PDR Guidelines for Use of Medications

PDR Guidelines for Use of Medications


Prescription drugs should be used only within the guidelines or recommended therapeutic range of the Physician’s Desk Reference.


The Physician’s Desk Reference (PDR) does not define the limits of good medical practice.  It is merely a re-statement of the package insert that are the FDA-approved-advertisements of the drug manufacturer that are written at the time of the release of the drug.   Unless mandated by the FDA (for example, a “black box” warning) or by the manufacturer (wanting to increase awareness of a new side-effect), no further additions are permitted without going through the extensive and costly FDA approval process.  Due to these costs, most drug manufacturers shy away from adding “indications” to labeling even when their drugs gain wide acceptance for off-label uses.

Therefore, for example, the Lyrica™ (pregabalin) package insert indicates maximum dosing to 600mg/day. Nevertheless, Pfizer’s own safety data indicates safety up to the limits they tested (1050mg) and the medication has been used, in both neurology and psychiatry at doses up to 1000mg per day. Notably, the drug is so safe that, according to the Lyrica™ package insert, “the highest reported accidental overdose of pregabalin during the clinical development program was 8000 mg, and there were no notable clinical consequences. In clinical studies, some patients took as much as 2400 mg/day. The types of adverse events experienced by patients exposed to higher doses (=900 mg) were not clinically different from those of patients administered recommended doses of pregabalin.”

When medications like Equetro™, Carbatrol™ or Tegretol™, brand names for long-acting carbamazepine are prescribed, the liver is “induced” and becomes a more efficient “filter” of other liver-metabolized medications – decreasing their “bioavailability” and, therefore, effectiveness.  So, if carbamazepine is co-administered with Lamictal™ (lamotrigine) the effective dose of lamotrigine is decreased by 50% and, if carbamazepine is co-administered with Topamax™ (topiramate) the effective dose is decreased by 40%.  Thus, the prescribed dose of the co-administered medication must often be increased, by necessity, to maintain the same effective dose.

According to the Handbook of Drug Therapy, a commonly used psychiatric text, “statements…published in the PDR are not always clinically accurate”.  Nevertheless, it is all too common for the uninformed to assume the PDR is the best source of information.  In the Manual of Clinical Psychopharmacology, Schatzberg and Cole state that, “additional studies to further document the efficacy of high dosages would be too costly for drug manufacturers, who can no longer hope to recoup the costs of such a study since the patent for the drug may have long expired.”  Further, they state, “the American Medical Association and the FDA have taken the position that the use of any marketed drug for ‘non-approved’ indications or at higher dosages for individual patients is within the purview of the clinician.”


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