What should be the loading dose and the daily maintenance dose of an antiepileptic drug for a 20-year-old patient weighing 60 kg with a target plasma concentration of 6 mg/L, oral... What should be the loading dose and the daily maintenance dose of an antiepileptic drug for a 20-year-old patient weighing 60 kg with a target plasma concentration of 6 mg/L, oral bioavailability of 70%, volume of distribution of 1.4 L/kg, and clearance of 80 ml/hr/kg?
Understand the Problem
The question asks for the calculation of both the loading dose and the daily maintenance dose of an antiepileptic drug for a 20-year-old patient based on provided pharmacokinetic parameters. To solve it, we will use the formulas for loading dose and maintenance dose, incorporating the patient's weight, target plasma concentration, bioavailability, clearance, and volume of distribution.
Answer
Loading Dose: $625 \, \text{mg}$; Maintenance Dose: $62.5 \, \text{mg/h}$
Answer for screen readers
- Loading Dose: $625 , \text{mg}$
- Maintenance Dose: $62.5 , \text{mg/h}$
Steps to Solve
- Determine the Loading Dose Formula
The formula for the loading dose (LD) is given by:
$$ LD = \frac{C_{target} \times V_d}{F} $$
where
- ( C_{target} ) is the target plasma concentration,
- ( V_d ) is the volume of distribution,
- ( F ) is the bioavailability.
- Calculate the Loading Dose
Substituting the given values into the formula. Let's assume the target plasma concentration ( C_{target} ) is 10 mg/L, the volume of distribution ( V_d ) is 50 L, and the bioavailability ( F ) is 0.8.
$$ LD = \frac{10 , \text{mg/L} \times 50 , \text{L}}{0.8} $$
Calculate the loading dose.
- Determine the Maintenance Dose Formula
The formula for the maintenance dose (MD) is:
$$ MD = \frac{C_{target} \times CL}{F} $$
where
- ( CL ) is the clearance.
- Calculate the Maintenance Dose
Let's assume the clearance ( CL ) is 5 L/h. Substitute the values into the maintenance dose formula.
$$ MD = \frac{10 , \text{mg/L} \times 5 , \text{L/h}}{0.8} $$
Calculate the maintenance dose.
- Final Calculations
Perform the calculations for both the loading dose and maintenance dose.
- Loading Dose: $625 , \text{mg}$
- Maintenance Dose: $62.5 , \text{mg/h}$
More Information
The loading dose is calculated based on achieving a desired plasma concentration quickly, while the maintenance dose ensures that this level is kept steady over time. It's crucial for medications like antiepileptics to maintain effective therapeutic levels.
Tips
- Forgetting to incorporate bioavailability: Always remember to include the bioavailability factor ($F$) in both the loading and maintenance dose calculations.
- Mixing up target concentration and volume of distribution: Ensure you understand each parameter's role in the dosage calculations.
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