Advice on dosage adjustment in renal impairment in Appendix 3 of the latest BNF (58) will now be expressed in terms of eGFR rather than creatinine clearance in the majority of cases. This is further qualified with information on the limitations of eGFR, such as:

• eGFR should not be used to adjust dosages of nephrotoxic drugs or drugs with a narrow therapeutic index; in such cases, use plasma-drug levels to adjust dose or creatinine clearance calculated using the Cockcroft and Gault formula.

• eGFR should not be used to adjust drug dosages in patients at both extremes of weight; in such cases, use the absolute glomerular filtration rate or creatinine clearance calculated using the Cockcroft and Gault formula.

• The MDRD formula is not validated for use in children under 18 years; see BNF for Children for advice on drug dosage adjustment in renal impairment in children.