UTI used to be the easiest thing to treat. Today, not so much. We have resistance not only in the hospital but in the community. Historically we used sulfonamides.
- Increasing resistance in hospital and community acquired infections
- Sulfonamides (Sulfa) alone are not very useful any more
Today a sulfa drug by itself can’t be used because resistance is very high. One way around it is by using a combination agent. We add trimethoprim with a sulfa drug to make a combination drug called Co-Trimoxazole (Bactrin).
We’ve talked about folic acid before in detail in regards to anemia. We said, folic acid is not an active vitamin. It takes two enzymatic steps to make the active vitamin, called folinic acid (tetrahydrofolate). The sulfa drug blocks one of the enzymatic steps, killing the bacteria. But the bacteria found a way around this problem so it became useless. The trimethoprim, however, blocks the other enzymatic step. So now when we use this combination drug (co-trimoxazole), we’re blocking both steps and now the organism has to find a way around both blockages. Fortunately for us, the organisms haven’t figured out a way around this for UTI and other uses.
- High acquired resistance
- Use in combination with trimethoprim to overcome resistance
- Trimethoprim/sulfamethoxazole (co-trimoxazole) inhibits bacteria ability to activate folic acid to tetrahydrofolate
Co-trimoxazole is used for UTI and respiratory infections. In very high doses it’s used in HIV patients to treat pneumocystis carinii (a parasite that gets into patients lungs). We need high doses to treat that that and it affects not only the organism but also the host. Since it stops the conversion of folic acid, we get megaloblastic anemia. For these patients, they get leucovorin (which is the active form of folic acid: folinic acid;tetrahydrofolate).
- Respiratory Infection
- Pneumocystis Carinii (high dose therapy)
- Adverse Reactions
- Anemia associated with high dose therapy
- Serious Skin Rashes