her to treat an asymptomatic male partner who has a negative culture or one for whom no culture has been attempted is an individual one. in making this decision, it should be noted that there is evidence that a woman may become reinfected if her sexual partner is not treated. also, since there can be considerable difficulty in isolating the organism from the asymptomatic male carrier, negative smears and cultures cannot be relied upon in this regard. in any event, the sexual partner should be treated with metronidazole tablets usp in cases of reinfection. amebiasis. metronidazole tablets usp are indicated in the treatment of acute intestinal amebiasis (amebic dysentery) and amebic liver abscess. in amebic liver abscess, metronidazole tablet usp therapy does not obviate the need for aspiration or drainage of pus. anaerobic bacterial infections. metronidazole tablets usp are indicated in the treatment of serious infections caused by susceptible anaerobic bacteria. indicated surgical procedures should be performed in conjunction with metronidazole tablets usp therapy. in a mixed aerobic and anaerobic infection, antimicrobials appropriate for the treatment of the aerobic infection should be used in addition to metronidazole tablets usp. intra-abdominal infections, including peritonitis, intra-abdominal abscess, and liver abscess, caused by bacteroides species including the b. fragilis group ( b. fragilis, b. distasonis, b. ovatus, b. thetaiotaomicron, b. vulgatus ), clostridium species, eubacterium species, peptococcus species, and peptostreptococcus species. skin and skin structure infections caused by bacteroides species including the b. fragilis group, clostridium species, peptococcus species, peptostreptococcus species, and fusobacterium species. gynecologic infections, including endometritis, endomyometritis, tubo-ovarian abscess, and postsurgical vaginal cuff infection, caused by bacteroides species including the b. fragilis group, clostridium species, peptococcus species, peptostreptococcus species, and fusobacterium species. bacterial septicemia caused by bacteroides species including the b. fragilis group and clostridium species. bone and joint infections, (as adjunctive therapy), caused by bacteroides species including the b. fragilis group. central nervous system (cns) infections, including meningitis and brain abscess, caused by bacteroides species including the b. fragilis group. lower respiratory tract infections, including pneumonia, empyema, and lung abscess, caused by bacteroides species including the b. fragilis group. endocarditis caused by bacteroides species including the b. fragilis group. to reduce the development of drug-resistant bacteria and maintain the effectiveness of metronidazole tablets usp and other antibacterial drugs, metronidazole tablets usp 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.

earance of abnormal neurologic signs and symptoms demands the prompt evaluation of the benefit/risk ratio of the continuation of therapy (see adverse reactions ).

ot be treated during the first trimester (see contraindications ). in pregnant patients for whom alternative treatment has been inadequate, the one-day course of therapy should not be used, as it results in higher serum levels which can reach the fetal circulation (see precautions, pregnancy ). when repeat courses of the drug are required, it is recommended that an interval of four to six weeks elapse between courses and that the presence of the trichomonad be reconfirmed by appropriate laboratory measures. total and differential leukocyte counts should be made before and after re-treatment. in the male: treatment should be individualized as it is for the female. amebiasis adults: for acute intestinal amebiasis (acute amebic dysentery): 750 mg orally three times daily for 5 to 10 days. for amebic liver abscess: 500 mg or 750 mg orally three times daily for 5 to 10 days. pediatric patients : 35 to 50 mg/kg/24 hours, divided into three doses, orally for 10 days. anaerobic bacterial infections in the treatment of most serious anaerobic infections, intravenous metronidazole is usually administered initially. the usual adult oral dosage is 7.5 mg/kg every six hours (approx. 500 mg for a 70-kg adult). a maximum of 4 g should not be exceeded during a 24-hour period. the usual duration of therapy is 7 to 10 days; however, infections of the bone and joint, lower respiratory tract, and endocardium may require longer treatment. dosage adjustments patients with severe hepatic impairment for patients with severe hepatic impairment (child-pugh c), the dose of metronidazole tablets should be reduced by 50% (see clinical pharmacology and precautions ). patients undergoing hemodialysis: hemodialysis removes significant amounts of metronidazole and its metabolites from systemic circulation. the clearance of metronidazole will depend on the type of dialysis membrane used, the duration of the dialysis session, and other factors. if the administration of metronidazole cannot be separated from the hemodialysis session, supplementation of metronidazole dosage following the hemodialysis session should be considered, depending on the patient’s clinical situation (see clinical pharmacology ).

