# Multiple Oral - Example Calculations

Question 1. A drug is to be given by multiple oral doses every 3 hr. After consideration of the patient's clinical condition it is decided that the average drug concentrations should be maintained at 9 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 0.59 and the absorption rate constant is 1.35 hr-1. The kel and V for this drug in this patient are 0.131 hr-1 and 46.4 L, respectively. Calculate the dose that will achieve this average concentration of 9 mg/L.
Question 2. A drug was given by multiple oral doses of 25 mg every 6 hr. Assume a one compartment linear model applies to this drug in this concentration range. For this dosage form and patient the bioavailability is 0.8 and the absorption rate constant is 2.34 hr-1. The kel and V for this drug in this patient (88.4 kg) are 0.258 hr-1 and 0.52 L/kg, respectively. Calculate the average drug concentration.
Question 3. A drug has been given by multiple oral dose of 75 mg every 6 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 (100.9 kg) are 5.2 hr and 0.4 L/kg, respectively. For this dosage form and patient the bioavailability is 0.81 and the absorption rate constant is 2.69 hr-1. Calculate the expected Cpaverage, Cpmin value and a 'very' approximate Cpmax 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 Equation 26.1.2 Minimum Drug Concentration at Steady State after Multiple Oral Doses

If ka >> kel then ka/(ka-kel) approaches 1. Equation 26.1.3 Minimum Drug Concentration at Steady State after Multiple Oral Doses

Estimate, very approximately, Cpmax Equation 26.1.4 Approximate value of Cpmax Equation 26.1.5 Average Drug Concentration, Cp(bar)

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