1. VANCO Dr. Muslim Suardi Faculty of Pharmacy University of Andalas 2013

2. Example JM is a 50yo, 70-kg (5 ft 10 in) male with a methicillin-resistant S. aureus (MRSA) wound infection. His current SCr is 0.9 mg/dL, & it has been stable over the last 5d since admission. Compute a VANCO dose for this patient.

3. 1. Estimate the CrCl This patient has a stable Scr & is not obese. The Cockcroft-Gault Eq. can be used to estimate CrCl. CrClest = [(140−age)BW] / (72*SCr) = [(140−50 y)70 kg] / (72*0.9 mg/dL) = 97 mL/min.

4. 2. Estimate VANCO Cl VANCO Cl vs CrCl relationship is used to estimate the VANCO Cl for this patient. Cl = 0.695(CrCl) + 0.05 = 0.695[(97mL/min)/70kg] + 0.05 = 1.015 mL/min/kg.

5. 3. Estimate VANCO Vd Ẋ Vd for VANCO is 0.7 L/kg: V = 0.7 L/kg*70 kg = 49 L.

6. 4. Estimate Vanco ke & t1/2 Ke= Cl/V = (1.015 mL/min/kg*60 min/h) / (0.7L/kg*1000 mL/L) = 0.087 h –1 t1/2= 0.693 / ke = 0.693 / 0.087 h –1 = 8 h

7. 5. Choose Desired SS Serum Concentrations Patients with S. aureus wound infections need to be carefully assessed. This patient did not appear to be in acute distress, with a normal temperature & slightly elevated WBC count. The wound was warm & red with a slight amount of purulent discharge. Because the infection was localized to the wound area, a Cssmin = 7 µg/mL & Cssmax = 20µg/mL were chosen

8. 6. Use iv Bolus Eq. to Compute Dose (Table 5-2) Calculate required dosage τ τ = (ln Cssmax − ln Cssmin) / ke = (ln 20µg/mL − ln 7 µg/mL) / 0.087 h –1 = 12.1 h Dosage intervals, τ, should be rounded to clinically acceptable intervals of 12, 18, 24, 36, 48, 72h, & multiples of 24h thereafter, whenever possible. In this case, τ would be rounded to 12h.

9. 6. Continued Calculate required dose (D): D = Cssmax V(1− e −ke τ ) = 20 mg/L*49 L [1 − e −(0.087 h–1)(12 h) ] = 635 mg VANCO doses should be rounded to the nearest 100–250 mg. This dose would be rounded to 750 mg. The prescribed MD would be 750 mg every 12h