DIPHENHYDRAMINE ALTERNATE DOSING REGIMEN
This article was originally published in The Tan Sheet
DIPHENHYDRAMINE ALTERNATE DOSING REGIMEN of 25-50 mg every four to six hours is suggested by Procter & Gamble to cover use of the ingredient as both an antitussive and an antihistamine. In February comments to FDA, P&G said that "when labeled exclusively as either an antitussive or as an antihistamine, diphenhydramine should bear the corresponding dosage regimen given in the respective OTC monograph." However, "the dosage for concurrent use as both an antitussive and an antihistamine should be permitted to encompass the total range of both indications in order to provide maximum effectiveness for all consumers who concurrently suffer from cough and histaminic symptoms." FDA's suggested dosage for diphenhydramine as an antihistamine is 25-50 mg every four to six hours, while the proposed antitussive dose is 25 mg every four hours. Diphenhydramine also is allowed as an antiemetic at 25-50 mg every four to six hours, and as a sleep-aid at 50 mg at bedtime. SmithKline Beecham, in separate Feb. 23 comments to FDA, also suggested an alternate dose for diphenhydramine as an antitussive. SmithKline submitted pharmacokinetic data that, according to the company, show that 50 mg diphenhydramine taken orally every six hours "produces plasma levels of the drug which are the same or higher than those produced" by the regular 25 mg every four hours dose, "but for a longer duration." Both firms were responding to a Dec. 9, 1992 proposed amendment to the OTC Antitussive Products Monograph that placed diphenhydramine HCI and diphenhydramine citrate in Category I (safe and effective) for use alone in OTC cough syrups. In the December notice, FDA said that it would address combination cough/cold products containing diphenhydramine in a future Federal Register notice. Until then, diphenhydramine- containing OTC cough/cold combination products labeled for antitussive use can only be marketed under an approved NDA or ANDA, the agency stated. P&G argued, however, that "this position appears to be inconsistent with the FDA's general provisions and administrative procedures for marketing combination products." P&G asserted that FDA guidelines for combo products allow marketing if each active ingredient in the combination has been marketed on or before May 11, 1972; each ingredient has been classified by an OTC advisory review panel in Category I; and the combination of ingredients has been deemed Category I. P&G maintained that diphenhydramine, marketed since the late 1940s, meets all of these criteria. P&G concluded its comments by stating that diphenhydramine "positioning and its intended uses should be directly linked to the statement of identity and the stated indications for the product." The firm recommended, for example, that "in the same way that the analgesic/antipyretics may be identified as 'pain reliever-fever reducer,' diphenhydramine, when intended for concurrent use as both an antitussive and as an antihistamine, could be listed in the product statement of identity as 'cough suppressant-antihistamine.'" "Directions should be consistent to provide the needed effectiveness of the product at the upper range of dose and dosing interval for the antihistamine use," P&G urged, adding that "labeling for diphenhydramine, a dual-action antitussive/antihistamine, [should] bear warnings for both indications regardless of the intended use of antitussive/antihistamine-containing products."
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