# Aminoglycoside Pharmacokinetics and Pharmacodynamics

# Steady State Dosing

## Questions provided by Michele Splinter, Pharm.D.

A 65 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 = 69 in. Wt = 70.5 kg. Scr = 1.33 mg/dL.

The following represent the dosing history:

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

**The Data**
Date | Time | Dosage | Infusion Duration | Serum Concentration |

09/17/15 | 0900 | 180 mg | 1 hr | |

09/17/15 | 2100 | 180 mg | 1 hr | |

09/18/15 | 0900 | 180 mg | 1 hr | |

09/18/15 | 2100 | 180 mg | 1 hr | |

09/19/15 | 0900 | 180 mg | 1 hr | |

09/19/15 | 2059 | | | 3.28 mg/L |

09/19/15 | 2100 | 180 mg | 1 hr | |

09/19/15 | 2335 | | | 9.08 mg/L |

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**Some Equations:**

Equation 27.4.1 IBW for Male Patients

Equation 27.4.2 IBW for Female Patients

Equation 27.4.3 Creatinine Clearance (Cockcroft-Gault Equation)

Equation 27.4.4 Apparent Volume of Distribution, Vd

Equation 27.4.5 Dosing Interval, τ

Equation 27.4.6 Loading Dose

Equation 27.4.7 Maintenance Dose

Last update: Sat 20 Apr 2019 05:52:22 pm

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