Answer: Recognizing the possible need to modify the dose of a medicine because of reduced kidney function is a defensive attitude that will protect the questioner. Once dialysis and kidney transplantation extended life in kidney failure, the safety of usual drug doses was questioned, especially for toxic antibiotics. As an example, to avoid deafness, a side effect of streptomycin (the first effective treatment for tuberculosis), injected once or twice daily in those with normal kidneys, the drug is given every five days when the kidneys have failed.

Today, this lesson carries over to the management of infection in peritoneal dialysis patients who (if their bug is sensitive) are successfully treated with a single injection of Vancomycin that stays in the blood for a week. The wise kidney patient reviews the dose and side effects of every prescribed medication. There are excellent books covering all usually prescribed drugs such as: "Drug Prescribing in Renal Failure. Dosing Guidelines for Adults."*

Drugs given for hypertension, the most commonly prescribed drugs in patients with kidney disease, fall into several different classes that are metabolized (excreted) differently and must be checked individually. Diuretics - drugs that increase the excretion of salt and water - are of two main types. Potassium-sparing drugs (amiloride, spironolactone and triamterene) may raise the potassium level in advanced kidney disease and must be avoided. Thiazide diuretics such as hydrochlorthiazide lose their effectiveness in renal failure but loop diuretics including furosemide, bumetanide and ethacrynic acid are still useful and safe in higher than normal doses.

Every hypertensive drug can be toxic. In general, the maximal dose of a drug of one class (calcium channel blocker) should be reached before adding a second or third drug. No modification of dose in kidney failure is needed for: clonidine, doxazosin, prazosin, terazosin, losartin, labetalol, metoprolol, minoxidil or nitroprusside. Similarly, the calcium channel blockers (amlodipine, diltiazem, felodidpine, isradipine, nicaropine, nifedipine, nisoldipine and verapamil) are safely given in kidney failure in the same dose used in normal kidney function.

Angiotensin converting enzyme (ACE) inhibitors (benazepril, captopril, enalapril, fosinopril, lisinopril, pentopril, quinapril, ramapril) must be individualized with close attention paid to blood pressure and the potassium level. Only 25 to 50 percent of the usual dose is required in advanced kidney failure or in dialysis patients. The serum creatinine may rise but this is reversible when the drug is withdrawn. About one in 10 patients will develop a reversible dry cough.

Any drugs not listed above should be checked before acceptance. This can be done in several ways but the best approach is to ask the pharmacist dispensing the medication. Each of the large pharmacy chains now includes a sheet detailing side effects and dangers for every medication. Try these excellent sources of information on the Internet: (www.medbroadcast.com, www.nlm.nih.gov/medlineplus/druginfo). If you still can't get the answer easily, call AAKP.

*Fourth Editions. George R. Aronoff, MD and others. American College of Physicians. Customer Service Center, 190 N. Independence Mall West, Philadelphia, PA 19106. 1-800-523-1546, extension 2000.

Answer provided by Eli Friedman, MD. Dr. Friedman is the Chief, Division of Renal Disease for SUNY, Health Science Center at Brooklyn. Dr. Friedman serves as Chairperson of the AAKP Medical Advisory Board.

The Dear Doctor column provides readers with an opportunity to submit renal related health questions to healthcare professionals who specialize in the area of concern. The answers are not to be construed as a diagnosis and therefore, altercations in current healthcare should not occur until the patient's physician is consulted.

This article originally appeared in November 2001 aakpRENALIFE, Vol. 17, No. 3.

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