Aminoglycoside Pharmacokinetics and Pharmacodynamics

Non Steady State Dosing

Questions provided by Michele Splinter, Pharm.D.

You are asked to revise dosing tobramycin therapy in a pulmonary patient who has pneumonia secondary to Klebsiella pneumoniae. The patient is also receiving ceftazidime 2 g every 8 hours.

Patient characteristics
Age: 84 yrGender: maleWeight: 50.5 kght: 70 in
Scr: 1.59 mg/dLOrganism MIC 0.5 mg/L

Based on the following doses and serum concentrations, calculate the following: kel, t1/2, Vd, CL, infusion dose (down to the nearest 10 mg) over 1 hr, dosing interval (up to the nearest 12 hr), projected Cpmaxss and Cpminss with target Cpmaxss = 8 mg/L and Cpminss = less than 1 mg/L.

The Data
DateTimeDosageInfusion DurationSerum Concentration
09/17/15220080 mg1 hr 
09/18/15100080 mg1 hr 
09/18/15220080 mg1 hr 
09/19/150950  3.54 mg/L
09/19/15100080 mg1 hr 
09/19/151230  10.46 mg/L
09/19/152130  4.42 mg/L

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Some Equations:

IBW equation (male)
Equation 27.4.1 IBW for Male Patients

IBW equation (female)
Equation 27.4.2 IBW for Female Patients

Creatine Clearance C-G Equation
Equation 27.4.3 Creatinine Clearance (Cockcroft-Gault Equation)

Volume of Distribution
Equation 27.4.4 Apparent Volume of Distribution, Vd

Dosing Interval
Equation 27.4.5 Dosing Interval, τ

Loading Dose
Equation 27.4.6 Loading Dose

Maintenance Dose
Equation 27.4.7 Maintenance Dose

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