Chapter 1 Pharmacokinetics

1-1 Schematic representation of the fate of a drug in the body (pharmacokinetics). Orange arrows indicate passage of drug through the body (intake to output). Orange circles represent drug molecules. RBC, red blood cell.

1-2 Overview of various types of membrane-transport mechanisms. Open circles represent molecules that are moving down their electrochemical gradient by simple or facilitated diffusion. Shaded circles represent molecules that are moving against their electrochemical gradient, which requires an input of cellular energy by transport. Primary active transport is unidirectional and utilizes pumps, while secondary active transport takes place by cotransport proteins.
(From Pelley JW and Goljan EF. Rapid Review Biochemistry, 2nd ed. Philadelphia, Mosby, 2007, Figure 3-1.)
Drugs given intramuscularly are absorbed much faster than those given subcutaneously.
Absorbing surface of intestine is much greater than stomach.

1-3 Examples of the ionization of a weak organic acid (salicylate, top) and a weak organic base (amphetamine, bottom).
where HA = weak acid; H+ = proton; A− = anion
Weak organic acids pass through membranes best in acidic environments.
Weak organic bases pass through membranes best in basic environments.
Bioavailability depends on the extent of an orally administered drug getting into the systemic circulation
Slow release formulations are designed to extend the time it takes a drug to be absorbed so that the drug can be administered less frequently.
TABLE 1-1 Routes of Administration
Route | Advantages | Disadvantages |
---|---|---|
Enteral | ||
Oral |
Destruction of drug by enzymes or low pH (e.g., peptides, proteins, penicillins) Poor absorption of large and charged particles
| |
Rectal | ||
Sublingual/buccal | Rapid absorption Avoids first-pass metabolism | Absorption of only small amounts (e.g., nitroglycerin) |
Parenteral | ||
Intravenous | ||
Intramuscular |
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