What is the recommended dosing of Aztreonam (Aztreonam) for a patient with impaired renal function on hemodialysis (HD)?

Aztreonam Dosing in Hemodialysis Patients

For patients on hemodialysis, administer aztreonam 500 mg, 1 g, or 2 g as an initial loading dose, followed by one-fourth of that initial dose at the usual fixed interval (every 6,8, or 12 hours), with an additional one-eighth of the initial dose given after each hemodialysis session. 1

Standard Dosing Algorithm for HD Patients

Loading and Maintenance Dosing:

• Give the full standard dose (500 mg, 1 g, or 2 g depending on infection severity) as the initial loading dose 1
• Maintenance dose = one-fourth (25%) of the initial loading dose, given at standard intervals (every 6,8, or 12 hours) 1
• Post-dialysis supplemental dose = one-eighth (12.5%) of the initial dose after each hemodialysis session 1

Timing of Administration:

• Always administer aztreonam immediately after hemodialysis completion, never before dialysis 2
• This prevents premature drug removal during dialysis (hemodialysis removes 27-58% of the drug over 4 hours) 3
• Post-dialysis dosing also facilitates directly observed therapy 2

Infection Severity-Based Dosing Examples

For serious or life-threatening infections:

• Initial loading dose: 2 g IV 1
• Maintenance dose: 500 mg every 6-8 hours 1
• Post-HD supplemental: 250 mg after each dialysis session 1

For moderate systemic infections:

• Initial loading dose: 1 g IV 1
• Maintenance dose: 250 mg every 8-12 hours 1
• Post-HD supplemental: 125 mg after each dialysis session 1

For urinary tract infections:

• Initial loading dose: 500 mg IV 1
• Maintenance dose: 125 mg every 8-12 hours 1
• Post-HD supplemental: 62.5 mg after each dialysis session 1

Pharmacokinetic Rationale

Dialysis Clearance Characteristics:

• Aztreonam serum half-life increases from 1.7 hours (normal renal function) to 7.9 hours between dialysis sessions 4, 3
• During hemodialysis, the half-life decreases to 2.7 hours due to dialytic clearance 3
• Hemodialysis clearance of aztreonam is 36.6-43.2 mL/min, which is 50-77% greater than interdialytic clearance 3
• The aztreonam-to-urea clearance ratio during hemodialysis is 0.28-0.33, indicating significant dialytic removal 3

Why Maintain Dose Amount:

• Do not reduce the milligram dose per administration—only extend the dosing interval 2
• Aztreonam exhibits concentration-dependent bactericidal activity, requiring adequate peak levels for efficacy 2
• Smaller doses may reduce drug efficacy against gram-negative pathogens, particularly Pseudomonas aeruginosa 2

Monitoring Requirements

Serum Drug Concentration Monitoring:

• Consider therapeutic drug monitoring in hemodialysis patients to ensure adequate absorption without excessive accumulation 2
• This is particularly important for avoiding toxicity while maintaining therapeutic efficacy 2

Clinical Response Assessment:

• Continue therapy for at least 48 hours after the patient becomes asymptomatic or bacterial eradication is documented 1
• Persistent infections may require several weeks of treatment 1

Common Pitfalls to Avoid

Critical Timing Errors:

• Never administer aztreonam before hemodialysis—this results in immediate drug removal (38.2% removed over 4 hours) and subtherapeutic levels 3
• Avoid giving the dose during dialysis, as this leads to premature clearance 2

Dosing Errors:

• Do not reduce the milligram dose per administration; maintain 12-15 mg/kg per dose to preserve concentration-dependent killing 2
• Do not use doses smaller than indicated, as this compromises efficacy 1
• Do not forget the post-dialysis supplemental dose (one-eighth of initial dose), as this compensates for dialytic removal 1

Monitoring Oversights:

• Do not rely solely on serum creatinine to estimate renal function in elderly patients—calculate creatinine clearance using the Cockcroft-Gault equation 1
• Do not assume standard dosing is appropriate without confirming the patient's dialysis schedule 2