C3.1 R4(e): Perform & document a vancomycin or aminoglycoside pharmacokinetic interpretation

ID: 42 yo female admitted for query septic arthritis/deep tissue infection/myositis

s/o:
Current Abx Therapy:

  1. Pip/Taz 3.375mg IV Q6H
  2. Vancomycin 2g IV Loading Dose x 1 dose on August 31 1530
    Currently on 1g IV Q12H (at 330, 1530)

Vital Signs (Sept 2/16): Temp 37.4, BP 119/79, HR 99, RR 18, O2 sats 95% RA
(receives APAP PRN for pain)

Labs:
↓ WBC (Aug 31: 22.2 –> Sept 2: 10.5)
↓ sCr (Aug 31: 98 –> Sept 2: 45)
↑ eGFR (Aug 31: 62 –> Sept 2: 118)

Micro: MRSA screen pending. Blood Cxs on Aug 31/16 are negative.
Urine Cxs + For E. Coli 90 mega CFU/L

Vanco trough level: 6.2 mg/L (target 15-20mg/L)
– drawn 30 mins prior to Sept 2 330 dose (4th dose, including LD)

A/Checklist:

  1. Is the drug indicated?: Although patient is improving (decreased WBC, afebrile, improving overall) and is tolerating vancomycin (urinating well, no compliants, sCr stable), cultures are still pending.
  2. Were all the doses given on time?: All doses were given on time
  3. Was the level drawn at steady state?: Trough level was at steady state (pre-4th dose)
  4. Was the level drawn appropriately?: Level was drawn appropriately 30 mins prior to the 4th dose
  5. Assess the level: Vanco trough level = 6.2, which is below target

P: As discussed with MD:

  1. Discontinue previous vancomycin IV orders.
  2. Increase vancomycin to 1.25g IV Q8H – next dose due at 1530 today
  3. Vancomycin level on Sept 3 at 1500 (30 mins prior to 1530 dose)
  4. Will continue to monitor: renal function, temperature, pain/swelling, WBC, CRP
  5. Pharmacy will continue to follow and adjust dose accordingly. MD to reassess need for vancomycin.

Rationale for vancomycin 1.25g IV Q8H:

  • Improving renal function requires increased frequency (Q8H) to ensure concentrations stay above vancomycin’s MIC
  • Following linear pharmacokinetics:
    • Would expect that we would need to target a daily dose of ~5500mg
      (~1800g IV Q8H)
  • Although we want to ideally target 15-20mg/L, the benefits of ~doubling the dose to target 15-20mg/L likely won’t outweigh the risks (e.g. risk of accumulation
    → increased risk of nephrotoxicity and ototoxicity) when the patient is already improving at a significantly sub-therapeutic level.
  • Therefore: ↑ dosing frequency and ↑ the dose by 250mg (minimum dosing increment)
  • Keeping in mind: patient improving at sub-therapeutic level may indicate that patient is improving on other antibiotic therapy and that coverage against MRSA may not be warranted. Pharmacy should follow up with MRSA screen.
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