IV Dilution &
Medication Reference

Metronidazole (Flagyl ®)

Usual Diluents

Standard Dilutions [Amount of drug] [Infusion volume] [Infusion rate]

2B3421 NDC 0338-1055-48 - 500 mg/100 mL

Store at controlled room temperature, 59° to 86°F (15° to 30°C) and protect from light during storage. Do not remove unit from overwrap until ready for use. The overwrap is a moisture barrier. The inner bag maintains the sterility of the product. After removing overwrap, check for minute leaks by squeezing inner bag firmly. If leaks are found, discard solution as sterility may be impaired.

------------- Other - Reconstituted vials --------------------------
[500 mg] [100 ml] [60 min]
[Over 500 mg] [250 ml] [60 min]

Stability / Miscellaneous

Reconstituted vials must be neutralized with 5 meq sodium bicarbonate for each 500 mg used.

CLINICAL PHARMACOLOGY
Metronidazole is a synthetic antibacterial compound. Disposition of metronidazole in the body is similar for both oral and intravenous dosage forms, with an average elimination half-life in healthy humans of eight hours.

The major route of elimination of metronidazole and its metabolites is via the urine (60-80% of the dose), with fecal excretion accounting for 6-15% 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. Renal clearance of metronidazole is approximately 10 mL/min/1.73 m2.

Metronidazole is the major component appearing in the plasma, with lesser quantities of the 2-hydroxymethyl metabolite also being present. Less than 20% of the circulating metronidazole is bound to plasma proteins. Both the parent compound and the metabolite possess in vitro bactericidal activity against most strains of anaerobic bacteria.

Metronidazole appears in cerebrospinal fluid, saliva and breast milk in concentrations similar to those found in plasma. Bactericidal concentrations of metronidazole have also been detected in pus from hepatic abscesses.

Plasma concentrations of metronidazole are proportional to the administered dose. An eight-hour intravenous infusion of 100-4,000 mg of metronidazole in normal subjects showed a linear relationship between dose and peak plasma concentration.

In patients treated with intravenous metronidazole, using a dosage regimen of 15 mg/kg loading dose followed six hours later by 7.5 mg/kg every six hours, peak steady-state plasma concentrations of metronidazole averaged 25 mcg/mL with trough (minimum) concentrations averaging 18 mcg/mL.

Decreased renal function does not alter the single-dose pharmacokinetics of metronidazole. However, plasma clearance of metronidazole is decreased in patients with decreased liver function.

In one study newborn infants appeared to demonstrate diminished capacity to eliminate metronidazole. The elimination half-life, measured during the first three 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:
Metronidazole is active in vitro against most obligate anaerobes, but does not appear to possess any clinically relevant activity against facultative anaerobes or obligate aerobes. Against susceptible organisms, metronidazole is generally bactericidal at concentrations equal to or slightly higher than the minimal inhibitory concentrations. Metronidazole has been shown to have in vitro and clinical activity against the following organisms:

Anaerobic gram-negative bacilli, including:
Bacteroides species, including the Bacteroides fragilis group (B. fragilis, B. distasonis, B. ovatus, B. thetaiotaomicron, B. vulgatus)

Fusobacterium species

Anaerobic gram-positive bacilli, including:
Clostridium species and susceptible strains of Eubacterium
Anaerobic gram-positive cocci, including:
Peptococcus species
Peptostreptococcus species

INDICATIONS AND USAGE

Treatment of Anaerobic Infections
Metronidazole Injection, USP RTU® is indicated in the treatment of serious infections caused by susceptible anaerobic bacteria. Indicated surgical procedures should be performed in conjunction with Metronidazole Injection, USP RTU® therapy. In a mixed aerobic and anaerobic infection, antibiotics appropriate for the treatment of the aerobic infection should be used in addition to Metronidazole Injection, USP RTU®.

Metronidazole Injection, USP RTU® is effective in Bacteroides fragilis infections resistant to clindamycin, chloramphenicol and penicillin.

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 andFusobacterium 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,Peptostreptococcus species and Fusobacterium species.

Bacterial Septicemia caused byBacteroides 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.

Prophylaxis
The prophylactic administration of Metronidazole Injection, USP RTU® preoperatively, intraoperatively and postoperatively may reduce the incidence of postoperative infection in patients undergoing elective colorectal surgery which is classified as contaminated or potentially contaminated. Prophylactic use of Metronidazole Injection, USP RTU® should be discontinued within 12 hours after surgery. If there are signs of infection, specimens for cultures should be obtained for the identification of the causative organism(s) so that appropriate therapy may be given (see DOSAGE AND ADMINISTRATION).

To reduce the development of drug-resistant bacteria and maintain the effectiveness of Metronidazole Injection, USP RTU® and other antibacterial drugs, Metronidazole Injection, USP RTU® 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.

CONTRAINDICATIONS
Metronidazole Injection, USP RTU® is contraindicated in patients with a prior history of hypersensitivity to metronidazole or other nitroimidazole derivatives.

WARNINGS
Convulsive Seizures and Peripheral Neuropathy
Convulsive seizures and peripheral neuropathy, the latter characterized mainly by numbness or paresthesia of an extremity, have been reported in patients treated with metronidazole. The appearance of abnormal neurologic signs demands the prompt evaluation of the benefit/risk ratio of the continuation of therapy.

OVERDOSAGE
Use of dosages of intravenous metronidazole higher than those recommended has been reported. These include the use of 27 mg/kg three times a day for 20 days, and the use of 75 mg/kg as a single loading dose followed by 7.5 mg/kg maintenance doses. No adverse reactions were reported in either of the two cases.

