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2nd Year MBBS Pharmacology - Complete Answer Key

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Q1. P-drug Selection for Newly Diagnosed Hypertension Using STEP Criteria

What is a P-drug?

The STEP Criteria

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Applying STEP to Hypertension Drug Classes

1. Thiazide diuretics (Hydrochlorothiazide / Chlorthalidone)
2. ACE Inhibitors - ACEIs (Enalapril, Ramipril)
3. Angiotensin Receptor Blockers - ARBs (Losartan, Telmisartan)
4. Calcium Channel Blockers - CCBs (Amlodipine)
5. Beta-blockers (Atenolol, Metoprolol)

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STEP Analysis Table

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P-drug Selection: Enalapril/Amlodipine as P-drug

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Q2. Antimicrobial Choice for Community-Acquired Pneumonia (CAP)

Etiology of CAP

• Most common: Streptococcus pneumoniae (pneumococcus)
• Atypicals: Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella
• Others: Haemophilus influenzae, Klebsiella (alcoholics, elderly)
• Viruses: Influenza, SARS-CoV-2

Drug of Choice

Justification Based on STEP Criteria

• Amoxicillin has proven bactericidal activity against S. pneumoniae - the commonest CAP pathogen
• Azithromycin covers atypical organisms (Mycoplasma, Chlamydophila, Legionella) which are common in young adults presenting to OPD
• The combination therefore provides broad empiric coverage for CAP without requiring hospitalization
• Fluoroquinolones (Levofloxacin, Moxifloxacin) are reserved for severe CAP or treatment failure to preserve efficacy

• Amoxicillin: excellent safety profile; GI upset (nausea, diarrhea) in ~10%; allergy in penicillin-sensitive patients
• Azithromycin: generally well tolerated; QT prolongation risk (check ECG if risk factors); mild GI side effects
• Doxycycline: photosensitivity, esophageal irritation (take upright); avoid in pregnancy and children <8 years

• Oral route suitable for OPD patient (not severely ill - no need for IV antibiotics)
• Once-daily azithromycin improves compliance over TDS amoxicillin
• Doxycycline: twice daily, suitable for adherence
• If patient is allergic to penicillin: use Azithromycin or Doxycycline as sole agent

• Amoxicillin generics (Amoxil, Novamox): Rs. 5-8 per capsule - very affordable
• Azithromycin generics (Azithral, Zithromax): Rs. 20-30 per tablet - moderate cost but 3-5 day course
• Doxycycline: Rs. 2-5 per tablet - cheapest option with dual coverage

Preferred Regimen Summary

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Q3. Rational vs Irrational Fixed Dose Combinations (FDCs)

Definition of FDC

Rational FDC - Criteria (KD Tripathi)

1. Both drugs are needed simultaneously in the given condition
2. The fixed ratio is therapeutically appropriate for the target population
3. The combination has additive or synergistic benefit over individual drugs
4. Combining improves compliance, convenience, or reduces pill burden
5. The combination does NOT increase toxicity
6. Each component has a similar pharmacokinetic profile (compatible half-lives, routes of elimination)
7. There is clinical evidence supporting the combination

Rational FDC Examples

Irrational FDC Examples

Why Irrational FDCs are Discouraged

1. No therapeutic advantage - individual drugs suffice; combination adds no benefit
2. Increased adverse effects - two drugs at fixed doses may produce additive/synergistic toxicity (e.g., two NSAIDs double GI bleed risk)
3. Inflexibility in dosing - cannot adjust individual drug doses as clinical need changes
4. Pharmacokinetic incompatibility - drugs may have different half-lives, absorption characteristics; one component may be subtherapeutic while other is toxic
5. Masking of diagnosis - "shotgun therapy" masks true clinical diagnosis and delays specific treatment
6. Antibiotic stewardship concerns - irrational antibiotic FDCs promote resistance
7. Medico-legal and regulatory concerns - CDSCO (India) has banned hundreds of FDCs (2016, 2018, 2023 gazette notifications) on grounds of irrationality

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Q4. Methotrexate in Rheumatoid Arthritis

Drug Classification

Mechanism of Action

1. MTX enters cells via folate carriers and is polyglutamated intracellularly
2. MTX polyglutamates inhibit dihydrofolate reductase (DHFR) - prevents conversion of DHF to THF (tetrahydrofolate)
3. MTX also directly inhibits thymidylate synthase and other folate-dependent enzymes
4. This depletes purines and thymidylate needed for DNA synthesis - anti-proliferative effect on rapidly dividing immune cells
5. Additionally, MTX increases adenosine release - adenosine has potent anti-inflammatory effects by inhibiting neutrophil function, cytokine production (TNF-α, IL-1, IL-6), and lymphocyte proliferation
6. MTX inhibits T-cell activation and reduces synovial inflammation

