Tinidazole (Page 4 of 5)

12.4 Microbiology

Mechanism of Action: Tinidazole is an antiprotozoal, antibacterial agent. The nitro- group of tinidazole is reduced by cell extracts of Trichomonas. The free nitro- radical generated as a result of this reduction may be responsible for the antiprotozoal activity. Chemically reduced tinidazole was shown to release nitrites and cause damage to purified bacterial DNA in vitro. Additionally, the drug caused DNA base changes in bacterial cells and DNA strand breakage in mammalian cells. The mechanism by which tinidazole exhibits activity against Giardia and Entamoeba species is not known.

Antibacterial: Culture and sensitivity testing of bacteria are not routinely performed to establish the diagnosis of bacterial vaginosis [see Indications and Usage ( 1.4) ]; standard methodology for the susceptibility testing of potential bacterial pathogens, Gardnerella vaginalis, Mobiluncus spp. or Mycoplasma hominis , has not been defined. The following in vitro data are available, but their clinical significance is unknown. Tinidazole is active in vitro against most strains of the following organisms that have been reported to be associated with bacterial vaginosis:

Bacteroides spp.

Gardnerella vaginalis

Prevotella spp.

Tinidazole does not appear to have activity against most strains of vaginal lactobacilli.

Antiprotozoal: Tinidazole demonstrates activity both in vitro and in clinical infections against the following protozoa: Trichomonas vaginalis ; Giardia duodenalis (also termed G. lamblia); and Entamoeba histolytica.

For protozoal parasites, standardized susceptibility tests do not exist for use in clinical microbiology laboratories.

Drug Resistance: The development of resistance to tinidazole by G. duodenalis, E. histolytica , or bacteria associated with bacterial vaginosis has not been examined.

Cross-resistance: Approximately 38% of T. vaginalis isolates exhibiting reduced susceptibility to metronidazole also show reduced susceptibility to tinidazole in vitro. The clinical significance of such an effect is not known.

of Tinidazole Tablets with food resulted in a delay in Tmax of approximately 2 hours and a decline in Cmax of approximately 10%, compared to fasted conditions. However, administration


13.1 Carcinogenesis & Mutagenesis & Impairment of Fertility

Metronidazole, a chemically-related nitroimidazole, has been reported to be carcinogenic in mice and rats but not hamsters. In several studies metronidazole showed evidence of pulmonary, hepatic, and lymphatic tumorigenesis in mice and mammary and hepatic tumors in female rats. Tinidazole carcinogenicity studies in rats, mice or hamsters have not been reported.

Tinidazole was mutagenic in the TA 100, S. typhimurium tester strain both with and without the metabolic activation system and was negative for mutagenicity in the TA 98 strain. Mutagenicity results were mixed (positive and negative) in the TA 1535, 1537, and 1538 strains. Tinidazole was also mutagenic in a tester strain of Klebsiella pneumonia. Tinidazole was negative for mutagenicity in a mammalian cell culture system utilizing Chinese hamster lung V79 cells (HGPRT test system) and negative for genotoxicity in the Chinese hamster ovary (CHO) sister chromatid exchange assay. Tinidazole was positive for in vivo genotoxicity in the mouse micronucleus assay.

In a 60-day fertility study, tinidazole reduced fertility and produced testicular histopathology in male rats at a 600 mg/kg/day dose level (approximately 3-fold the highest human therapeutic dose based upon body surface area conversions). Spermatogenic effects resulted from 300 and 600 mg/kg/day dose levels. The no observed adverse reaction level for testicular and spermatogenic effects was 100 mg/kg/day (approximately 0.5-fold the highest human therapeutic dose based upon body surface area conversions). This effect is characteristic of agents in the 5-nitroimidazole class.

13.2 Animal Pharmacology & or Toxicology

In acute studies with mice and rats, the LD50 for mice was generally > 3,600 mg/kg for oral administration and was > 2,300 mg/kg for intraperitoneal administration. In rats, the LD50 was > 2,000 mg/kg for both oral and intraperitoneal administration.

A repeated-dose toxicology study has been performed in beagle dogs using oral dosing of tinidazole at 100 mg/kg/day, 300 mg/kg/day, and 1000 mg/kg/day for 28-days. On Day 18 of the study, the highest dose was lowered to 600 mg/kg/day due to severe clinical symptoms. The two compound-related effects observed in the dogs treated with tinidazole were increased atrophy of the thymus in both sexes at the middle and high doses, and atrophy of the prostate at all doses in the males. A no-adverse-effect level (NOAEL) of 100 mg/kg/day for females was determined. There was no NOAEL identified for males because of minimal atrophy of the prostate at 100 mg/kg/day (approximately 0.9-fold the highest human dose based upon plasma AUC comparisons).


14.1 Trichomoniasis

Tinidazole (2 g single oral dose) use in trichomoniasis has been well documented in 34 published reports from the world literature involving over 2,800 patients treated with tinidazole. In four published, blinded, randomized, comparative studies of the 2 g tinidazole single oral dose where efficacy was assessed by culture at time points post-treatment ranging from one week to one month, reported cure rates ranged from 92% (37/40) to 100% (65/65) (n=172 total subjects). In four published, blinded, randomized, comparative studies where efficacy was assessed by wet mount between 7 to 14 days post-treatment, reported cure rates ranged from 80% (8/10) to 100% (16/16) (n=116 total subjects). In these studies, tinidazole was superior to placebo and comparable to other anti-trichomonal drugs. The single oral 2 g tinidazole dose was also assessed in four open-label trials in men (one comparative to metronidazole and 3 single-arm studies). Parasitological evaluation of the urine was performed both pre- and post-treatment and reported cure rates ranged from 83% (25/30) to 100% (80/80) (n=142 total subjects).

