PH10.1-17 | Applied Pharmacology and Prescribing Skills — Practice Quiz

Correct! Nitrofurantoin has proven efficacy for lower UTI, good safety in non-pregnant non-renal-impaired adults, oral suitability, and low cost. It concentrates in urine and has preserved sensitivity unlike fluoroquinolones.

Review: P-drug selection requires balancing efficacy, safety, suitability, and cost. Amoxicillin has high resistance rates for UTI. Norfloxacin is a fluoroquinolone — WHO and India discourage first-line fluoroquinolone use for uncomplicated UTI to preserve its utility. IV gentamicin is inappropriate for an outpatient with a lower UTI.

Correct! Duration is the most commonly omitted element in routine prescriptions. Without explicit duration, the pharmacist may dispense an arbitrary quantity and the patient may self-extend therapy, risking adverse effects (nitrofurantoin pulmonary toxicity with prolonged use) or under-treatment.

Review: A legally valid Indian prescription must include patient name, date, prescriber's name/address/qualification/registration number, drug name, strength, dose, route, frequency, and duration. Duration is consistently the most omitted element in prescribing audits.

Correct! At eGFR <30 mL/min/1.73 m², metformin is contraindicated (risk of lactic acidosis) and sulphonylureas (especially glibenclamide) carry high hypoglycaemia risk due to accumulation of active metabolites. Both must be stopped. A renally-safe agent such as a DPP-4 inhibitor (dose-adjusted sitagliptin/saxagliptin) or insulin is appropriate.

Prescription appraisal in CKD: metformin is contraindicated at eGFR <30 (lactic acidosis); glibenclamide is the most dangerous sulphonylurea in renal impairment (active metabolites accumulate → prolonged hypoglycaemia). Safe alternatives include gliclazide MR (cautiously) or DPP-4 inhibitors/insulin.

Review: Severe renal impairment (eGFR <30) mandates removal of both metformin (lactic acidosis risk) and glibenclamide (prolonged hypoglycaemia from metabolite accumulation). Prescription appraisal must always check renal function against every drug on the list.

Correct! The NLEM selection framework requires a drug to demonstrate superior cost-effectiveness compared to existing alternatives — not merely novel mechanism or theoretical resistance advantages. A patented drug at 10× the cost of an equally effective generic fails the cost-effectiveness criterion, regardless of novelty.

NLEM criteria: public health relevance (burden of disease), evidence of efficacy and safety (from robust clinical trials), and comparative cost-effectiveness (not just cheaper, but better value per outcome). A drug with novel mechanism but high cost fails criterion 3 unless it provides significantly better outcomes.

Review: NLEM selection requires three criteria: (1) public health relevance, (2) proven efficacy and safety, and (3) comparative cost-effectiveness. The argument about 'novel mechanism + no resistance' touches efficacy but entirely ignores whether the cost per cure is superior to what is already available.

Correct! TPMT*3A/*3A homozygous loss-of-function means the patient cannot methylate thiopurine metabolites via TPMT, causing accumulation of cytotoxic 6-thioguanine nucleotides → severe myelotoxicity at standard doses. CPIC guidelines recommend starting at ~10% of standard dose with very close monitoring, not zero therapy, unless clinically impractical.

TPMT pharmacogenomics is one of the strongest clinical pharmacogenomic tests (CPIC Level A). Homozygous loss-of-function (1/300 people): standard dose causes fatal myelosuppression. Dose at 10% standard and monitor CBC twice weekly for 4 weeks, then weekly, then monthly. TPMT heterozygotes: reduce dose by 30-70%.

Review: TPMT catalyses the inactivation of thiopurine drugs (azathioprine, mercaptopurine). Homozygous loss-of-function = almost no TPMT activity → catastrophic 6-TGN accumulation at standard doses → severe, potentially fatal myelosuppression. Dose reduction to 10% with intensive monitoring is CPIC-recommended.

Correct! Digoxin undergoes a bi-phasic distribution — plasma levels are very high immediately post-absorption (distribution phase), then fall sharply over 6-8 hours as the drug partitions into cardiac and skeletal muscle. A level drawn before distribution is complete overestimates the tissue concentration and would falsely suggest toxicity or lead to inappropriate dose reduction.

Digoxin TDM sampling rule: always at trough (just before next dose) or ≥6-8 h after an oral dose. Therapeutic range: 0.5-0.9 ng/mL for heart failure (lower end); 1.5-2.0 ng/mL was the old range (now associated with higher mortality). The reason for the sampling window is the prolonged tissue distribution phase.

Review: Digoxin TDM requires pre-dose (trough) sampling or sampling at least 6-8 hours post-oral dose. Both statements are factually correct and causally linked — early sampling gives unreliable readings specifically because distribution is incomplete.

Correct! 3 mg/kg/day × 20 kg = 60 mg/day (minimum) and 5 mg/kg/day × 20 kg = 100 mg/day (maximum). The dose range is 60-100 mg/day. Always calculate weight-based paediatric doses rather than extrapolating adult doses.

Paediatric dose calculation: always use mg/kg/day recommendation × actual weight. Check against the maximum adult dose as a ceiling (do not exceed). For phenobarbitone: 3-5 mg/kg/day; in a 20 kg child = 60-100 mg/day. Divide into once or twice daily dosing per pharmacokinetics.

Review: Paediatric dosing = recommended dose per kg × patient weight. For phenobarbitone (3-5 mg/kg/day) in a 20 kg child: 3 × 20 = 60 mg/day to 5 × 20 = 100 mg/day. Never use adult doses or simple fractions of adult doses for children.

