10th July 2026

Antimicrobials

Most antimicrobials are excreted renally. The majority have a wide therapeutic index, and apart from gentamicin and vancomycin, dose reduction is only required when the eGFR is <20 mL/min. 

In accumulation, aminoglycosides can cause severe nephrotoxicity and ototoxicity, therefore dose adjustments are crucial in renal impairment. 

With gentamicin intramuscular or intravenous use in adults, an adequate loading dose is required initially, depending on the indication and creatinine clearance. The trough level, which is the level immediately before the next dose, should be <2 mg/litre. The peak level, taken one hour after the dose administration, should be 5-10 mg/litre.  In renal impairment, trough levels must be measured after every dose. Creatinine clearance can be calculated using the Cockcroft and Gault formula:

Estimated Creatining Clearance   =          (140 – Age ) x Weight x Constant 

• Age in years
• Weight in kilograms (use ideal body weight where fat is likely to be the major contributor to body mass)
• Serum creatinine in micromol/litre
• Constant = 1.23 for men; 1.04 for women 

Vancomycin loading dose should be based on actual body weight. Maintenance doses should be prescribed after creatinine clearance is calculated and, based on this, the initial dose level, administration rate, and timing of trough level are determined; these are found in local guidelines. In renal impairment, trough levels and renal function should be monitored daily. 

Penicillins (e.g. amoxicillin, benzylpenicillin, co-amoxiclav), cefotaxime, ceftazidime, ciprofloxacin, clarithromycin, meropenem, metronidazole and trimethoprim can be cleared by haemodialysis. B-Lactam accumulation significantly increases the risk of seizures when high doses are used in patients with renal impairment. 

Amoxicillin: The doses should be reduced if eGFR is 30 mL/minute/1.73 m² or less. 

Benzylpenicillin: Use normal dose every 8–12 hours if estimated glomerular filtration rate 10–50 mL/minute/1.73 m²; use normal dose every 12 hours if estimated glomerular filtration rate less than 10 mL/minute/1.73 m².

Co-amoxiclav: if eGFR < 30 mL/minute/1.73 m², reduce dose and extend dose interval.

Cefotaxime: If eGFR less than 5 mL/minute/1.73 m², reduce dose.

Ceftazidime: Reduce dose if creatinine clearance 50 mL/minute or less

Ciprofloxacin: if eGFR < 60 mL/minute/ 1.73m² reduce dose and extend dose interval

Clarithromycin: Avoid if severe hepatic impairment also present.

For modified-release preparations, avoid if creatinine clearance < 30 mL/minute, reduce dose if creatinine clearance 30–60 mL/minute.

For immediate-release preparations, reduce dose if creatinine clearance < 30 mL/minute, max. duration 14 days.

Meropenem: if creatinine clearance 50 mL/minute, reduce dose and extend dose interval

Trimethoprim: if eGFR < 30 mL/minute/1.73 m², reduce dose. 

Macrolides, metronidazole, cloxacillin and clindamycin do not require renal dose adjustments.