Flashcards
Pharmacokinetics: absorption and distribution
Cards in this deck (5)
- 1What is bioavailability?The fraction of an orally administered drug that reaches the systemic circulation as an intact drug, taking into account both absorption across the intestinal mucosa, and metabolic degradation by enzymes encountered in the liver and intestines.
- 2What is the equation to calculate bioavailability (F)?F = amount of drug absorbed in the systemic circulation following oral administration/amount of drug absorbed when the same dose is administered intravenously
- 3How are the values for calculating bioavailability obtained?These are gathered by administering a drug orally and intravenously to the same individuals but on separate occasions, then measuring the concentration over time and plotting this graphically. The area under the curve between the minimum effective concentration and the maximum concentration achieved (hopefully well below the minimum toxic concentration) is calculated for both the oral and intravenous administrations and put into the bioavailability equation.
- 4How are the values to calculate bioavailability obtained?These are gathered by administering a drug orally and intravenously to the same individuals but on separate occasions, then measuring the concentration over time and plotting this graphically. The area under the curve between the minimum effective concentration and the maximum concentration achieved (hopefully well below the minimum toxic concentration) is calculated for both the oral and intravenous administrations and put into the bioavailability equation.
- 5Why is bioavailability not always a useful measure?Variations in enzyme activity of the gut wall or liver, as well as variations in gastric pH or intestinal motility, all affect bioavailability, and will vary greatly between individuals, as well as between healthy volunteer groups and patients with gastrointestinal or circulatory diseases. Bioavailability only relates to the total proportion of drug that reaches the systemic circulation, not the rate at which it does so. Further, the drug preparations for oral and I.V. administration are likely to be different and these physicochemical properties cannot be compared.
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- From the 20-11-13 Drugs and Disease lecture.
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- sophietevans
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