Pharmacokinetics and Pharmacodynamics Chapter 2 Pharmacokinetics and Pharmacodynamics

Pharmacotherapeutics The study of how drugs are used to treat, prevent, and diagnose disease and illness Pharmacokinetics – how the body assimilates, incorporates, and eliminates a drug Pharmacodynamics – how a drug affects the body

You will be able to explain to an athlete… Why it is important to take medications as prescribed by a physician How drugs work Why drugs work How long a drug remains active What the potential drug adverse effects are Other general questions they ask

What is a Drug? A chemical that interacts with and affects living organisms to produce a biological response A drug alters physiological functions by replacing, interrupting, or potentiating existing cellular functions Primary or secondary effects

Pharmacodynamics Receptor Sites – a component of a cell to which a drug binds to produce an effect Most drugs act at specific locations in tissues or organs “lock and key” analogy (pgs 18-19) Affinity – the force that makes 2 agents bind or unite Efficacy – the capacity to elicit a response

Dose Response Threshold – lowest dose capable of producing a perceivable response Potency – amount of a drug necessary to produce a desired effect Figure 2-2 Pg 19

Determining the time response of a dose: Latency – “onset of action”, time required to produce an observable effect Maximal Effect – time required to reach peak efficacy Duration of Action – time period over which a drug produces a response after a single dose

Time Response Influenced by: Route of administration Solubility of the drug How fast the drug is distributed to action site Time it takes to be inactivated and excreted from the body

Therapeutic Index – the range in which desired effects are produced Used to determine the safety parameters of doses

Half-Life – determined by the time required to reduce by one-half the amount of the drug present in the body Drugs have different & distinct half-lives Comparison for drug elimination rates Determines frequency with which multiple doses of a drug can be safely administered Half-life does not change with the drug dose

Pharmacokinetics Absorption – speed, rate, and extent of absorption is dependant on its’ physical and chemical properties Solubility of the drug Surface area of intended site of action Specific route of administration

Enteral Oral ingestion - safest, most common, convenient, economical route of administration Taken by mouth = onset of action within 1 hour Oral mucosa – sublingual or buccal routes Vast capillary blood supply = dissolve rapidly

Enteral Preliminary passage or “first-pass metabolism” Figure 2-7 pg 24 Solutions Liquid form, syrups, elixirs Capsules and tablets Sustained-release

Parenteral Non-oral route of administration Drug delivered directly to target site Not subjected to first-pass metabolism Routes include Subcutaneous Intramuscular Intravenous Intrathecal Intra-articular

Inhalation Form of gases or fine mists Lungs: large surface area and rich blood supply = effective means of absorbing and transporting meds into blood supply rapidly Special devices propel meds onto alveolar and bronchial tissues

Topical Applied to skin or mucous membranes Difficult to reach systemic circulation Used to treat skin problems Routes Ointments Creams Transdermal patches

Pharmacokinetics Distribution – to act on a specific receptor site, the drug must pass through the different biological layers and then be transported to the site via the bloodstream Cell membrane review

Modes of transportation across cell membrane Filtration Diffusion Active transport

Pharmacokinetics Metabolism – process of ridding the body of foreign substance (biotransformation) Breakdown of original drug compound into metabolites, which are eliminated Rate of metabolism Liver is primary organ, specialized enzymes that metabolize drugs or foreign compounds

Pharmacokinetics Excretion Routes of drug elimination Urine, bile, feces Lungs, salivary, sweat, mammary glands Kidney is major organ Patient Health

Factors Affecting Drug Response Age Infants & older adults Weight & Gender Men vs. women Dosing based on weight Time of administration With food vs. before meals

Barriers to Drug Distribution Blood-brain barrier Placental barrier Barriers inhibit certain chemicals in the bloodstream that may be dangerous or toxic to the individual or fetus

Drug Safety Five Rights of Drug Administration Right drug Right patient Right dose Right route Right time

Other guidelines: Drug prescribed = Drug dispensed Read Directions carefully Missed dosing Proper storage Safe storage Know medical history Potentiation