PHARMACY TECHNICIAN CHAPTER NINETEEN

Pharmacodynamics The study of the biochemical and physiologic effects of drugs The study of the mechanisms of action of drugs The study of how drugs affect the body

Pharmacokinetics The study of the time course of a drug and its metabolites in the body following drug administration The study of how the body handles drugs The study of how the body changes a drug from its original form into something that the body can use The study of how the body secretes and eliminates metabolized drugs The study of how the body affects drugs

Receptor site.

Receptors Most drugs affect the body by interacting with specific drug receptors This process is likened to a lock and key Each cell in the body has receptors (“locks”) requiring a specific “key” to produce an effect Specific drugs are developed to “unlock” certain receptors in the body, producing the desired effect

Mechanism of Action Refers to how a drug works and produces its desirable (and sometimes undesirable) effects Key factor is the drug’s ability to bind to receptor sites Once a drug binds to a receptor site, it may stimulate or prevent cellular activity Agonist—drug binds to receptor sites and causes some action to occur Antagonist—drug binds to receptor sites and prevents other chemicals or drugs from affecting the cell

Example of agonistic and antagonistic drug action.

Drug Absorption How a drug enters the body and eventually enters the bloodstream Largely dependent upon the type of the drug and reason for use Based on route of administration (oral, parenteral, etc.)

Drug Distribution Once absorbed, drug is distributed throughout the body by circulatory system Some of the drug binds to plasma proteins Some of the drug “floats” through the bloodstream “Floating” drug may interact with receptors, producing therapeutic effect

Drug Metabolization Once distributed, drug is broken down or “metabolized” for use Typically but not always metabolized in the liver The body metabolizes or “digests” drugs into usable products that cause desired effects

Drug Excretion After being metabolized and used, drug becomes a waste product Must be cleared from the body Ideally, drugs metabolize and are cleared at a steady rate Steady metabolism and excretion ensure that the patient has a consistent amount of medication in the body

The path.

Solubility The ability of a material to dissolve in a given medium Water-soluble drugs dissolve in the presence of water Fat- (or lipid-) soluble drugs dissolve in the presence of fats (lipids) Drug solubility affects the ability of the body to absorb the medication Fat-soluble drugs are very quickly absorbed into the body Water-soluble drugs are usually only partially soluble, preventing the product from being absorbed too rapidly

Bioavailability The amount of drug that is available for use Determined by the body’s ability to absorb the drug Several factors influence absorption: Solubility of the medication How the drug is manufactured Presence of different buffers Salt forms vs. nonsalt forms Rate and volume of distribution Clearance from the body

Addiction Defined as both a psychological and a physiological dependency Specific withdrawal symptoms must present following abrupt change in use Some signs of addictive behavior include: Absorbing focus on the substance Increased tolerance Painful withdrawal

Medications That May Cause Problems When Mixed with Alcohol