Complete Detailed Answers — Pharmacology Exam

Q-1 (Option A): Bioavailability

Definition (2 marks)

Bioavailability = F = f × (1 − ER) where f = fraction absorbed from the gut, ER = hepatic extraction ratio — Katzung's Basic and Clinical Pharmacology, 16th Ed.

Five Factors Affecting Oral Bioavailability (5 marks)

• Example: Morphine — almost completely absorbed (f ≈ 1), but hepatic extraction ratio = 0.67, giving oral bioavailability of only ~33%. Other examples: propranolol, lidocaine, nitroglycerin, meperidine.

• If a drug is too hydrophilic (e.g., atenolol), it cannot cross the lipid cell membranes of the gut wall.
• If too lipophilic (e.g., acyclovir), it is not soluble enough to cross the aqueous layer adjacent to cells.
• Both extremes lead to incomplete absorption and reduced bioavailability.

• Gastric pH affects ionization and solubility; acidic drugs (e.g., aspirin) are absorbed better in the acidic stomach while basic drugs are absorbed better in the alkaline small intestine.
• Delayed gastric emptying (food, anticholinergic drugs) slows drug entry into the small intestine, delaying and sometimes reducing absorption (e.g., levodopa absorption is delayed by food because amino acids compete for its transport).
• GI motility changes — rapid transit reduces contact time for absorption; malabsorption states reduce bioavailability.

Route with Maximum Bioavailability: Intravenous (IV) Route (4 + 4 marks)

Advantages of IV Route:

1. Complete and immediate bioavailability (100%) — no absorption step required.
2. Rapid onset of action — drug reaches target tissues almost instantly; ideal in emergencies (e.g., IV morphine for acute pain, IV diazepam for status epilepticus).
3. Precise control of dose — the exact amount delivered can be titrated carefully.
4. Large volumes can be infused when needed (e.g., IV fluids, antibiotics).
5. Drugs destroyed in the GI tract (e.g., insulin, heparin, proteins) can still be given.
6. Predictable plasma concentrations — eliminates variability from absorption.

Disadvantages of IV Route:

1. Irreversibility — once administered IV, the drug cannot be "taken back." Overdose is dangerous.
2. Risk of infection — venous access breaches skin integrity; risk of local thrombophlebitis, septicemia, and IV-site infection.
3. Requires trained personnel and sterile technique; not suitable for self-administration.
4. Painful — repeated injections cause discomfort; requires vascular access.
5. Incompatibility issues — drugs may precipitate or interact with IV fluids or other IV drugs.
6. Rapid delivery can cause adverse effects — bolus injections may cause "speed shock" (cardiovascular collapse, arrhythmias).
7. Not suitable for oily or insoluble preparations.

Q-1 (Option B): Classification of Anti-Hypertensive Drugs + ACE Inhibitors

Classification of Antihypertensive Drugs (3 marks)

• Thiazides: Hydrochlorothiazide, Chlorthalidone
• Loop diuretics: Furosemide, Bumetanide
• Potassium-sparing: Spironolactone, Amiloride

• ACE Inhibitors: Captopril, Enalapril, Lisinopril, Ramipril
• Angiotensin Receptor Blockers (ARBs): Losartan, Valsartan, Candesartan
• Direct Renin Inhibitors: Aliskiren

• Dihydropyridines: Amlodipine, Nifedipine (peripheral vasodilators)
• Non-dihydropyridines: Verapamil (cardiac), Diltiazem (cardiac + vascular)

• Beta-blockers: Propranolol, Atenolol, Metoprolol, Carvedilol
• Alpha-1 blockers: Prazosin, Terazosin, Doxazosin
• Combined alpha+beta blockers: Labetalol, Carvedilol
• Central-acting agents: Clonidine, Methyldopa

• Arteriolar: Hydralazine, Minoxidil
• Arteriolar + venous: Sodium nitroprusside

ACE Inhibitors — Mechanism of Action (4 marks)

1. Reduced Angiotensin II formation — Angiotensin II is a potent vasoconstrictor and stimulates aldosterone release. By blocking ACE:
   • Peripheral vascular resistance decreases → Blood pressure falls
   • Aldosterone secretion is reduced → Less sodium and water retention
   • Blood volume decreases
2. Reduced aldosterone secretion → Decreased sodium and water retention in the kidney → Reduced preload and blood pressure
3. Kinin accumulation — ACE also degrades bradykinin. When ACE is inhibited, bradykinin levels rise, leading to vasodilation via stimulation of prostacyclin and nitric oxide. This contributes to the antihypertensive effect but is also responsible for the characteristic dry cough side effect.
4. Renal hemodynamic effect — Angiotensin II preferentially constricts the efferent arteriole of the glomerulus. ACE inhibitors dilate the efferent arteriole, reducing intraglomerular pressure — this is beneficial in diabetic nephropathy to slow progression.

