Extent of Absorption

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Absorption and Bioavailability Irrespective of the reason that is responsible for the incomplete absorption of the chemical as the parent compound, it is essential that there is a parameter which defines the extent of transfer of the intact chemical from the site of administration into the general circulation. This parameter is the bioavailability, , which is simply the fraction of the dose administered that reaches the general circulation as the parent compound. (The term bioavailability is perhaps the most misused of all kinetic parameters and is sometimes used incorrectly in a general sense as the amount of drug available specifically to the site of toxicity.) ٢١
Calculation of Bioavailability The fraction absorbed as the intact compound or bioavailability (F)) is determined by comparison with intravenous (i.v( i.v.) .) dosing (where F = 1 by definition). The bioavailability can be determined from the area under the plasma concentration–time time curve (AUC) of the parent compound , or the percentage dose excreted in urine as the parent compound, i.e. for an oral dose: ٢٢
Page 1 and 2: Extent of Absorption The extent of
Page 3: ٢٠
Page 7 and 8: 2. Distribution Distribution is the
Page 9 and 10: The rate of distribution is indicat
Page 11 and 12: 4. Effect of pH The pH of the blood
Page 13 and 14: Lipid-soluble compounds frequently
Page 15 and 16: The parameter used to reflect the e
Page 17 and 18: when a chemical shows a more extens
Page 19 and 20: Elimination The parameter most comm
Page 21 and 22: The mechanisms of elimination depen
Page 23 and 24: If a chemical undergoes metabolic a
Page 25 and 26: The best measure of the ability of
Page 27 and 28: It is measured from the total amoun
Page 29 and 30: Measurement of dose/AUC for an oral
Page 31 and 32: Summary of Toxicokinetic Parameters
Page 33 and 34: • Example - If you know that 3 mg
Page 35 and 36: • Clearance (Cl( Cl) • A ratio
Page 37 and 38: • Half-life life (t 1/2 1/2 ) •
Page 39 and 40: • Classical toxicokinetics • On
Page 41 and 42: • Two compartment model • The e
Page 43 and 44: Chronic Administration The kinetic
Page 45 and 46: ٦٢
Page 47 and 48: Because the plasma and therefore ti
Page 49 and 50: In simple mathematical terms this m
Page 51 and 52: • Example: Cholinesterase is an e
Page 53 and 54: • Types of Biotransformation Reac
Page 55 and 56:
• Anything that affects the activ
Page 57 and 58:
• Phase II reactions • Involve
Page 59 and 60:
• Acetylation • Replacement of
Page 61 and 62:
• Significance of Biotransformati
Page 63 and 64:
• Another good example - metaboli
Page 65 and 66:
• Induction - an increase in the
Page 67 and 68:
• Inhibition - a decrease in the
Page 69 and 70:
Factors affecting metabolism 1. Age
Page 71 and 72:
4. Excretion • Excretion • The
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Extent of Absorption

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