a, sometimes accompanied by headache, anorexia, and occasionally vomiting; diarrhea; epigastric distress; and abdominal cramping and constipation. mouth : a sharp, unpleasant metallic taste is not unusual. furry tongue, glossitis, and stomatitis have occurred; these may be associated with a sudden overgrowth of candida which may occur during therapy. dermatologic : erythematous rash and pruritus. hematopoietic : reversible neutropenia (leukopenia); rarely, reversible thrombocytopenia. cardiovascular : flattening of the t-wave may be seen in electrocardiographic tracings. hypersensitivity : urticaria, erythematous rash, stevens-johnson syndrome, toxic epidermal necrolysis, flushing, nasal congestion, dryness of the mouth (or vagina or vulva), and fever. renal : dysuria, cystitis, polyuria, incontinence, and a sense of pelvic pressure. instances of darkened urine have been reported by approximately one patient in 100,000. although the pigment which is probably responsible for this phenomenon has not been positively identified, it is almost certainly a metabolite of metronidazole and seems to have no clinical significance. other : proliferation of candida in the vagina, dyspareunia, decrease of libido, proctitis, and fleeting joint pains sometimes resembling “serum sickness.” rare cases of pancreatitis, which generally abated on withdrawal of the drug, have been reported. patients with crohn’s disease are known to have an increased incidence of gastrointestinal and certain extraintestinal cancers. there have been some reports in the medical literature of breast and colon cancer in crohn’s disease patients who have been treated with metronidazole at high doses for extended periods of time. a cause and effect relationship has not been established. crohn’s disease is not an approved indication for metronidazole tablets.

found in plasma. bactericidal concentrations of metronidazole have also been detected in pus from hepatic abscesses. metabolism/excretion the major route of elimination of metronidazole and its metabolites is via the urine (60% to 80% of the dose), with fecal excretion accounting for 6% to 15% of the dose. the metabolites that appear in the urine result primarily from side-chain oxidation [1-(ß-hydroxyethyl)-2-hydroxymethyl-5-nitroimidazole and 2-methyl-5-nitroimidazole-1-yl-acetic acid] and glucuronide conjugation, with unchanged metronidazole accounting for approximately 20% of the total. both the parent compound and the hydroxyl metabolite possess in vitro antimicrobial activity. renal clearance of metronidazole is approximately 10 ml/min/1.73 m 2 . the average elimination half-life of metronidazole in healthy subjects is eight hours. renal impairment decreased renal function does not alter the single-dose pharmacokinetics of metronidazole. subjects with end-stage renal disease (esrd; cl cr = 8.1±9.1 ml/min) and who received a single intravenous infusion of metronidazole 500 mg had no significant change in metronidazole pharmacokinetics but had 2-fold higher cmax of hydroxy-metronidazole and 5-fold higher cmax of metronidazole acetate, compared to healthy subjects with normal renal function (cl cr = 126±16 ml/min). thus, on account of the potential accumulation of metronidazole metabolites in esrd patients, monitoring for metronidazole associated adverse events is recommended (see precautions ). effect of dialysis following a single intravenous infusion or oral dose of metronidazole 500 mg, the clearance of metronidazole was investigated in esrd subjects undergoing hemodialysis or continuous ambulatory peritoneal dialysis (capd). a hemodialysis session lasting for 4 to 8 hours removed 40% to 65% of the administered metronidazole dose, depending on the type of dialyzer membrane used and the duration of the dialysis session. if the administration of metronidazole cannot be separated from the dialysis session, supplementation of metronidazole dose following hemodialysis should be considered (see dosage and administration ). a peritoneal dialysis session lasting for 7.5 hours removed approximately 10% of the administered metronidazole dose. no adjustment in metronidazole dose is needed in esrd patients undergoing capd. hepatic impairment following a single intravenous infusion of 500 mg metronidazole, the mean auc 24 of metronidazole was higher by 114% in patients with severe (child-pugh c) hepatic impairment, and by 54% and 53% in patients with mild (child-pugh a) and moderate (child-pugh b) hepatic impairment, respectively, compared to healthy control subjects. there were no significant changes in the auc 24 of hydroxyl-metronidazole in these hepatically impaired patients. a reduction in metronidazole dosage by 50% is recommended in patients with severe (child-pugh c) hepatic impairment (see dosage and administration ). no dosage adjustment is needed for patients with mild to moderate hepatic impairment. patients with mild to moderate hepatic impairment should be monitored for metronidazole associated adverse events (see precautions and dosage and administration ). geriatric patients following a single 500 mg oral or iv dose of metronidazole, subjects >70 years old with no apparent renal or hepatic dysfunction had a 40% to 80% higher mean auc of hydroxy-metronidazole (active metabolite), with no apparent increase in the mean auc of metronidazole (parent compound), compared to young healthy controls <40 years old. in geriatric patients, monitoring for metronidazole associated adverse events is recommended (see precautions ). pediatric patients in one study, newborn infants appeared to demonstrate diminished capacity to eliminate metronidazole. the elimination half-life, measured during the first 3 days of life, was inversely related to gestational age. in infants whose gestational ages were between 28 and 40 weeks, the corresponding elimination half-lives ranged from 109 to 22.5 hours. microbiology mechanism of action metronidazole, a nitroimidazole, exerts antibacterial effects in an anaerobic environment against most obligate anaerobes. once metronidazole enters the organism by passive diffusion and activated in the cytoplasm of susceptible anaerobic bacteria, it is reduced; this process includes intracellular electron transport proteins such as ferredoxin, transfer of an electron to the nitro group of the metronidazole, and formation of a short-lived nitroso free radical. because of this alteration of the metronidazole molecule, a concentration gradient is created and maintained which promotes the drug’s intracellular transport. the reduced form of metronidazole and free radicals can interact with dna leading to inhibition of dna synthesis and dna degradation leading to death of the bacteria. the precise mechanism of action of metronidazole is unclear. drug resistance a potential for development of resistance exists against metronidazole. resistance may be due to multiple mechanisms that include decreased uptake of the drug, altered reduction efficiency, overexpression of the efflux pumps, inactivation of the drug, and/or increased dna damage repair. metronidazole does not possess any clinically relevant activity against facultative anaerobes or obligate aerobes. activity in vitro and in clinical infections metronidazole has been shown to be active against most isolates of the following bacteria both in vitro and in clinical infections as described in the indications and usage section. gram-positive anaerobes clostridium species eubacterium species peptococcus species peptostreptococcus species gram-negative anaerobes bacteroides fragilis group ( b. fragilis, b. distasonis, b. ovatus, b. thetaiotaomicron, b.vulgatus ) fusobacterium species protozoal parasites entamoeba histolytica trichomonas vaginalis the following in vitro data are available, but their clinical significance is unknown: metronidazole exhibits in vitro minimal inhibitory concentrations (mic’s) of 8 mcg/ml or less against most (≥ 90%) isolates of the following bacteria; however, the safety and effectiveness of metronidazole in treating clinical infections due to these bacteria have not been established in adequate and well-controlled clinical trials. gram-negative anaerobes bacteroides fragilis group ( b. caccae, b. uniformis ) prevotella species ( p. bivia, p. buccae, p. disiens ) susceptibility tests: when available, the clinical microbiology laboratory should provide results of in vitro susceptibility test results for antimicrobial drug products used in resident hospitals to the physician as periodic reports that describe the susceptibility profile of nosocomial or community-acquired pathogens. these reports should aid the physician in selecting an antibacterial drug product for treatment. for anaerobes: quantitative methods are used to determine antimicrobial inhibitory concentrations (mics). these mics provide estimates of the susceptibility of bacteria to antimicrobial compounds. for anaerobic bacteria, the susceptibility to metronidazole can be determined by the reference broth and/or agar method 1,2 . the mic values should be interpreted according to the criteria provided in the following table susceptibility test interpretive criteria for metronidazole against anaerobes*† mic (mcg/ml) interpretation ≤8 susceptible (s) 16 intermediate (i) ≥32 resistant (r) *agar dilution method is recommended for all anaerobes †broth dilution method is recommended for testing of bacteroides fragilis group only; for this group, mic values by agar and broth dilution methods are considered equivalent a report of “susceptible” (s) indicates that the antimicrobial is likely to inhibit growth of the pathogen if the antimicrobial compound reaches the concentrations at the infection site necessary to inhibit growth of the pathogen. a report of “intermediate” (i) implies that an infection due to the isolate may be appropriately treated in the body sites where the drugs are physiologically concentrated or when a high dosage of drug is used. a report of “resistant” (r) indicates that the antimicrobial is not likely to inhibit growth of the pathogen if the antimicrobial compound reaches the concentration usually achievable at the infection site; other therapy should be selected. quality control standardized susceptibility test procedures require the use of laboratory controls to monitor and ensure the accuracy and precision of supplies and reagents used in the assay, and the techniques of the individuals performing the test. 1,2 standard metronidazole powder should provide a value within the mic ranges noted in the following table: acceptable quality control ranges for metronidazole against anaerobes quality control strain minimum inhibitory concentration (mcg/ml) agar broth bacteroides fragilis atcc 25285 0.25 to 1 0.25 to 2 bacteroides thetaiotaomicron atcc 29741 0.5 to 2 0.5 to 4 clostridium difficile atcc 700057 0.125 to 0.5 - eggerthella lenta atcc 43055 - 0.125 to 0.5 for protozoal parasites: standardized tests do not exist for use in clinical microbiology laboratories.