• Captopril — active drug (contains a sulfhydryl group)
• Enalapril, Lisinopril, Ramipril, Benazepril — prodrugs (ester prodrugs converted in the liver to active diacid form)

Uses of ACE Inhibitors (4 marks)

1. Hypertension — first-line for most patients, especially those with diabetes or proteinuria
2. Heart failure — reduce afterload and preload; improve survival; reduce hospitalization
3. Post-myocardial infarction — reduce cardiovascular mortality and development of heart failure
4. Diabetic nephropathy — reduce proteinuria and slow progression of kidney disease
5. Chronic kidney disease — nephroprotection regardless of diabetic status
6. Left ventricular hypertrophy — regression of LVH

Adverse Effects of ACE Inhibitors (4 marks)

1. Dry, persistent cough — most common (10–20% of patients); due to bradykinin accumulation; reason to switch to ARBs
2. Hyperkalemia — due to reduced aldosterone; caution with potassium supplements, potassium-sparing diuretics
3. First-dose hypotension — especially in volume-depleted patients or heart failure patients on diuretics
4. Renal impairment/Acute kidney injury — by dilating efferent arterioles; dangerous in bilateral renal artery stenosis (contraindicated)
5. Angioedema — rare but potentially life-threatening; bradykinin-mediated; swelling of face, lips, tongue, larynx; contraindication to future ACE inhibitor use
6. Teratogenicity — contraindicated in pregnancy (causes fetal renal agenesis, oligohydramnios, neonatal renal failure — pregnancy Category D/X in 2nd and 3rd trimesters)
7. Rash and taste disturbance — particularly with captopril (due to its SH group)
8. Neutropenia — rare; more with captopril

Q-2a: β-Blockers — Classification and Therapeutic Uses

Classification of Beta-Blockers

• Propranolol, Timolol, Nadolol, Pindolol (partial agonist), Sotalol

• Atenolol, Metoprolol, Bisoprolol, Acebutolol (partial agonist), Esmolol (ultra-short-acting IV)

• Labetalol — α1 + β1 + β2 blockade (ratio β:α = 3:1 oral)
• Carvedilol — non-selective β + α1 blockade; antioxidant properties
• Nebivolol — β1-selective + vasodilation via endothelial NO release (nitric oxide synthase induction)

• With ISA: Pindolol, Acebutolol (cause less bradycardia at rest)
• Without ISA: Propranolol, Atenolol, Metoprolol

• Lipophilic (CNS penetration): Propranolol, Metoprolol → risk of nightmares, depression
• Hydrophilic (renal excretion): Atenolol, Nadolol → fewer CNS effects

Mechanism of Action

1. Reducing heart rate and cardiac output (β1-blockade)
2. Reducing renin release from juxtaglomerular cells (β1)
3. Central reduction in sympathetic outflow
4. Blocking presynaptic β2 receptors reduces norepinephrine release over time

Therapeutic Uses

1. Hypertension — especially with coexisting angina, tachycardia, post-MI
2. Angina pectoris — reduce myocardial O₂ demand by reducing heart rate and contractility
3. Cardiac arrhythmias — atrial fibrillation rate control, SVT, ventricular arrhythmias post-MI; sotalol for ventricular arrhythmias
4. Heart failure — carvedilol, metoprolol succinate, bisoprolol reduce mortality in chronic stable heart failure
5. Post-myocardial infarction — reduce reinfarction risk and sudden death
6. Glaucoma — timolol eye drops reduce intraocular pressure (reduce aqueous humor formation)
7. Hyperthyroidism — propranolol controls tachycardia and tremor; blocks peripheral T4→T3 conversion
8. Migraine prophylaxis — propranolol, metoprolol
9. Essential tremor — propranolol
10. Pheochromocytoma — propranolol used after alpha-blockade to control tachycardia
11. Anxiety and performance anxiety — propranolol (peripheral symptoms)

