Sulfamethoxazoleinteractions
sulfamethoxazole 40 MG/ML / trimethoprim 8 MG/ML Oral Suspension [Sulfatrim]
This is the interactions section of this product’s FDA label — what the manufacturer documented for this drug. It is not a check of your medication list, and a drug missing from it has not been cleared: licensed clinical databases list far more interactions than any single label does. Before combining medicines, ask a pharmacist, who can check everything you take at once and will do it for free.
Named on this label
Every name above is printed in the text below. This is not the full set of drugs that interact with this one — it is the set this manufacturer wrote down.
Drug interactions
In elderly patients concurrently receiving certain diuretics, primarily thiazides, an increased incidence of thrombocytopenia with purpura has been reported. It has been reported that sulfamethoxazole and trimethoprim may prolong the prothrombin time in patients who are receiving the anticoagulant warfarin. This interaction should be kept in mind when sulfamethoxazole and trimethoprim is given to patients already on anticoagulant therapy, and the coagulation time should be reassessed. Sulfamethoxazole and trimethoprim may inhibit the hepatic metabolism of phenytoin. Sulfamethoxazole and trimethoprim, given at a common clinical dosage, increased the phenytoin half-life by 39% and decreased the phenytoin metabolic clearance rate by 27%. When administering these drugs concurrently, one should be alert for possible excessive phenytoin effect. Sulfonamides can also displace methotrexate from plasma protein binding sites and can compete with the renal transport of methotrexate, thus increasing free methotrexate concentrations. There have been reports of marked but reversible nephrotoxicity with coadministration of sulfamethoxazole and trimethoprim and cyclosporine in renal transplant recipients. Increased digoxin blood levels can occur with concomitant sulfamethoxazole and trimethoprim therapy, especially in elderly patients. Serum digoxin levels should be monitored. Increased sulfamethoxazole blood levels may occur in patients who are also receiving indomethacin. Occasional reports suggest that patients receiving pyrimethamine as malaria prophylaxis in doses exceeding 25 mg weekly may develop megaloblastic anemia if sulfamethoxazole and trimethoprim is prescribed. The efficacy of tricyclic antidepressants can decrease when coadministered with sulfamethoxazole and trimethoprim. Like other sulfonamide-containing drugs, sulfamethoxazole and trimethoprim potentiates the effect of oral hypoglycemics. In the literature, a single case of toxic delirium has been reported after concomitant intake of sulfamethoxazole/trimethoprim and amantadine. In the literature, three cases of hyperkalemia in elderly patients have been reported after concomitant intake of sulfamethoxazole/trimethoprim and an angiotensin converting enzyme inhibitor. 7,8
Text above is quoted in full from the FDA-approved drug label published by openFDA, effective January 5, 2026. Matched to this product by RxNorm code. Cross-references to other sections of the full prescribing information have been removed, since they point to a document not shown here. Nothing else is changed: no sentence is shortened, reworded or summarised.
This page reproduces regulatory text for reference. It is not medical advice, and KenyRx is not a pharmacy or a prescriber. Talk to a doctor or pharmacist about whether a medicine is right for you.
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