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International Association Against Painful Experiments on Animals

101 Misleading results from Vivisection Animal Experiments

53: Rifampcin & The Pill

In 1971 doctors reported unexpected pregnancies among women taking the "pill".(1) Of 88 women taking oral contraceptives in addition to the antituberculous drug rifampicin, 75% suffered disturbances to their menstrual cycle, and 5 became pregnant. The rifampicin had stimulated the patient's liver to metabolise, or breakdown, the pill more rapidly. Consequently, far less contraceptive remained to protect the women from pregnancy. The British National Formulary (1993) now tells doctors prescribing rifampicin to “advise patients on oral contraceptives to use additional means (of contraception).”

Further reports showed that rifampicin accelerates the breakdown of many other medicines.(2) An example is methadone where rifampicin led to withdrawal symptoms by reducing the amount of drug. Another patient rejected their kidney graft because rifampicin had diminished the dose of immunosuppressive drug cyclosporin.

Rifampicin's peculiar effect had not been predicted by animal experiments.(3) Following discovery of the effects in people, further animal tests were carried out but these proved contradictory. For instance, the drug's action could not be reproduced in rats.(4) In mice, however, prolonged treatment with rifampicin did stimulate the liver's metabolic processes but a single dose had the opposite effect, slowing down metabolism.(4) Nevertheless, the problems with rifampicin might have been predicted had scientists used human liver tissue for their tests.(5)

References

1) Reported in J.P.Mumford, Brifish Medical Journal, 1974, May 11, 333-334.
2) H.Meyer et al in Meyler's Side Effects of Drugs, 11th edition, Ed. M.N.G.Dukes (Elsevier, 1988).
3) E.Nieschlag, Pharmacology & Therapeutics, 1979, vol.5, 407-409. 4) D.Pessayre & P.Mazel, Biochemical Pharmacology, 1976, vol.25, 943-949.
5) A.M.Jezequel et al, Gut, 1971, vol.l2, 984-987.

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