General
Hepatic Impairment
Patients with hepatic impairment metabolize metronidazole slowly, with resultant accumulation of metronidazole and increase the plasma concentrations. Reduce the dose of Metronidazole Injection, USP by 50% in patients with severe hepatic impairment (Child-Pugh C). For patients with mild to moderate hepatic impairment, no dosage adjustment is needed but these patients should be monitored for metronidazole associated adverse events (see CLINICAL PHARMACOLOGY and DOSAGE AND ADMINISTRATION).
Patients with severe hepatic encephalopathy metabolize metronidazole slowly, with resultant accumulation of metronidazole. This may cause exacerbation of CNS adverse effects. Reduce the dose of Metronidazole Injection, USP as necessary.
Renal Impairment
For patients with mild to moderate renal impairment dose adjustment is not considered necessary as elimination half-life is not significantly altered. In patients with severe renal impairment or end stage of renal disease, metronidazole and metronidazole metabolites may accumulate significantly because of reduced urinary excretion in those patients.
Monitoring for metronidazole associated adverse events is recommended when metronidazole is administered in patients with severe renal impairment or end stage of renal disease who are not undergoing hemodialysis (see CLINICAL PHARMACOLOGY).
Hemodialysis removes significant amounts of metronidazole and its metabolites from systemic circulation. Therefore, supplementation of metronidazole following a hemodialysis session may be necessary.
Patients receiving peritoneal dialysis should be monitored for signs of toxicity due to the potential accumulation of metronidazole metabolites.
Fungal Superinfections
Known or previously unrecognized candidiasis may present more prominent symptoms during therapy with Metronidazole Injection, USP and requires treatment with a candicidal agent.
Use in Patients with Blood Dyscrasias
Metronidazole is a nitroimidazole, and should be used with care in patients with evidence of or history of blood dyscrasia. Agranulocytosis, leukopenia and neutropenia have been associated with metronidazole administration. Monitor complete blood count in these patients.
Monitoring for Leukopenia
Monitoring of complete blood count (CBC) is recommended before, during, and after prolonged or repeated courses of metronidazole therapy.
Sodium Retention
Metronidazole Injection, USP contains 790 mg of sodium per 100 mL. Care should be taken when administering Metronidazole Injection, USP to patients receiving a controlled sodium diet or corticosteroids or to patients predisposed to edema.
Drug-Resistant Bacteria
Prescribing Metronidazole Injection, USP 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.
Information for Patients
Interaction with Alcohol
Discontinue consumption of alcoholic beverages or products containing propylene glycol while taking Metronidazole Injection, USP and for at least three days afterward because abdominal cramps, nausea, vomiting, headaches, and flushing may occur (see CONTRAINDICATIONS
,
PRECAUTIONS-Drug Interactions).
Treatment of Bacterial Infections
Patients should be counseled that antibacterial drugs including Metronidazole Injection, USP should only be used to treat bacterial infections. They do not treat viral infections (e
.g., the common cold). When Metronidazole Injection, USP is prescribed to treat a bacterial infection, patients should be told that although it is common to feel better early in the course of therapy, the medication should be taken exactly as directed. Skipping doses or not completing the full course of therapy may (1) decrease the effectiveness of the immediate treatment and (2) increase the likelihood that bacteria will develop resistance and will not be treatable by Metronidazole Injection, USP or other antibacterial drugs in the future.
Drug Interactions
Disulfiram
Psychotic reactions and confusion have been reported in alcoholic patients who are using metronidazole and disulfiram concurrently. Do not administer Metronidazole Injection, USP to patients who have taken disulfiram within the last two weeks (see CONTRAINDICATIONS).
Alcoholic Beverages
Abdominal cramps, nausea, vomiting, headaches, tachycardia and flushing may occur if alcoholic beverages or products containing propylene glycol are consumed during or following metronidazole therapy. Discontinue consumption of alcohol or products containing propylene glycol before, during and up to 72 hours after therapy with Metronidazole Injection, USP (see CONTRAINDICATIONS).
Warfarin and other Oral Anticoagulants
Metronidazole has been reported to potentiate the anticoagulant effect of warfarin and other oral coumarin anticoagulants, resulting in a prolongation of prothrombin time and increased risk of hemorrhages. When Metronidazole Injection, USP is prescribed for patients on this type of anticoagulant therapy, prothrombin time and international normalized ratio (INR) should be carefully monitored and their anticoagulant dose adjusted accordingly. Monitor patients for signs and symptoms of bleeding.
Lithium
In patients stabilized on relatively high doses of lithium, short-term metronidazole therapy has been associated with elevation of serum lithium and, in a few cases, signs of lithium toxicity. Lithium toxicity may lead to renal damage. Frequent monitoring of serum lithium and serum creatinine levels is necessary.
Busulfan
Metronidazole has been reported to increase plasma concentrations of busulfan, which can result in an increased risk for serious busulfan toxicity such as sinusoidal obstruction syndrome, gastrointestinal mucositis, and hepatic veno-occlusive disease. Metronidazole Injection, USP should not be administered concomitantly with busulfan unless the benefit outweighs the risk. If no therapeutic alternatives to metronidazole are available, and concomitant administration with busulfan is medically needed, frequent monitoring of busulfan plasma concentration should be performed and the busulfan dose should be adjusted accordingly.
Drugs that Inhibit CYP450 Enzymes
The simultaneous administration of drugs that decrease microsomal liver enzyme activity, such as cimetidine, may decrease metabolism and reduce plasma clearance of metronidazole which may result in metronidazole toxicity.
Drugs that Induce CYP450 Enzymes
The simultaneous administration of drugs that induce microsomal liver enzyme activity, such as phenytoin or phenobarbital, may accelerate the elimination of metronidazole and therefore decrease its efficacy.
Cytochrome P450 3A4 (CYP3A4) substrates
Concomitant use of Metronidazole Injection, USP and CYP3A4 substrates (e.g., amiodarone, tacrolimus, cyclosporine, carbamazepine, phenytoin, and quinidine) may increase respective CYP3A4-substrate plasma levels. Monitoring of plasma concentrations of CYP3A4 substrates may be necessary.
5-Fluorouracil
Metronidazole Injection, USP decreases the clearance of 5-fluorouracil and may therefore cause 5-fluorouracil toxicity.
Vecuronium
Metronidazole Injection, USP may potentiate the effects of vecuronium.
Drugs that Prolong the QT interval
QT prolongation has been reported, particularly when metronidazole was administered with drugs with the potential for prolonging the QT interval.