Use of Renally Inappropriate Medications in Older Veterans: A National Study

Abstract

Objectives: To determine how many ambulatory older adults with chronic kidney disease receive medications that are contraindicated or dosed excessively given their level of renal function.

Design: Cross-sectional retrospective study.

Setting: U.S. Department of Veterans Affairs (VA) clinics.

Participants: Individuals aged 65 and older with a creatinine clearance (CrCl) of 15 to 49 mL/min (N = 83,850; mean age 80; 96% male).

Measurements: Forty medications that require dose adjustment or are contraindicated in people with impaired renal function were examined. Medication use and CrCl (calculated using the Cockroft-Gault equation) were assessed using VA pharmacy, laboratory, and other data sources as of October 2007.

Results: Thirteen percent of older veterans with a CrCl of 30 to 49 mL/min and 32% of those with a CrCl of 15 to 29 mL/min received one or more drugs that were contraindicated or prescribed at an excessive dose given the individual's level of renal function. The strongest risk factor for renally inappropriate prescribing was number of medications used; the risk of receiving renally inappropriate medications was 5.5 times as high (95% confidence interval = 5.1-5.9) in older adults taking 10 or more medications as in those taking one to three medications. Ranitidine, allopurinol, and metformin together accounted for 76% of renally misprescribed medications in individuals with a CrCl of 30 to 49 mL/min. Glyburide, ranitidine, gemfibrozil, carvedilol, and allopurinol accounted for 47% of renally misprescribed drugs for individuals with a CrCl of 15 to 29 mL/min.

Conclusion: Inappropriate prescribing of renally cleared medications is common in ambulatory older veterans, with only a few medications accounting for most of these prescribing problems.

Keywords: chronic kidney disease; drug use; pharmacoepidemiology; quality of care; veterans.

Figure 1. Use of renally inappropriate medications among patients with CrCl 30–49 ml/min

Some patients were prescribed both medications that are contraindicated and those that are inappropriately dosed at their level of creatinine clearance. * All criteria are specific to each patient’s level of renal function. Renal prescribing guidelines include drugs which are considered contraindicated below a given level of creatinine clearance (in which case any use is considered inappropriate), and drugs for which reduced doses are recommended (in which case use of a higher-than-recommended dose is considered inappropriate).

Figure 2. Most common medications with renally inappropriate prescribing

This figure shows all drugs that were renally misprescribed for at least 1% (rounded) of patients with creatinine clearance 30–49 ml/min (panel A) and creatinine clearance 15–29 ml/min (panel B). For medications that require dose adjustment, black bars represent the percent of patients who received the drug at an inappropriately high dose, and the white bars represent the percent of patients who received the drug at an appropriate dose.

Figure 3. Patterns of renally inappropriate medication use by level of renal function

Graphs show percent of all patients at each level of renal function who used metformin (panel A), ranitidine (panel B), and gabapentin (panel C), and the percentage of these prescriptions that were written at doses above and below recommended dose limits. Metformin is contraindicated at creatinine clearance <30 ml/min, so all prescriptions for this drug among patients with creatinine clearance <30 ml/min are considered renally inappropriate. Ranitidine and gabapentin have dose restrictions but not an absolute contraindication across the range of creatinine clearances shown.

Figure 3. Patterns of renally inappropriate medication use by level of renal function

Graphs show percent of all patients at each level of renal function who used metformin (panel A), ranitidine (panel B), and gabapentin (panel C), and the percentage of these prescriptions that were written at doses above and below recommended dose limits. Metformin is contraindicated at creatinine clearance <30 ml/min, so all prescriptions for this drug among patients with creatinine clearance <30 ml/min are considered renally inappropriate. Ranitidine and gabapentin have dose restrictions but not an absolute contraindication across the range of creatinine clearances shown.