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)
Gentamicin and Tobramycin Dose
1 mg/kg (gentamicin only)
Urinary tract infection
Bacteremia/skin and soft tissue infection
- 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.
- 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.
- 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.
- Loading dose
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