Q-2b: Drugs for Gout — Classification and Drugs Used in Chronic Gout

Classification of Drugs for Gout

1. NSAIDs — Indomethacin, Naproxen (first-line)
2. Colchicine — used when NSAIDs contraindicated
3. Corticosteroids — oral prednisone or intra-articular injection

1. Xanthine oxidase inhibitors: Allopurinol, Febuxostat
2. Uricosuric agents: Probenecid, Sulfinpyrazone
3. Uricase (recombinant): Pegloticase (for refractory gout)

Drugs Used in Chronic Gout

1. Allopurinol (Xanthine Oxidase Inhibitor)

• Mechanism: Allopurinol and its active metabolite oxypurinol inhibit xanthine oxidase, the enzyme that converts hypoxanthine → xanthine → uric acid. This reduces uric acid production.
• Uses: First-line agent for chronic gout prevention; patients with frequent attacks (>2–3/year), tophi, nephrolithiasis, or renal impairment. Also used in tumor lysis syndrome prophylaxis.
• Dose: 100–300 mg/day (titrate); start low; also note that when starting allopurinol, colchicine or an NSAID should be co-administered for the first 3–6 months to prevent acute attacks triggered by mobilization of urate crystals.
• Adverse effects: Rash (common), hypersensitivity syndrome (Stevens–Johnson syndrome — rare but serious), GI upset, increased azathioprine/6-MP toxicity (xanthine oxidase normally inactivates these; inhibition causes toxicity — dose must be reduced)

2. Febuxostat (Xanthine Oxidase Inhibitor)

• Second-generation xanthine oxidase inhibitor; not a purine analog → fewer drug interactions
• Used when allopurinol is not tolerated
• Associated with slightly higher cardiovascular mortality in clinical trials → allopurinol preferred per current guidelines

3. Probenecid (Uricosuric Agent)

• Mechanism: Blocks URAT1 (urate transporter 1) in the proximal renal tubule, reducing tubular reabsorption of uric acid → increased urinary uric acid excretion
• Uses: Chronic gout in patients with normal renal function and under-excretors of urate
• Contraindications: Renal impairment (GFR < 50 mL/min), uric acid overproducers, renal stones
• Adverse effects: Renal calculi (risk reduced by high fluid intake and urine alkalinization), GI upset; also inhibits renal secretion of penicillin (used historically to prolong penicillin levels)

4. Colchicine (in chronic gout)

• Used at low doses (0.5–0.6 mg once or twice daily) as prophylaxis against acute flares, particularly when starting urate-lowering therapy
• Mechanism: Binds tubulin → inhibits microtubule polymerization → impairs neutrophil migration and urate crystal phagocytosis → anti-inflammatory
• Adverse effects: Diarrhea, nausea, vomiting (dose-limiting); rarely myopathy, neuropathy

Q-2c: Levodopa — Mechanism of Action, Adverse Effects, and Rationale for Combining with Carbidopa

Background — Parkinson's Disease

Levodopa — Mechanism of Action

• Dopamine itself does not cross the blood–brain barrier (BBB) and is therefore ineffective when given systemically.
• Levodopa (L-DOPA) is the immediate metabolic precursor of dopamine. It crosses the BBB via an L-amino acid transporter (LAT), where it is decarboxylated to dopamine by aromatic amino acid decarboxylase (DOPA decarboxylase).
• The newly formed dopamine stimulates D1 and D2 receptors in the striatum (primarily D2 receptors for therapeutic benefit), restoring dopaminergic tone and relieving parkinsonian symptoms.

Adverse Effects of Levodopa

• Nausea, vomiting, anorexia — due to dopamine stimulation of the chemoreceptor trigger zone (CTZ) in the area postrema (which lies outside the BBB). This effect is reduced when levodopa is combined with carbidopa.

