Metronidazole dose

Reading File

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Reading File

Here is a complete metronidazole dosing reference, compiled from the Harriet Lane Handbook (23rd ed.) and Sleisenger & Fordtran's GI and Liver Disease:

Metronidazole (Flagyl) - Dosing by Indication

Amebiasis

Patient	Dose
Child	35-50 mg/kg/24 hr PO divided Q8 hr x 10 days; max 750 mg/dose
Adult	500-750 mg PO Q8 hr x 10 days

Anaerobic Infections

Patient	Dose
Neonate (loading)	15 mg/kg x 1, then maintenance by postmenstrual age (PMA):
PMA 24-25 wk	7.5 mg/kg Q24 hr
PMA 26-27 wk	10 mg/kg Q24 hr
PMA 28-33 wk	7.5 mg/kg Q12 hr
PMA 34-40 wk	7.5 mg/kg Q8 hr
PMA >40 wk	7.5 mg/kg Q6 hr
Infant/Child/Adolescent PO	30-50 mg/kg/24 hr divided Q8 hr; max 2250 mg/24 hr
Infant/Child/Adolescent IV	22.5-40 mg/kg/24 hr divided Q6-8 hr; max 4 g/24 hr
Adult PO/IV	30 mg/kg/24 hr divided Q6-8 hr; max 4 g/24 hr. (Give 15 mg/kg IV loading dose over 1 hr, 6 hr before maintenance for IV route)

Bacterial Vaginosis

Route	Dose
PO (child >45 kg, adolescent, adult)	500 mg BID x 7 days
Vaginal gel 0.75%	~37.5 mg (1 applicatorful) QHS x 5 days
Vaginal gel 1.3% (≥12 yr)	~65 mg (1 applicatorful) at bedtime x 1

Note: Single-dose oral regimen is no longer recommended for BV due to poor efficacy.

Giardiasis

Patient	Dose
Child	15-30 mg/kg/24 hr PO divided TID x 5-7 days; max 750 mg/24 hr
Adult	250 mg PO TID x 5 days

Trichomoniasis (treat sexual contacts)

Patient	Dose
Child <45 kg	45 mg/kg/24 hr PO divided TID x 7 days; max 2000 mg/24 hr
Child ≥45 kg, adolescent, adult	2 g PO x 1 (single dose), OR 500 mg PO BID x 7 days

Multi-dose regimen (500 mg BID x 7 days) shows increased efficacy in women over the single 2 g dose.

C. difficile Infection (CDI)

Patient	Dose
Child	30 mg/kg/24 hr divided Q6 hr PO/IV x 10-14 days; max 2000 mg/24 hr
Child - severe fulminant (+ oral/rectal vancomycin)	30 mg/kg/24 hr divided Q8 hr IV x 10 days; max 500 mg/dose
Adult	500 mg TID PO/IV x 10-14 days
Adult - severe fulminant (+ oral/rectal vancomycin)	500 mg IV Q8 hr

Important: Metronidazole is now considered inferior to vancomycin and fidaxomicin for CDI. Failure rate ~19% vs 4% for vancomycin. IV may be used when oral is not tolerated, as it reaches bactericidal levels in inflamed colon.

H. pylori Eradication (combination therapy)

Patient	Dose
Child	20 mg/kg/24 hr (max 1000 mg/24 hr) divided BID PO x 10-14 days
Adult	250-500 mg TID-QID (with meals and at bedtime) PO x 10-14 days

Rosacea (Topical)

Formulation	Frequency
0.75% cream/gel	Apply BID
1% cream/gel	Apply once daily

Key Safety Points

Alcohol: Avoid for 24-48 hr after dose (disulfiram-like reaction)
Hepatic impairment: Reduce dose by 50% with Child-Pugh C
Renal impairment: Use caution if GFR <10 mL/min
Pregnancy: Contraindicated in first trimester; single 2 g dose - withhold breastfeeding for 12-24 hr
Cockayne syndrome: Contraindicated (fatal liver failure reported)
Drug interactions: Increases levels of phenytoin, lithium, warfarin; phenobarbital and rifampin increase metronidazole metabolism; QT prolongation with other QT-prolonging agents
IV infusion: Must be given slowly over 1 hr
Side effects: Nausea, metallic taste, peripheral neuropathy (especially prolonged use), leukopenia, urticaria, can worsen candidiasis, may discolor urine

- The Harriet Lane Handbook, 23rd ed. | Sleisenger & Fordtran's GI and Liver Disease

For diarrhea

Finding Sources

Here is metronidazole dosing specifically for diarrheal illnesses, based on the textbook sources:

Metronidazole for Diarrhea - by Cause

1. Giardiasis (Giardia lamblia)

Patient	Dose
Adult	250 mg PO TID x 5 days
Child	15-30 mg/kg/day divided Q8 hr x 5-10 days; max 250 mg/dose

80-95% effective. Tinidazole (single dose) is preferred where available - it is superior to metronidazole. FDA has not formally approved metronidazole for Giardia but it is widely used.

2. Amoebiasis (Entamoeba histolytica - amoebic dysentery)

Patient	Dose
Adult	500-750 mg PO TID x 10 days
Child	35-50 mg/kg/24 hr divided Q8 hr x 10 days; max 750 mg/dose

Must follow with a luminal agent (e.g. paromomycin or diloxanide furoate) to eradicate cysts.

3. Clostridioides (C.) difficile Infection (CDI)

Severity	Adult Dose
Non-severe	500 mg PO TID x 10-14 days
Cannot take oral	500 mg IV Q8 hr (reaches bactericidal levels via inflamed mucosa)
Severe/fulminant (adjunct to vancomycin)	500 mg IV Q8 hr

Important caveat: Metronidazole is no longer first-line for CDI. Vancomycin (125 mg QID) and fidaxomicin are preferred. Metronidazole failure rate is ~19% vs ~4% for vancomycin. Reserve metronidazole for mild cases only when vancomycin/fidaxomicin are unavailable or as an adjunct in fulminant disease with IV route.

Quick Summary Table

Cause	Adult Dose	Duration
Giardia	250 mg TID	5 days
Amoebiasis	500-750 mg TID	10 days
C. difficile (non-severe)	500 mg TID	10-14 days

- Sleisenger & Fordtran's GI and Liver Disease | Harriet Lane Handbook, 23rd ed. | Harrison's Principles of Internal Medicine 22E

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