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Mechanism of Action
Absorption: After oral administration, tinidazole is rapidly and completely absorbed. A bioavailability study of Tindamax (tinidazole) tablets was conducted in adult healthy volunteers. All subjects received a single oral dose of 2 g (four 500 mg tablets) of Tindamax (tinidazole) following an overnight fast. Oral administration of four 500 mg tablets of Tindamax (tinidazole) under fasted conditions produced a mean peak plasma concentration (Cmax) of 47.7 (±7.5) µg/mL with a mean time to peak concentration (Tmax) of 1.6 (±0.7) hours, and a mean area under the plasma concentration-time curve (AUC, 0-∞) of 901.6 (± 126.5) µg/hr/mL at 72 hours. The elimination half-life (T½) was 13.2 (±1.4) hours. Mean plasma levels decreased to 14.3 µg/mL at 24 hours, 3.8 µg/mL at 48 hours and 0.8 µg/mL at 72 hours following administration. Steady-state conditions are reached in 2½ - 3 days of multi-day dosing.
Administration of Tindamax (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 of Tindamax (tinidazole) with food did not affect AUC or T½ in this study.
In healthy volunteers, administration of crushed Tindamax (tinidazole) tablets in artificial cherry syrup, [prepared as described in DOSAGE AND ADMINISTRATION] after an overnight fast had no effect on any pharmacokinetic parameter as compared to tablets swallowed whole under fasted conditions.
Distribution: Tinidazole is distributed into virtually all tissues and body fluids and also crosses the blood-brain barrier. The apparent volume of distribution is about 50 liters. Plasma protein binding of tinidazole is 12%. Tinidazole crosses the placental barrier and is secreted in breast milk.
Metabolism: Tinidazole is significantly metabolized in humans prior to excretion. Tinidazole is partly metabolized by oxidation, hydroxylation, and conjugation. Tinidazole is the major drug-related constituent in plasma after human treatment, along with a small amount of the 2-hydroxymethyl metabolite.
Tinidazole is biotransformed mainly by CYP3A4. In an in vitro metabolic drug interaction study, tinidazole concentrations of up to 75 µg/mL did not inhibit the enzyme activities of CYP1A2, CYP2B6, CYP2C9, CYP2D6, CYP2E1, and CYP3A4.
The potential of tinidazole to induce the metabolism of other drugs has not been evaluated.
Elimination: The plasma half-life of tinidazole is approximately 12-14 hours. Tinidazole is excreted by the liver and the kidneys. Tinidazole is excreted in the urine mainly as unchanged drug (approximately 20-25% of the administered dose). Approximately 12% of the drug is excreted in the feces.
Patients with impaired renal function: The pharmacokinetics of tinidazole in patients with severe renal impairment (CrCL < 22 mL/min) are not significantly different from the pharmacokinetics seen in healthy subjects.
However, during hemodialysis, clearance of tinidazole is significantly increased; the half-life is reduced from 12.0 hours to 4.9 hours. Approximately 43% of the amount present in the body is eliminated during a 6-hour hemodialysis session [See Use in Specific Populations]. The pharmacokinetics of tinidazole in patients undergoing routine continuous peritoneal dialysis have not been investigated.
Patients with impaired hepatic function: There are no data on tinidazole pharmacokinetics in patients with impaired hepatic function. Reduction of metabolic elimination of metronidazole, a chemically-related nitroimidazole, in patients with hepatic dysfunction has been reported in several studies [See Use in Specific Populations].
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]; 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:
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.
Animal Toxicology and/or Pharmacology
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).
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 7-14 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).
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 x 1 day (50 mg/kg x 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 5-7 days of metronidazole are limited.
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 x 3 days. In four published, randomized, controlled studies (1 investigator single-blind, 3 open-label) of the 2 g/day x 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).
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 x 2-5 days. In seven published, randomized, controlled studies (1 double-blind, 1 single-blind, 5 open-label) of the 2 g/day x 2-5 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.
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 0-3 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 Tindamax (tinidazole) in the Treatment of Bacterial Vaginosis in a Randomized, Double-Blind, Double-Dummy, Placebo-Controlled Trial: Modified Intent-to-Treat Population1 (n=227)
|Outcome|| Tindamax (tinidazole)
1 g x 5 days
| Tindamax (tinidazole)
2 g x 2 days
|% Cure||% Cure||% Cure|
|Nugent Score Cure||38.2||27.4||5.1|
| 1Modified Intent-to-Treat defined as all patients
randomized with a baselineNugent score of at least 4
2Difference in cure rates (Tindamax (tinidazole) -placebo)
3CI: confidence interval
p-values for both Tindamax (tinidazole) regimens vs. placebo for therapeutic, clinical andNugent score cure rates for both 2 and 5 days <0.001
The therapeutic cure rates reported in this clinical study conducted with Tindamax (tinidazole) 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.
Last reviewed on RxList: 8/14/2007
This monograph has been modified to include the generic and brand name in many instances.
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