Prescribing for patients with chronic kidney disease

clinical response and plasma drug concentration, where measurement is possible. Other important factors that need to be taken into consideration include dehydration, pre-existing heart failure and concomitant drug therapy.2 On the whole, loading doses do not usually need to be adjusted in patients with chronic kidney disease and dose adjustments can be made by reducing the maintenance dose of the drug, less frequent dosing intervals or both. Information in the BNF1 is based on creatinine clearance, because published information on the effects of renal impairment or drug elimination is usually given in terms of creatinine clearance as a surrogate of GFR. However, serum creatinine concentration is unreliable and the creatinine clearance test is now rarely used, having been replaced by the estimated GFR (eGFR). The two measures of renal function are not interchangeable but, in practice, eGFR can be used to determine dosage adjustments in place of creatinine clearance for most drugs and for most patients of average build and height. However, for potentially toxic drugs with a small safety margin and for patients who are very underor overweight, the absolute GFR should be used. This is calculated by multiplying the eGFR by the individual patient’s body surface area/1.73. P atients with renal impairment, particularly when elderly, tolerate drug side-effects less well and, importantly, some drugs are not effective when renal function is reduced. The British National Formulary (BNF) provides some important principles of dose adjustment in renal impairment.1 The level of renal function below which the dose of a drug must be reduced depends on the proportion of the drug eliminated by renal excretion or its toxicity. Not all drugs are toxic and in this case precision in dosing is less important. However, for more toxic drugs, which may have a small safety margin, dose regimens based on glomerular filtration rate (GFR) should be used. When initiating drug treatment in patients with chronic kidney disease (CKD) stage 3A, caution and careful thought are needed rather than dose adjustment, but greater care is needed in CKD stages 3B, 4 and 5. There are situations where both efficacy and toxicity are closely related to plasma drug concentration. In these situations, careful observation is necessary and subsequent doses should be adjusted according to Chronic kidney disease (CKD) affects renal drug elimination and other important processes involved in drug disposition, including absorption, drug distribution and non-renal clearance. As a result, the reduced renal excretion of a drug or its metabolites can cause toxicity and the sensitivity to some drugs is increased even if elimination is unimpaired. THERAPEUTICS REVIEW