• Postural (orthostatic) hypotension — due to peripheral dopamine acting on vascular receptors
• Cardiac arrhythmias (rare) — reduced significantly when carbidopa is co-administered

• Dyskinesias (involuntary movements — peak-dose dyskinesia) — a major long-term complication
• Psychiatric disturbances: vivid dreams, hallucinations, confusion, psychosis, paranoia — particularly in elderly
• Hypersexuality, impulsive behavior

• "Wearing-off" phenomenon — duration of effect after each dose shortens; the drug works for progressively shorter periods
• "On-off" phenomenon — sudden, unpredictable fluctuations between mobile ("on") and immobile ("off") states

• Pyridoxine (vitamin B6) antagonism — large doses of B6 enhance peripheral metabolism of levodopa, reducing its efficacy unless carbidopa is also given
• Dark discoloration of urine, sweat (dopamine metabolites)
• Contraindicated in psychosis and narrow-angle glaucoma

Rationale for Combining Levodopa with Carbidopa

• Only 1–3% of orally administered levodopa actually enters the brain. The remaining 97–99% is metabolized peripherally (in the gut wall, liver, and plasma) by peripheral dopa decarboxylase → converted to dopamine outside the CNS.
• This peripheral dopamine cannot cross the BBB and is responsible for all the peripheral side effects: nausea, vomiting, cardiac arrhythmias, postural hypotension.
• To achieve adequate brain dopamine levels, large doses of levodopa are needed (up to 8 g/day), which worsens peripheral side effects.

• It inhibits DOPA decarboxylase peripherally but, because it does not cross the BBB, it does NOT inhibit decarboxylation of levodopa in the brain.
• Result: Levodopa is protected from peripheral conversion → more levodopa remains available in the plasma → more levodopa enters the brain.

1. Daily levodopa dose reduced by ~75% (from 8 g/day to ~1–2 g/day)
2. Nausea and vomiting markedly reduced (less peripheral dopamine)
3. Cardiac arrhythmias reduced
4. Postural hypotension reduced
5. Plasma half-life of levodopa prolonged
6. Pyridoxine (B6) interactions eliminated — carbidopa blocks peripheral decarboxylase so B6 can no longer enhance peripheral levodopa breakdown

Q-2d: Drugs for Anemia — Classification and Pharmacological Management of Iron Deficiency Anemia

Classification of Drugs Used in Treatment of Anemia

• Oral iron: Ferrous sulfate, Ferrous gluconate, Ferrous fumarate
• Parenteral iron: Iron dextran, Iron sucrose, Ferric carboxymaltose

• Vitamin B12 (Cyanocobalamin, Hydroxocobalamin) — for pernicious anemia / B12 deficiency
• Folic acid — for folate deficiency megaloblastic anemia

• Corticosteroids (autoimmune hemolytic anemia)
• Immunosuppressants

• Antithymocyte globulin (ATG), Cyclosporine, Bone marrow transplant

• Erythropoietin (Epoetin alfa), Darbepoetin — for anemia of chronic kidney disease, chemotherapy-induced anemia

• Hydroxyurea — increases fetal hemoglobin (HbF)

Pharmacological Management of Iron Deficiency Anemia

Step 1: Identify and Treat the Cause

Step 2: Oral Iron Therapy (First-Line)

• Contains 20% elemental iron (65 mg elemental iron per 200 mg tablet)
• Other salts: ferrous gluconate (12% elemental iron), ferrous fumarate (33%)

• Ferrous iron (Fe²⁺) is absorbed better than ferric iron (Fe³⁺)
• Absorbed in the duodenum and proximal jejunum
• Vitamin C (ascorbic acid) enhances absorption by maintaining iron in the ferrous state and forming soluble iron complexes
• HCl in the stomach promotes absorption; gastric acid reducers (PPIs, antacids) reduce it

• Reticulocytosis peaks at 7–10 days (earliest sign of response)
• Hemoglobin should rise 1–2 g/dL per month
• Serum ferritin should normalize before stopping

• GI upset: nausea, constipation, abdominal cramps, diarrhea (dose-related)
• Black/dark stools (harmless; differentiate from melena)
• Management: Take with food (reduces absorption but improves tolerability), use lower doses initially, use liquid formulations

Step 3: Parenteral Iron (when oral iron fails or is contraindicated)

• Malabsorption (celiac disease, Crohn's disease)
• Intolerance to oral iron
• Non-compliance
• Functional iron deficiency in dialysis patients on erythropoietin
• Rapid replenishment required (e.g., pre-surgery)

