Examkin

Question

Difficulty: MediumPharmacokinetic and Pharmacodynamic Principles

An 80-kg80 \text{-kg}, 60-year-old60 \text{-year-old} male patient is undergoing treatment in the intensive care unit for severe hospital-acquired pneumonia. The clinical team initiates continuous intravenous therapy with a novel narrow-therapeutic-index antimicrobial agent. The pharmacokinetic profile of this drug in the patient indicates a volume of distribution of 0.5 L/kg0.5 \text{ L/kg} and a systemic clearance of 0.04 L/hr/kg0.04 \text{ L/hr/kg}. The desired steady-state plasma concentration of the medication is 20 mg/L20 \text{ mg/L}.

To maintain this target steady-state concentration, what should be the continuous intravenous infusion rate in mg/hr?

Answer: 64 mg/hr

Answer

64
To maintain a steady-state concentration of a drug, the rate of drug administration must equal the rate of drug elimination. The elimination rate is calculated as the product of the total systemic clearance and the target steady-state concentration. First, the total clearance is found by multiplying the weight-adjusted clearance by the patient's weight (0.04 L/hr/kg×80 kg=3.2 L/hr0.04 \text{ L/hr/kg} \times 80 \text{ kg} = 3.2 \text{ L/hr}). Then, the maintenance infusion rate is calculated by multiplying the total clearance by the target concentration (3.2 L/hr×20 mg/L=64 mg/hr3.2 \text{ L/hr} \times 20 \text{ mg/L} = 64 \text{ mg/hr}).

Step-by-Step Solution

1
Calculate the patient's total systemic clearance.
0.04 L/hr/kg×80 kg=3.2 L/hr0.04 \text{ L/hr/kg} \times 80 \text{ kg} = 3.2 \text{ L/hr}
Clearance is provided on a per-kilogram basis and must be scaled to the patient's actual body weight to determine the total drug elimination rate.
2
Calculate the continuous maintenance infusion rate.
3.2 L/hr×20 mg/L=64 mg/hr3.2 \text{ L/hr} \times 20 \text{ mg/L} = 64 \text{ mg/hr}
The maintenance dose rate is the product of clearance and the target steady-state concentration.

Key Concept

Maintenance dose rate is determined solely by the drug's clearance and the desired steady-state plasma concentration.
Rate this question

Topics

Pharmacokinetic and Pharmacodynamic Principles

More questions from this topic