antimicrobial drug interactions

Question 1

ampicillin with

Answer 1

gentamycin/aminoglycoside: synergistic, enhances bactericidal effect. decrease dose to minimize nephrotoxicity and ototoxicity

Question 2

vancomycin/ampicillin with

Answer 2

gentamycin/aminoglycoside: ampicillin or vancomycin makes pores in bacterial cell wall, amino glycoside gets into bacteria. Since amino glycosides are + charged, can’t get in cell readily on its own

Question 3

erythromycin, fungal azoles, metronidazole with:

Answer 3

cyclosporin, warfarin

• inhibit cyt p450, decreases metabolism of drugs above. Also excess immune suppression and renal toxicity of CSA
• warfarin increases PT time and bleeding
• decrease CSA and warfarin dose

Question 4

rifampin or isoniazid with:

Answer 4

fungal azoles, warfarin, cyclosporine, theophyllin, sulfonylureas,
-rifampin and isoniazide induce cytp450, increases metabolism of drugs above and shortens their duration of action

Question 5

Sulfonamides with

Answer 5

methotrexate, warfarin, sulfonylurea
-sulfonamides at high doses occupy more sites on albumin and displaces other drugs and increases their levels and toxicity

Question 6

TMP-SMX with

Answer 6

warfarin

• TMP-SMX inhibits cyt P450 and prevents metabolism of warfarin, increases its plasma level
• need to decrease dose of warfarin

Question 7

Fluoroquinolones with

Answer 7

caffeine and theophyllin

• cipro inhibits microsomal enzymes invovled in metabolism of caffeine and theophyllin and increase their levels
• avoid coffee–>seizures

Question 8

Tetracyclines and fluoroquinolones with

Answer 8

milk products

• the drugs chelate metals and products with metals interfere with absorption of these drugs
• avoid dairy products