Week 2: Pharmacokinetics/Pharmacodynamics

Pharmacokinetics

The study of drug movement and concentration in the body (what the body does to the drug). It encompasses Absorption, Distribution, Metabolism, and Excretion (ADME).

Absorption

The movement of drug molecules from the site of entry into the body to the circulating fluids. The rate of absorption determines the drug's onset of action.

Distribution

The transportation of a drug via blood and tissue fluids to its action sites, metabolism sites, and excretion sites.

Metabolism (Biotransformation)

The process by which drugs are inactivated or biotransformed by the body, primarily in the liver, often involving enzymes like Cytochrome P450 (CYP).

Excretion

The process by which drugs and their metabolites are eliminated from the body, primarily via the kidneys.

First-Pass Effect

The initial metabolism of a drug in the liver (or gut) after oral administration, before it reaches the systemic circulation. This reduces the drug's bioavailability.

Cytochrome P450 (CYP) Enzymes

The major enzyme system responsible for metabolizing many drugs.

CYP Substrate

A drug that is metabolized by the Cytochrome P450 enzyme pathway.

Enzyme Inducer

A substance that increases the production of CYP enzymes, which can lead to decreased effects of other drugs metabolized by the same enzymes.

Enzyme Inhibitor

A substance that decreases the activity of CYP enzymes, which can lead to increased or toxic effects of other drugs metabolized by the same enzymes.

Plasma Protein Binding

The process where drugs reversibly bind to proteins like albumin in the blood. The bound drug is inactive; only the "free" drug is active.

Minimum Effective Concentration (MEC)

The minimum serum level of a drug required to produce a therapeutic effect.

Therapeutic Range

The range of drug concentration in the blood between the MEC and the toxic concentration, where the drug is effective and safe.

Peak Concentration

The highest serum level of a drug after administration.

Trough Concentration

The lowest serum level of a drug, measured right before the next dose is administered.

Therapeutic Index (TI)

A measure of a drug's safety margin. A low TI indicates a narrow margin between an effective dose and a toxic dose, requiring close monitoring.

Half-Life (T 1/2)

The time required for the serum concentration of a drug to decrease by 50%. It takes about 4-5 half-lives to eliminate a drug.

Steady State (Plateau)

The point at which the amount of drug administered equals the amount eliminated per unit of time, resulting in a consistent therapeutic level. Reached in 4-5 half-lives.

Bioavailability

The percentage of an administered drug that reaches the systemic circulation unchanged and is available to produce an effect.

Bioequivalence

When two chemically equivalent drugs, given in the same dose, have the same bioavailability and produce the same therapeutic effect.

Pharmacodynamics

The study of the biochemical and physiologic effects of drugs and their mechanisms of action (what the drug does to the body).

Agonist

A drug that binds to a receptor and activates it, producing a biological response.

Antagonist

A drug that binds to a receptor but does not activate it, thereby blocking the receptor from being activated by agonists.

Partial Agonist

A drug that binds to and activates a receptor but has less efficacy than a full agonist. It can also act as an antagonist if a full agonist is present.

Adverse Effect

A predictable, often unavoidable secondary effect of a drug produced at therapeutic doses.

Allergic Reaction

An adverse drug reaction that involves the immune system.

Idiosyncratic Effect

An uncommon, unpredictable drug response resulting from a genetic predisposition.

Teratogenic Effect

A drug-induced birth defect.

Black Box Warning

The strictest warning put on the labeling of prescription drugs by the FDA, indicating significant risk of serious or life-threatening adverse effects.

Primary Nursing Action for a Drug with a Low TI

Reviewing lab results (e.g., INR for warfarin) to ensure the patient is in the therapeutic range prior to administration.

Key Factor in Older Adult Pharmacokinetics: Distribution

Reduced serum albumin concentration leads to decreased protein binding, resulting in higher levels of active "free" drug.

Key Factor in Older Adult Pharmacokinetics: Excretion

Decline in renal function is common and is a major cause of adverse drug reactions due to drug accumulation.