Multiple Oral - Example Calculations

Question 1. A drug is to be given by multiple oral doses every 8 hr. After consideration of the patient's clinical condition it is decided that the average drug concentrations should be maintained at 30 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 0.83 and the absorption rate constant is 2.13 hr-1. The kel and V for this drug in this patient (70.6 kg) are 0.211 hr-1 and 0.54 L/kg, respectively. Calculate the dose that will achieve this average concentration of 30 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 0.87 and the absorption rate constant is 1.49 hr-1. The half-life and V for this drug in this patient are 4 hr and 37.8 L, respectively. Calculate the average drug concentration.
Question 3. A drug has been given by multiple oral dose of 25 mg every 12 hours. Assume a one compartment linear model applies to this drug in this concentration range. The half-life and V for this drug in this patient (49.8 kg) are 2.7 hr and 1.05 L/kg, respectively. For this dosage form and patient the bioavailability is 0.88. Assume that e-ka • τ approaches 0 and ka >> kel. Calculate the expected Cpaverage, Cpmin value and a 'very' approximate Cpmax value at steady state.


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Some Equations:

Cp(min) no assumptions

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, Cpmax

Cp(max) very approximately

Equation 26.1.4 Approximate value of Cpmax

Cp(average)

Equation 26.1.5 Average Drug Concentration, Cp(bar)


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