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PDR, Guidelines Differ on Antihypertensive Dosages

Kate Traynor

A new study claims that physicians who turn to their Physicians’ Desk Reference (PDR) for information on antihypertensive drug dosages may overmedicate patients, possibly driving them to quit the therapy.

The report, published in the Mar. 26 Archives of Internal Medicine, found that the PDR often offered "substantially higher" initial starting dosages for antihypertensive drugs than recommended by the Sixth Report of the Joint National Committee on the Detection, Evaluation, and Treatment of High Blood Pressure (JNC VI).

Dosage information for 45 drugs was included in both the JNC VI guidelines and the 1999 or 2000 editions of the PDR. The researcher determined that five of these drugs were available in forms that did not allow for doses lower than what was stated in the PDR. For the remaining 40 drugs, just over half of the PDR-based starting dosages at least twice as high as those recommended by JNC.

Although published reports advise starting elderly patients at low dosages of antihypertensive drugs, the researcher found that the PDR made such recommendations for 18 percent of the 45 drugs.

Drugs examined in the study included diuretics, angiotensin-converting-enzyme inhibitors, angiotensin II-receptor blockers, beta-blockers, and calcium antagonists. According to the trade magazine Pharmacy Times, several of the products studied, including amlodipine, lisinopril, enalapril, furosemide, atenolol, diltiazem, and metoprolol, were among the most-prescribed drugs in 1999.

Jay S. Cohen, M.D., the study’s sole author, attributed physicians’ reliance on the PDR to the fact that the publication is well indexed, easy to use, and free to them. But information contained in the PDR, he said, comes directly from drug manufacturers and does not usually reflect dosage data obtained after the Food and Drug Administration approves the product for marketing.

Antihypertensive drugs, Cohen said, cause dosage-dependent adverse effects that may lead patients to stop taking their medication. To minimize this, he recommended that clinicians start with low dosages of antihypertensive drugs and work up to the minimal effective dosage.

Cohen mentioned specific instances in which ASHP’s AHFS Drug Information advises that antihypertensive therapy start at dosages even lower than those recommended by JNC VI.