Antibiotics Bacitracin and Daptomycin Overview

Questions and Answers

What is the mechanism of action (MOA) of Bacitracin?

Inhibits NAG-NAM linear strand synthesis via dephosphorylation of the lipid carrier.

What is the spectrum of activity for Bacitracin?

No activity

Gram + only (correct)

Both Gram + and Gram -

Gram - only

What are therapeutic uses of Bacitracin?

Used topically to treat superficial skin or wound infections, used on mucus membranes, combined with polymyxin and/or neomycin.

What are the drug interactions and adverse effects of Bacitracin?

Highly nephrotoxic when administered systemically; clinical use is limited to superficial skin infections. Signup and view all the answers

What is the mechanism of action (MOA) of Daptomycin?

Produces calcium dependent depolarization of the bacterial cell membrane. Signup and view all the answers

What is the spectrum of activity of Daptomycin?

Gram + bacteria Signup and view all the answers

What are the therapeutic uses of Daptomycin?

Complicated skin and skin structure infections, bacteremia. Signup and view all the answers

What are the drug interactions, kinetics, and resistance issues related to Daptomycin?

Inactivated by pulmonary surfactants; treatment failures have been reported. Signup and view all the answers

What is the mechanism of action (MOA) of Fosfomycin?

Inhibits the enzyme that catalyzes the first step in peptidoglycan synthesis. Signup and view all the answers

What is the spectrum of activity of Fosfomycin?

Both A and B Signup and view all the answers

What are the therapeutic uses of Fosfomycin?

Used for treating urinary tract infections (UTI). Signup and view all the answers

What are the drug interactions and kinetics of Fosfomycin?

Rapid absorption after oral administration; high urinary concentrations. Signup and view all the answers

What are the adverse effects of Fosfomycin?

Diarrhea, vaginitis, nausea, and headache. Signup and view all the answers

Resistance is currently an issue with Fosfomycin.

False Signup and view all the answers

What is the mechanism of action (MOA) of Polymyxins?

Possess a detergent-like effect that disrupts cell membrane rigidity. Signup and view all the answers

What is the spectrum of activity of Polymyxins?

Only Gram negative Signup and view all the answers

What are the therapeutic uses of Polymyxins?

Topical application for superficial skin infection; IV salvage therapy for multidrug-resistant Gram negative organisms. Signup and view all the answers

What are the drug interactions and adverse effects of Polymyxins?

Highly nephrotoxic and neurotoxic with high systemic levels; careful monitoring is required. Signup and view all the answers

Proteus and Serratia are intrinsically resistant to Polymyxins.

True Signup and view all the answers

What are the formulations of Polymyxins?

Polymyxin B (IV, ophthalmic, otic, topical), Colistin (IV or inhaled via nebulizer). Signup and view all the answers

Study Notes

Bacitracin

Mechanism of Action: Inhibits NAG-NAM linear strand synthesis through dephosphorylation of the lipid carrier.
Spectrum of Activity: Effective only against Gram-positive bacteria.
Therapeutic Uses:
- Topical treatment for superficial skin or wound infections.
- Applicable on mucus membranes for nasal MRSA infections.
- Often combined with polymyxin and/or neomycin, marketed as Neosporin or triple antibiotic ointment, for polymicrobial infections.
Drug Interactions and Resistance:
- Highly nephrotoxic if given systemically, limited to topical use to avoid toxicity.
- Poorly absorbed topically; effective for superficial infections without systemic toxicity.
- Currently, resistance is not an issue.

Daptomycin

Mechanism of Action: Causes calcium-dependent depolarization of the bacterial cell membrane.
Spectrum of Activity: Targets Gram-positive bacteria, including MRSA and VRE, equally effective as vancomycin.
Therapeutic Uses:
- Indicated for complicated skin and skin structure infections and bacteremia.
- Not recommended for pneumonia due to inactivation by pulmonary surfactants.
Drug Interactions and Resistance:
- Pulmonary surfactants inactivate daptomycin, leading to treatment failures and increased MIC during therapy.

Fosfomycin

Mechanism of Action: Inhibits UDP-N-acetylglucosamine enolpyruvyl transferase, crucial for peptidoglycan synthesis.
Spectrum of Activity: Effective against E. coli and E. faecalis.
Therapeutic Uses: Primarily used for urinary tract infections (UTIs).
Drug Interactions and Kinetics:
- Rapidly absorbed orally, achieving high distribution, especially in the kidneys, bladder, and prostate.
- Excreted unchanged in urine with high urinary concentrations maintained for several days; often a single dose suffices for uncomplicated UTIs.
Adverse Effects: Commonly includes diarrhea, vaginitis, nausea, and headache.
Resistance: No current issues; unique analog of phosphoenolpyruvate contributing to low resistance rates.

Polymyxins

Mechanism of Action: Detergent-like effect disrupts cell membrane rigidity, causing leakage and cell death; specifically targets LPS of Gram-negative bacteria.
Spectrum of Activity: Only effective against Gram-negative bacteria, with resistance noted in Proteus and Serratia due to their envelope.
Therapeutic Uses:
- Topical applications for superficial skin infections, often combined with agents like bacitracin.
- Renewed interest for systemic use due to increasing antimicrobial resistance; used as IV salvage therapy for multidrug-resistant Gram-negative organisms post-carbapenem treatments.
Drug Interactions and Adverse Effects:
- Exhibits concentration-dependent bactericidal activity.
- Highly nephrotoxic and neurotoxic at high systemic levels; close monitoring is crucial during IV administration.
Resistance: Proteus and Serratia are intrinsically resistant to polymyxins.
Formulations:
- Available as polymyxin B (IV, ophthalmic, otic, topical) and Colistin (colistimethate sodium), administered IV or by inhalation via nebulizer, especially beneficial for CF patients combating Pseudomonas infections.

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Description

This quiz covers the mechanisms of action, spectrum of activity, and therapeutic uses of Bacitracin and Daptomycin. You'll learn about their effectiveness against Gram-positive bacteria and important considerations regarding drug interactions and resistance. Test your knowledge on these crucial antibiotics used in clinical practice.