In a CAPD patient with peritonitis receiving exchanges every 4 hours with 1.5% dextrose and an 8‑hour dwell for intraperitoneal cefepime, should cefepime be dosed daily or every 48 hours, and how should intraperitoneal vancomycin be dosed and monitored?

Intraperitoneal Antibiotic Dosing for CAPD-Associated Peritonitis

For your CAPD patient with peritonitis, cefepime should be dosed at 1 gram intraperitoneally once daily (not every 48 hours), and vancomycin should be given as a loading dose of 15-20 mg/kg intraperitoneally, then redosed based on serum trough levels drawn 5-7 days later (not 4 days), targeting troughs of 15-20 mg/L.

Cefepime Dosing in CAPD Peritonitis

Your current regimen needs adjustment. The FDA label clearly states that for CAPD patients, cefepime should be dosed every 48 hours for systemic infections 1. However, this is for intravenous administration in non-peritonitis situations.

For intraperitoneal cefepime in peritonitis:

• The evidence strongly supports 1 gram IP once daily rather than every 48 hours 2, 3
• Pharmacokinetic studies demonstrate that IP cefepime at 15 mg/kg (approximately 1 gram) achieves therapeutic serum levels exceeding MIC (>8 mcg/mL) within 1 hour and maintains levels of 15.8 mcg/mL at 24 hours 2
• The bioavailability is 84%, with a half-life of 13.8 hours in CAPD patients, supporting once-daily dosing 2
• Clinical trial data shows 1 gram IP daily cefepime monotherapy achieved 82% primary response and 72% cure rates in CAPD peritonitis 3

Your current every-4-hour exchanges are appropriate for peritonitis management, as more frequent exchanges improve antibiotic distribution and remove inflammatory mediators. The 8-hour dwell for the cefepime-containing exchange is reasonable, though the drug can be given in any exchange with once-daily dosing.

Vancomycin Dosing and Monitoring

Your vancomycin approach requires significant modification:

Loading dose:

• Give 15-20 mg/kg IP (not just "one dose") 4
• The 2022 ISPD guidelines specifically recommend this weight-based loading approach

Redosing interval:

• Do NOT redose at 4 days - this is too early
• Redose every 5-7 days based on PD modality (CAPD typically 5 days) 4
• The FDA label for IV vancomycin in CAPD suggests every 48 hours for systemic dosing 5, but IP dosing for peritonitis follows different kinetics

Monitoring strategy:

• Draw serum vancomycin trough on day 5 (not day 4) before the second dose 6, 7
• Target trough: 15-20 mg/L for adequate gram-positive coverage
• Critical caveat: 60% of patients have subtherapeutic levels (<15 mg/L) after the loading dose, but therapeutic levels after subsequent doses 6

Why your 4-day plan is problematic:

• Vancomycin has a prolonged half-life in CAPD patients (peritoneal clearance ~4 mL/min) 8
• Drawing levels at 4 days doesn't align with the recommended 5-7 day redosing interval
• Most patients achieve therapeutic levels only after the second dose, so premature redosing based on a 4-day level may lead to supratherapeutic concentrations

Alternative Continuous Dosing Approach

The most recent evidence suggests considering continuous IP vancomycin instead of intermittent dosing 7:

• Loading dose: 20 mg/kg IP
• Maintenance: 50 mg/L in each dialysate bag
• This provides more consistent intraperitoneal exposure
• Measure serum level on day 5 to ensure levels aren't toxic

Practical Algorithm

Day 1:

• Cefepime 1 gram IP in one exchange (can use your 8-hour dwell)
• Vancomycin 15-20 mg/kg IP in the same or different exchange

Days 2-4:

• Cefepime 1 gram IP daily
• No vancomycin

Day 5:

• Draw serum vancomycin trough (before any dose)
• If trough <15 mg/L: give second vancomycin dose (15-20 mg/kg IP)
• If trough 15-20 mg/L: hold and recheck in 2-3 days
• If trough >20 mg/L: hold and recheck in 3-5 days
• Continue cefepime 1 gram IP daily

Days 6-10:

• Continue cefepime 1 gram IP daily
• Redose vancomycin based on levels, typically every 5-7 days

Common Pitfalls to Avoid

1. Don't use IV dosing schedules for IP antibiotics - pharmacokinetics differ substantially
2. Don't assume all patients need the same vancomycin redosing interval - residual renal function significantly affects clearance (though this wasn't statistically significant in one study 6)
3. Don't draw vancomycin levels at random times - must be trough levels before the next scheduled dose
4. Don't continue every-4-hour exchanges indefinitely - once clinical improvement occurs (typically 48-72 hours), can transition to standard CAPD schedule

The 2022 ISPD guidelines emphasize that empirical therapy should cover both gram-positive and gram-negative organisms, which your cefepime + vancomycin regimen appropriately addresses 4. However, the dosing intervals you've chosen don't align with current pharmacokinetic evidence or guideline recommendations.