Dosing in RA

• Starting dose: 7.5-10 mg once weekly (oral or IM/SC)
• Increase by 2.5 mg every 4-6 weeks
• Target dose: 15-25 mg/week
• Always given once weekly - daily dosing causes severe toxicity
• Folic acid 1-5 mg daily (on non-MTX days) is mandatory to reduce toxicity

Adverse Effects

Monitoring (KD Tripathi / ACR guidelines)

• CBC with differential
• Liver function tests (ALT, AST, albumin, bilirubin)
• Serum creatinine and urinalysis
• Chest X-ray (pulmonary baseline + TB screening)
• Hepatitis B and C serology
• Pregnancy test in women of childbearing age

• CBC and LFTs every 2-4 weeks for first 3 months, then every 4-8 weeks
• Serum creatinine every 3-6 months
• Discontinue if: WBC <3,000/mm³, neutrophils <1,500/mm³, platelets <100,000/mm³, ALT >3x ULN

Patient Counseling

1. Dosing schedule: Take MTX only ONCE a week on the same day (e.g., every Monday). Daily dosing is life-threatening.
2. Folic acid: Take folic acid 1-5 mg every day except the day of MTX. This reduces side effects without reducing efficacy.
3. Alcohol: Strictly avoid alcohol during MTX therapy - dramatically increases hepatotoxicity risk.
4. Contraception: Women of childbearing age MUST use effective contraception. Stop MTX at least 3 months before planned pregnancy. Men should also use contraception during treatment.
5. Sun protection: Use sunscreen as MTX increases photosensitivity.
6. Infections: Report any fever, sore throat, or unusual infections immediately. Avoid live vaccines.
7. Warning signs: Mouth sores (stomatitis), unusual bruising/bleeding (thrombocytopenia), severe fatigue, shortness of breath (pneumonitis), jaundice - report immediately.
8. Interactions: Avoid NSAIDs in high doses (reduce MTX clearance); avoid trimethoprim (additive folate antagonism); avoid OTC medications without consulting the physician.
9. Lab tests: Regular blood tests and LFTs are mandatory - do not skip follow-ups.
10. Onset of action: Takes 4-6 weeks to see benefit, maximum effect at 3-6 months - do not stop early.

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Q5. Comparison: Aspirin, Paracetamol, and Diclofenac

Background: Arachidonic Acid Pathway

• Arachidonic acid → (COX-1/COX-2) → Prostaglandins, Thromboxane A2, Prostacyclin
• Prostaglandins cause: pain sensitization, fever (via PGE2 acting on hypothalamus), inflammation

Mechanism of Action

Uses

Adverse Effects

Key Differentiating Points

• Aspirin: ONLY drug with antiplatelet use; ONLY one causing Reye's syndrome
• Paracetamol: ONLY one safe in pregnancy, ONLY one safe in PUD; has NO anti-inflammatory effect
• Diclofenac: Highest cardiovascular risk among the three; available as IM/IV for acute pain; also available as topical gel

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Q6. Pharmacological Management of Anaphylaxis

Definition

Pathophysiology (Brief)

Immediate Management - "ABCDE"

• Dose: 0.3-0.5 mg (0.3-0.5 mL of 1:1000 solution) intramuscularly (anterolateral thigh) - IM is preferred over SC (faster absorption)
• Repeat every 5-15 minutes if no improvement

• Alpha-1 agonism: Vasoconstriction → reverses hypotension, reduces mucosal edema (counters angioedema, urticaria)
• Beta-1 agonism: Increases heart rate and cardiac contractility → treats cardiovascular collapse
• Beta-2 agonism: Bronchodilation → reverses bronchospasm
• Inhibits further mediator release from mast cells (via increased cAMP)
• Adrenaline is the ONLY drug that addresses ALL pathophysiological components simultaneously

• IV crystalloid (Normal saline or Ringer's lactate) - 1-2 litres rapidly - for hypotension/circulatory collapse
• Restores intravascular volume lost due to massive vasodilation and capillary leak

• H1 blocker: Chlorpheniramine 10 mg IV/IM (1st generation preferred for acute use)
• H2 blocker: Ranitidine 50 mg IV (adds benefit - 15% of skin H-receptors are H2)
• Rationale: Block remaining histamine at receptors; reduce urticaria/pruritus; do NOT reverse bronchospasm or cardiovascular collapse - adjunctive only, NEVER first-line alone

