ID Lecture 17: Pharmacokinetics of Antibiotics w/ Emphasis on Aminoglycosides and Vancomycin | Quizlet

One compartment model

drug undergoes absorption into the blood at a rate constant Ka and elimination at a constant Ke

Two compartment model

Drugs are absorbed into the central compartment (blood), distributed from the central compartment to the peripheral compartment (tissues), and eliminated from the central compartment

How many half lives does it take to achieve steady state?

3-5

Are Aminoglycosides concentration or time dependent?

Concentration dependent

Do Aminoglycosides have a post antibiotic effect?

yes

Half life of Aminoglycosides

1.5-3 hours (~2)

How are Aminoglycosides eliminated?

>90% excreted unchanged via glomerular filtration

What is the volume of distribution of Aminoglycosides?

0.26L/kg

Aminoglycosides are considered to be what?

water soluble

What peak and trough concentrations of Gentamicin, Tobramicin, or Netilmicin do we see ototoxicity or nephrotoxicity?

Peak: >12-14

Trough: >2-3

What peak and trough concentrations of Amikacin do we see ototoxicity or nephrotoxicity?

Peak: >35-40

Trough: >10

Therapeutic Drug Monitoring

The process of measuring drug levels to identify a patient's drug exposure and to allow adjustment of dosages with the goals of maximizing therapeutic effects and minimizing toxicity.

IBW equation

Males = 50+ (2.3) (height - 60)

Females: 45 +(2.3) (height - 60)

Male Cockgroft-Gault Equation

Conventional dosing of Aminoglycosides

reduced doses administered frequently and by using PK parameters to determine dosing to achieve target peak and trough values

Extended spectrum dosing of Aminoglycosides

Hartford Nomogram is typically used to determine this dosing regimen

Hartford Nomogram

taking a single random blood sample from a patient to determine dosing of Aminoglycosides

Fixed dose of 4-7mg/kg IBW

When should sampling be done for TDM?

1 hour after the start of infusion

30 mins after infusion if infusion time >40 minutes

Cmin measurements should be taken before the start of the next dose

What describes the PK of Vancomycin?

2-3 compartment body model

What is the half life of Vancomycin?

~8 hours

What is the clearance of Vancomycin?

nearly the same a CrCl (primary renally eliminated)

What are the Vancomycin dosing guidelines?

25-35 mg/kg in non-obese patients

20-25 mg/kg for obese patients

What is the maximum loading dose for Vancomycin?

3 grams

How long are Vancomycin infusions?

Typically 2-3 hours

What is Vancomycin's volume of distribution?

0.7 L/kg

What is the desired peak and trough concentrations of Vancomycin?

Peak: 25-40 mg/L

Trough: 5-15 mg/L