Absorption and excretion of metronidazole. II. Studies on primary failures

Potentiating Metronidazole Scaffold against Resistant Trichomonas: Design, Synthesis, Biology and 3D-QSAR Analysis

Metronidazole (MTZ), the FDA-approved drug against Trichomonas vaginalis (TV), is being challenged seriously by drug resistance, while its inertness to sperm makes it ineffective as a vaginal contraceptive. Thirteen piperidine dithiocarbamate hybrids of 2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethane (8-20) were designed to potentiate the MTZ framework against drug resistance and sperm. New compounds were 1.2-12.1 times more effective against MTZ-susceptible and -resistant strains of TV. All of the compounds exhibited high safety toward cervical (HeLa) cells and Lactobacillus. Thirty-eight compounds were scrutinized by CoMFA and CoMSIA techniques of 3D quantitative structure-activity relationship. Good predictive r pred (2) values for CoMFA and CoMSIA models reflected the robustness of the predictive ability. This was validated by designing five new analogues (46-50), which were potently microbicidal (3-10 and 10-20 times against MTZ-susceptible and -resistant TV, respectively) and spermicidal. This in vitro study may have significant clinical relevance, which could become evident in due course.

Treatment of infections caused by metronidazole-resistant Trichomonas vaginalis

Infections with the sexually transmitted protozoan Trichomonas vaginalis are usually treated with metronidazole, a 5-nitroimidazole drug derived from the antibiotic azomycin. Metronidazole treatment is generally efficient in eliminating T. vaginalis infection and has a low risk of serious side effects. However, studies have shown that at least 5% of clinical cases of trichomoniasis are caused by parasites resistant to the drug. The lack of approved alternative therapies for T. vaginalis treatment means that higher and sometimes toxic doses of metronidazole are the only option for patients with resistant disease. Clearly, studies of the treatment and prevention of refractory trichomoniasis are essential. This review describes the mechanisms of metronidazole resistance in T. vaginalis and provides a summary of trichomonicidal and vaccine candidate drugs.

An in vitro metronidazole susceptibility test for trichomoniasis using the InPouch TV test

OBJECTIVE

An efficient anaerobic culture system, the InPouch TV test, was used to determine the susceptibility of Trichomonas vaginalis to metronidazole. Glacial acetic acid was employed as a solvent for metronidazole.

METHODS

T vaginalis isolates were cultured from 16 symptomatic female patients. The 11 who responded to oral metronidazole, 250 mg tid for 7 days, were considered as having sensitive trichomonads; the 5 who remained infected after treatment were considered to have resistant organisms. All isolates were cultured for minimum lethal concentrations (MLC). Metronidazole was added to a series of pouches; two-fold dilution of the most concentrated was 50 micrograms/ml and the least was 0.4 micrograms/ml. The inoculum of viable trichomonads was 1 x 105/ml in each pouch. Pouches were incubated at 37 degrees C for 48 h, examined microscopically for motile trichomonads, and then 0.5 ml was subcultured to drug free pouches. After 5 days incubation at 37 degrees C, each subculture and culture were examined microscopically for viable trichomonads.

RESULTS

Eleven isolates of T vaginalis from patients responding to metronidazole treatment had MLC between 0.4 to 3.1 micrograms/ml. The MLC from the 5 treatment failure patients were between 12.5 to 50 micrograms/ml.

CONCLUSIONS

For the 16 patients in this study, the MLC values determined with the InPouch TV test differentiated between infection caused by metronidazole sensitive and resistant trichomonads. The mean MLC of clinically resistant isolates was approximately eleven fold higher than the mean MLC of clinically sensitive isolates (15 micrograms/ml vs 1.32 micrograms/ml). There was a significant difference between clinically resistant and sensitive isolates (t = 5.47, p < 0.0005). This study suggests that the InPouch TV test could be used for distinguishing between metronidazole resistant and sensitive isolates.

