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

Correct! Step 1 of the WHO six-step process is to define the patient's problem — without a clear problem definition, drug selection and treatment objectives cannot be formulated rationally.

WHO six-step prescribing: Define problem → Specify therapeutic objective → Select P-drug (efficacy/safety/suitability/cost) → Write prescription → Inform patient → Monitor. Skipping step 1 leads to treating symptoms rather than causes.

Review: WHO six steps: (1) Define the problem, (2) Specify the treatment objective, (3) Select the P-drug, (4) Write the prescription, (5) Inform the patient, (6) Monitor and stop. Steps must occur in this sequence.

Correct! Trailing zeros (5.0 mg) are a documented cause of 10-fold dosing errors — '5.0 mg' can be misread as '50 mg' if the decimal point is smudged or unclear. The correct notation is '5 mg' (no trailing zero). Warfarin has a narrow therapeutic index, making this error potentially fatal.

Prescription notation safety rules: (1) Never trailing zeros: '5 mg' not '5.0 mg'; (2) Always leading zero: '0.5 mg' not '.5 mg'; (3) Avoid ambiguous abbreviations (IU, U, QD, cc); (4) Write drug names clearly — avoid abbreviations for look-alike/sound-alike drugs. Most critical for anticoagulants, digoxin, insulin, methotrexate.

Review: Safe prescribing notation rules: never use trailing zeros (5.0 mg → write '5 mg'); always use a leading zero for sub-milligram doses (0.5 mg, not .5 mg). This applies to all drugs but is most critical for narrow-therapeutic-index drugs like warfarin, digoxin, and methotrexate.

Correct! The India NLEM 2022 lists approximately 384 drugs. This revision expanded from 376 (NLEM 2015) by adding newer antivirals, oncology drugs, and hepatitis medications while maintaining the core essential medicines framework.

Key NLEM 2022 facts: ~384 drugs; organised by pharmacological class; revised from NLEM 2015 (376 drugs); new additions include new antivirals (COVID treatments), oncology drugs, and hepatitis medications; freely accessible at CDSCO/Ministry of Health website. Essential = public health relevance + proven efficacy/safety + best cost-effectiveness.

Review: India NLEM 2022 ≈ 384 drugs. The WHO Model EML (2023) lists approximately 502 medicines. Familiarity with the approximate size of the NLEM helps prescribers appreciate the core 'essential' concept — a curated, evidence-based minimum formulary for India's public health needs.

Correct! Codeine is a prodrug requiring CYP2D6 conversion to morphine (its active analgesic). Ultra-rapid metabolisers convert codeine to morphine far faster than normal → excess morphine → opioid toxicity risk (sedation, respiratory depression). This is the reason FDA and EMA have restricted codeine use in children and nursing mothers.

Codeine-CYP2D6 pharmacogenomics: codeine → morphine (10%) via CYP2D6; Ultra-rapid metabolisers (2-5% of population) → excessive morphine → respiratory depression risk. Avoid codeine in: ultra-rapid CYP2D6 metabolisers, post-tonsillectomy children (OSA risk), nursing mothers (infant morphine exposure). Poor metabolisers: no analgesic effect from codeine.

Review: CYP2D6 phenotypes and codeine: Poor metaboliser = no analgesia (no morphine formed); Normal = expected analgesia; Ultra-rapid = excess morphine formed rapidly = opioid toxicity. This is one of the strongest clinical pharmacogenomic examples — the FDA black box warning for codeine in children is based on CYP2D6 ultra-rapid metabolism deaths.

Correct! The Cockcroft-Gault equation (CrCl = [(140-age) × weight × 0.85 for women] / [72 × serum creatinine]) is validated for adults with stable renal function and normal muscle mass. It is the most commonly used equation for drug dosing adjustments in clinical practice.

Cockcroft-Gault CrCl = [(140-age) × weight in kg × (0.85 if female)] / (72 × serum Cr in mg/dL). Use for: adult drug dosing decisions. Limitations: assumes stable renal function, normal muscle mass. Schwartz formula for children; eGFR (CKD-EPI) for CKD staging (not drug dosing). Cachectic patients: low creatinine does not mean good renal function — use ideal body weight or adjust.