• Hydrocortisone 200 mg IV bolus, OR Methylprednisolone 1-2 mg/kg IV, OR Dexamethasone 8 mg IV
• Rationale: Suppress the late-phase inflammatory response (which can occur 4-8 hours after initial reaction - "biphasic anaphylaxis"); reduce recurrence
• NOT first-line - onset of action is delayed (4-6 hours); do not rely on steroids for acute management

• Salbutamol (Albuterol) nebulization 2.5-5 mg
• Ipratropium bromide nebulization if needed
• Rationale: Direct Beta-2 agonism; useful adjunct when bronchospasm persists despite adrenaline

• For patients on beta-blockers who don't respond to adrenaline
• Glucagon 1-2 mg IV; bypasses beta-receptors to increase cardiac cAMP

Summary Algorithm

Bee sting → Anaphylaxis
    ↓
ADRENALINE 0.3 mg IM (anterolateral thigh) ← FIRST
    ↓
Position + O2 + IV access + Fluids
    ↓
H1 antihistamine (Chlorpheniramine) + H2 (Ranitidine) - IV
    ↓
Hydrocortisone 200 mg IV - prevent biphasic reaction
    ↓
Salbutamol nebulization if bronchospasm persists
    ↓
Observe 4-6 hours (biphasic risk); discharge with EpiPen + antihistamine

Discharge Counseling

• Prescribe self-injectable epinephrine (EpiPen) for future episodes
• Refer to allergist for skin prick testing and venom immunotherapy
• Medical alert bracelet
• Oral antihistamine + prednisolone for 3-5 days after discharge

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Q7. Oral Iron Therapy for Iron Deficiency Anemia

Diagnosis Basis

Drug of Choice

Treatment Plan

• Adults: Ferrous sulfate 200 mg (containing 60 mg elemental iron) TDS on empty stomach
  • Total elemental iron: ~180 mg/day
• Alternatively: Ferrous gluconate 300 mg or Ferrous fumarate 200 mg TDS

• Continue until hemoglobin normalizes (usually 4-8 weeks)
• Then continue for additional 3-6 months to replenish iron stores (ferritin)
• Total duration: typically 4-6 months

• Take with Vitamin C (ascorbic acid 200 mg) or citrus juice - reduces Fe3+ to Fe2+, chelates iron, increases absorption by 2-3 fold
• Take on empty stomach (1 hour before or 2 hours after meals) for maximum absorption

• Reticulocyte count rises in 5-10 days (first sign of response)
• Hemoglobin rises ~1-2 g/dL per 3-4 weeks
• Check Hb at 4 weeks; if no response, reassess diagnosis (poor compliance, malabsorption, ongoing blood loss, incorrect diagnosis)

Adverse Effects

Patient Counseling Points

1. Compliance: Complete the full course even after Hb normalizes - iron stores take months to replenish
2. Timing: Take on empty stomach for best absorption; if GI upset is severe, take with food (reduces absorption by ~40% but is acceptable)
3. With Vitamin C: Take with a glass of orange juice or a Vitamin C tablet to maximize absorption
4. Avoid with: Tea, coffee, milk, antacids, calcium supplements, tetracyclines - these reduce iron absorption; separate by at least 2 hours
5. Black stools: Normal - iron turns stools dark; not blood
6. Constipation: Increase fluid and fiber intake; mild laxative if needed
7. Dietary advice: Increase dietary iron - red meat, liver, leafy greens (spinach, methi), dates, jaggery; note that non-heme iron from plants is less well absorbed
8. Identify cause: IDA should prompt investigation for cause - menorrhagia, GI bleed, hookworm infestation, poor diet - and treatment of underlying cause
9. Parenteral iron: If oral iron is not tolerated, IV iron sucrose or iron dextran may be used (also for malabsorption, inflammatory bowel disease, pre-operative optimization)
10. In pregnancy: Continue iron + folic acid throughout pregnancy (prophylactic: 60 mg/day elemental iron + 500 mcg folic acid - Government of India program)

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Q8. Antimicrobial Resistance and Antibiotic Stewardship

Antimicrobial Resistance (AMR) - Definition

Causes of Antimicrobial Resistance

1. Overuse and overprescribing - antibiotics for viral infections (common cold, sore throat, influenza) where they have no effect
2. Underdosing - subtherapeutic doses allow resistant mutants to survive and proliferate
3. Incomplete courses - premature stopping when feeling better; sensitive organisms die first, resistant ones remain
4. Wrong antibiotic selection - broad-spectrum antibiotics used empirically when not needed
5. Self-medication - over-the-counter antibiotic purchase without prescription (major problem in India)

