Laboratory studies with the systemic trichomonacide, metronidazole

In vitro induced anaerobic resistance to metronidazole in Trichomonas vaginalis

Resistance to metronidazole detectable under anaerobic conditions was induced in two Trichomonas vaginalis strains (TV 10-02 and MRP-2) by cultivation at gradually increasing pressure of the drug (1-100 micrograms/ml) for 12 to 21 months. The resistant derivatives reproduced in anaerobic trypticase-yeast-extract-maltose medium at 100 micrograms/ml metronidazole and showed very high values of minimal lethal concentration for metronidazole in anaerobic in vitro assays (556-1,600 micrograms/ml at 48-h exposure to the drug). Stepwise selection was necessary to develop the resistance in either strain. Attempts to induce resistance by prolonged maintenance of trichomonads with constant, low or moderate drug concentrations (3-10 micrograms/ml) were unsuccessful. Freshly developed resistance to high concentrations of metronidazole was unstable in absence of drug pressure as well as after cryopreservation. Development of stable resistance required further cultivation at 100 micrograms/ml metronidazole. Unstable substrains did not revert to original susceptibility. They retained a moderate level of resistance, being able to grow at 10 micrograms/ml metronidazole. The strains with fully developed resistance had no activity of the hydrogenosomal enzymes pyruvate: ferredoxin oxidoreductase and hydrogenase and ceased uptake of [14C]-metronidazole. These findings indicate that the pyruvate oxidizing pathway responsible for metronidazole activation was inactivated and metabolism of the drug stopped.

Aerobic resistance of Trichomonas vaginalis to metronidazole induced in vitro

Aerobic resistance of Trichomonas vaginalis to metronidazole was induced in vitro by anaerobic cultivation of drug-susceptible trichomonads with low concentrations of the drug (2-3 micrograms/ml) for 50 days. Minimal lethal concentrations (MLC) for metronidazole of the resistant derivatives were high in aerobic susceptibility assays (MLC = 216-261.5 micrograms/ml) but low in anaerobic assays (MLC = 4.2-6.3 micrograms/ml), surpassing MLC values of their parent strain approximately 50-fold and 3-fold under aerobiosis and anaerobiosis, respectively. Sensitivity to metronidazole under anaerobic conditions and activity of the hydrogenosomal enzyme pyruvate: ferredoxin oxidoreductase indicated that the resistance was of the aerobic type. Dependence of the resistance manifestation on O2 was further confirmed by susceptibility assays in vitro performed in defined gas mixtures of different oxygen content (1-20%). Five percent concentration of O2 proved to be the threshold required for resistance demonstration and the MLC values further increased with increasing O2 concentrations. The in vitro-induced resistance was also demonstrated in vivo by subcutaneous mouse assay. The dose of metronidazole needed to cure 50% of infected mice (DC50) was 223 mg/kg x 3 for resistant derivative MR-3a but 6.6 mg/kg x 3 only for its drug-susceptible parent strain. The metronidazole-resistant strains developed in this study correspond by their properties to drug-resistant T. vaginalis strains isolated from patients refractory to treatment, and promise to be a useful tool in the study of 5-nitroimidazole aerobic resistance.

Medicated tampons: intravaginal sustained administration of metronidazole and in vitro-in vivo relationships

The technical feasibility of utilizing tampons as a drug delivery system for prolonged intravaginal drug administrations was studied. Several commercially available brands of tampons were examined. The methodology for the incorporation of various doses of metronidazole, an antitrichomonas agent, in tampons was described. The sustained-release profile of metronidazole from these medicated tampons was characterized. Intravaginal administration of metronidazole via the medicated tampons was investigated in rhesus monkeys and human volunteers, and in vitro-in vivo correlations were established. The biopharmaceutics of intravaginal absorption of metronidazole via medicated tampons was analyzed in comparison with a vaginal solution formulation.

In vitro sensitivity of Trichomonas vaginalis and Candida albicans to chemotherapeutic agents

Strains of fresh clinical isolates of Trichomonas vaginalis and Candida albicans have been tested in vitro for their sensitivity to eight drugs used in the therapy of monilial and trichomonal vaginitis. Three of the chemotherapeutic agents, chlorchinaldol, clotrimazole and broxyquinoline were effective against both organisms. Tinidazole and metronidazole were active against T. vaginalis. The strains of C. albicans were also sensitive to trichomycin, natamycin and nystatin. Tinidazole was the most effective trichomonacide, clotrimazole and chlorchinaldol were most effective against C. albicans, while chlorchinaldol had the best in vitro effect against both organisms. The ranges of the MICs are compared to values previously reported.

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).

