Sulfonamides - The Veterinary Site



Sulfonamides are amides of sulfanilic acid. These are:
1)      Sulfadiazine
2)      Sulfamerazine
3)      Sulfadimidine
4)      Sulfasalazine
5)      Sulfaquinoxaline
6)      Sulfanilamide
All these above mentioned drugs are derivatives of sulphanilamide which is obtained from an azolide ‘Prontosil’. Prontosil itself is non-antibiotic.
These are structurally similar to Paraminobenzoic Acid (PABA). These are effective against bacterial as well as protozoal infections i.e. coccidiosis
These are white crystalline powder. These are weak acids. These have variable (5-90%) opacity to bind with plasma proteins for their distribution in the body.
Adverse Reactions of Sulfonamides
In dehydrated animals, these induce metabolic acidosis which causes crystal urea and nephrotoxicity. So, renal compromised patients should not administer with them. Don’t administer them in chicks for more than 3-4 days.
Mode of Action
These are folic acid inhibitors. These inhibit the synthesis of folic acid by blocking the enzyme ‘Dihydrofolate Synthase’. Mammals can’t synthesize folic acid but bacteria can synthesize folic acid to make nitrogenous proteins i.e. purines and pyrimidines.
Folic acid’s synthesis inhibited => No purines and pyrimidines => No DNA => No life
They have no effect in mammalian cell. These are used in combination with Diaminopyridines because already present dihydrofolate, inhibited by Diaminopyridines, can be used by the bacteria for their survival.
Tetrahydrofolate is used by bacteria for synthesis of purines and pyrimidines.
These are weak organic bases. These are:
1)      Trimethoprim
2)      Aditoprim
·         Dose rate = 5mg/kg
·         Has high volume of distribution (Vd)
·         Has longer half life than Trimethoprim
3)      Tetroxoprim
·         Dose rate = 5mg/kg
4)      Ormetoprim
·         Dose rate = 5.5mg/kg
5)      Methoprim
·         Dose rate = 5mg/kg
Combination of diaminopyridines and sulfonamides decreases the minimum inhibitory concentration of sulfonamides many folds e.g. Tribursin is combination of Trimethoprim and Sulfadiazine.
Diaminopyridines + Sulfonamides
Narrow spectrum
Narrow spectrum
Broad spectrum
No affinity for mammalian cell’s folic acid
No affinity for mammalian cell’s folic acid
More affinity for mammalian cell’s folic acid

These, sulfonamides and diaminopyridines, are metabolized by oxidation and conjugation. These are mostly used in combination and rarely used alone in veterinary.

Sulfonamides Sulfonamides Reviewed by Maaz ahmed siddiqui on 09 May Rating: 5

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