Misc Antibiotics

Question 1

Chloramphenicol

Answer 1

• IV for resistant & serious G+/G- infections like meningitis
• Mechanism: inhibits binding of aminoacyl-tRNA to acceptor site & inhibits cytochrome P450
• Risks: fatal blood dyscrasias, gray baby syndrome (cyanosis)
- Gray Baby results from insufficient glucoronyl transferase and underdeveloped renal function

Question 2

Quinupristin/Dalfopristin

Answer 2

• Synergistically given IV for MRSA & vancomycin-resistant infections
• Mechanism: Quin releases peptidyl-tRNA from donor site; Dalf inhibits binding of aminoacyl-tRNA to acceptor site
• Inhibit CYP3A4 → lowered metabolism of warfarin
• Rarely used because too many side effects
• Side effects: superinfection, arthralgias, hyperbilirubinemia, venous irritation

Question 3

Linezolid

Answer 3

• Static or cidal depending on org
• Used for Enterococcus faecium, MSSA, MRSA & other vancomycin-resistant infections
• Mechanism: inhibits formation of initiation complex on ribosome
• Risks: blood dyscrasias, colitis and 5-HT syndrome (when taken w/anti-depressants)
• Chronic use can cause reversible optic neuropathy, irreversible peripheral neuropathy & lactic acidosis
• Do not use longer than 28 days; weekly CBC required

Question 4

Clindamycin

Answer 4

• Penetrates most tissues except CNS
• Risk of pseudomembranous colitis (C. diff infection)
• Topical - acne
• Suppository - vaginosis
• Mechanism: inhibits translocation from A site to P site of ribosome
• Immunomodulatory activity (used w/high rise PCN for Group A strep)

Question 5

Polymyxin B

Answer 5

• Effective vs G- orgs
• Very nephrotoxic and neurotoxic
• Mechanism: cidal cationic detergent
• Used for infection of conjunctiva
• Available alone or w/other Rxs
• Has a posantibiotic effect

Question 6

Colistimethate

Answer 6

• Cidal catatonic detergent
• Very nephrotoxic and neurotoxic
• IV/IM for various G- rods

Question 7

Rifaximin

Answer 7

• No significant systemic absorption
• Used for traveler’s diarrhea (E. coli)
• Mechanism: binds DNA-dependent RNA polymerase
• Side effects: farts, stomach pain, urge to poop
• Structurally similar to rifampin leading to cross-resistance

Question 8

Mupirocin

Answer 8

• Ointment/cream for impetigo from Group A Strep or S. aureus

Question 9

Retapamulin

Answer 9

• First pleuromutilin for humans

* Topical ointment for impetigo

Question 10

Nitrofurantoin

Answer 10

• For prevention and tx of G+ & G- UTIs
• Mechanism: reduced by UT bacteria to intermediates that damage ribosomes & cell wall
• Side effects: discolors urine brown, pulmonary reactions (can lead to death)

Question 11

Daptomycin

Answer 11

• Cidal parenteral for G+ and MRSA skin & systemic infection
• Not for pneumonia b/c inactivated by pulmonary surfactant → Loss of K → depolarization
• Mechanism: Forms pores in cytoplasmic membrane
• Side effect: increased creatine kinase

Question 12

Quinidine

Answer 12

• IV for life-threatening Plasmodium falciparum

* Can cause arrhythmias (monitor ECG continuously)

Question 13

Rifampin

Answer 13

• Effective vs G+ and G- (especially staph & MRSA)
• Mechanism: inhibits DNA-dependent RNA polymerase → no RNA synthesis
• Kills intra and extracellular orgs
• Excreted thru bile
• Do not give for < 2 weeks
• Side effects: discolors urine, feces, saliva, and sweat, stains contacts, jaundice, hepatitis