Review: Cockcroft-Gault limitations: unreliable in pregnancy (altered physiology/volume), children (use Schwartz formula), and cachectic/obese patients (muscle mass affects creatinine generation, so the formula overestimates or underestimates CrCl). Use actual body weight for underweight patients, ideal body weight for obese.

Correct! Vancomycin nephrotoxicity is the primary toxicity that TDM aims to prevent. High trough levels (>20 mg/L) are associated with nephrotoxicity. Current guidelines recommend AUC/MIC-guided dosing (targeting AUC 400-600 mg·h/L) rather than trough-only monitoring, but preventing nephrotoxicity remains the key safety goal.

Vancomycin TDM: narrow therapeutic window (toxicity vs sub-therapeutic). Nephrotoxicity risk with high troughs (>20 mg/L) or AUC >600 mg·h/L. 2020 guidelines: AUC/MIC-guided dosing preferred over trough-only. Empiric dosing: 15-20 mg/kg Q8-12h; adjust based on renal function. TDM sampling: steady-state (after 3-4 doses); trough = 30 min before 4th dose.

Review: Vancomycin TDM key points: (1) primary toxicity = nephrotoxicity (dose-dependent); (2) ototoxicity is also possible but less common; (3) hepatotoxicity is not a primary vancomycin concern; (4) current ASHP/IDSA guidelines (2020) recommend AUC-guided monitoring over trough-only. Therapeutic AUC target: 400-600 mg·h/L for MRSA.

Correct! Tramadol is a Schedule H1 drug in India, reflecting its dependence potential. Schedule H1 drugs require: (1) prescription by a Registered Medical Practitioner, (2) the prescription must be retained by the pharmacist for 2 years, and (3) prescribers must maintain records of prescriptions for H1 drugs.

Indian drug schedule summary: OTC = no prescription needed; Schedule H = prescription required (pharmacist retains); Schedule H1 = prescription + prescriber records (high-risk: strong antibiotics, tramadol, some antifungals); Schedule X = NDPS drugs (narcotics/psychotropics, strictest control). Schedule H1 was introduced in 2013 specifically to combat antibiotic resistance and tramadol misuse.

Review: Schedule H1 includes high-risk drugs with abuse/dependence potential — tramadol, certain antibiotics with high resistance risk (third-generation cephalosporins, carbapenems, fluoroquinolones), and some others. Amoxicillin and cefixime are Schedule H (not H1). Metformin is an OTC drug in some contexts (oral antidiabetic without Schedule H classification).

Correct! Orange-red urine discolouration from rifampicin is an expected, predictable, and harmless side effect — it belongs under 'What to expect,' the element covering both expected therapeutic effects and predictable, non-harmful side effects. Counselling this prevents unnecessary anxiety and premature self-discontinuation.

Anti-TB drug counselling: rifampicin — orange-red urine/body fluids (expected, harmless — reassure); INH — peripheral neuropathy (supplement with pyridoxine 10 mg/day); pyrazinamide — hepatotoxicity (report jaundice, nausea, RUQ pain — what to REPORT); ethambutol — visual changes (report — what to REPORT). Differentiating expected vs reportable effects is key to patient safety.

Review: WHO five elements: (1) Why — indication; (2) How — dose, timing, missed doses; (3) What to expect — expected effects and predictable side effects; (4) What to report — danger signs requiring medical attention; (5) When to return. The distinction between 'what to expect' (normal/harmless) and 'what to report' (action required) is clinically important.

Correct! The WHO 2003 report 'Adherence to Long-Term Therapies' estimates that approximately 50% of patients in developed countries adhere to chronic disease medications. In lower-income countries, the rates are even lower. Non-adherence is 'the next frontier' of chronic disease management.