• Iron sucrose — safest, preferred for CKD/dialysis patients
• Ferric carboxymaltose — high dose, single-infusion possible
• Iron dextran — higher risk of anaphylaxis; test dose required

• Anaphylaxis / hypersensitivity (especially IV iron dextran)
• Pain at injection site (IM route)
• Hemosiderosis (iron overload) if overdosed
• Flushing, hypotension (IV infusion)

Q-3a: Drugs in Bronchial Asthma — Classification and Management of Acute Attack

Classification of Drugs Used in Bronchial Asthma

• Short-Acting (SABA): Salbutamol (albuterol), Terbutaline — "relievers"
• Long-Acting (LABA): Salmeterol, Formoterol — "controllers" (must use with ICS)

• Theophylline, Aminophylline (IV for acute severe asthma)

• Short-acting: Ipratropium bromide (adjunct in acute severe asthma)
• Long-acting: Tiotropium (add-on for severe asthma)

• Beclomethasone, Budesonide, Fluticasone, Mometasone, Ciclesonide

• Prednisolone (oral), Hydrocortisone (IV) — for acute exacerbations and severe disease

• Montelukast, Zafirlukast — oral; especially useful in aspirin-sensitive and exercise-induced asthma

• Sodium cromoglycate, Nedocromil — prophylaxis; especially in childhood asthma and exercise-induced

• Anti-IgE: Omalizumab (for allergic asthma)
• Anti-IL-5: Mepolizumab, Reslizumab (eosinophilic asthma)
• Anti-IL-4/IL-13: Dupilumab

Pharmacological Management of Acute Attack of Asthma

Mild-to-Moderate Acute Attack:

1. Inhaled SABA (salbutamol) via metered-dose inhaler (MDI) with spacer or nebulizer — 2.5–5 mg every 20 minutes × 3 doses in the first hour. This is the cornerstone of immediate treatment. β2-agonists activate β2 receptors on bronchial smooth muscle → increase cAMP → relax airway smooth muscle → bronchodilation.
2. Oxygen supplementation — maintain SpO₂ 93–95% (94–98% in children)
3. Oral prednisolone — 40–50 mg/day for 5–7 days if not improving immediately; reduces airway inflammation

Severe Acute Attack:

1. Inhaled SABA (salbutamol via nebulizer) — continuous or back-to-back every 20 minutes
2. Inhaled ipratropium bromide + salbutamol (combined nebulization) — additive bronchodilation via anticholinergic mechanism (blocks M3 receptors → reduces bronchoconstriction)
3. Systemic corticosteroids — IV hydrocortisone 100–200 mg every 6 hours OR oral prednisolone 40–60 mg/day; reduce airway inflammation, restore β2-receptor responsiveness
4. Oxygen — high-flow
5. IV aminophylline (methylxanthine) — for patients not responding to the above; inhibits phosphodiesterase → increases cAMP → bronchodilation; narrow therapeutic window (5–15 μg/mL); monitor for toxicity (arrhythmias, seizures)
6. IV magnesium sulfate (2g slow IV) — for life-threatening asthma; causes bronchial smooth muscle relaxation (calcium antagonism)
7. Heliox (helium-oxygen mixture) — reduces work of breathing in severe obstruction
8. Mechanical ventilation — if all else fails (intubation with caution due to risk of air trapping)

• Non-selective beta-blockers (propranolol) — cause bronchoconstriction
• Aspirin/NSAIDs — precipitate aspirin-sensitive asthma
• Sedatives — depress respiratory drive
• Morphine — causes histamine release → bronchoconstriction

Q-3b: Nitrates as Antianginal Drugs — Classification, Mechanism of Action, Uses

Classification of Nitrates

Mechanism of Action

1. Nitrate → releases NO (nitric oxide) in vascular smooth muscle
2. NO activates guanylyl cyclase → increased synthesis of cGMP (cyclic guanosine monophosphate)
3. cGMP activates protein kinase G → dephosphorylation of myosin light chain → smooth muscle relaxation → vasodilation

