PHARMACOLOGY CH. 5 Pharmacokinetics

Pharmacokinetics explained… How the body handles the drugs that are administered to it, how the drugs are changed from the original form into something that the body can use and how they are secreted from the body and eliminated.

Plasma Concentration Once absorption is complete, the level and concentration of the drug in the body is the plasma concentration The affinity of a drug effects plasma concentration The bloodstream is the “vehicle” which will deliver the drug to the parts of the body where the drug will have an effect

Drug Absorption How the drug enters the body Dependent on the type of drug, how it is designed and the reason for the use. Liquids are more readily absorbed than tablets or capsules because they are already “broken down” Cell membranes contain both lipids and proteins This makes them semi-permeable; allows and prevents the entrance and exit of materials. Other than IV and intra-arterial(straight into the bloodstream), a certain amount of time is required before they start to work in the body

Absorption cont. Absorption does not always go by way of the stomach to the blood stream. Example= Inhalations Also rectal and vaginal medications are very slow release rates; they are considered topical applications Topical medications are not necessarily absorbed through the skin into the bloodstream

Absorption Injections by-pass the absorption phase-results are achieved quicker Inhalations enter the bloodstream via the alveoli Rectal and vaginal administrations are considered topical and have the slowest rate of absorption

Drug Distribution Using the circulatory system (heart and bloodstream), the body distributed the molecules Some drugs bind to plasma proteins Some drugs “float” through the bloodstream and interact with receptors

Membrane Transport Mechanisms The way in which drugs get from outside of the cell into the cell

Diffusion Passive Diffusion-across the cell membrane. -is another term for passive transport The force that permits the substance to be transported from outside the cell into the cell depends on the concentration difference Generally, move from high to low concentration Facilitated Diffusion- carrier protein permits molecules to pass through the certain parts of the cell

Active Transport Costs the cell energy Also uses a concentration gradient to move substances into and out of the cell

Pinocytosis Cell engulfs the substance, thereby allowing the substance to enter the cell Most drugs and foods are absorbed at a much faster rate in the small intestines than in the stomach.

Solubility The more lipid-soluble the drug, the faster the drug will be absorbed into the cell The PDR( Physician’s Desk Reference) defines drugs in terms of their chemical structure; also brief descriptions of drugs make up including drug solubility For a drug to be absorbed via the gastrointestinal tract, the drug must be both water and lipid soluble

Ionization The charge of a molecule Bioavailability is what? If a chemical is ionized, it will not readily cross the cell membrane barrier Un- ionized drugs are more readily absorbed into the cell

SSRI

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