Tinidazole

INDICATIONS & USAGE Tinidazole Tablets is a nitroimidazole antimicrobial indicated for: Trichomoniasis ( 1.1 ) Giardiasis: in patients age 3 and older ( 1.2 ) Amebiasis: in patients age 3 and older ( 1.3 ) Bacterial Vaginosis: in adult women ( 1.4 , 8.1 ) To reduce the development of drug-resistant bacteria and maintain the effectiveness of tinidazole tablets and other antibacterial drugs, tinidazole tablets should be used only to treat or prevent infections that tinidazole tablets are proven or strongly suspected to be caused by bacteria (1.5). 1.1 Trichomoniasis Tinidazole is indicated for the treatment of trichomoniasis caused by Trichomonas vaginalis. The organism should be identified by appropriate diagnostic procedures. Because trichomoniasis is a sexually transmitted disease with potentially serious sequelae, partners of infected patients should be treated simultaneously in order to prevent re-infection [see Clinical Studies ( 14.1 )]. 1.2 Giardiasis Tinidazole is indicated for the treatment of giardiasis caused by Giardia duodenalis (also termed G. lamblia ) in both adults and pediatric patients older than three years of age [ see Clinical Studies ( 14.2 ) ]. 1.3 Amebiasis Tinidazole is indicated for the treatment of intestinal amebiasis and amebic liver abscess caused by Entamoeba histolytica in both adults and pediatric patients older than three years of age. It is not indicated in the treatment of asymptomatic cyst passage [ see Clinical Studies ( 14.3 , 14.4 ) ]. 1.4 Bacterial Vaginosis Tinidazole is indicated for the treatment of bacterial vaginosis (formerly referred to as Haemophilus vaginitis, Gardnerella vaginitis, nonspecific vaginitis, or anaerobic vaginosis) in adult women [ see Use in Specific Populations ( 8.1 ) and Clinical Studies ( 14.5 ) ]. Other pathogens commonly associated with vulvovaginitis such as Trichomonas vaginalis, Chlamydia trachomatis, Neisseria gonorrhoeae, Candida albicans and Herpes simplex virus should be ruled out. To reduce the development of drug-resistant bacteria and maintain the effectiveness of tinidazole tablets and other antibacterial drugs, tinidazole tablets should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy. 1.5 Usage To reduce the development of drug-resistant bacteria and maintain the effectiveness of tinidazole tablets and other antibacterial drugs, tinidazole tablets should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy.

DOSAGE AND ADMINISTRATION Trichomoniasis: a single 2 g oral dose taken with food. Treat sexual partners with the same dose and at the same time ( 2.3 ) Giardiasis: Adults: a single 2 g dose taken with food. Pediatric patients older than three years of age: a single dose of 50 mg/kg (up to 2 g) with food ( 2.4 ) Amebiasis, Intestinal: Adults: 2 g per day for 3 days with food. Pediatric patients older than three years of age: 50 mg/kg/day (up to 2 g per day) for 3 days with food ( 2.5 ). Amebic liver abscess: Adults: 2 g per day for 3-5 days with food. Pediatric patients older than three years of age: 50 mg/kg/day (up to 2 g per day) for 3-5 days with food ( 2.5 ) Bacterial vaginosis: Non-pregnant, adult women: 2 g once daily for 2 days taken with food, or 1 g once daily for 5 days taken with food ( 2.6 ) 2.1 Dosing Instructions It is advisable to take tinidazole with food to minimize the incidence of epigastric discomfort and other gastrointestinal side-effects. Food does not affect the oral bioavailability of tinidazole [see Clinical Pharmacology ( 12.3 )]. Alcoholic beverages should be avoided when taking tinidazole and for 3 days afterwards [see Drug Interactions ( 7.1 )]. 