What is the proper dosage and treatment plan for Flagyl (metronidazole)?

Metronidazole (Flagyl) Dosage and Treatment Plan

For trichomoniasis, the recommended regimen is metronidazole 2 g orally in a single dose, which achieves cure rates of approximately 90-95%. 1

Treatment Options by Indication

Trichomoniasis

• First-line treatment:
  • Metronidazole 2 g orally in a single dose 1
• Alternative regimen:
  • Metronidazole 500 mg orally twice daily for 7 days 1
• FDA-approved alternative:
  • Flagyl 375 mg twice daily for 7 days (based on pharmacokinetic equivalency to metronidazole 250 mg three times daily for 7 days) 1
• For treatment failures:
  • Re-treat with metronidazole 500 mg twice daily for 7 days 1
  • For repeated failures: metronidazole 2 g once daily for 3-5 days 1

Bacterial Vaginosis (BV)

• Recommended regimens for non-pregnant women:
  • Metronidazole 500 mg orally twice daily for 7 days 1
  • Metronidazole gel 0.75%, one full applicator (5 g) intravaginally twice daily for 5 days 1
  • Flagyl ER 750 mg once daily for 7 days (FDA-approved) 1
• Alternative regimen:
  • Metronidazole 2 g orally in a single dose (note: lower efficacy for BV) 1

Amebiasis

• For acute intestinal amebiasis (dysentery):
  • Adults: 750 mg orally three times daily for 5-10 days 2
• For amebic liver abscess:
  • Adults: 500-750 mg orally three times daily for 5-10 days 2
• Pediatric dosing:
  • 35-50 mg/kg/day divided into three doses for 10 days 2

Anaerobic Bacterial Infections

• Adult dosage:
  • 7.5 mg/kg orally every 6 hours (approximately 500 mg for a 70 kg adult) 2
  • Maximum: 4 g per 24-hour period 2
  • Duration: 7-10 days (longer for bone/joint, respiratory, or endocardial infections) 2

Special Populations

Pregnant Women

• Trichomoniasis:
  • Should not be treated during first trimester 2
  • When treatment is necessary after first trimester: 2 g metronidazole in a single dose 1
  • The 7-day course is preferred over single-dose therapy during pregnancy 2

HIV-Infected Patients

• Same treatment regimens as HIV-negative patients 1

Elderly Patients

• Pharmacokinetics may be altered; monitoring of serum levels may be necessary 2
• Dose adjustments based on monitoring results 2

Patients with Severe Hepatic Disease

• Doses below those usually recommended should be administered cautiously 2
• Close monitoring of plasma metronidazole levels and toxicity is recommended 2

Management of Treatment Failures

• For initial treatment failure: metronidazole 500 mg twice daily for 7 days 1
• For repeated failures: metronidazole 2 g once daily for 3-5 days 1
• For persistent infection despite appropriate therapy, consult with an expert and consider susceptibility testing 1

Important Precautions

• Patients should avoid alcohol during treatment and for 24 hours afterward 1
• Recent research suggests that the 7-day dosing regimen may be more effective than single-dose therapy for trichomoniasis, with relative risk of 0.55 (95% CI 0.34-0.70) for treatment failure 3
• Sex partners should be treated concurrently to prevent reinfection 1
• Patients should avoid sex until they and their partners complete treatment and are asymptomatic 1

Side Effects and Monitoring

• Most common side effects: nausea (23%), headache (7%), and vomiting (4%) 3
• For patients with treatment failure, rule out reinfection before considering alternative regimens 1
• No specific follow-up is needed for asymptomatic patients after treatment 1