What are the indications and dosages for Metronidazole (antibiotic)?

Metronidazole Indications and Dosages

Metronidazole is indicated for trichomoniasis, bacterial vaginosis, amebiasis, giardiasis, and anaerobic bacterial infections with specific dosing regimens for each condition. 1, 2

Indications and Dosages

Trichomoniasis

• Recommended regimen: Metronidazole 2g orally in a single dose 1
• Alternative regimen: Metronidazole 500mg orally twice daily for 7 days 1
• For treatment failure: Re-treat with metronidazole 500mg twice daily for 7 days; if failure occurs again, treat with 2g once daily for 3-5 days 1

Bacterial Vaginosis

• Metronidazole 500mg orally twice daily for 7 days 3
• Alternative: Metronidazole gel 0.75%, one full applicator (5g) intravaginally once daily for 5 days 3

Amebiasis

• Acute intestinal amebiasis: 750mg orally three times daily for 5-10 days 2
• Amebic liver abscess: 500mg or 750mg orally three times daily for 5-10 days 2
• Pediatric dosing: 35-50 mg/kg/day divided into three doses, orally for 10 days 2

Anaerobic Bacterial Infections

• 7.5 mg/kg orally every 6 hours (approximately 500mg for a 70kg adult) 2
• Maximum: 4g per 24-hour period 2
• Duration: Typically 7-10 days; longer for bone/joint, lower respiratory tract, and endocardium infections 2

Skin and Soft Tissue Infections (Anaerobic Coverage)

• 250-500mg orally 4 times per day 1
• Good activity against anaerobes but no activity against aerobes 1

Special Populations

Pregnancy

• Contraindicated during first trimester 3, 2
• May be used after first trimester when necessary 3
• For pregnant women requiring treatment after first trimester:
  • Bacterial vaginosis: Metronidazole 500mg orally twice daily for 7 days 3
  • Trichomoniasis: 2g orally in a single dose (after first trimester) 3

Elderly Patients

• Pharmacokinetics may be altered; monitoring of serum levels may be necessary to adjust dosage 2

Hepatic Impairment

• Patients with severe hepatic disease metabolize metronidazole slowly
• Lower doses should be administered cautiously with close monitoring of plasma levels and toxicity 2

Renal Impairment

• Dose reduction not specifically required in anuric patients as metabolites are rapidly removed by dialysis 2

Important Considerations

• For mixed infections involving both anaerobes and aerobes, metronidazole must be combined with other agents (usually aminoglycosides) as it lacks activity against aerobic bacteria 4
• Avoid alcohol during treatment and for 24 hours afterward to prevent disulfiram-like reactions 3
• For trichomoniasis, treating sexual partners is recommended to prevent reinfection 1
• Follow-up is unnecessary for patients who become asymptomatic after treatment, except for high-risk pregnant women 3

Advantages

• Most active agent available against obligate anaerobes 5
• Excellent penetration into tissues including the central nervous system 6
• Bactericidal at low concentrations against most anaerobic bacteria 4

Common Adverse Effects

• Gastrointestinal disturbances
• Metallic taste
• Disulfiram-like reaction with alcohol
• Potential for peripheral neuropathy with prolonged use 6

Metronidazole remains a cornerstone antimicrobial for anaerobic and protozoal infections due to its excellent activity, tissue penetration, and established clinical efficacy.