Pharmacology & Prescribing Flashcards

A patient on lithium for bipolar disorder presents with coarse tremor, confusion, and vomiting. His serum lithium level is 2.3 mmol/L. What is the most appropriate immediate management?

Answer: Cease lithium immediately and consider haemodialysis

A lithium level above 2.0 mmol/L with clinical symptoms represents severe toxicity requiring immediate cessation; haemodialysis is indicated to rapidly remove lithium when toxicity is severe or the patient is deteriorating.

A patient with rheumatoid arthritis is commenced on weekly oral methotrexate. Which supplement must be co-prescribed to reduce the risk of mucositis and haematological side effects?

Answer: Folic acid

Folic acid supplementation is co-prescribed with methotrexate because methotrexate inhibits dihydrofolate reductase; folic acid reduces mucositis, bone marrow suppression, and hepatotoxicity without significantly impairing efficacy.

Which antibiotic class is generally contraindicated in children under 12 years due to the risk of arthropathy and potential damage to developing cartilage?

Answer: Fluoroquinolones (e.g., ciprofloxacin)

Fluoroquinolones are contraindicated in children under 12 (and generally under 18 in most guidelines) due to evidence of arthropathy and cartilage toxicity demonstrated in animal studies and paediatric case reports.

A patient taking ramipril (ACE inhibitor) is commenced on spironolactone (a potassium-sparing diuretic). Which electrolyte imbalance must be closely monitored?

Answer: Hyperkalaemia

Both ACE inhibitors (which reduce aldosterone-mediated potassium excretion) and potassium-sparing diuretics retain potassium, creating a significant risk of dangerous hyperkalaemia when combined.

A patient with type 2 diabetes has a new eGFR of 25 mL/min/1.73m². What change should be made to their metformin therapy?

Answer: Cease metformin as it is contraindicated at this eGFR

Metformin is contraindicated when eGFR falls below 30 mL/min/1.73m² due to impaired renal excretion leading to drug accumulation and the risk of potentially fatal lactic acidosis.

A patient stabilised on warfarin is commenced on amiodarone for persistent atrial fibrillation. What effect does amiodarone have on warfarin anticoagulation?

Answer: Increases warfarin effect by inhibiting CYP2C9

Amiodarone is a potent inhibitor of CYP2C9 (the primary enzyme metabolising warfarin), reducing warfarin clearance and significantly increasing anticoagulation — the INR must be monitored closely and the warfarin dose reduced.

A patient at 10 weeks gestation develops an uncomplicated urinary tract infection. Which antibiotic should be AVOIDED in the first trimester primarily due to its folate antagonism?

Answer: Trimethoprim

Trimethoprim inhibits dihydrofolate reductase, acting as a folate antagonist; it is avoided in the first trimester due to the risk of neural tube defects and other folate-deficiency related complications.