Synopsis
Choose the correct kidney-function estimate, individualise medicine exposure and monitor or restart essential treatment safely across CKD, AKI, dialysis and intercurrent illness.
- Start with the medicine's indication and urgency. Dose adjustment that makes an antimicrobial ineffective or permanently removes kidney- and heart-protective treatment can be as harmful as accumulation.
- Decide whether kidney function is stable. Creatinine-based eGFR and Cockcroft–Gault creatinine clearance assume relative steady state and can substantially mislead during rapidly evolving AKI.
- For most medicines in an average-sized stable adult, BNF renal advice commonly uses eGFR, but the exact monograph or Summary of Product Characteristics determines which estimate and threshold apply.
- Use Cockcroft–Gault creatinine clearance for direct-acting oral anticoagulants and consider it for nephrotoxic or narrow-therapeutic-index medicines, older people and extremes of body composition in line with MHRA advice.
- A renal dose may mean a smaller maintenance dose, a longer interval, both, a different formulation or avoidance. Loading doses are often governed more by distribution and clinical urgency than by renal clearance.
- Ask whether the person receives haemodialysis, haemodiafiltration, peritoneal dialysis or continuous kidney replacement therapy, when the last and next sessions occur, and whether residual urine function remains.
- Nephrotoxicity is contextual. NSAIDs may reduce renal perfusion; aminoglycosides and vancomycin can injure tubules; ACE inhibitors, ARBs and SGLT2 inhibitors can alter creatinine yet provide substantial long-term cardiorenal benefit.
- During vomiting, diarrhoea, sepsis or hypotension, temporarily withholding selected haemodynamically active or accumulation-prone medicines may be appropriate, but every hold requires an indication-specific restart and monitoring plan.
- Reconcile community prescriptions, inpatient charts, over-the-counter analgesics, herbal products, recent contrast and short antibiotic courses. Hidden ibuprofen or duplicate metformin frequently defeats an otherwise careful review.
- When the licensed information is unclear, or the patient has AKI, dialysis, unusual body size, pregnancy, transplant immunosuppression or several interacting drugs, use a renal pharmacist and specialist resources rather than improvising.
Key red flags
Intercurrent volume loss or sepsis combined with NSAID exposure, renin–angiotensin blockade and diuretic treatment can sharply reduce glomerular perfusion. The physiology and original indications determine which items are paused and restored.
New drowsiness, myoclonus, confusion, hallucinations, ataxia or respiratory depression after opioids, gabapentinoids, sedatives or certain antimicrobials suggests parent-drug or metabolite accumulation.
Bleeding, bruising, haemoglobin fall or occult blood after dehydration or renal decline may reflect excessive DOAC exposure, especially when eGFR rather than current Cockcroft–Gault clearance guided selection.
Nausea, visual disturbance or arrhythmia with digoxin; tremor, ataxia or confusion with lithium; and seizures or marrow suppression with other high-risk agents require immediate medicine-specific assessment and levels where interpretable.
AKI after NSAIDs, antimicrobial exposure, proton-pump inhibitors, immune therapies, contrast or calcineurin inhibitors can be haemodynamic, tubular, interstitial, crystal-related or microangiopathic. Urine and systemic findings help localise the mechanism.
Investigation priorities
Determine whether renal function is stable enough for an estimate and identify the direction and speed of change.
Management branches
A medicine is being started or renewed in a person with known or suspected kidney impairment.
- Confirm indication, urgency, allergy, pregnancy, current and baseline renal trajectory, recent weight, body composition, dialysis status and all interacting or duplicate products.
- Consult the current BNF monograph and SmPC to identify whether eGFR, Cockcroft–Gault clearance or specialist monitoring drives the dose, interval, contraindication and loading strategy.
- Prescribe the selected regimen with explicit review parameters, duration and escalation threshold; seek renal-pharmacy advice for AKI, dialysis, narrow-index treatment or disagreement between estimates.