Vexsilva Drug Interactions

The action of sulfonamides may be antagonised by p-aminobenzoic acid and compounds derived from it, particularly potassium aminobenzoate and the procaine group of local anaesthetics.
Sulfamethoxazole and other sulfonamides may potentiate the effects of some drugs, such as oral anticoagulants, methotrexate, and phenytoin; this may be due to displacement of the drug from plasma protein binding sites or to inhibition of metabolism. However, the clinical significance of these interactions appears to depend on the particular sulfonamide involved.
The possibility of interactions with other highly protein-bound drugs, such as NSAIDs, should be considered.
High doses of sulfonamides have been reported to have a hypoglycaemic effect; the antidiabetic effect of the sulfonylurea compounds may be enhanced by the concomitant administration of sulfonamides. Some sulfonamides have been associated with a decrease in plasma-ciclosporin concentrations when used concomitantly. Isolated reports have described possible failures of hormonal contraceptives resulting in pregnancy in patients given sulfonamides.
The administration of compounds which render the urine acidic may increase the risk of crystalluria.