In patients with renal impairment many drugs or their metabolites are excreted more slowly. It is therefore important to know what drugs will require dose reduction or are to be avoided altogether. An exception to this rule is gentamicin where careful use of a nomogram and monitoring of blood levels (peak one (1) hour after i.m. dose and trough before next dose) make its use relatively safe. (see nomogram on p. 21).

Most drugs are conveniently given at an interval equal to the half-life. If a drug is excreted exclusively by the kidney a reduction in Glomerular Filtration Rate (and hence creatinine clearance) will produce a corresponding reduction in drug excretion.

Thus if GFR falls by half the drug half-life can be expected to double; the dosage interval should therefore be doubled, while the loading dose and maintenance dose are not changed.

For practical purposes serum creatinine gives the most useful index of renal function. It does however fall with age and may not reflect the true state in the elderly, who may be assumed to have a GFR of 50ml/min even if serum creatinine is within normal limits.

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Drugs to be avoided or used with caution in renal failure
Active Ingredient GFR Dosage recommendations Comments
Chloral Hydrate see Anxiolytics and Hypnotics
Chloramphenicol <10 Avoid unless no alternative Dose-related depression of haematopoiesis
Chlordiazepoxide see Anxiolytics and Hypnotics
Chloroquine 20-50 – 10-20 Reduce dose avoid Only on prolonged use
Chlorothiazide see Thiazides
Chlorpromazine see Antipsychotics
Chlorpropamide 20-50 Avoid Tolbutamide and gliquidone suitable alternative
Chlortetracycline see Tetracyclines
Chlorthalidone see Thiazides
Cilastatin see Primaxin®
Cimetidine 20-50 - 10-20 600-800mg Occasional risk of confusion
Ciprofibrate 10-20 100mg on alternate days
Ciprofloxacin 10-20 Use half dose
Cisapride 20-Oct Start with half
Cisplatin 20-50 Avoid if possible Nephrotoxic and neurotoxic
Citalopram 10-20 - <10 No information available
Citrates Absorption of alumimium from aluminium salts is increased by citrates , which ar More ...
Clarithromycin 10-20 - <10 Use half dose
Clobazam see Anxiolytics and Hypnotics
Clofibrate 20-50 - 10-20 Reduce dose Further deterioration in renal function