Clinical Case: Renal Impairment and a Renally Cleared Drug

A 69-year-old man with chronic kidney disease collects a new prescription for an antibiotic. The dose written is the standard adult dose, but his kidney function is significantly reduced, and the drug is primarily cleared by the kidneys.

Chronic kidney disease (eGFR around 30 mL/min). Hypertension (controlled). No known allergies. The antibiotic was prescribed for a urinary tract infection. The patient is unaware that kidney function affects dosing.

Nitrofurantoin (standard adult dose, for a UTI). Antihypertensive (long-term).

Reduced renal function can reduce urinary nitrofurantoin exposure and increase adverse-effect concerns. Eligibility depends on the measured function, local guidance and infection site. An eGFR around 30 warrants verification and prescriber clarification rather than automatic approval or a blanket claim that every prescription is contraindicated.

• Confirm renal function and its current relevance.
• Check product- and jurisdiction-specific thresholds and exceptions.
• Nitrofurantoin is not a routine agent for upper UTI or sepsis.
• Clarify a safe and timely plan with the authorised clinician.

1. Why is the standard dose inappropriate for this patient?
2. What renal threshold applies to this drug, and where do you verify it?
3. How do you communicate the concern to the prescriber?
4. What do you counsel the patient while the alternative is arranged?

The pharmacist verifies the renal result, units and timing, checks whether the infection is confined to the lower urinary tract and contacts the prescriber about suitability. MHRA guidance generally restricts nitrofurantoin below 45, but allows a cautious short course in selected patients at 30 to 44 when specific conditions are met. The decision is not a guessed dose reduction. In this older man the possibility of complicated or prostatic infection also matters. A prompt agreed plan, red-flag advice and documented rationale are needed.