GH is a 63 year old female who was admitted to the medical ward after presenting to the emergency department with a 3-day history of worsening shortness of breath, subjective fever, cough, and chest pain when coughing. She was discharged 4 days ago after an episode of DKA due to nonadherence with insulin therapy for her type I diabetes. 

Labs/vitals:

Ht: 5’8”

Wt: 182 lbs

BP: 133/87 mmHg

HR: 97 bpm

RR: 20 breaths per minute

Temp: 101.6 F

WBC: 11,300 µL

SCr: 1.1 mg/dL (baseline of 1.0 mg/dL)

CXR: bilateral infiltrates

GH was diagnosed with hospital-acquired pneumonia and started on vancomycin 1250 mg IV q12h, and piperacillin/tazobactam 4.5 gm IV q6h.  Her trough is 23 mg/L before her 5th dose.  How would you adjust GH’s dose to target a trough of 15-20 mcg/mL? 

A. 750 mg IV q12h

B. 1000 mg IV q12h

C. 1500 mg IV q12h

D. 2750 mg IV daily

Answer with rationale:

Vancomycin is commonly used in the hospital setting as both empiric and definitive treatment of nosocomial bacterial infections. It is most commonly used when methicillin-resistant Staphylococcus aureus (MRSA) is suspected or confirmed. Vancomycin can be dosed and monitoring using a trough-based approach or an area under the curve (AUC)-based approach.  Increasing numbers of hospitals are using an AUC-based dosing and monitoring approach due to some studies demonstrating less nephrotoxicity compared to trough-based approaches and the current ASHP/IDSA guidelines no longer recommending a trough-based approach.  However, many institutions still use a trough-based approach for vancomycin as AUC-based approaches due to ideally a requirement for dose optimization software.

The easiest solution to our problem considering there is no second level to calculate a specific elimination rate constant (k) and half-life would be to do a simple ratio and proportion using her total dose of vancomycin of 2500mg daily and current trough level of 23 mcg/mL. Keep in mind that mg/L and mcg/mL are the same and interchangeable.  Because the trough was drawn prior to the 5th dose and the patient's renal function appears to be stable and similar to baseline, a ratio and proportion approach is reasonable. 

Answer A is incorrect.  A vancomycin regimen of 750 mg IV q12h gives a total daily dose of 1500 mg which does not meet the required total daily dose needed to achieve a trough of 15-20 mcg/mL. The approximate level using a ratio proportion where 2500mg/23mcg/mL = 1500mg/x would give 13.8 mcg/mL which is below the goal level. 

Answer B is correct.  A vancomycin regimen of 1000 mg IV q12h would give a total daily dose of 2000 mg. When doing ratio and proportion of 2500mg/23 mcg/mL = 2000mg/x would give a trough of 18.4 mcg/mL which is within the goal range. 

Answer C is incorrect.  This regimen would increase the trough level as it is a higher overall dose than the current regimen and therefore is incorrect. 

Answer D is incorrect. A vancomycin regimen of 2750 mg IV daily has a total daily dose greater than that of the current regimen even though it is once daily. Therefore this would not be the most appropriate compared to answer B. 

Brands/generics covered:

Vancocin (vancomycin), Zosyn (piperacillin/tazobactam)

Naplex content domains covered:

1.C

Pharmaceutical calculations