Single oral dose of metronidazole, up to 15 g, have been reported in suicide attempts and accidental overdoses. Symptoms reported included nausea, vomiting and ataxia.

Oral metronidazole has been studied as a radiation sensitizer in the treatment of malignant tumors. Neurotoxic effects, including seizures and peripheral neuropathy, have been reported after 5 to 7 days of doses of 6 to 10.4 g every other day.

Treatment: There is no specific antidote for overdose; therefore, management of the patient should consist of symptomatic and supportive therapy.

DOSAGE AND ADMINISTRATION
In elderly patients the pharmacokinetics of metronidazole may be altered and therefore monitoring of serum levels may be necessary to adjust the metronidazole dosage accordingly.

Treatment of Anaerobic Infections
The recommended dosage schedule for adults is:

Parenteral therapy may be changed to oral metronidazole when conditions warrant, based upon the severity of the disease and the response of the patient to Metronidazole Injection, USP RTU® treatment. The usual adult oral dosage is 7.5 mg/kg every six hours.

A maximum of 4 g should not be exceeded during a 24-hour period.

Patients with severe hepatic disease metabolize metronidazole slowly, with resultant accumulation of metronidazole and its metabolites in the plasma. Accordingly, for such patients, doses below those usually recommended should be administered cautiously. Close monitoring of plasma metronidazole levels2 and toxicity is recommended.

In patients receiving Metronidazole Injection, USP RTU® in whom gastric secretions are continuously removed by nasogastric aspiration, sufficient metronidazole may be removed in the aspirate to cause a reduction in serum levels.

The dose of Metronidazole Injection, USP RTU® should not be specifically reduced in anuric patients since accumulated metabolites may be rapidly removed by dialysis.

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.

Prophylaxis
For surgical prophylactic use, to prevent postoperative infection in contaminated or potentially contaminated colorectal surgery, the recommended dosage schedule for adults is:

a.] 15 mg/kg infused over 30 to 60 minutes and completed approximately one hour before surgery; followed by

b.] 7.5 mg/kg infused over 30 to 60 minutes at 6 and 12 hours after the initial dose.

It is important that (1) administration of the initial preoperative dose be completed approximately one hour before surgery so that adequate drug levels are present in the serum and tissues at the time of initial incision, and (2) Metronidazole Injection, USP RTU® be administered, if necessary, at 6-hour intervals to maintain effective drug levels. Prophylactic use of Metronidazole Injection, USP RTU® should be limited to the day of surgery only, following the above guidelines.

Caution: Metronidazole Injection, USP RTU® is to be administered by slow intravenous drip infusion only, either as a continuous or intermittent infusion. Additives should not be introduced into Metronidazole Injection, USP RTU®. If used with a primary intravenous fluid system, the primary solution should be discontinued during metronidazole infusion. DO NOT USE EQUIPMENT CONTAINING ALUMINUM (e.g., NEEDLES, CANNULAE) THAT WOULD COME IN CONTACT WITH THE DRUG SOLUTION.

Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit.

HOW SUPPLIED
Metronidazole Injection, USP RTU® is supplied in 100 mL single dose plastic containers, each containing an iso-osmotic, buffered solution of 500 mg metronidazole as follows:

2B3421 NDC 0338-1055-48 500 mg/100 mL

Store at controlled room temperature, 59° to 86°F (15° to 30°C) and protect from light during storage. Do not remove unit from overwrap until ready for use. The overwrap is a moisture barrier. The inner bag maintains the sterility of the product. After removing overwrap, check for minute leaks by squeezing inner bag firmly. If leaks are found, discard solution as sterility may be impaired.

DIRECTIONS FOR USE OF VIAFLEX PLUS PLASTIC CONTAINER
Metronidazole Injection, USP RTU® is a ready-to-use iso-osmotic solution. No dilution or buffering is required. Do not refrigerate. Each container of Metronidazole Injection, USP RTU® contains 14 mEq of sodium.

Warning: Do not use plastic containers in series connections. Such use could result in air embolism due to residual air being drawn from the primary container before administration of the fluid from the secondary container is completed.

To open
Tear overwrap down side at slit and remove solution container. Some opacity of the plastic due to moisture absorption during the sterilization process may be observed. This is normal and does not affect the solution quality or safety. The opacity will diminish gradually. Check for leaks. Do not add supplementary medication.

Preparation for Administration
1.] Suspend container from eyelet support.
2.] Remove plastic protector from outlet port at bottom of container.
3.] Attach administration set. Refer to complete directions accompanying set.

REFERENCES
1.] M11-A5-Methods for Antimicrobial Susceptibility Testing of Anaerobic Bacteria; approved Standard-Fifth Edition, National Committee for Clinical Laboratory Standards; and Sutter, et al.: Collaborative Evaluation of a Proposed Reference Dilution Method of Susceptibility Testing of Anaerobic Bacteria, Antimicrob. Agents Chemother. 16:495-502 (Oct.) 1979; and Tally, et al.: In Vitro Activity of Thienamycin, Antimicrob. Agents Chemother. 14:436-438 (Sept.) 1978.

2.] Ralph, E.D. and Kirby, W.M.M.: Bioassay of Metronidazole with Either Anaerobic and Aerobic Incubation, J. Infect. Dis. 132:587-591 (Nov.) 1975; or Gulaid, et al.: Determination of Metronidazole and its Major Metabolites in Biological Fluids by High Pressure Liquid Chromatography. BR.J.Clin. Pharmacol. 6:430-432, 1978.

Baxter Healthcare Corporation
Deerfield, IL 60015 USA
Printed in USA

Source: [package insert]