Common Pharmacokinetics

Common Pharmacokinetics is a topic covered in the Pocket ICU Management.

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First Things First (assess & treat for the following)

Pharmacokinetics is a description of the absorption, distribution, metabolism & excretion of a drug.

  • Common pharmacokinetic abbreviations
    • Ro: dose/(amount of time the drug infused over)
    • Vd: volume of distribution
    • ke: elimination rate constant
    • T1/2: half-life
    • ti: amount of time the drug infused over
    • ∆t: time between the level should have been drawn and the drawn level
    • τ: dosing interval
  • Before you monitor a medication, you have to dose it. Below are listed some commonly used agents that require pharmacokinetic monitoring that need weight-based dosing.
  • Aminoglycosides (Conventional Dosing)

    Indication

    Gentamicin and Tobramycin Dose

    Amikacin Dose

    Gram-positive synergy

    1 mg/kg (gentamicin only)

    NA

    Urinary tract infection

    1-1.3 mg/kg

    5-6 mg/kg

    Bacteremia/skin and soft tissue infection

    1.5-1.7 mg/kg

    6 mg/kg

    Pneumonia/septic shock

    1.7-2.5 mg/kg

    7-8 mg/kg

    Cystic fibrosis

    2-3 mg/kg

    7-8 mg/kg

  • Aminoglycoside dosing weight: IBW + 0.4 (TBW - IBW)
    • Ideal Body Weight (IBW) for men in kg: 50 + 2.3 (# of inches above 5 ft)
    • Ideal Body Weight for women in kg: 45.5 + 2.3 (# of inches above 5 ft)
    • Total Body Weight (TBW) in kg: Patient’s actual body weight
  • Aminoglycoside dosing interval determination
    • ke: 0.00293 x Creatinine Clearance + 0.014
    • τ: ((ln (Goal Trough/Goal Peak)/ (-ke)) + ti
      • Use 8, 12, or 24 hours.
      • If >24 hours, dose intermittently based on levels.
  • Vancomycin
    • Dose
      • 15 mg/kg for most infections
      • 20 mg/kg for meningitis or pneumonia
      • Use TBW in most patients.
        • Use Adjusted Body Weight (ABW) in obese patients
        • ABC = IBW + 0.2 (TBW - IBW)
    • Dosing Interval
      • k: 0.00083 x Creatinine Clearance + 0.004
      • τ: ((ln (Goal Trough/Goal Peak)/ (-k)) + ti
      • Use 8, 12, 24, or 48 hours.
      • If >48 hours, dose intermittently based on levels.
  • Phenytoin
    • Loading dose
      • IV: 20 mg/kg
      • PO: 20 mg/kg given in doses of 200-400 mg q2h
    • Maintenance dose
      • 5-6 mg/kg/day
      • Do not give single dose >400 mg; divide it and give bid.

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Last updated: April 14, 2010