2.2 Compounding of the Oral Suspension For those unable to swallow tablets, tinidazole tablets may be crushed in artificial cherry syrup to be taken with food. Procedure for Extemporaneous Pharmacy Compounding of the Oral Suspension: Pulverize four 500 mg oral tablets with a mortar and pestle. Add approximately 10 mL of cherry syrup to the powder and mix until smooth. Transfer the suspension to a graduated amber container. Use several small rinses of cherry syrup to transfer any remaining drug in the mortar to the final suspension for a final volume of 30 mL. The suspension of crushed tablets in artificial cherry syrup is stable for 7 days at room temperature. When this suspension is used, it should be shaken well before each administration. 2.3 Trichomoniasis The recommended dose in both females and males is a single 2 g oral dose taken with food. Since trichomoniasis is a sexually transmitted disease, sexual partners should be treated with the same dose and at the same time. 2.4 Giardiasis The recommended dose in adults is a single 2 g dose taken with food. In pediatric patients older than three years of age, the recommended dose is a single dose of 50 mg/kg (up to 2 g) with food. 2.5 Amebiasis Intestinal: The recommended dose in adults is a 2 g dose per day for 3 days taken with food. In pediatric patients older than three years of age, the recommended dose is 50 mg/kg/day (up to 2 g per day) for 3 days with food. Amebic Liver Abscess: The recommended dose in adults is a 2 g dose per day for 3-5 days taken with food. In pediatric patients older than three years of age, the recommended dose is 50 mg/kg/day (up to 2 g per day) for 3-5 days with food. There are limited pediatric data on durations of therapy exceeding 3 days, although a small number of children were treated for 5 days without additional reported adverse reactions. Children should be closely monitored when treatment durations exceed 3 days. 2.6 Bacterial Vaginosis The recommended dose in non-pregnant females is a 2 g oral dose once daily for 2 days taken with food or a 1 g oral dose once daily for 5 days taken with food. The use of tinidazole in pregnant patients has not been studied for bacterial vaginosis.

WARNINGS AND PRECAUTIONS Seizures and neuropathy have been reported. Discontinue tinidazole tablets if abnormal neurologic signs develop ( 5.1 ) Vaginal candidiasis may develop with tinidazole tablets and require treatment with an antifungal agent ( 5.2 ) Use tinidazole tablets with caution in patients with blood dyscrasias. Tinidazole tablets may produce transient leukopenia and neutropenia ( 5.3 , 7.3 ) 5.1 Potential for Genotoxicity and Carcinogenicity Carcinogenicity has been seen in mice and rats treated chronically with nitroimidazole derivatives, which are structurally related to tinidazole [see Nonclinical Toxicology (13.1)]. Although such data have not been reported for tinidazole, the two drugs are structurally related and have similar biologic effects. However, it is unclear if the positive tumor findings in lifetime rodent studies indicate a risk to patients taking a short course or single dose of tinidazole tablets. Use should be limited to approved indications only. Avoid chronic use. 5.2 Neurological Adverse Reactions Convulsive seizures and peripheral neuropathy, the latter characterized mainly by numbness or paresthesia of an extremity, have been reported in patients treated with tinidazole. The appearance of abnormal neurologic signs demands the prompt discontinuation of tinidazole therapy. 5.3 Vaginal Candidiasis The use of tinidazole may result in Candida vaginitis. In a clinical study of 235 women who received tinidazole for bacterial vaginosis, a vaginal fungal infection developed in 11 (4.7%) of all study subjects [ see Clinical Studies ( 14.5 ) ]. 5.4 Blood Dyscrasia Tinidazole should be used with caution in patients with evidence of or history of blood dyscrasia [ see Drug Interactions ( 7.3 ) ]. 5.5 Development of Drug Resistant Bacteria Prescribing tinidazole tablets in the absence of a proven or strongly suspected bacterial infection or a prophylactic indication is unlikely to provide benefit to the patient and increases the risk of the development of drug-resistant bacteria.

