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Executive Summary

ZANTAC (RANITIDINE) REVISED LABELING: ANTI-ANDROGENIC ACTIVITY IS "UNCLEAR" in many cases. Labeling states that adverse reactions "have been reported as events in clinical trials or in the routine management of patients treated with Zantac" but adds that "the relationship to Zantac therapy has been unclear in many cases." Glaxo's revised labeling, dated July 1984, states that "controlled studies in animals and man have shown no stimulation of any pituitary hormone by Zantac, no anti-androgenic activity, and cimetidine-induced gynecomastia and impotence in hypersecretory patients have been resolved when Zantac was substituted." However, the labeling adds, "occasional cases of gynecomastia, impotence and loss of libido have been reported in male patients receiving Zantac, but the incidence did not differ from that in the general population." Previous labeling stated that "no clinically significant interference with endocrine or gonadal function have been reported." In contrast, labeling for SmithKline's H[2] antagonist Tagamet notes in the "precautions" section that the drug has "demonstrated a weak anti-androgenic effect." Under the adverse reactions section, Tagamet labeling states that "mild gynecomastia has been reported in patients treated for one month or longer"; and "reversible impotence has been reported in patients with pathological hypersecretory disorders, e.g., Zollinger-Ellison Syndrome, receiving Tagamet, particularly in high doses, for at least 12 months." Other adverse reactions that have been added to the revised Zantac labeling include "rare reports of tachycardia, bradycardia, premature ventricular beats"; "rare reports of reversible leukopenia, granulocytopenia, thrombocytopenia and pancytopenia"; "rare reports of arthralgias"; and "rare cases of hypersensitivity reactions (e.g., bronchospasm, fever, rash, eosinophilia), small increases in serum creatinine." Labeling also notes under "Drug Interactions" that "there have been isolated reports of drug interactions which suggest that Zantac may affect the bioavailability of certain drugs by some mechanism as yet unidentified (e.g., a pH dependent effect on absorption or a change in volume of distribution)." The new labeling also deletes the statement and accompanying chart which notes that during clinical trials, some patients not healed at four weeks were re-randomized to either placebo or ranitidine. Trends for the re-randomized patients weakly favored ranitidine, but there was no statistically significant differences.

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