Norfloxacin 400 mg, Tinidazole 600 mg Tablets

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 Giardiaand Entamoebaspecies is not known.

Absorption — After oral administration, tinidazole is rapidly and completely absorbed. A bioavailability study of tinidazole tablets was conducted in adult healthy volunteers. All subjects received a single oral dose of 2 g (four 500 mg tablets) of tinidazole tablets following an overnight fast. Oral administration of four 500 mg tablets of tinidazole tablets under fasted conditions produced a mean peak plasma concentration (C max) of 47.7 (±7.5) μg/mL with a mean time to peak concentration (T max) of 1.6 (±0.7) hours, and a mean area under the plasma concentration-time curve (AUC 0 to ∞) of 901.6 (± 126.5) μg hr/mL at 72 hours. The elimination half-life (T 1/2) 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 to 3 days of multi-day dosing.

Administration of tinidazole tablets with food resulted in a delay in T maxof approximately 2 hours and a decline in C maxof approximately 10%, compared to fasted conditions. However, administration of tinidazole tablets with food did not affect AUC or T 1/2in this study.

In healthy volunteers, administration of crushed tinidazole tablets in artificial cherry syrup, [prepared as described in Dosage and Administration (2.2) ] 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%.

Elimination — The plasma half-life of tinidazole is approximately 12 to 14 hours.

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 vitrometabolic 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.

Excretion: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.

Specific Populations — 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 (8.6)] . 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 (8.7)] .

Norfloxacin inhibits bacterial DNA synthesis. The cited molecular studies describe inhibition of DNA-gyrase-mediated supercoiling and effects on DNA relaxation and strand integrity. Antibacterial activity depends on organism susceptibility.

In healthy volunteers, the reference reports absorption of at least 30–40% of an oral dose, with a serum peak approximately 1 hour after 400 mg. Mean serum half-life is 3–4 hours and protein binding 10–15%. Renal elimination involves glomerular filtration and tubular secretion; 33–48% is recovered unchanged in urine within 24 hours, with additional less-active metabolites. These oral-tablet findings do not apply directly to eye drops or injections.