CONTRAINDICATIONS 4 CONTRAINDICATIONS The use of tinidazole is contraindicated: In patients with a previous history of hypersensitivity to tinidazole or other nitroimidazole derivatives. Reported reactions have ranged in severity from urticaria to Stevens-Johnson syndrome [see Adverse Reactions (6.1, 6.2)]. In patients with Cockayne syndrome. Severe irreversible hepatotoxicity/acute liver failure with fatal outcomes have been reported after initiation of metronidazole, another nitroimidazole drug, structurally related to tinidazole, in patients with Cockayne syndrome [see Adverse Reactions (6.2)] Prior history of hypersensitivity to tinidazole or other nitroimidazole derivatives (4, 6.1, 6.2) Patients with Cockayne syndrome (4, 6.2)

DRUG INTERACTIONS The following drug interactions were reported for metronidazole, a chemically-related nitroimidazole and may therefore occur with tinidazole: Warfarin and other oral coumarin anticoagulants: Anticoagulant dosage may need adjustment during and up to 8 days after tinidazole therapy ( 7.1 ) Alcohol-containing beverages/preparations: Avoid during and up to 3 days after tinidazole therapy ( 7.1 ) Lithium: Monitor serum lithium concentrations ( 7.1 ) Cyclosporine, tacrolimus: Monitor for toxicities of these immunosuppressive drugs ( 7.1 ) Fluorouracil: Monitor for fluorouracil-associated toxicities ( 7.1 ) Phenytoin, fosphenytoin: Adjustment of anticonvulsant and/or tinidazole dose(s) may be needed ( 7.1 , 7.2 ) CYP3A4 inducers/inhibitors: Monitor for decreased tinidazole effect or increased adverse reactions ( 7.2 ) Although not specifically identified in studies with tinidazole, the following drug interactions were reported for metronidazole, a chemically-related nitroimidazole. Therefore, these drug interactions may occur with tinidazole. 7.1 Potential Effects of Tinidazole on Other Drugs Warfarin and Other Oral Coumarin Anticoagulants: As with metronidazole, tinidazole may enhance the effect of warfarin and other coumarin anticoagulants, resulting in a prolongation of prothrombin time. The dosage of oral anticoagulants may need to be adjusted during tinidazole co-administration and up to 8 days after discontinuation. Alcohols, Disulfiram: Alcoholic beverages and preparations containing ethanol or propylene glycol should be avoided during tinidazole therapy and for 3 days afterward because abdominal cramps, nausea, vomiting, headaches, and flushing may occur. Psychotic reactions have been reported in alcoholic patients using metronidazole and disulfiram concurrently. Though no similar reactions have been reported with tinidazole, tinidazole should not be given to patients who have taken disulfiram within the last two weeks. Lithium : Metronidazole has been reported to elevate serum lithium levels. It is not known if tinidazole shares this property with metronidazole, but consideration should be given to measuring serum lithium and creatinine levels after several days of simultaneous lithium and tinidazole treatment to detect potential lithium intoxication. Phenytoin, Fosphenytoin: Concomitant administration of oral metronidazole and intravenous phenytoin was reported to result in prolongation of the half-life and reduction in the clearance of phenytoin. Metronidazole did not significantly affect the pharmacokinetics of orally-administered phenytoin. Cyclosporine, Tacrolimus : There are several case reports suggesting that metronidazole has the potential to increase the levels of cyclosporine and tacrolimus. During tinidazole co-administration with either of these drugs, the patient should be monitored for signs of calcineurin-inhibitor associated toxicities. Fluorouracil : Metronidazole was shown to decrease the clearance of fluorouracil, resulting in an increase in side-effects without an increase in therapeutic benefits. If the concomitant use of tinidazole and fluorouracil cannot be avoided, the patient should be monitored for fluorouracil-associated toxicities. 7.2 Potential Effects of Other Drugs on Tinidazole CYP3A4 Inducers and Inhibitors: Simultaneous administration of tinidazole with drugs that induce liver microsomal enzymes, i.e., CYP3A4 inducers such as phenobarbital , rifampin, phenytoin , and fosphenytoin (a pro-drug of phenytoin), may accelerate the elimination of tinidazole, decreasing the plasma level of tinidazole. Simultaneous administration of drugs that inhibit the activity of liver microsomal enzymes, i.e., CYP3A4 inhibitors such as cimetidine and ketoconazole , may prolong the half-life and decrease the plasma clearance of tinidazole, increasing the plasma concentrations of tinidazole. Cholestyramine : Cholestyramine was shown to decrease the oral bioavailability of metronidazole by 21%. Thus, it is advisable to separate dosing of cholestyramine and tinidazole to minimize any potential effect on the oral bioavailability of tinidazole. Oxytetracycline : Oxytetracycline was reported to antagonize the therapeutic effect of metronidazole. 7.3 Laboratory Test Interactions Tinidazole, like metronidazole, may interfere with certain types of determinations of serum chemistry values, such as aspartate aminotransferase (AST, SGOT), alanine aminotransferase (ALT, SGPT), lactate dehydrogenase (LDH), triglycerides, and hexokinase glucose. Values of zero may be observed. All of the assays in which interference has been reported involve enzymatic coupling of the assay to oxidation-reduction of nicotinamide adenine dinucleotide (NAD + ↔ NADH). Potential interference is due to the similarity of absorbance peaks of NADH and tinidazole. Tinidazole, like metronidazole, may produce transient leukopenia and neutropenia; however, no persistent hematological abnormalities attributable to tinidazole have been observed in clinical studies. Total and differential leukocyte counts are recommended if re-treatment is necessary.