Correct! Self-prescribing violates objectivity (the prescriber cannot adequately examine themselves), bypasses proper diagnosis (empirical antibiotic for what might be viral pharyngitis or peritonsillar abscess), contributes to antimicrobial resistance (inappropriate use), and risks missing a serious diagnosis. Multiple medical councils and the MCI code of ethics explicitly discourage self-prescribing.

Self-prescribing ethical issues: loss of objectivity (cannot examine oneself adequately), risk of missed diagnosis (peritonsillar abscess may present like pharyngitis), inappropriate antibiotic use (most sore throats are viral), and emotional bias in clinical decision-making. India's Schedule H drugs require prescriber signature — self-prescribing creates a conflict of interest.

Review: Azithromycin is a Schedule H drug, not Schedule X. Self-prescribing — particularly antibiotics — is ethically problematic regardless of which drug is chosen because it impairs clinical objectivity, encourages antibiotic overuse, and may delay diagnosis of serious pathology.

Correct! Missed-dose management falls under 'How to take the drug' — this element covers not only the standard administration schedule but also special situations: what to do if a dose is missed, whether to take with food, timing relative to meals, and storage. For OCP: a missed pill within 24 h — take immediately; ≥48 h — take both pills, use barrier contraception for 7 days.

WHO drug counselling elements: Why / How / What to expect / What to report / When to return. 'How' includes route, timing, missed dose action, and storage — not just the dosing schedule. For OCP: counsel on missed dose protocol, drug interactions (rifampicin, carbamazepine reduce efficacy), and signs of serious complications (ACHES: Abdominal pain, Chest pain, Headache, Eye problems, Severe leg pain).

Review: The WHO five-element framework: (1) Why — indication; (2) How — administration (dose, frequency, timing, missed dose management, storage); (3) What to expect — expected and side effects; (4) What to report — adverse effects and danger signs; (5) When to return — follow-up. Missed-dose management is a sub-element of 'How to take the drug.'

Correct! Habit-stacking (linking medication to an existing routine such as brushing teeth or morning tea) is a simple, low-cost, evidence-based behavioural strategy that significantly improves adherence for once-daily asymptomatic medications. It uses the patient's existing habit as a cue, reducing the cognitive load of remembering a new behaviour.

Adherence barrier classification: intentional (patient chooses not to take) vs unintentional (forgets/practical barriers). Habit-stacking addresses unintentional forgetting effectively. For intentional non-adherence: motivational interviewing, education about symptom-less hypertension consequences. Tools: teach-back, pill diaries, blister packs, pharmacy refill records, and medication event monitors.

Review: For a patient who 'sometimes forgets,' the primary barrier is unintentional non-adherence. The most effective and evidence-based intervention is a behavioural strategy — linking pill-taking to an existing routine. Pill organisers help but are insufficient alone; switching to a costlier drug addresses cost (not relevant here); adding more drugs increases complexity.

Correct! Tramadol is Schedule H1 (documented prescribing required) and should always be used at the lowest effective dose for the shortest duration — core principles of cautious dependence-risk prescribing. Tramadol has documented abuse potential (mu-opioid partial agonist activity) and serious SSRI interaction risk (serotonin syndrome + lowered seizure threshold).

Tramadol (Schedule H1 in India): has opioid dependence potential (mu-receptor partial agonism); avoid in patients with seizure history; SSRI combination risks serotonin syndrome AND seizures; maximum dose 400 mg/day; prescribe with documented indication, lowest dose, defined duration, and plan for tapering if prolonged use is needed.

Review: Tramadol is a weak mu-opioid agonist and serotonin-noradrenaline reuptake inhibitor. Schedule H1 status reflects its recognised abuse potential. Tramadol + SSRI is a clinically significant interaction: serotonin syndrome risk and tramadol lowers the seizure threshold (SSRIs also lower it). Always use lowest dose/shortest duration for dependence-risk drugs.

Correct! Under the New Drugs and Clinical Trials Rules 2019, a new FDC of two already-approved drugs constitutes a 'new drug' if the combination has not been previously approved. CDSCO review is mandatory, including safety, efficacy, and pharmacokinetic interaction data. Several irrational FDCs have been banned by CDSCO in India under this framework.

CDSCO under the NDCT Rules 2019 regulates new drugs, new FDCs, and new clinical trials. An FDC is a 'new drug' if: (1) any component is new to India, or (2) the combination is not previously approved, even if both individual drugs are approved. CDSCO has banned 344 FDCs (2016 Kokate committee) for being irrational — this regulatory power matters clinically.

Review: A new FDC is classified as a 'new drug' under NDCT Rules 2019 even if both components are individually approved. CDSCO is the central authority — state drug controllers cannot approve new drugs for marketing nationally. IMA has no regulatory function.

Correct! The brochure leads with '35% relative risk reduction' — which sounds impressive — but the absolute risk reduction is only 0.7% (NNT=87, meaning 87 patients must be treated to prevent one event). Promotional literature routinely highlights RRR while omitting ARR because RRR always appears numerically larger. A prescriber must always calculate ARR and NNT from RRR data.

Promotional distortion hierarchy: (1) RRR without ARR — most common quantitative trick; (2) surrogate endpoints (HbA1c vs mortality); (3) cherry-picked subgroups; (4) misleading graphs (truncated axes); (5) unfair comparators (inadequate dose of comparator). When evaluating any drug claim: always ask for ARR and NNT. A 35% RRR with NNT=87 means the drug prevents one event in 87 treated patients over the trial duration.

Review: RRR = (risk_control - risk_treatment) / risk_control. ARR = risk_control - risk_treatment. NNT = 1/ARR. In this case: ARR = 0.7%, so NNT = 143 (approximately). The p-value is disclosed and the comparator is stated (placebo) — the distortion is specifically the reliance on RRR without ARR. This is the most common quantitative distortion in drug promotion.