Methotrexate should be used with caution in patients taking drugs known to have antifolate potential including nitrous oxide and trimethoprim.
Immunodeficient individuals are at higher risk for infection with Pneumocystis carinii and are frequently put on a regular preventive drug regimen of trimethoprim sulfa and/or inhaled pentamidine to avoid pneumocystis pneumonia.
These include penicillin, ampicillin, and amoxicillin; sulfisoxazole or sulfamethoxazole; trimethoprim; nitrofurantoin; cephalosporins; or fluoroquinolones.
Trimethoprim and nitrofurantoin are preferred for treating recurrent UTIs in women.
Women and teens with two or more UTIs within a six-month period sometimes are given prophylactic treatment, usually nitrofurantoin or trimethoprim for three to six months.