What are the commonly used antibiotics in Outpatient Parenteral Antibiotic Therapy (OPAT)?

Commonly Used Antibiotics in Outpatient Parenteral Antibiotic Therapy (OPAT)

Ceftriaxone, vancomycin, and ertapenem are the most commonly used antibiotics in OPAT settings due to their favorable dosing schedules, stability profiles, and broad spectrum of activity against common pathogens. 1

First-Line OPAT Antimicrobials

Once-Daily Administration Agents

These are preferred due to convenience and reduced disruption to patients' daily activities:

• Ceftriaxone: Most frequently used (33% of OPAT courses) 1

  • Dosing: 1-2g daily
  • Half-life: 5.4-10.9 hours
  • Stability: 3 days at room temperature, 10 days refrigerated
  • Common indications: Skin/soft tissue infections, osteomyelitis, pneumonia

• Ertapenem: Excellent for OPAT due to once-daily dosing 2

  • Dosing: 1g daily
  • Half-life: 4 hours
  • Stability: 6 hours at room temperature, 24 hours refrigerated
  • Particularly useful for complicated intra-abdominal infections and ESBL-producing Enterobacterales
  • Not active against Pseudomonas or Acinetobacter

• Daptomycin: Once-daily administration

  • Used for gram-positive infections including MRSA

Twice-Daily Administration Agents

• Vancomycin: Second most commonly used (20% of OPAT courses) 1

  • Dosing: Usually every 12 hours (adjusted based on renal function)
  • Half-life: 4-6 hours
  • Stability: 7 days at room temperature, 63 days refrigerated
  • Requires therapeutic drug monitoring
  • Used for MRSA and other resistant gram-positive infections

• Cefazolin: (6% of OPAT courses) 1

  • Dosing: Every 8-12 hours
  • Half-life: 1-2 hours
  • Stability: 1 day at room temperature, 10 days refrigerated
  • Common for MSSA infections

Special Considerations for OPAT

Pharmacokinetic/Pharmacodynamic Principles

• β-lactams (penicillins, cephalosporins): Time-dependent killing with brief post-antibiotic effect

  • May require multiple daily doses or continuous infusion
  • Ceftriaxone and ertapenem are exceptions due to longer half-lives 1

• Aminoglycosides: Concentration-dependent killing with prolonged post-antibiotic effect

  • Can be given once daily
  • Require monitoring of drug levels and renal function 1

Stability and Administration Considerations

• Drug stability varies significantly and affects administration scheduling:
  • Ampicillin: Only stable for 8 hours at room temperature 3
  • Vancomycin: Stable for 7 days at room temperature 4
  • Ceftriaxone: Stable for 3 days at room temperature 1

Delivery Methods

• Elastomeric devices: Simple to use but not covered by all insurance
• Programmable pumps: Allow for complex dosing schedules
• Gravity infusion: Less expensive but requires longer infusion times
• IV push: Convenient for rapid administration of certain antibiotics 1

Common Infections Treated with OPAT

1. Skin and soft tissue infections (23% of OPAT courses)
2. Osteomyelitis (15%)
3. Septic arthritis/bursitis (5%)
4. Bacteremia (5%)
5. Wound infections (4%)
6. Pneumonia (4%)
7. Pyelonephritis (3%) 1

Special OPAT Regimens

Complex Regimens for Specific Infections

For Enterococcus faecalis endocarditis, specialized regimens have been developed:

• Ampicillin (2g every 4 hours) plus ceftriaxone (4g once daily) using programmable pumps 5
• This approach allows treatment at home rather than requiring hospitalization for 6 weeks

MSSA Bloodstream Infections

• Ceftriaxone has been shown to be non-inferior to cefazolin for MSSA bloodstream infections in the OPAT setting, with the advantage of once-daily dosing 6

Monitoring Requirements

Frequency of monitoring varies by antimicrobial:

Antimicrobial	Common Adverse Effects	Monitoring Requirements
Vancomycin	Rash (2.29%), fever (1.18%)	Drug levels, renal function
Ceftriaxone	Rash (1.39%), diarrhea (0.45%)	CBC, liver function
Cefazolin	Rash (1.92%), nausea (0.77%)	CBC, renal function
Aminoglycosides	Vestibular toxicity (3.06%), renal toxicity (2.75%)	Drug levels, renal function, hearing tests

Pitfalls and Caveats

1. Drug stability: Some antibiotics have limited stability after reconstitution, requiring more frequent home delivery or preparation

2. Vascular access complications: Choose appropriate vascular access based on anticipated duration of therapy and drug properties (e.g., phlebitis risk)

3. Monitoring requirements: Ensure proper laboratory monitoring based on the specific antimicrobial agent

4. Patient selection: Not all patients are suitable for OPAT; assess ability to comply with treatment and monitoring

5. First dose observation: Always administer the first dose of an antibiotic in a supervised setting to monitor for adverse reactions 1

6. Antimicrobial resistance: Consider local resistance patterns when selecting agents for OPAT

7. Insurance coverage: Medicare patients without secondary infusion benefits may have limited options for OPAT 1

By selecting appropriate antimicrobials with convenient dosing schedules and establishing proper monitoring protocols, OPAT can effectively treat serious infections while allowing patients to recover at home, improving quality of life and reducing healthcare costs.