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Drug dosage identifier

Metronidazole

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Dose and administration

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  1. IV infusion by syringe pump over 30 minutes.
  2. Preterm infants less than one month of age: 7.5 mg/kg/dose 12 hourly.
  3. All other infants: 7.5 mg/kg/dose 8 hourly.

Indications

  1. Suspected/proven anaerobic infection, especially Bacteroides fragilis.
  2. Necrotising enterocolitis.
  3. Peritonitis.

Contraindications and precautions

  1. Known hypersensitivity to metronidazole.
  2. Infants with biliary tract obstruction.
  3. Caution in preterm infants especially extreme immaturity.
  4. Caution in infants with jaundice, liver dysfunction and biliary tract disease.

Clinical pharmacology

Metronidazole is active against a wide range of anaerobic micro-organisms, including Bacteroides species, Fusobacteria, Clostridia, Eubacteria and anaerobic cocci. Also active against Gardnerella vaginalis, Trichomonas, Entamoeba histolytica, Giardia lamblia and Balantidium coli. The precise mode of action is not clear. Active metabolites of metronidazole appear to bind to DNA and disrupt protein synthesis.

Readily absorbed after oral administration. Slower and more variable absorption from the rectum. Diffuses throughout the body and readily penetrates CSF and cerebral abscesses. High apparent distribution volume similar to that of total body water. Low binding (20%) to human plasma protein. Elimination mainly by hepatic biotransformation, resulting from side chain oxidation, hydroxylation or conjugation of the parent compound. The major metabolites are active. Elimination half-life remains unchanged in renal failure. Rapidly removed from the plasma by dialysis.

Possible adverse effects

  • Venous irritation, soft tissue injury at IV injection site.
  • Gastrointestinal disturbance (nausea, vomiting)
  • Peripheral neuropathy, encephalopathy (usually during intensive and/or prolonged therapy).
  • Neutropenia (moderate, reversible).
  • Hypersensitivity reactions rare (urticaria, skin eruptions, anaphylaxis).

Special considerations

  • Lengthen dosing interval if extreme immaturity, severe jaundice, and/or hepatic dysfunction.
  • Neonates receiving phenobarbitone metabolise metronidazole at a much greater rate than normal, reducing half life by approximately 50-75%.
  • Darkening of the urine, due to metronidazole metabolites, has been reported.
  • Serum levels should be measured if toxicity suspected (toxic levels greater than 300 umol/L).
  • Is considered safe by National Women's paediatricians, that mothers receiving metronidazole breast feed their babies.

Management of Metronidazole administration

Description

  • Clear, pale yellow solution (500mg/100ml) with anhydrous citric acid 0.4 mg/ml.
  • Sodium content 13.5 mmol/100ml.

Prescription

Intravenous:  Maintenance doses are charted on prescription sheet.

Administration

Slow IV Infusion

  • Further dilution not required.
  • Filter prior to administration through a Pall 0.22 micron filter.
  • Administer by slow IV infusion over 30 minutes using a syringe pump (maximum rate of administration 25 mg/minute).
  • Is compatible with NS, D5W, D10W.
  • Do NOT mix other drugs, IV solutions, blood or blood products.
  • Flush line with NS before and after infusion of metronidazole.

Observation and documentation

  • Observe for signs of adverse effects.
  • Observe for signs of renal, hepatic and haematological dysfunction during prolonged therapy.

Storage

  • Unopened. Stable at room temperature.
  • Once opened not suitable for storage. Discard after use.

Selected references

  1. Brogdon RN, Heel RC, Speight TM, Avery GS. Metronidazole in anaerobic infections: a review of its activity. Pharmacokinetics and therapeutic use. Drugs 1978; 16:387-417.
  2. Jager Roman E, Doyle PE, Baird-Lambert J, Cvejic M, Buchanan N. Pharmacokinetics and tissue distribution of metronidazole in the newborn infant. J Pediatr 1982; 100:651-654.
  3. Amon I, et al. Disposition kinetics of metronidazole in children. Eur J Clin Pharmacol 1983; 24:113
  4. Paediatrician/Senior Nurse Meeting, National Women's Hospital. 20.02.97.

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Document Control

  • Date last published: 30 November 2011
  • Document type: Drug Dosage Guideline
  • Services responsible: ADHB Pharmacy, Neonatology
  • Editor: Sarah Bellhouse
  • Review frequency: 2 years