WHO 2003 Adherence Report key fact: 50% adherence in developed countries for long-term therapy. Non-adherence determinants: patient factors (forgetfulness, denial), therapy factors (side effects, complexity, cost), provider factors (poor counselling, short consultations), health system factors (drug availability), social factors (stigma, family support). Address all 5 dimensions.

Review: WHO adherence data: ~50% of chronic disease patients adhere in developed countries; lower in resource-limited settings. Non-adherence costs lives (preventable CVD events, TB drug resistance, diabetes complications) and drives healthcare costs. It is a major public health problem for hypertension, diabetes, asthma, HIV, TB, and mental health conditions.

Correct! Benzodiazepine withdrawal after chronic use can cause life-threatening seizures — unlike opioid withdrawal (severe but rarely fatal in otherwise healthy patients). GABA-A receptor down-regulation during chronic benzodiazepine use leads to CNS hyperexcitability on abrupt withdrawal → seizures, delirium, and potentially death. Always taper over weeks to months.

Benzodiazepine withdrawal is potentially FATAL — seizures and delirium can occur. Key rule: NEVER stop abruptly after >2-4 weeks of daily use. Management: switch to long-acting agent (diazepam if not already), taper 10% per week over 8-16 weeks. Opioid withdrawal: adrenaline-storm symptoms, intensely unpleasant, but not directly fatal in healthy patients (compare with benzodiazepine).

Review: Benzodiazepine withdrawal vs opioid withdrawal: Benzodiazepine = GABA-A hyperexcitability → seizures/delirium (potentially fatal — NEVER stop abruptly after chronic use); Opioid = adrenergic storm (sweating, tachycardia, myalgia, diarrhoea — intensely unpleasant but rarely fatal). Taper benzodiazepines over 8-16 weeks using a long-acting agent (diazepam) if switching from a short-acting one.

Correct! Textbooks are tertiary sources — they synthesise and summarise information but have a publication lag of 2-4 years before reaching the reader. Post-marketing safety data, label updates (new contraindications, dosing changes for special populations), and updated clinical guidelines are not reflected. For a recently-approved drug, the prescribing information (SmPC/PI) or a live clinical database is more current.

Drug information source hierarchy: Primary (RCTs, observational studies) → most current, needs critical appraisal; Secondary (databases, systematic reviews) → regularly updated, synthesised, practical; Tertiary (textbooks) → broadest coverage, easiest to use, but publication lag = 2-4 years. For prescribing decisions on recently-approved drugs: always cross-check with prescribing information or a live clinical database.

Review: Tertiary sources (textbooks): broad coverage, easy to read, good for established knowledge, but subject to publication lag (2-4 years). Secondary sources (clinical databases like UpToDate, BNF): synthesise and regularly updated — preferred for practical decisions. Primary sources (original RCTs): most current evidence, but require critical appraisal. Use tertiary for background, secondary/primary for current decisions.

Correct! Methotrexate for rheumatoid arthritis is prescribed ONCE WEEKLY, not daily. Daily methotrexate causes life-threatening bone marrow suppression and hepatotoxicity. This is one of the most dangerous prescription errors in rheumatology — 'weekly' must be explicitly written on the prescription to prevent dispensing as a daily drug.

Methotrexate weekly dosing for RA is one of the most important prescription safety checks. Standard prescription practice: write 'ONCE WEEKLY on [day]' explicitly. Folic acid supplementation (5 mg/week, alternate day from MTX) is always co-prescribed. Monitor: FBC, LFTs, renal function every 1-3 months. Methotrexate pneumonitis (interstitial lung disease) — always ask about cough and dyspnoea.

Review: Methotrexate dosing error is a notorious and fatal prescribing mistake. RA dose: 7.5-25 mg ONCE WEEKLY (oral or subcutaneous). Daily dosing causes: pancytopenia, severe mucositis, hepatotoxicity, pneumonitis. Many countries require 'ONCE WEEKLY' to be written explicitly on the prescription. Folic acid 5 mg once weekly (not on the same day as MTX) reduces side effects.