Multiple Oral - Example Calculations

Question 1. A drug is to be given by multiple oral doses every 12 hr. After consideration of the patient's clinical condition it is decided that the average drug concentrations should be maintained at 4 mg/L. Assume a one compartment linear model applies to this drug in this concentration range. For this dosage form and patient the bioavailability is 0.98 and the absorption rate constant is 2.26 hr^-1. The half-life and V for this drug in this patient (47.2 kg) are 6.2 hr and 1.03 L/kg, respectively. Calculate the dose that will achieve this average concentration of 4 mg/L.

Question 2. A drug was given by multiple oral doses of 500 mg every 3 hr. Assume a one compartment linear model applies to this drug in this concentration range. For this dosage form and patient the bioavailability is 0.92 and the absorption rate constant is 3.62 hr^-1. The kel and V for this drug in this patient (77.1 kg) are 0.162 hr^-1 and 0.55 L/kg, respectively. Calculate the average drug concentration.

Question 3. A drug has been given by multiple oral dose of 30 mg every 12 hours. Assume a one compartment linear model applies to this drug in this concentration range. The kel and V for this drug in this patient (54.4 kg) are 0.278 hr and 0.49 L/kg, respectively. For this dosage form and patient the bioavailability is 0.61 and the absorption rate constant is 1.8 hr^-1. Calculate the expected Cp_average, Cp_min value and a 'very' approximate Cp_max value at steady state.

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Some Equations:

Equation 26.1.1 Minimum Drug Concentration at Steady State after Multiple Oral Doses

If e^{-ka • τ} approaches zero

Cp(min) if exp(-ka*tau) -> zero

Equation 26.1.2 Minimum Drug Concentration at Steady State after Multiple Oral Doses

If ka >> kel then ka/(ka-kel) approaches 1.

Cp(min) with ka >> kel

Equation 26.1.3 Minimum Drug Concentration at Steady State after Multiple Oral Doses

Estimate, very approximately, Cp_max

Equation 26.1.4 Approximate value of Cp_max

Cp(average)

Equation 26.1.5 Average Drug Concentration, Cp(bar)

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