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Mechanism of Action
Interfere with bacterial synthesis of folic acid which leads to a decrease in tetrahydrofolic acid which is necessary for purine, thymidine and DNA synthesis.
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Absorption
Good oral bioavailablity
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Sulfisoxazole
- Short Acting
- QID
- Used to treat Otitis Media and sometimes UTIs (good urine solubility)
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Sulfadiazine
- Short Acting
- Passes into CSF due to minimal protein binding
- Used in combination to treat nocardial infections and toxoplasmosis.
- Low urine solubility
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Sulfamethoxazole
- Intermediate Acting
- Less solube in urine & slower excretion then sulfisoxazole
- BID
- Combined with trimethoprim for synergistic bactericidal effect.
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Sulfacetamide
- Ophthalmic preparation used to treat superficial infections of the eye.
- Doesn't penetrate systemically well due to PK.
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Mafenide
- Broad Spectrum topical sulfa
- Used primarily in burn patents
- Effective against Pseudomonas
- Diffuses well through devascularized areas.
- Mafenide and it's metabolite are carbonic anhydrase inhibitiors. (Used with caution in patient with renal or pulmonary insufficiencies)
- Adverse effects: Hypersensitivity, fungal colonization, local pain, and burning sensation.
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Silver Sulfadiazine
- Tropical Sulfa used in burn patients
- Effective against pseudomonas
- Less pain than with mafenide and few applications needed
- Sulfadiazine is absorbed & high concentrations can be achieved.
- Crystaluria can be a problem.
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Sulfasalazine
- Combination of a sulfa and antiinflammatory agent.
- Used in treatment of IBD
- Poor absorbed from GI tract
- Metabolized by bacteria to sulfapyridine and 5-aminosalicylic acid.
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Trimethoprim-Sulfamethoxazole (Bactrim)
Mechanism of Action
- TMP-SMX
- Combines two agents that inhibits bacteria synthesis at two sequential steps.
- Bactericidal-synergistic activity
- Slow development of resistance
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Trimethoprim-Sulfamethoxazole (Bactrim)-Mechanisms of Resistance
- Increased production of PABA
- Synthesis of altered enzymes
- Increased production of dihydropteroate synthetase
- Reduced Drug uptake
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Trimethoprim-Sulfamethoxazole (Bactrim) - Dosing
- Optimal synergistic ratio of serum conc. is 1:20.
- Achieved by a fixed dose ratio of 1:5.
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Trimethoprim-Sulfamethoxazole (Bactrim) - Spectrum of Activity
- Gram Positive - MSSA, MRSA, S. epidermidis, S. pneumoniae.
- Gram Negative - Most enterobacteriaceae, H. flu, M. catarrhalis, Salmonella, Shigella
- Not active againist Pseudomonas and poor anaerobic coverage.
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