14.2 Giardiasis

Tinidazole (2 g single dose) use in giardiasis has been documented in 19 published reports from the world literature involving over 1,600 patients (adults and pediatric patients). In eight controlled studies involving a total of 619 subjects of whom 299 were given the 2 g × 1 day (50 mg/kg × 1 day in pediatric patients) oral dose of tinidazole, reported cure rates ranged from 80% (40/50) to 100% (15/15). In three of these trials where the comparator was 2 to 3 days of various doses of metronidazole, reported cure rates for metronidazole were 76% (19/25) to 93% (14/15). Data comparing a single 2 g dose of tinidazole to usually recommended 5 to 7 days of metronidazole are limited.

14.3 Intestinal Amebiasis

Tinidazole use in intestinal amebiasis has been documented in 26 published reports from the world literature involving over 1,400 patients. Most reports utilized tinidazole 2 g/day × 3 days. In four published, randomized, controlled studies (1 investigator single-blind, 3 open-label) of the 2 g/day × 3 days oral dose of tinidazole, reported cure rates after 3 days of therapy among a total of 220 subjects ranged from 86% (25/29) to 93% (25/27).

14.4 Amebic Liver Abscess

Tinidazole use in amebic liver abscess has been documented in 18 published reports from the world literature involving over 470 patients. Most reports utilized tinidazole 2 g/day × 2 to 5 days. In seven published, randomized, controlled studies (1 double-blind, 1 single-blind, 5 open-label) of the 2 g/day × 2 to 5 days oral dose of tinidazole accompanied by aspiration of the liver abscess when clinically necessary, reported cure rates among 133 subjects ranged from 81% (17/21) to 100% (16/16). Four of these studies utilized at least 3 days of tinidazole.

14.5 Bacterial Vaginosis

A randomized, double-blind, placebo-controlled clinical trial in 235 non-pregnant women was conducted to evaluate the efficacy of tinidazole for the treatment of bacterial vaginosis. A clinical diagnosis of bacterial vaginosis was based on Amsel’s criteria and defined by the presence of an abnormal homogeneous vaginal discharge that (a) has a pH of greater than 4.5, (b) emits a “fishy” amine odor when mixed with a 10% KOH solution, and (c) contains ≥20% clue cells on microscopic examination. Clinical cure required a return to normal vaginal discharge and resolution of all Amsel’s criteria. A microbiologic diagnosis of bacterial vaginosis was based on Gram stain of the vaginal smear demonstrating (a) markedly reduced or absent Lactobacillus morphology, (b) predominance of Gardnerella morphotype, and (c) absent or few white blood cells, with quantification of these bacterial morphotypes to determine the Nugent score, where a score ≥4 was required for study inclusion and a score of 0 to 3 considered a microbiologic cure. Therapeutic cure was a composite endpoint, consisting of both a clinical cure and microbiologic cure. In patients with all four Amsel’s criteria and with a baseline Nugent score ≥4, tinidazole oral tablets given as either 2 g once daily for 2 days or 1 g once daily for 5 days demonstrated superior efficacy over placebo tablets as measured by therapeutic cure, clinical cure, and a microbiologic cure.

Table 2. Efficacy of Tinidazole Tablets in the Treatment of Bacterial Vaginosis in a Randomized, Double-Blind, Double-Dummy, Placebo-Controlled Trial: Modified Intent-to-Treat Population1 (n=227)
Outcome Tinidazole Tablets1 g × 5 days(n=76) Tinidazole Tablets2 g × 2 days(n=73) Placebo (n=78)
% Cure % Cure % Cure
1 Modified Intent-to-Treat defined as all patients randomized with a baseline Nugent score of at least 4
2 Difference in cure rates (Tinidazole Tablets-placebo)
3 CI: confidence interval
Therapeutic CureDifference2 97.5% CI3 36.831.7(16.8, 46.6) 27.422.3(8.0, 36.6) 5.1
Clinical CureDifference2 97.5% CI3 51.339.8(23.3, 56.3) 35.624.1(7.8, 40.3) 11.5
Nugent Score CureDifference2 97.5% CI3 38.233.1(18.1, 48.0) 27.422.3(8.0, 36.6) 5.1

p-values for both Tinidazole Tablets regimens vs. placebo for therapeutic, clinical and Nugent score cure rates for both 2 and 5 days <0.001

The therapeutic cure rates reported in this clinical study conducted with Tinidazole Tablets were based on resolution of 4 out of 4 Amsel’s criteria and a Nugent score of <4. The cure rates for previous clinical studies with other products approved for bacterial vaginosis were based on resolution of either 2 or 3 out of 4 Amsel’s criteria. At the time of approval for other products for bacterial vaginosis, there was no requirement for a Nugent score on Gram stain, resulting in higher reported rates of cure for bacterial vaginosis for those products than for those reported here for tinidazole.

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