Aminoglycoside Pharmacokinetics and Pharmacodynamics

Steady State Dosing

Questions provided by Michele Splinter, Pharm.D.

A 66 y/o male is found to have sepsis secondary to an urinary tract infection, Escherichia coli, MIC = 0.25 mg/L. He is started on gentamicin.

Patient data is as follows: Ht = 70 in. Wt = 79.1 kg. Scr = 2.12 mg/dL.

The following represent the dosing history:

Based on the following doses and serum concentrations, calculate the following: ke, t1/2, Vd, CL, infusion dose (round down to the nearest 10 mg) over 1 hr, dosing interval (round up to the nearest 12 hr), projected Cpmaxss and Cpminss with target Cpmaxss = 9 mg/L and Cpminss = less than 1 mg/L and time from the last sample to starting the next dose (to the nearest hour).

The Data
DateTimeDosageInfusion DurationSerum Concentration
09/17/150900140 mg1 hr 
09/17/152100140 mg1 hr 
09/18/150900140 mg1 hr 
09/18/152100140 mg1 hr 
09/19/150900140 mg1 hr 
09/19/152059  3.3 mg/L
09/19/152100140 mg1 hr 
09/19/152300  11.09 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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