Antibiotics and oral contraceptives

With the exception of rifampin-like drugs, there is a lack of scientific evidence supporting the ability of commonly prescribed antibiotics, including all those routinely employed in outpatient dentistry, to either reduce blood levels and/or the effectiveness of oral contraceptives. To date, all clinical trials studying the effects of concomitant antibiotic therapy (with the exception of rifampin and rifabutin) have failed to demonstrate an interaction. Like all drugs, oral contraceptives are not 100 per cent effective with the failure rate in the typical United States population reported to be as high as 3 per cent. It is thus possible that the case reports of unintended pregnancies during antibiotic therapy may simply represent the normal failure rate of these drugs. Considering that both drug classes are prescribed frequently to women of childbearing potential, one would expect a much higher rate of oral contraceptive failure in this group of patients if a true drug:drug interaction existed. On the other hand, if the interaction does exist but is a relatively rare event, occurring in, say, 1 in 5000 women, clinical studies such as those described in this article would not detect the interaction. The pharmacokinetic studies of simultaneous antibiotic and oral contraceptive ingestion, and the retrospective studies of pregnancy rates among oral contraceptive users exposed to antibiotics, all suffer from one potential common weakness, i.e., their relatively small sample size. Sample sizes in the pharmacokinetic trials ranged from 7 to 24 participants, whereas the largest retrospective study of pregnancy rates still evaluated less than 800 total contraceptive users. Still, the incidence of such a rare interaction would not differ from the accepted normal failure rate of oral contraceptive therapy. The medico-legal ramifications of what looks like at best a rare interaction remains somewhat "murky." On one hand, we have medico-legal experts advising the profession to exercise caution and warn all oral contraceptive users of a potential reduction in efficacy during antibiotic therapy. These opinions are not evidence-based and rely heavily on one or two legal proceedings that cannot even be substantiated. On the other hand, there is one recently published legal proceeding in which the outcome was in favor of the oral surgeon. There is clearly...

The activity of rifabutin against Mycobacterium leprae in armadillos.

The activity of rifabutin (LM 427) against Mycobacterium leprae was evaluated in armadillos inoculated earlier with human-derived M. leprae. Rifabutin was administered daily at a dose of 6 mg/kg body weight/day. The effect of rifabutin on M. leprae harvested from armadillos was determined by measuring the intracellular levels of ATP (an indicator of metabolic activity) of M. leprae and also their ability to multiply in the mouse footpads and in vitro in DH medium. Within 2 weeks of initiating the treatment, ATP levels declined to 21% of the original (pre-treatment level) and these M. leprae failed to multiply in the footpads of mice as well as in the in vitro culture system. This suggests that rifabutin was able to kill all M. leprae within 2 weeks. After 8 weeks the treatment was terminated and results showed that M. leprae from the treated armadillos remained non-viable in the mouse footpad system as well as in the in vitro system, indicating bactericidal action of rifabutin. The results suggest that rifabutin can be a substitute for rifampin in the leprosy multi-drug therapy regimen.

ICAAC update on opportunistic infections.

AIDS: Recent research on the effects of opportunistic infections (OIs) on HIV replication suggests that the OIs can actually increase HIV replication through the production of cytokines. Treatment options for thrush include antifungal treatments for early episodes and reserving fluconazole for patients with difficult to treat infections. Other studies show that prevention and treatment of Mycobacterium avium complex (MAC) increases survival rates. Drugs and dosages are described.^ieng

In vivo susceptibility of Mycobacterium leprae to ofloxacin either singly or in combination with rifampicin and rifabutin. Anti-leprosy activity of ofloxacin and ansamycins in mice.

The antimicrobial effects of ofloxacin against Mycobacterium leprae, either alone or in combination with rifampicin and rifabutin, were studied using mouse foot pad assay technique. When used singly, the minimum concentrations of the drugs needed to completely inhibit the growth of Mycobacterium leprae in foot pads of mice were 50 mg/kg body weight for ofloxacin and 0.003% and 0.0001%, respectively, for rifampicin and rifabutin. However, excellent synergistic effects were observed when mice were fed with 25 mg/kg body weight of ofloxacin along with 0.00003% rifabutin, but not rifampicin. Thus, incorporation of ofloxacin and rifabutin in the multiple drug therapy of leprosy patients is suggested.