Updated Contraindications for Metronidazole

The product information for metronidazole intravenous infusion (Pfizer) has recently been updated to include new contraindications. The contraindications now include disulfiram therapy in the previous two weeks, and consumption of alcohol or products containing propylene glycol.

Interactions with disulfiram and alcohol have long been associated with metronidazole, although the incidence is uncertain and the severity varied. Psychotic reactions and confusion have been reported when disulfiram is administered with metronidazole. Disulfiram-like reactions have been described when metronidazole is combined with alcohol or propylene glycol. These reactions may include tachycardia, flushing, or vomiting.

The updated product information recommends that alcohol and products containing propylene glycol be discontinued during metronidazole therapy and for at least three days after the last metronidazole dose. Avoiding these agents requires some care as alcohol and propylene glycol are excipients in many medications.

Medications containing ethanol and propylene glycol include:

• Diazepam for injection;
• Phenobarbital (phenobarbitone) injection;
• Phenytoin injection;
• Glyceryl trinitrate injection;
• Digoxin (Lanoxin® Paediatric Elixir, Lanoxin® Paediatric Injection, Lanoxin® Adult Injection); and
• Lopinavir + ritonavir (Kaletra®) oral solution.

Medicines that may contain ethanol include:

• Ranitidine oral liquid;
• Furosemide oral solution;
• Trimethoprim + sulfamethoxazole oral liquid; and
• Iron liquids (e.g. Maltofer® Syrup)

The approved product information should be reviewed to determine if a medicine contains ethanol or propylene glycol.