Tell your doctor if you have kidney disease, or liver disease. You may not be able to take trimethoprim, or you may require a lower dose or special monitoring during treatment if you have any of the conditions listed above.

Anemia, caused by a reduction in folic acid, can occur in persons receiving trimethoprim in combination with divalproex, valproic acid, methotrexate, pyrimethamine, triamterene, or trimetrexate.

Trimethoprim may increase the effects of phenytoin (Dilantin®) and lead to dangerous side effects. If you are taking phenytoin, notify your doctor of any unusual side effects during treatment with trimethoprim.

The combination of trimethoprim and cyclosporine can increase the risk of kidney damage from cyclosporine.

When trimethoprim and dapsone are used together, increased blood concentrations of both drugs can occur, sometimes with side effects that include a toxic condition called methemoglobinemia.

Rifampin can increase the elimination of trimethoprim by the kidneys and may reduce the effectiveness of trimethoprim.

Trimethoprim is in the FDA pregnancy category C. This means that it is not known whether trimethoprim will harm an unborn baby. Do not take this medication without first talking to your doctor if you are pregnant.

Trimethoprim passes into breast milk and may harm a nursing infant. Do not take this medication without first talking to your doctor if you are breast-feeding a baby.

Trimethoprim is not approved for use by children younger than 2 months of age.

 

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