ADVERSE REACTIONS 6 ADVERSE REACTIONS 6.1 Clinical Studies Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. Among 3669 patients treated with a single 2 g dose of tinidazole, in both controlled and uncontrolled trichomoniasis and giardiasis clinical studies, adverse reactions were reported by 11.0% of patients. For multi-day dosing in controlled and uncontrolled amebiasis studies, adverse reactions were reported by 13.8% of 1765 patients. Common (≥ 1% incidence) adverse reactions reported by body system are as follows. (Note: Data described in Table 1 below are pooled from studies with variable designs and safety evaluations.) Other adverse reactions reported with tinidazole include: Central Nervous System: Two serious adverse reactions reported include convulsions and transient peripheral neuropathy including numbness and paresthesia [see Warnings and Precautions (5.1)]. Other CNS reports include vertigo, ataxia, giddiness, insomnia, drowsiness. Gastrointestinal: tongue discoloration, stomatitis, diarrhea Hypersensitivity: urticaria, pruritis, rash, flushing, sweating, dryness of mouth, fever, burning sensation, thirst, salivation, angioedema Renal: darkened urine Cardiovascular: palpitations Hematopoietic: transient neutropenia, transient leukopenia Other: Candida overgrowth, increased vaginal discharge, oral candidiasis, hepatic abnormalities including raised transaminase level, arthralgias, myalgias, and arthritis. Table 1. Adverse Reactions Summary of Published Reports Adverse Reactions in Pediatric Patients: In pooled pediatric studies, adverse reactions reported in pediatric patients taking tinidazole were similar in nature and frequency to adult findings including nausea, vomiting, diarrhea, taste change, anorexia, and abdominal pain. Rare reported adverse reactions include bronchospasm, dyspnea, coma, confusion, depression, furry tongue, pharyngitis and reversible thrombocytopenia. Bacterial vaginosis: The most common adverse reactions in treated patients (incidence >2%), which were not identified in the trichomoniasis, giardiasis and amebiasis studies, are gastrointestinal: decreased appetite, and flatulence; renal: urinary tract infection, painful urination, and urine abnormality; and other reactions including pelvic pain, vulvo-vaginal discomfort, vaginal odor, menorrhagia, and upper respiratory tract infection [See Clinical Studies (14.5)]. 6.2 Postmarketing Experience The following adverse reactions have been identified and reported during post-approval use of Tindamax or other nitroimidazole agents. Because the reports of these reactions are voluntary and the population is of uncertain size, it is not always possible to reliably estimate the frequency of the reaction or establish a causal relationship to drug exposure. Tindamax: Severe acute hypersensitivity reactions have been reported on initial or subsequent exposure to tinidazole. Hypersensitivity reactions may include urticaria, pruritis, angioedema, Stevens-Johnson syndrome and erythema multiforme. Metronidazole, Another Nitroimidazole Product, Structurally Related to Tinidazole: Cases of severe irreversible hepatotoxicity/acute liver failure, including cases with fatal outcomes with very rapid onset after initiation of systemic use of metronidazole, another nitroimidazole agent structurally related to tinidazole, have been reported in patients with Cockayne syndrome (latency from drug start to signs of liver failure as short as 2 days) [see Contraindications (4)] . Most common adverse reactions for a single 2 g dose of tinidazole (incidence >1%) are metallic/bitter taste, nausea, weakness/fatigue/malaise, dyspepsia/cramps/epigastric discomfort, vomiting, anorexia, headache, dizziness and constipation (6.1) To report SUSPECTED ADVERSE REACTIONS, contact Mission Pharmacal Company at 1-800-298-1087 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch Table 6.1 Clinical Studies Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. Among 