Key points


Beneficial actions and effects

Figure 1
sulfonamide mechanism of action
Antibacterial activity (sulfonamides)
Antibacterial activity (potentiators)
Resistance (by bacteria)

Adverse effects


Sulfonamide pharmacokinetics follow some general patterns

Trimethoprim, ormetoprim and pyrimethamine share similar pharmacokinetic patterns.

Veterinary Sulfonamide products

There are a limited number of sulfonamides approved for veterinary use and even fewer are currently being marketed.

Sulfonamide Feature Comment
Long-half life allows once-daily administration. Good oral absorption. Injectable product for IV use. Likely the most commonly used single un-potentiated sulfonamide in use (excepting medicated water applications).
sulfadiazine/trimethoprim Pharmacokinetics of sulfadiazine and trimethoprim are not well matched. Sulfadiazine should be dosed BID and trimethoprim QD. Tissue distribution of trimethoprim, especially CNS and prostate, is much better than that of sulfadiazine. Injectable forms do not perform particularly well (toxicity), especially IV.
sulfamethoxazole/trimethoprim Almost identical to sulfadiazine/trimethoprim. Generally less expensive human generic often substituted for sulfadiazine/trimethoprim
sulfadimethoxine/ormetoprim Pharmacokinetics of the two drugs are much better matched. Sulfadimethoxine does not cross blood-brain and blood-prostate barriers particularly well.
sulfaquinoxaline Little to no oral absorption "Enteric" sulfonamide
sulfadiazine/pyremethamine CSF concentrations of sulfadiazine ~50% of serum (inflammed meningies). Role of sulfadiazine in therapy during recovery phase is questionable. Equine product for treatment of protozoal encephalopathy.
"triple sulfa" (sulfathiazole + sulfamethazine + sulfamerazine) independent solubilities of these three allow higher doses than would otherwise be tolerated (crystalluria is avoided) Only ornamental fish products marketed
USP/AAVPT Monograph for Sulfonamides
USP/AAVPT Monograph for Potentiated Sulfonamides
USP/AAVPT Monograph for Pyrimethamine