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20 Cards in this Set
- Front
- Back
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What is the mechanism of action for sulfonamides?
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Sulfonamides mimic PABA and compete with PABA for binding to dihydropteroate synthase
- sulfonamides will inhibit dihydropteroate synthase so that folic acid cannot be made for the bacteria - will inhibit growth but not kill = bacteriostatic |
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What is the mechanism of resistance to sulfonamides?
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bacteria can either...
- change dihydropteroate synthase so that sulfas can't bind - increase production of PABA so the sulfas are out-competed There is actually widespread resistance to sulfonamides so these are NOT used alone to treat infections |
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What is the absorption of sulfonamides?
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Oral
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What is the distrubution of sulfonamides?
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- goes to all tissues including CSF!
(in the past sulfas were used to treat meningitis, but not anymore because of the resistance) |
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Metabolism of sulfonamides?
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Liver; with variable half life
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Excretion of sulfonamides
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- mostly glomerular filtration
- achieve high concentration in urine (why they are good to help treat UTIs!) |
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Describe the synergistic activity of sulfamethoxazole and trimethoprim
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When TMP and SMX are given together you need less than half of each drug to achieve MIC
- basically they are more effective together (beyond an additive effect) |
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Why was sulfamethoxazole chosen for a combination with trimethoprim?
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- synergistic antibacterial activity
- when used alone experience widespread resistance - both have a similar half life (11 hrs) - can tx gram + and - - good for UTIs, RTIs, Shigella - effective with 3 day dosing |
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What is the difference between sulfonamides and trimethoprim?
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sulfonamides inhibit dihydropteroate synthase and trimethoprim inhibits dihydrofolate reductase
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What are the limitations to the use of sulfonamides?
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experience widespread resistance when used alone
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Adverse effects of sulfonamides
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- crystalline aggregates in urine
- hematologic disorders - hypersensitivity (skin rash is common) - GI irritation |
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Why might you need to watch out for patients with G6PD deficiency if you administer sulfonamides?
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- sulfonamides can cause acute hemolytic anemia (destroy erythrocytes) in patients with G6PD deficiency
- this is particularly common in malaria prone regions |
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What must be considered if administering sulfonamides / trimethoprim with warfarin?
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- warfarin is metabolized by CYP enzymes
- both sulfas and trimethoprim inhibit (different) cyp enzymes - leads to a potentiation effect on the activity of warfarin ... basically the drug (warfarin) will build up because it is not being broken down by cyp |
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What is the mechanism of action for trimethoprim?
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- inhibits bacterial folate synthesis
- will inhibit the enzyme dihyrofolate reductase (DHFR) - this enzyme is common to bacteria and humans, but trimethoprim is much more selective for the bacterial form of DHFR |
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What are the mechanisms of resistance to trimethoprim
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- bacteria can increase the production of DHFR (make too much enzyme for the drug to inhibit)
- can change the DHFR enzyme so that the drug can no longer bind as well |
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Absorption of trimethoprim
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oral
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distribution of trimpethoprim
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- goes pretty much anywhere, will penetrate the CSF
(like sulfas not used to treat meningitis anymore because of resistance) |
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metabolism of trimethoprim
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- minimally metabolized
- 11 hour t1/2 |
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excretion of trimethoprim
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renally excreted and will build up in urine
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Adverse rxns of TMP / SMX combo
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- derm reactions (itchy!!)
- be careful in folate-deficient patients... - be careful with AIDS patients... - GI disturbances |