3669 patients treated with a single 2 g dose of tinidazole, in both controlled and uncontrolled trichomoniasis and giardiasis clinical studies, adverse reactions were reported by 11.0% of patients. For multi-day dosing in controlled and uncontrolled amebiasis studies, adverse reactions were reported by 13.8% of 1765 patients. Common (≥ 1% incidence) adverse reactions reported by body system are as follows. (Note: Data described in Table 1 below are pooled from studies with variable designs and safety evaluations.) Other adverse reactions reported with tinidazole include: Central Nervous System: Two serious adverse reactions reported include convulsions and transient peripheral neuropathy including numbness and paresthesia [see Warnings and Precautions ( 5.1 )]. Other CNS reports include vertigo, ataxia, giddiness, insomnia, drowsiness. Gastrointestinal: tongue discoloration, stomatitis, diarrhea Hypersensitivity: urticaria, pruritis, rash, flushing, sweating, dryness of mouth, fever, burning sensation, thirst, salivation, angioedema Renal: darkened urine Cardiovascular: palpitations Hematopoietic: transient neutropenia, transient leukopenia Other: Candida overgrowth, increased vaginal discharge, oral candidiasis, hepatic abnormalities including raised transaminase level, arthralgias, myalgias, and arthritis. Table 1. Adverse Reactions Summary of Published Reports 2 g single dose Multi-day dose GI: Metallic/bitter taste 3.7% 6.3% Nausea 3.2% 4.5% Anorexia 1.5% 2.5% Dyspepsia/cramps/epigastric discomfort 1.8% 1.4% Vomiting 1.5% 0.9% Constipation 0.4% 1.4% CNS: Weakness/fatigue/malaise 2.1% 1.1% Dizziness 1.1% 0.5% Other: Headache 1.3% 0.7% Total patients with adverse reactions 11.0% (403/3669) 13.8% (244/1765) Rare reported adverse reactions include bronchospasm, dyspnea, coma, confusion, depression, furry tongue, pharyngitis and reversible thrombocytopenia. Adverse Reactions in Pediatric Patients: In pooled pediatric studies, adverse reactions reported in pediatric patients taking tinidazole were similar in nature and frequency to adult findings including nausea, vomiting, diarrhea, taste change, anorexia, and abdominal pain. Bacterial vaginosis: The most common adverse reactions in treated patients (incidence >2%), which were not identified in the trichomoniasis, giardiasis and amebiasis studies, are gastrointestinal: decreased appetite, and flatulence; renal: urinary tract infection, painful urination, and urine abnormality; and other reactions including pelvic pain, vulvo-vaginal discomfort, vaginal odor, menorrhagia, and upper respiratory tract infection [See Clinical Studies ( 14.5 )]. 6.2 Postmarketing Experience The following adverse reactions have been identified and reported during post-approval use of Tindamax. Because the reports of these reactions are voluntary and the population is of uncertain size, it is not always possible to reliably estimate the frequency of the reaction or establish a causal relationship to drug exposure. Severe acute hypersensitivity reactions have been reported on initial or subsequent exposure to tinidazole. Hypersensitivity reactions may include urticaria, pruritis, angioedema, Stevens-Johnson syndrome and erythema multiforme.

CLINICAL PHARMACOLOGY 12.1 Mechanism of Action Tinidazole is an antiprotozoal, antibacterial agent. [see Clinical Pharmacology (12.4) ]. 12.3 Pharmacokinetics 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-∞) 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 max of approximately 2 hours and a decline in C max of approximately 10%, compared to fasted conditions. However, administration of tinidazole tablets with food did not affect AUC or T 1/2 in 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 - 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 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. 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) ]. 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.