• Enzymatic inactivation: Beta-lactamases inactivate penicillins/cephalosporins; aminoglycoside-modifying enzymes
• Efflux pumps: Active extrusion of antibiotic from cell (tetracycline, fluoroquinolone resistance)
• Altered target site: Mutations in penicillin-binding proteins (PBP2a in MRSA); altered DNA gyrase (fluoroquinolone resistance)
• Reduced permeability: Loss of outer membrane porins in Gram-negatives limits antibiotic entry
• Plasmid-mediated resistance transfer (horizontal gene transfer): Most dangerous; resistance genes spread between species via conjugation, transduction, transformation

Antibiotic Stewardship

• Minimize AMR development
• Reduce adverse effects (C. difficile colitis, superinfections)
• Reduce cost
• Improve patient outcomes

• Prescribe antibiotics only when indicated
• Choose the right drug at the right dose for the right duration
• Use culture-sensitivity results to guide therapy (not empirical treatment indefinitely)
• Avoid broad-spectrum when narrow-spectrum suffices
• Reserve "last resort" antibiotics (carbapenems, colistin, linezolid) for truly resistant infections
• Never prescribe antibiotics for pressure from patients/families

• Schedule H1 antibiotics (2013) - require prescription; pharmacist must record patient details
• National Action Plan on AMR 2017-2021 (NAP-AMR) - India's commitment to WHO Global Action Plan
• Red Line Campaign - red line on antibiotic packages to differentiate from OTC drugs

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Q9. Histamine in Allergic Disorders + Comparison of 1st vs 2nd Generation Antihistamines

Histamine - Source and Storage

• Stored in mast cell and basophil granules (as histamine-heparin complex)
• Also found in enterochromaffin-like cells (ECL cells) of gastric mucosa
• Formed by decarboxylation of histidine by histidine decarboxylase
• Released by: IgE-mediated (Type I hypersensitivity), physical stimuli (cold, pressure), drugs (morphine, tubocurarine, vancomycin - "red man syndrome")

Histamine Receptors and Their Roles

Role of Histamine in Allergic Disorders

• H1 activation → nasal mucosal edema, sneezing, rhinorrhea, pruritus
• Early phase (minutes): histamine dominates
• Late phase (hours): cytokines and leukotrienes dominate

• H1 + H2 activation → vasodilation + increased vascular permeability → wheal (local edema) and flare (erythema)
• Pruritus from H1 activation on sensory nerve endings

• Massive histamine release + other mediators → bronchospasm (H1), hypotension (H1 + H2), urticaria, angioedema, GI cramps
• Note: antihistamines alone insufficient for anaphylaxis (adrenaline required)

• H1-mediated bronchoconstriction (along with LTC4, LTD4 which are more potent bronchoconstrictors)
• Antihistamines are NOT first-line for asthma (leukotrienes are more important)

• Pruritus is mainly H1-mediated; antihistamines used for symptomatic relief

Comparison: 1st vs 2nd Generation Antihistamines

• Allergic rhinitis, urticaria, atopic dermatitis
• Patients who need to drive or operate machinery
• Daytime use

• Motion sickness (promethazine/dimenhydrinate - CNS penetration required)
• Acute severe urticaria (IV chlorpheniramine for rapid effect)
• As premedication sedation
• Patients needing sedation as therapeutic benefit (insomnia with urticaria)

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Q10. Critical Evaluation: Diclofenac + Ibuprofen FDC - Rational or Irrational?

Verdict: IRRATIONAL FDC

Step-by-Step Critical Analysis

• Diclofenac: slightly COX-2 preferential but still inhibits COX-1
• Ibuprofen: non-selective COX-1 and COX-2 inhibitor

• Dose escalation of the single NSAID
• Addition of a different class (e.g., paracetamol, opioid, adjuvant)
• Not adding a second NSAID with the same target

• Ibuprofen and diclofenac compete for the same COX active site
• Ibuprofen can competitively block the irreversible acetylation of platelet COX-1 by aspirin (relevant in aspirin users)
• Both are highly protein-bound (~99%); displacement interactions may alter free drug levels
• Ibuprofen antagonizes the cardioprotective antiplatelet effect of aspirin by competing for COX-1 binding - similar competition exists between these two NSAIDs at COX sites

• This combination has no approval from any major regulatory authority (FDA, EMA, CDSCO)
• CDSCO India has specifically banned many such irrational NSAID combinations
• No evidence-based guideline recommends dual NSAID therapy for any condition

Summary

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Quick Reference Summary Table

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