Metronidazole resistance of Trichomonas vaginalis as a cause of treatment failure in trichomoniasis--A case report

Six isolates of a strain (MRP-MT) of Trichomonas vaginalis obtained from a woman before and after unsuccessful treatment with metronidazole had an appreciably lower susceptibility to metronidazole both in vitro in the aerobic tube assay and in vivo in the mouse assay than did control strains from patients cured with standard doses of the drug. Our results support recent evidence that metronidazole-resistant strains of T vaginalis do cause treatment failure. Resistance of these strains could be detected in vitro under only aerobic but not anaerobic conditions. The prevalence of metronidazole-resistant strains of T vaginalis should be kept under surveillance in order to estimate their clinical importance. The patient harbouring the resistant strain MRP-MT was finally cured with increased doses of ornidazole.

Strain of Trichomonas vaginalis resistant to metronidazole and other 5-nitroimidazoles

A strain of Trichomonas vaginalis (IR-78), recently isolated from a patient afflicted with recurrent symptomatic trichomoniasis, showed resistance to metronidazole, tinidazole, and nimorazole in vitro as well as in vivo. In a serial dilution test using cysteine monohydrochloride-peptone-liver infusion-maltose medium, T. vaginalis IR-78 was only resistant under aerobic conditions. Under anaerobic conditions it was as susceptible as the normal reference strain. The minimal lethal concentrations of metronidazole, tinidazole, and nimorazole for IR-78 were 100, 50, and 50 mug/ml aerobically and 0.4, 0.4, and 0.2 mug/ml anaérobically, respectively. The efficacy of metronidazole, tinidazole, and nimorazole was assessed in vivo by oral administration to mice simultaneously infected with IR-78 both subcutaneously and intraperitoneally. The CD(50) (dose needed to cure 50% of infections) of each compound was significantly higher for the subcutaneous than for the intraperitoneal infection. In contrast, there was little difference in CD(50) for these infections in mice inoculated with a susceptible trichomonas strain. The CD(50)'s for all three compounds against intraperitoneal and subcutaneous infections with IR-78 were 2 to >70 times higher than for susceptible strain E. Both forms of infection with IR-78 could always be cured with therapeutically acceptable doses of tinidazole and nimorazole; subcutaneous infections could not be cured with tolerated doses of metronidazole.

Studies on strain sensitivity of Trichomonas vaginalis to metronidazole

Ninety-four strains of Trichomonas vaginalis isolated from unselected patients in Vienna during the period from November 1975 to November 1975 were subjected to sensitivity tests against metronidazole in vitro and in vivo. Nearly 90% of the isolates examined showed in vitro growth inhibition at concentrations of 0.4 to 1.6 microgram metronidazole/ml and only about 10% at concentrations of less than 0.4 microgram/ml. All isolates showed some inhibition of growth after incubation for 48 hours with 3.2 microgram metroidazole/ml. Tests on treatment carried out on experimentally infected mice revealed that all strains of T. vaginalis examined were sensitive to metronidazole (MDE: less than 3 x 35 mg/kg peroral).

Treatment of trichomoniasis in females with and without gonorrhoea

46 women with trichomoniasis and gonorrhea were treated with nimorazole (300 mg twice daily for 7 days) and a trichomonal cure rate of 90-2 per cent. was noted. In addition, 53 of 112 patients with trichomoniasis but without gonorrhoea, were treated with metronidazole (200 mg three times a day for 7 days) and 59 with nimorazole (300 mg twice daily for 7 days) in a randomized trial. The cure rates were 96 and 90-5 per cent. respectively. There was no significant difference in the results noted in the two groups. Neither the trichomonal infection itself nor the result of antitrichomonal therapy was affected by antigonococcal therapy (one-day treatment with ampicillin or single-dose therapy with doxycycline). No increase was noted in the frequency of candidiasis after antitrichomonal therapy (in patients without gonorrhoea) or after antigonococcal therapy, but there was substantial variation between consecutive specimens in the prevalence of C. albicans.

Nitrimidazine compared with metronidazole in the treatment of vaginal trichomoniasis

A new substituted nitroimidazole, nitrimidazine (Naxogin), is compared with the established drug, metronidazole (Flagyl), for the treatment of vaginal trichomoniasis in a randomized double-blind trial. Nitrimidazine cured 39 (68%) out of 57 patients and showed no undesirable effects other than nausea in one patient. Metronidazole cured 51 (89%) out of 57 patients and also caused nausea in one patient; this cure rate corresponds with that previously reported in other trials. In the recommended dosage nitrimidazine is inferior to metronidazole, but is sufficiently effective to be useful in cases of intolerance to metronidazole.