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

Sept 6: Dosing

ID: AIA is a 30 yo female [163cm (5 feet 4 inches), 66.3 kg] admitted on for meningitis (Listeria).

ID consult – orders to:

  • Discontinue dexamethasone, acyclovir, ceftriaxone and vancomycin
  • Continue Ampicillin 2g IV Q4H x 20 days
  • Start Gentamicin 100mg IV Q8H x 5 days – Pharmacy to dose

s/o:
4 day history of severe headache, neck pain, diffuse myalgias, multiple episodes of emesis throughout the day, mild sore throat and rhinorrhea.
x cough x photophobia x fevers/chills

Sept 6/2016
Vitals: Temp 36.4,  BP 98/59,  HR 69,  RR 18,  O2Sats 98% RA

Labs:
↓ WBC (Sept 5: 11.1 → Sept 6: 9.5)
eGFR: >120mL/min/1.73m2 (stable)
↓ sCr: (Sept 4: 49  → Sept 5: 40 → Sept 6: 35)
Calculated CrCl (CG): 217.46 mL/min

Micro:

  • 02/09: Lumbar puncture – CSF: No growth
    CSF WBC: 471 (H), Cloudy appearance (Tubes 1+2), CSF RBC 12(H), Neutrophils 6%, Glucose 2.5 (N), LDH 31 (H), Total Protein 2559 (H)
  • 02/09: Lumbar puncture – CSF: Viral Cx, Fungal Cx, Mycobacterial Cx Pending
  • 03/09: Blood Cx: No growth after 48 hours incubation
  • 04/09: Lumbar puncture – CSF: Pending
  • Sent cultures off-site for PCR: Listeria Meningitis

A/Checklist:

  1. Is this drug indicated?: Yes
    IDSA 2004 Guidelines: Aminoglycosides could be considered in addition to Ampicillin or Penicillin G for Listeria monocytogenes
    Sanford’s: Listeria meningitis: Ampicillin 2gm IV Q4H + gentamicin 2mg/kg IV loading dose then 1.7mg/kg IV Q8H
    Treat for 21 days.
    ID consult – determined that gentamicin should be added on for synergy
  2. Is the dose appropriate?: Yes
    Usual conventional dose is 1-2mg/kg/dose every 8 hours (5mg/kg/day divided every 8 hours falls under this range). Sanford’s provides a dose of LD of 2mg/kg IV then 1.7mg/kg IV Q8H.
    LD determined to be unnecessary by ID.
    ? Duration of 5 days for synergy
  3. Is the dosing interval appropriate?: Yes
    based on sCr and age, every 8 hours is appropriate

Calculation:
IBW (kg) = 45kg + (2.3*4) = 54.2 kg
DBW (kg) = IBW + 0.4*(66.3-54.2) = 59.04kg
ABW is 22% greater (<25%) than IBW → use IBW to calculate dose (if >25%, use DBW)

5mg/kg/day * 54.2kg = 271mg/day → ~90mg IV Q8H

  • Gentamicin is available as 40 mg/mL solution (80 mg/2 mL vial) and premixed minibag (60 mg/50 mL NS, 80 mg/50 mL NS, 100 mg/100 mL NS, 120 mg/100 mL NS)
    ∴ ↑ to 100mg IV Q8H

100mg IV Q8H

  • Falls within 1-2mg/kg IV Q8H conventional dose (54.2-108.4mg IV)

P: As discussed with MD,

  1. Gentamicin 100mg IV Q8H x 5 days (1st dose given at 1715)
    ∴ dosing times – 1715, 0115, 0915
  2. Gentamicin Peak Concentration  (Target: 8-10 mg/L for meningitis)
    – 30 mins post 30 min infusion of 0915 dose (3rd dose)
  3. Gentamicin Trough Concentration (Target: 1-1.2mg/L for synergy)
    – 30 mins prior to 1715 dose (4th dose)

Dosing times slightly changed and 2nd, 3rd doses wer given at 0030 and 700

Orders:

  1. Please change gentamicin dosing times to 700, 1500, 2300
  2. Gentamicin peak concentration at 1600 today (30 mins after the 30 min infusion ends)
  3. Gentamicin trough concentration at 2300 today (30 mins before the 2300 dose)

Sept 8:

Vitals: Temp 36.4, BP 101/65, HR 69, RR 18, O2Sats: 97% RA (stable)

Labs:
WBC (Sept 7: 9.5 → Sept 8: 9.1)
↑ sCr (Sept 7: 42 → Sept 8: 56)
Calculated CrCl (CG): 135.91 mL/min

Micro:

  • 07/09: Lumbar Puncture – Preliminary: No Growth
    CSF WBC: 293 (H) ↓, Appearance Clear/Colourless (on all tubes), CSF Glucose 4.7 (H), Total Protein: 213 (N)

Levels:

  • Gentamicin Peak: 4.9 mg/L
  • Gentamicin Trough: < 0.5 mg/L

A/Checklist:

  1. Is this drug indicated?: Yes
    See above.
  2. Is the dose appropriate?: Yes
    See above.
  3. Is the dosing interval appropriate?: Yes
    Stable renal function, Q8H still appropriate
  4. Are all the doses given on time?: Yes
  5. Was the level drawn at steady state?: Yes
  6. How is the patient doing?:
    Overall, patient is clinically improving on his antibiotic therapy.
  7. Any side effects?: Renal function is stable. No changes in hearing.

P:
As her lumbar puncture has significantly improved, her gentamicin therapy will only be continued until discharge (likely only 3 days therapy total). Another serum drug concentration is not required.


Resources for AG:

 

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