Single dose of two grams of metronidazole for Trichomonas vaginalis infection

In this study, 243 women with symptomatic trichomonal vaginitis were treated with eight 250 mg. tablets of metronidazole for themselves, and eight tablets were given to each of their male consorts. They were given instructions to ingest "all eight in a row" and "avoid alcohol for 48 hours." Ninety-five per cent of 203 women that returned for re-examination were cured. This single-dose treatment is effective, well tolerated, and less expensive than current recommended dosages.

Sensitivity of Trichomonas vaginalis to metronidazole, tinidazole, and nifuratel in vitro

Prompted by the sensitivity of trichomonads to metronidazole and nifuratel in clinical practice, a study was conducted in 1971-1972 of 63 consecutive strains of Trichomonas vaginalis isolated from women with clinically refractory vaginal discharge. Their susceptibility to metronidazole, tinidazole, and nifuratel was tested, using a serial tube dilution technique. The minimum concentrations which in 48 hrs caused immobilization and lysis of trichomonads cultured in Diamond's medium was assessed. No differences in drug potency could be determined. The median trichomonistatic and trichomonicidal concentrations were 0-1 and 0-6 mug/ml. respectively when using an inoculum of 10,000 organisms per ml. An inoculum of 100,000 per ml. resulted in inhibitory concentrations of 1-0 and killing concentrations of 3-3 mug./ml. These levels are readily attained in blood and vaginal tissue after oral ingestion of the two imidazole derivatives. Thus, metronidazole has maintained its efficacy since it was first introduced more than a decade ago. The few therapeutic failures with metronidazole and tinidazole are considered to have been caused by pharmacokinetic deficiencies in the patients, or by re-infection.

In vitro effect of metronidazole on the ultrastructure of Trichomonas vaginalis donné

The effect of metronidazole on the growth and fine structure of exponeentially growing cells of Trichomonas vaginalis was examined. Cell division stopped about one hour after the addition of 1-4 mug/ml of metronidazole, and the cells were apparently arrested in the interphase. One to two hours after the addition of metronidazole, the movement of flagella and of the undulating membrane had decreased, but cell death had not occurred until 7-8 hours later. The fine structure of the cytoplasm was changed 30 to 60 minutes after addition of metronidazole. Proportionally, the number of polyribosomes had decreased whereas the number of single ribosomes in the cytoplasm had increased. The electron-density of the cytoplasmic matrix was higher in cells which were treated with metronidazole than in cells from control cultures. The findings of the present study indicate that the initial effect of metronidazole on T. vag. cells in vitro is an inhibition of cell multiplication as well as an impairment of protein synthesis.

Binding of metronidazole and its derivatives to plasma proteins: an assessment of drug binding phenomenon

Metronidazole and four derivatives were studied in vitro to investigate the differences in the extent of their binding to plasma proteins. Modification at the terminal portion of the alkyl side chain resulted in wide differences in the extent of binding. Molecular orbital calculations were performed by the CNDO and MINDO/2 methods to estimate the frontier electron density on the hetero atom at the 3'-position of the alkyl side chain. A linear correlation between the protein binding parameter (loge P) and the frontier electron density (qr) was observed for the binding of this group of trichomonicidal drugs. NMR spectroscopy was used to demonstrate that the alkyl side chain participated in the binding of these compounds to plasma proteins.

Interaction of metronidazole with metallic ions of biological importance

The possibility tht metronidazole exerts several of its biological actions via interaction with important metal ions was investigated. NMR spectroscopy and polarography (ac) were used to test for any interaction, to locate the probable sites for complexation, and to determine the molecular stoichiometry of any complexes formed. Of the series of divalent metal ions tests, only cupric ion showed detectable interaction with metronidazole. The predominant site of interaction of cupric ion was the unsubstituted nitrogen atom (N-3) on the metronidazole molecule. The stoichiometry of the complex was (Cu-(metronidazole)4)+2. A likely structure for the complex is presented.

Trichomoniasis. Clinical trial of metronidazole (Flagyl)

Metronidazole was given in various dosage regimens to 97 patients having microscopically diagnosed trichomoniasis. At the first examination after treatment all 97, including 76 to whom metronidazole had been given orally only, were found by culture and wet smear to be free of trichomonads. Reexamination of the 65 patients followed up for periods ranging from two weeks to 14 months revealed reappearance of trichomonads in eight cases. Nineteen husbands were treated. No patient had a recurrence after treatment of the husband. No effect of metronidazole on pregnancy or on fetal development was seen. Side effects, noted in 19 cases (20 per cent), generally were mild and transient and in no case were severe enough to terminate therapy before cure was effected.