Metronidazole

Question 1

What is the method of action of metronidazole?

Answer 1

• Enters the cell via passive diffusion
• Formation of a nitroso free radical → binds to DNA
• = ↓ synthesis, DNA degradation and cell death

Question 2

What are the indications for metronidazole?

Answer 2

• Anaerobic bacteria
• Antibiotic associated colitis – caused by C.diff
• Oral infections e.g. dental abscesses
• Aspiration pneumonia of gram -ve anaerobes from the mouth
• Surgical and gynaecological infections
• Protozoal infections e.g. trichomonal vaginalis infection, dysentery

Question 3

What are the contraindications for metronidazole?

Answer 3

• Hepatic disease – as metabolised by hepatic cytochrome P450 enzymes
• Alcohol – as inhibits acetaldehyde dehydrogenase so can cause headaches, flushing, nausea, vomiting etc.

Question 4

What are the side effects of metronidazole?

Answer 4

• GI upset
• Immediate and delayed hypersensitivity
• Peripheral and optic neuropathy – in ↑ doses
• Seizures – in ↑ doses
• Encephalopathy – in ↑ doses

Question 5

What drugs interact with metronidazole?

Answer 5

• Warfarin – metronidazole inhibits cytochrome P450 so ↑ risk of bleeding
• Phenytoin – metronidazole inhibits cytochrome P450 so ↑ risk of toxicity
• Rifampicin - ↓ plasma concentration as this drug is a cytochrome P40 inducer
• Lithium - ↑ risk of toxicity

Question 6

What organ eliminates metronidazole?

Answer 6

Kidney

Question 7

What information should you give to a patient taking metronidazole?

Answer 7

• Do not drink alcohol whilst on this medication and 48 hours after finishing the course