Vidal L et al. (2005) Systematic comparison of four sources of drug information regarding adjustment of dose for renal function. BMJ 331: 263–266

Secondary sources of drug information are remarkably inconsistent in their advice on adjusting dosages to account for impaired kidney function. This is the worrying conclusion of a systematic comparison of four widely used and hitherto well-respected publications: British National Formulary, Martindale: the Complete Drug Reference, Drug Prescribing in Renal Failure and American Hospital Formulary System Drug Information.

Vidal et al. found that each publication based its recommendations on a different definition of renal impairment, ranging from undefined qualitative terms to graded glomerular filtration rates. The rationale and search strategies underlying recommendations were not explained in detail. Most sources cited few or no primary references in support of their guidelines.

By comparing entries for the 100 drugs requiring dose-adjustment that were most commonly prescribed at Rabin Medical Center in 2003, including angiotensin-converting enzyme inhibitors, statins, antibiotics, corticosteroids, analgesics and diuretics, the authors also detected marked variation in the recommended dose modifications. For example, 11 drugs listed as requiring dose adjustment in one publication needed no modification according to another. Seven agents for which no adjustment was recommended in one source were categorized by a second as being contraindicated in patients with renal failure.

It seems that the standards of evidence-based practice are not being met by some producers of information upon which clinicians rely. A dearth of robust data might be contributing to the problem. Nevertheless, this analysis might spur those who compile drug-dosing guidelines to improve their data extraction methodologies, transparency of workflow, citation practices and consistency.