KEY POINTS
- Sulfamethoxaxole-trimethoprim (Bactrim, Septra, SMX/TMP) is a sulfonamide derivative antibiotic that interferes with bacterial folic acid synthesis and growth by blocking dihydrofolic acid formation from para-aminobenzoic acid.
- Active against a variety of organisms, including Staphylococcus species, E. coli, Stenotrophamonas maltophilia, Nocardia species, Toxoplasma gondii, Pneumocystis (PCP), and Isospora belli
- Healthcare associated MRSA is commonly resistant
- Available as injectable and oral
- Bactrim SS (single strength) = 400mg SMX + 80mg TMP
- Bactrim DS (double strength) = 800mg SMX + 160mg TMP
- Doses vary considerably depending on indication and should be adjusted for renal function
- Most dosage recommendations are based upon the trimethoprim component
- Bactrim IV has short expiration once mixed
- Some of the more concerning or common adverse effects: blood dycrasias, dermatologic reactions, hepatic necrosis, hyperkalemia, hypocalcemia, hyponatermia, hypersensitivity reaction and thrombocytopenia
- In general the frequency of toxicity increases when drug exposure increases. In particular watch out for hyperkalemia with higher doses
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