Before taking this medication, tell your doctor or pharmacist if you are allergic to sulfamethoxazole or trimethoprim; or to sulfa medications; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of: kidney disease, liver disease, certain blood disorders (such as porphyria, anemia due to folate vitamin deficiency), history of blood disorders caused by trimethoprim or sulfa medications, vitamin deficiency (folate or folic acid), severe allergies, asthma, decreased bone marrow function (bone marrow suppression), a certain metabolic disorder (G6PD deficiency), underactive thyroid, mineral imbalances (such as high level of potassium or low level of sodium in the blood).

This medication may cause live bacterial vaccines (such as typhoid vaccine) to not work well. Tell your health care professional that you are using this medication before having any immunizations/vaccinations.

Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

This medication may make you more sensitive to the sun. Limit your time in the sun. Avoid tanning booths and sunlamps. Use sunscreen and wear protective clothing when outdoors. Get medical help right away if you get sunburned or have skin blisters/redness.

If you have diabetes, this product may affect your blood sugar. Check your blood sugar regularly as directed and share the results with your doctor. Tell your doctor right away if you have symptoms of low blood sugar (see Side Effects section). Your doctor may need to adjust your diabetes medication, exercise program, or diet.

Older adults may be more sensitive to the side effects of this drug, especially skin reactions, blood disorders, easy bleeding/bruising, and a high potassium blood level.

Patients with AIDS may be more sensitive to the side effects of this drug, especially skin reactions, fever, and blood disorders.

Tell your doctor if you are pregnant or plan to become pregnant. You should not become pregnant while using sulfamethoxazole/trimethoprim. This medication may harm an unborn baby. If you become pregnant, talk to your doctor right away about the risks and benefits of this medication.

This drug passes into breast milk. While there have been no reports of harm to healthy infants, this drug may have undesirable effects on infants who are ill or premature or have certain disorders (jaundice, high blood levels of bilirubin, G6PD deficiency). Breastfeeding is not recommended for infants with these conditions. Consult your doctor before breastfeeding.