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21 Cards in this Set
- Front
- Back
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What are the Sulfonamides?
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Para-aminobenzoic acid
Sulfadiazine Sulfisoxazole Sulfamethoxazole |
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Sulfonamides mechanism
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Competitive inhibition of dihydropteroate synthase
Unable to create dihydropteroic acid from Pteridine + PABA Bacteriostatic |
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Sulfonamides resistance
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Most common: alteration of dihydropteroate synthase to decrease sulfonamide affinity
Increased PABA production |
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Sulfonamides absorption
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70-100% absorbed orally
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Sulfonamides distribution
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To all tissues, including CSF
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Sulfonamides metabolism
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Acetylated in the liver
T1/2 = 4 - 12 hr. INTERACT WITH THE P450s! |
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Sulfonamides excretion
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Glomerular filtration
Extremely high concentration in urine (good for UTIs!) |
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Sulfisoxazole absorption
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+++++
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Sulfamethoxazole absorption
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++
Less than sulfisoxazole |
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Sulfisoxazoel half life
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6 hours
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Sulfamethoxazole half life
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11 hr.
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Sulfonamides adverse effects
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-Crystalline aggregates in urine (no problem with sulfisoxazole)
-Acute hemolytic anemia in patients with G6PD deficiencies -Bone marrow toxicity -Hypersensitivity: rash, fever -Stevens Johnson syndrome (dermatitis of face) -GI upset |
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Sulfonamides drug interactions
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Inhibition of CYP2C9 (P450)
Problems with: -Warfarin -Sulfonylurea hypoglycemic drugs -Hydantoin anticonvulsants |
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Trimethoprim mechanism
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Inhibition of dihydrofolate reductase
Cannot convert dihydrofolic acid to tetrahydrofolic acid |
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Trimethoprim selectivity
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Very, very high.
Methotrexate is MUCH LOWER - cancer drug. |
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Trimethoprim resistance
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Increased DHFR production
Alteration of DHFR to decrease binding of Trimethoprim |
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Trimethoprim absorption
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60% bioavailable
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Trimethoprim distribution
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Well
Penetrates CSF |
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Trimethoprim metabolism
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minimal
T1/2 = 11 hr: same as sulfamethoxazole. Given together synergistically |
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Adverse effects of trimethoprim - sulfamethoxazole
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Increased dermatologic reactions with combination
Folate deficient patients may develop hematologic toxicities Patients with AIDS have adverse reactions GI upset |
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Clinical uses of trimethoprim - sulfamethoxazole
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Broad spectrum: gram +, gram -
UTIs: good for chronic cases Respiratory tract infections (PCP) Other infections: Shingella |
