrease depending on drug

Clinical relevance: Explains why oral and parenteral doses differ (e.g., IV morphine 10 mg ≈ oral morphine 30 mg); guides dose calculation when switching routes.

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