A number of drugs rely on the kidney for excretion and thus require their dose to be modified in any patients where there is renal impairment. Others are nephrotoxic and should be avoided completely in patients with renal disease. Traditionally clinicians have had to rely on serum creatinine to assess renal function but this may not accurately reflect the kidney function of an individual since its level also depends on muscle mass. In particular elderly females may have significant impairment of renal function despite a normal or near normal serum creatinine. The advent of automated reporting of estimated glomerular filtration rate (eGFR) provides the clinician with simple, easily understood and readily available measurement which more accurately reflects a patient’s renal function. In particular eGFR allows the clinician to readily identify and stratify patients with chronic kidney disease (CKD) and can allow a more rational and safer approach to prescribing in this group of high risk patients. This commentary suggests that national prescribing formularies should use eGFR to provide consistent advice about the appropriate dose adjustment and avoidance of potentially toxic drugs at various stages of CKD. Such an approach may prove invaluable in improving prescribing in CKD and avoiding drug toxicity in this group of patients.