Isoniazid/pyridoxine/sulfamethoxazole/trimethoprim (INH/B6/CTX) is a fixed-dose combination medication for the prevention of opportunistic infections in HIV/AIDS. It combines isoniazid, pyridoxine, sulfamethoxazole, and trimethoprim. Specifically it is used to prevent tuberculosis, toxoplasmosis, pneumonia, malaria, and isosporiasis. It is taken by mouth.