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This article was originally published in The Tan Sheet

Executive Summary

OTC ANTACID GENERAL WARNING FOR PRESCRIPTION DRUG INTERACTIONS will be required under a final rule amending the monograph for OTC antacid products. Published in the Aug. 26 Federal Register, the final reg requires that all OTC antacid products carry the statement: "Drug Interaction Precaution: Antacids may interact with certain prescription drugs. If you are presently taking a prescription drug, do not take this product without checking with your physician or other health professional." The warning is required to appear on OTC antacid labels by Aug. 26, 1994. Based on the 1974 antacid final monograph, aluminum-containing OTC antacid labels currently must caution consumers to avoid aluminum-containing antacid products if they are also taking prescription antibiotics containing any form of tetracycline. In 1979, FDA proposed extending that drug interaction precaution to antacids containing calcium or magnesium. In response to that proposal, the agency received comments noting that antacids have the potential to adversely interact with other prescription drugs besides tetracycline, such as congestive heart failure drug digoxin. Such comments, as well as "data in the literature," led the agency to withdraw the 1979 warning proposal and publish for public comment a proposed drug interaction statement encompassing all Rx drugs in July 1986. The proposal applied to all antacids, not only those containing aluminum. FDA said it determined that a drug interaction precaution "is needed in the labeling of all OTC antacid drug products (not just those containing aluminum) because the medical/scientific literature identifies a number of interactions that can occur between OTC antacids and prescription drugs." This warning "represents good health care and will serve as a reminder to consumers who are using antacids to contact their physicians or other health professionals for medication counseling if they are taking a prescription drug," FDA continued. The agency added that a "general warning statement" is the "most appropriate for this situation" because "it would be impossible to list every prescription drug that could possibly cause an interaction" with OTC antacids. Antacids can interact with a "wide range of primary drugs and can adversely affect the efficacy of the primary medication," FDA explained in the notice, by altering the rate of dissolution, absorption, bioavailability or renal elimination of the Rx drug. Literature reports have documented, for instance, that antacids decrease the bioavailability of cimetidine, ranitidine, nitrofurantoin, digoxin, ethambutol, some indomethacin, phenytoin, vitamin A, fluoride, phosphate, atenolol and propranolol, FDA said. The 1986 proposal warned: "Antacids may interact with certain prescription drugs. If you are presently taking a prescription drug, do not take this product without checking with your physician." FDA said it added "or other health professional" to the end of the proposed warning statement because physicians are not the only health professionals who can "help consumers determine whether the prescription drug they are taking interacts with an antacid." Based on a recent FDA initiative to allow interchangeable terms in labeling statements required by OTC monographs ("The Tan Sheet" April 5, p. 9), FDA also noted that manufacturers could substitute "doctor" for the term "physician" in the antacid labeling statement. In comments on the 1986 proposal, the Proprietary Association (now the Nonprescription Drug Manufacturers Association) complained that a general prescription drug interaction label warning on all OTC antacid labels would detract from the effect of "important warnings" and dosage recommendations.

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