Federal law restricts this drug to use by or on the order of a licensed veterinarian.

Primor is an antimicrobial drug containing sulfadimethoxine and ormetoprim in a 5 to 1 ratio. The combination of these 2 compounds results in the potentiation of sulfadimethoxine, providing increased efficacy, a broadened spectrum of activity to include some sulfonamide-resistant organisms, and reduction in the rate of resistance development.

Sulfadimethoxine is a white, almost tasteless and odorless powder. Chemically, it is N1-(2,6-dimethoxy-4-pyrimidinyl)-sulfanila-mide. The structural formula is:

Ormetoprim is a white, almost tasteless powder. Chemically, it is 2,4-diamino-5-(4,5-dimethoxy-2-methylbenzyl)-pyrimidine. The structural formula is:

Sulfadimethoxine is not acetylated in the dog, as in most other animals, and is excreted predominantly as the unchanged drug.3 Sulfadimethoxine has a relatively high solubility at the pH normally occurring in the kidney, precluding the possibility of precipitation and crystalluria. Slow renal excretion results from a high degree of tubular reabsorption. Plasma protein binding is very high, providing a blood reservoir of the drug. Thus sulfadimethoxine maintains higher blood levels than most other long-acting sulfonamides. Single, comparatively low doses of sulfadimethoxine give rapid and sustained therapeutic blood levels.4

The systemically active sulfonamides, which include sulfadimethoxine, are bacteriostatic agents. Sulfonamides competitively inhibit bacterial synthesis of folic acid (pteroylglutamic acid) from para-aminobenzoic acid. Mammalian cells are capable of utilizing folic acid in the presence of sulfonamides.

Ormetoprim, like other diaminopyrimidines, inhibits the reduction of dihydrofolic acid to tetrahydrofolic acid by bacterial cells.

Sulfadimethoxine/ormetoprim thus blocks 2 sequential steps of the folic acid metabolism of bacteria, depriving them of folate coenzymes. Potentiated sulfonamides have been shown to exhibit bactericidal as well as bacteriostatic action.

Primor is for the treatment of skin and soft tissue infections (wounds and abscesses) in dogs caused by strains of Staphylococcus aureus and Escherichia coli and urinary tract infections caused by Escherichia coli, Staphylococcus spp., and Proteus mirabilis susceptible to sulfadimethoxine/ormetoprim.

Primor should not be used in dogs showing marked liver parenchymal damage, blood dyscrasias, or in those with a history of sulfonamide hypersensitivity.

Not for human use. For use in dogs only. Keep out of reach of children.

Decreased water consumption and aciduria enhance the probability of the formation of sulfonamide crystals in the urine. Monitoring urine samples for crystal formation is recommended from animals with acid urine receiving the drug. As with any sulfonamide therapy, make certain dogs maintain adequate water intake. If dogs show no improvement within 2 or 3 days, reevaluate the diagnosis.

Safety in breeding dogs has not been established.

Conditions reported following use of sulfonamides or potentiated sulfonamides include polyarthritis, urticaria, facial swelling, fever, hemolytic anemia, polydypsia, polyuria, hepatitis, vomiting, anorexia, diarrhea, and neurologic disorders. In rare instances, neurologic signs including behavioral changes, ataxia, seizures, aggression, and hyperexcitability have been reported. Keratitis sicca, possibly due to prolonged use of sulfonamides, has been reported.

Individual animal hypersensitivity may result in local or generalized reactions. Anaphylactoid reactions, although rare, may also occur.

Antidote: Epinephrine for anaphylactoid reactions.

For a copy of the Safety Data Sheet or to report adverse reactions, call Zoetis Inc. at 1-888-963-8471. For additional information about adverse drug experience reporting for animal drugs, contact FDA at 1-888-FDA-VETS or www.fda.gov/reportanimalae.

Administer an initial oral dose of 25 mg/lb (55 mg/kg) of body weight on the first day of treatment. Administer subsequent daily doses at the rate of 12.5 mg/lb (27.5 mg/kg) of body weight. Continue treatment for at least 2 days after remission of clinical signs. Do not extend treatment for more than 21 consecutive days. Suggested dosage schedules follow:

For optimal therapeutic effect: (1) the drug must be given early in the course of the disease; (2) therapeutically effective levels must be maintained in the body throughout the treatment period; (3) treatment should continue for at least 2 days after remission of clinical signs; and (4) the causative bacterial agents must be sensitive to the drug.

TOXICITY AND SAFETY:1 Toxicity data for Primor indicate that the drug is safe when used at the recommended dosage.

Following oral administration of Primor to dogs at 27.5 mg/kg/day (12.5 mg/lb/day) for 8 weeks, no changes were noted in hematology, blood chemistry, urinalysis, gross pathology, and histopathology, except for elevated serum cholesterol, increased thyroid and liver weights, enlarged basophilic cells in the pituitary, and mild follicular thyroid hyperplasia. These changes are known to be associated with prolonged administration of sulfonamides to dogs and have been shown to be reversible.

Store at controlled room temperature 15°–30°C (59°–86°F)

Primor is available as scored tablets for the following potencies: 120 mg, 240 mg, 600 mg, and 1200 mg.

1. Data on file, Zoetis Inc.

2. Bevill RF: Sulfonamides. Booth NM, MacDonald LE (eds), Veterinary Pharmacology and Therapeutics, 5th ed, The Iowa State University Press, Ames, Iowa, chapter 48, 1982.

3. Bridges JW, Kirby MR, Walker SR, et al: Species differences in the metabolism of sulfadimethoxine. Biochem J 109:851, 1968.

4. Baggot JD: Some aspects of drug persistence in domestic animals. Res Vet Sci 11(2):130, 1970.

*BBL® and Sensi-Disc® are registered trademarks owned by Becton, Dickinson and Company, Paramus, New Jersey.

Approved by FDA under NADA # 100-929

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Zoetis Inc.
Kalamazoo, MI 49007

40034731
Revised: May 2021