• Venodilatation (primary effect): Nitrates preferentially dilate venous capacitance vessels → reduces venous return (preload) → reduces ventricular end-diastolic volume and pressure → reduces wall stress and myocardial O₂ demand
• Arterial dilation (at higher doses): Reduces systemic vascular resistance (afterload) → further reduces myocardial O₂ demand
• Coronary artery dilation: Dilates large epicardial coronary arteries (including stenotic segments); improves collateral flow; relieves coronary spasm in Prinzmetal's angina
• Net effect: Reduced myocardial O₂ demand + improved O₂ supply → relief of anginal ischemia

Uses of Nitrates

1. Stable (exertional) angina: Sublingual GTN for acute relief; long-acting nitrates for prophylaxis (but with nitrate-free interval of 8–12 hours/day to avoid tolerance)
2. Unstable angina/NSTEMI: IV nitroglycerin for symptom relief
3. Prinzmetal's (vasospastic) angina: Highly effective (coronary vasodilation relieves spasm)
4. Acute heart failure / Cardiogenic pulmonary edema: Vasodilation reduces preload and afterload; IV GTN/ISDN used
5. Hypertensive emergencies: IV GTN or nitroprusside to lower blood pressure rapidly
6. Esophageal spasm: Sublingual GTN relieves smooth muscle spasm

Adverse Effects of Nitrates

• Headache — most common (vasodilation of meningeal vessels); responds to analgesics
• Hypotension — especially postural hypotension; risk of syncope
• Reflex tachycardia — compensatory response to vasodilation (attenuated by beta-blockers)
• Tolerance — develops rapidly with continuous use (depletion of SH groups, neurohormonal activation); prevented by 8–12-hour nitrate-free interval
• Methemoglobinemia — rare; with large doses
• Contraindicated with PDE5 inhibitors (sildenafil/tadalafil) — potentially fatal hypotension due to additive cGMP elevation

Q-3c: Antiepileptic Drugs — Classification, Mechanism and Adverse Effects of Phenytoin

Classification of Antiepileptic Drugs (AEDs)

• Phenytoin (Dilantin), Carbamazepine, Oxcarbazepine, Lacosamide, Lamotrigine (also Ca²⁺)

• Benzodiazepines (Diazepam, Clonazepam, Lorazepam) — increase GABA-A Cl⁻ channel opening frequency
• Barbiturates (Phenobarbital) — increase GABA-A Cl⁻ channel opening duration
• Valproate (also blocks Na⁺ channels and T-type Ca²⁺ channels)
• Tiagabine — blocks GABA reuptake
• Vigabatrin — irreversible GABA transaminase inhibitor

• Ethosuximide — drug of choice for absence seizures
• Valproate (also T-type Ca²⁺)

• Perampanel (AMPA receptor antagonist)
• Felbamate (NMDA + AMPA)

• Levetiracetam — binds synaptic vesicle protein SV2A; reduces neurotransmitter release
• Gabapentin / Pregabalin — bind α2δ subunit of voltage-gated Ca²⁺ channels
• Topiramate — multiple: Na⁺ channels, GABA-A potentiation, AMPA antagonism, carbonic anhydrase inhibition

Phenytoin — Mechanism of Action

• Tonic-clonic (grand mal) seizures
• Partial (focal) seizures
• Status epilepticus (IV fosphenytoin, the prodrug)
• NOT effective for absence seizures

• Reduces the ability of neurons to fire at high frequencies ("frequency-dependent/use-dependent blockade")
• Does not affect normal low-frequency neuronal firing
• Selectively inhibits the rapidly firing neurons responsible for seizure propagation

• Absorption: Slow and sometimes incomplete orally; highly protein-bound (90–95%) → free drug is the active form
• Therapeutic plasma level: 10–20 μg/mL
• Metabolism: Hepatic hydroxylation (CYP2C9, CYP2C19); exhibits zero-order (saturation) kinetics within the therapeutic range — small dose increases can cause disproportionately large rises in plasma levels (important clinically — narrow therapeutic window)
• Drug interactions: Strong CYP inducer → reduces levels of other drugs (OCP, warfarin, other AEDs)

