Doses - METRONIDAZOLE
Dogs: 
For treatment of Giardia: a) 44 mg/kg PO initially, then 22 mg/kg PO q8h for 5 days. (Todd, Paul, and DiPietro1985)
b) 50 mg/kg PO per day for 5 days. (Jones 1985)
c) 25 - 65 mg/kg PO once daily for 5 days. (Longhofer 1988)
d) 30 - 60 mg/kg PO once daily for 5-7 days (also for trichomoniasis) (Chiapella 1988)
e) 25 mg/kg PO bid (Aronson and Aucoin 1989)
For anaerobic infections:
a) For anaerobic bacterial meningitis: 25 - 50 mg/kg PO q12h. (Schunk 1988)
b) For suppurative cholangitis: 25 - 30 mg/kg PO bid; may be used with chloramphenicol.
Therapy may be necessary for 4-6 weeks. (Cornelius and Bjorling 1988)
c) 30 mg/kg/day PO divided q6-8h. (Dow 1989)
d) 44 mg/kg PO q12h (Aronson and Aucoin 1989) For adjunctive therapy of plasmacytic/lymphocytic enteritis:
a) 30 - 60 mg/kg PO once daily. (Chiapella 1988)
b) 10 mg/kg PO tid for 2-4 weeks. (Magne 1989) For adjunctive therapy of plasmacytic/lymphocytic colitis:
a) 10 - 30 mg/kg PO q8-24h for 2-4 weeks in refractory cases. (Leib, Hay, and Roth1989)
b) For ulcerative colitis in dogs refractory to other therapies (e.g., sulfasalazine, immunosuppressants, diet, etc.): 10 - 15 mg/kg once to twice a day; discontinue after 2weeks if response is inadequate. (DeNovo 1988)
For amebiasis, balatidiasis:
a) 60 mg/kg PO once daily for 5 days (DeNovo 1988)
For adjunctive therapy of hepatic encephalopathy:
a) 20 mg/kg PO q8h (Hardy 1989)
Cats: 
For treatment of Giardia: a) 10 - 25 mg/kg PO once daily for 5 days. (Longhofer 1988)
b) 8 - 10 mg/kg PO bid for 10 days (also for trichomoniasis) (Chiapella 1988)
For anaerobic infections:
a) For adjunctive therapy of plasmacytic/lymphocytic enteritis: 10 mg/kg PO once daily.(Chiapella 1988)
b) For adjunctive therapy of hepatic lipidoses: 25 - 30 mg/kg PO bid for 2-3 weeks(unproven, but may be of benefit) (Cornelius and Bjorling 1988)
Horses: 
For susceptible anaerobic infections: a) 15 - 25 mg/kg PO q6h (Sweeney et al. 1986)
b) 20 - 25 mg/kg PO q12h as crushed tablets in an aqueous suspension. (Baggot, Wilson, and Hietela 1988)
Birds: 
For susceptible infections (anaerobes): a) 50 mg/kg PO once daily for 5 days (Bauck and Hoefer 1993)
Reptiles: 
a) For anaerobic infections in most species:150 mg/kg PO once; repeat in one week. For amoeba and flagellates in most species: 100 - 275 mg/kg PO once; repeat in 1-2weeks. In Drymarchon spp., Lampropeltis pyromelana, & lampropeltis zonata: 40mg/kg PO once; repeat in 2 weeks (Gauvin 1993)
Monitoring Parameters -
Client Information - Report any neurologic symptoms to veterinarian (see Overdose section).
Dosage Forms/Preparations/FDA Approval Status/Withholding Times - Veterinary-Approved Products: None
Human-Approved Products:
Metronidazole Tablets 250 mg, 500 mg; Capsules 375 mg; Flagyl® (Searle); Metric 21®(Fielding); Protostat® (Ortho); Flagyl 375® (Searle); generic; (Rx)Metronidazole HCl Powder for Injection 500 mg/vial; Flagyl®IV (Searle); (Rx)Metronidazole 500 mg/100 ml injection (ready to use); Flagyl®I.V. (Searle); Metro®I.V.(McGaw); Metronidazole Redi-Infusion® (Elkins-Sinn); Metronidazole® (Abbott); (Rx)