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 bodyDependent 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 proteinsThis 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= InhalationsAlso 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 proteinsSome 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 energyAlso 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 moleculeBioavailability is what?If a chemical is ionized, it will not readily

cross the cell membrane barrierUn- ionized drugs are more readily absorbed

into the cell

SSRI

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