Adverse Effects of Phenytoin

1. Gingival hyperplasia (gum overgrowth) — occurs in ~20% of patients; due to altered collagen metabolism; more common in younger patients; preventable with good oral hygiene
2. Hirsutism — increased facial and body hair; cosmetically problematic, especially in young women
3. Coarsening of facial features — broadening of nose, thickening of lips, acne
4. Peripheral neuropathy — with long-term use; sensorimotor; reversible
5. Cerebellar atrophy — chronic high-level exposure
6. Megaloblastic anemia — due to impaired folate absorption/metabolism; folate supplementation required
7. Osteomalacia/Rickets — CYP induction increases metabolism of vitamin D → reduced bone density; risk fractures
8. Teratogenicity — "Fetal Hydantoin Syndrome": cleft lip/palate, cardiac defects, digital hypoplasia, growth retardation; Category D in pregnancy

• Hypersensitivity reactions: Rash (common, 5–10%), Stevens–Johnson syndrome (rare, severe)
• Hepatotoxicity (rare)
• Lymphadenopathy
• Agranulocytosis/aplastic anemia (very rare)

• Cardiac arrhythmias and hypotension — give IV at <50 mg/min
• Purple glove syndrome — IV extravasation causing discoloration and necrosis
• Use fosphenytoin instead of phenytoin for IV/IM routes due to better safety profile

Sources: Katzung's Basic and Clinical Pharmacology, 16th Edition; Tietz Textbook of Laboratory Medicine, 7th Edition; Morgan and Mikhail's Clinical Anesthesiology, 7th EditionAll questions have been answered comprehensively. Here's a quick index of what was covered:

Summary of Answers

Q-1 (Option A) — Bioavailability (2+5+4+4 = 15 marks)

• Definition: Fraction of unchanged drug reaching systemic circulation; IV = 100%; oral < 100% due to incomplete absorption + first-pass metabolism
• 5 Factors: (1) First-pass hepatic metabolism, (2) Physicochemical properties (lipophilicity/hydrophilicity), (3) P-glycoprotein efflux, (4) Drug formulation/dissolution, (5) GI factors (pH, gastric emptying, food)
• IV route = maximum bioavailability (100%) — advantages: immediate onset, precise dosing, bypasses GI | disadvantages: irreversibility, infection risk, needs trained personnel, rapid toxicity possible

Q-1 (Option B) — Anti-Hypertensives + ACE Inhibitors (3+4+4+4 = 15 marks)

• Classification: Diuretics, RAS agents, CCBs, Sympathoplegics, Direct vasodilators
• ACE Inhibitor mechanism: Block Ang I → Ang II conversion + bradykinin accumulation + efferent arteriolar dilation
• Uses: Hypertension, heart failure, post-MI, diabetic nephropathy, CKD
• Adverse effects: Dry cough, hyperkalemia, first-dose hypotension, AKI, angioedema, teratogenicity

Q-2 Short Notes

• Q-2a — Beta-blockers: 3 generations (non-selective, cardioselective, vasodilating); uses in HTN, angina, arrhythmias, heart failure, glaucoma, thyrotoxicosis, migraine
• Q-2b — Gout drugs: Classification; chronic gout: allopurinol (xanthine oxidase inhibitor), febuxostat, probenecid (uricosuric), colchicine (prophylaxis)
• Q-2c — Levodopa/Carbidopa: Mechanism (dopamine precursor crossing BBB); adverse effects (GI, CV, CNS, dyskinesias, on-off); carbidopa rationale (reduces peripheral decarboxylation → 75% dose reduction + fewer peripheral ADRs)
• Q-2d — Iron Deficiency Anemia: Drug classification; management: oral ferrous sulfate, parenteral iron (iron sucrose, ferric carboxymaltose) when oral fails

Q-3 Short Notes

• Q-3a — Asthma drugs: Classification (SABAs, LABAs, theophylline, anticholinergics, ICS, LTRAs, biologics); acute attack management (salbutamol + ipratropium nebulization, IV corticosteroids, O₂, IV aminophylline/magnesium if severe)
• Q-3b — Nitrates: Classification by duration (GTN, ISDN, ISMN); mechanism (NO → cGMP → smooth muscle relaxation); uses (stable angina, Prinzmetal's, unstable angina, acute heart failure); adverse effects (headache, hypotension, tolerance, PDE5 inhibitor contraindication)
• Q-3c — Phenytoin: AED classification; mechanism (Na⁺ channel inactivation → frequency-dependent block); adverse effects (nystagmus → ataxia → confusion; chronic: gingival hyperplasia, hirsutism, megaloblastic anemia, osteomalacia, fetal hydantoin syndrome)