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UF PHA 5127 - Case Study VI Questions

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Case Study VI Questions PHA 5127 – Fall 2006 Question 1. A patient is given a 250 mg immediate-release theophylline tablet (Tablet A). A week later, the same patient is given a 250 mg sustained-release theophylline tablet (Tablet B). The tablets follow a one-compartmental model and have a first-order absorption and elimination. The bioavailability is 90% for both tablets. The plasma drug concentration-time profiles for both tablets are as follows: Plasma Drug Conc. (mg/L) Time (hrs) Tablet A Tablet B 0.5 2.52 0.11 1 4.04 0.21 2 5.36 0.39 3 5.56 0.55 6 4.47 0.90 12 2.38 1.23 18 1.26 1.28 24 0.66 1.20 36 0.18 0.93 48 0.68 72 0.34 96 0.16 Determine ke, ka, and Vd for both tablets. Question 2. For a one-compartment, first-order absorption and elimination, multiple oral administration, state whether the follows parameters will increase, decrease, or no change. (Hint: Use simulation files to answer this question) Css,avgFluctuation, F tmaxCL in halved τ is doubled F is halved ka is doubled Question 3. A patient is to be put on a continuous iv infusion. Devise a dosing regimen (including a loading dose) for the patient. (Assume the drug to follow a one-compartment model and has a first-order elimination). Following are the properties of the drug and the patient: Patient Weight 130 lbs Drug’s half-life (t1/2) 3 hrs Volume of distribution (Vd) 1.8 L/kg Desired average steady state concentration (Css) 7.5 μg/mL 1Case Study VI Questions PHA 5127 – Fall 2006 Question 4. True and False 1. The absorption rate constant (ka) is always larger than the elimination rate constant (ke). 2. The oral bioavailiability of a very lipophilic, neutral, high extraction drug (showing linear pharmacokinetics) after oral administration of a tablet is significantly affected by the liver blood flow, the plasma protein binding, and the dissolution rate. 3. Cpmax and tmax are sufficient to assess bioequivalency. Question 5. Fill in the blanks 1. If ka << ke for a drug administered orally (typical of a sustained release formulation), the drug is said to follow “________________” kinetics. 2. The method of residuals, also known as “________________”, is means by which ke and ka may be separated and calculated when oral data is analyzed. 3. The ________________ is the fraction of an oral dose that enters systemic circulation after administration. 4. Once a constant rate infusion is started, the time required to reach steady state levels is dependent on the _________________ (multiplied by 5) of the drug.


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