Master CPS - Pharmacology
for MSRA

What the MSRA Tests in CPS - Pharmacology

CPS - Pharmacology on the MSRA tests applied clinical pharmacology in the context of prescribing decisions, adverse drug reactions, drug interactions, and therapeutic monitoring. Candidates must demonstrate knowledge of first-line treatments for common conditions (e.g., hypertension, diabetes, asthma, infections) per NICE/SIGN guidelines, including drug classes, doses, and contraindications. Emphasis is on safe prescribing: recognising high-risk medications (e.g., warfarin, methotrexate, lithium), managing overdoses (e.g., paracetamol, opioids), and interpreting therapeutic drug levels (e.g., digoxin, gentamicin). Questions often present a clinical scenario where you must choose the most appropriate drug, adjust a dose for renal/hepatic impairment, or identify a drug causing a specific adverse effect (e.g., ACE inhibitor cough, statin myopathy).

High-Yield Concepts

• Antihypertensives: first-line and combination therapy: NICE CG136: first-line for <55 years is ACE inhibitor (e.g., ramipril) or ARB (e.g., losartan); for ≥55 years or Black patients, calcium channel blocker (e.g., amlodipine). Add thiazide-like diuretic (e.g., indapamide) as second step. Avoid verapamil with beta-blockers due to bradycardia risk. Target BP clinic <140/90 (or <130/80 if CKD/diabetes).
• Anticoagulants: indications and reversal: DOACs (apixaban, rivaroxaban, edoxaban, dabigatran) first-line for AF and VTE. Warfarin reserved for mechanical valves or antiphospholipid syndrome. INR target 2.5 (range 2.0-3.0) for most indications. Reversal: warfarin with vitamin K (IV if life-threatening bleed) and PCC (Beriplex); dabigatran with idarucizumab; factor Xa inhibitors with andexanet alfa (if available) or PCC.
• Antibiotics: sepsis and common infections: Sepsis (per NICE NG51): IV piperacillin-tazobactam (Tazocin) or carbapenem if severe, plus gentamicin if suspected gram-negative. Community-acquired pneumonia: amoxicillin (first-line) or doxycycline (if penicillin allergy). Urinary tract infection: nitrofurantoin (if eGFR >30) or trimethoprim. Avoid fluoroquinolones (e.g., ciprofloxacin) as first-line due to tendonitis risk.
• Diabetes medications: metformin and beyond: Metformin first-line for type 2 diabetes (start 500 mg BD, max 2 g/day). If HbA1c >58 mmol/mol on metformin, add SGLT2 inhibitor (e.g., empagliflozin) or GLP-1 agonist (e.g., liraglutide) if ASCVD or CKD. Insulin therapy: start with basal (e.g., insulin glargine) 10 units or 0.1-0.2 units/kg. Avoid metformin if eGFR <30.
• Opioid prescribing and overdose management: Morphine equivalent daily dose (MEDD) >120 mg/day requires specialist input. Naloxone (IV/IM 0.4-2 mg) for opioid overdose, repeated every 2-3 minutes if no response. Respiratory rate <8 or pinpoint pupils indicate toxicity. Avoid codeine in children <12 years due to CYP2D6 variability. Tramadol lowers seizure threshold.
• Drug interactions: CYP450 and QT prolongation: CYP3A4 inhibitors (e.g., clarithromycin, fluconazole, grapefruit juice) increase levels of simvastatin, amlodipine, and DOACs. CYP3A4 inducers (e.g., rifampicin, carbamazepine) reduce efficacy. QT-prolonging drugs: amiodarone, citalopram (>40 mg/day), erythromycin, methadone. Check QTc before starting; avoid combinations if QTc >500 ms.
• Paracetamol overdose: nomogram and treatment: Use Rumack-Matthew nomogram for single acute ingestion: treat with acetylcysteine if level above treatment line (100 mg/L at 4 hours, 15 mg/L at 15 hours). For staggered or chronic overdose, treat if >150 mg/kg or >75 mg/kg in high-risk (malnourished, liver disease). Acetylcysteine IV: 150 mg/kg in 200 mL D5W over 1 hour, then 50 mg/kg over 4 hours, then 100 mg/kg over 16 hours.
• Lithium monitoring and toxicity: Therapeutic range: 0.6-1.0 mmol/L (maintenance), 1.0-1.5 mmol/L (acute). Toxic >1.5 mmol/L: symptoms (tremor, ataxia, confusion). Severe toxicity >2.5 mmol/L: consider haemodialysis. Monitor renal function (eGFR), TFTs, and calcium every 6 months. Avoid NSAIDs, ACE inhibitors, and thiazides (increase lithium levels).

Common Traps in CPS - Pharmacology Questions

• Confusing thiazide-like (indapamide, chlortalidone) with thiazide (bendroflumethiazide) – NICE now prefers thiazide-like diuretics for hypertension.
• Using amoxicillin for atypical pneumonia (e.g., Mycoplasma) – need macrolide (azithromycin) or doxycycline.
• Assuming all statins are equally potent – atorvastatin and rosuvastatin are high-intensity; simvastatin and pravastatin are moderate.
• Forgetting that digoxin toxicity presents with arrhythmias (e.g., atrial tachycardia with block) and visual disturbances (yellow-green halos) – check digoxin level (therapeutic 0.8-2.0 ng/mL).
• Giving naloxone for respiratory depression from benzodiazepines – naloxone only reverses opioids; flumazenil for benzodiazepines (but risk of seizures).
• Prescribing metformin in acute kidney injury (AKI) – stop metformin if eGFR drops acutely or <30; risk of lactic acidosis.

How to Revise CPS - Pharmacology for the MSRA

Focus on safe prescribing and guideline-driven management. Prioritise NICE guidelines for hypertension, diabetes, anticoagulation, and infections. Practice interpreting drug levels (digoxin, lithium, gentamicin) and overdose nomograms (paracetamol). Questions are often scenario-based: 'A 68-year-old with CKD stage 3 and AF – which anticoagulant?' or 'A patient on warfarin presents with INR 8.5 and minor bleed – what next?' Expect 2-3 questions on drug interactions (CYP450, QT prolongation). Revise common adverse effects (ACE cough, statin myopathy, metformin GI upset, opioid constipation). Use the BNF or NICE summaries for dose adjustments in renal/hepatic impairment. Practice calculations: loading doses, infusion rates, and paediatric doses (mg/kg).

Practise it: MedLumen has 50 CPS - Pharmacology questions for the MSRA, each with a full explanation and references.