Ch. 4: Pharmacokinetics and Pharmacodynamics: Drug Absorption, Metabolism, and Tolerance

What is pharmacokinetics?

The 'life cycle' of a drug in the body, from how it gets in to how it leaves.

What factors influence the bioavailability of a drug?

Absorption, distribution, metabolism, and elimination.

What is absorption in pharmacokinetics?

The movement of a drug from the site of administration to its target.

What are the advantages of oral drug administration?

Easy and painless, but must be resistant to stomach fluids.

What is first-pass metabolism?

The reduction of drug availability due to metabolism in the liver before reaching systemic circulation.

intravenous (IV) injections

the most rapid method of administration

What is depot binding?

Non-selective drug binding at inactive sites, affecting the therapeutic outcome and drug availability.

What is the significance of half-life in drug elimination?

It is the time needed to remove 50% of the drug from the blood; after 6 half-lives, the drug should be eliminated.

first-order kinetics

involves a set fraction of drug removed at each time interval

What is pharmacodynamics?

The study of physiological and biochemical interactions of drug molecules with target tissues responsible for drug effects.

agonists in drug action

trigger activity by fitting a receptor

What is tolerance in the context of drug use?

A diminished drug effect after repeated use, requiring higher doses to achieve the same effect.

What is cross-tolerance?

Diminished effect for similar drugs due to tolerance developed for one drug.

What is metabolic tolerance?

Increased liver enzyme production due to repeated drug use, leading to faster metabolism of the drug.

What is behavioral tolerance?

Reduced behavioral response to a drug due to practice, even though physiological effects remain.

What is conditioned tolerance?

Tolerance that develops in the same environment where the drug is usually administered.

What are withdrawal symptoms?

A collection of symptoms experienced when drug use is stopped, often opposite to the drug's effects.

What factors influence biotransformation?

Enzyme induction, enzyme inhibition, drug competition, and individual differences (genetic, age, sex, nutrition).

What is the role of cytochrome P450 in drug metabolism?

A family of enzymes that oxidize a majority of psychoactive drugs during biotransformation.

What is the significance of lipid solubility in drug transport?

allows drugs can pass through membranes via passive diffusion, while water-soluble drugs cannot.

What is the effect of food on oral drug absorption?

especially fatty food, can delay the movement of drugs into the small intestine, affecting onset.

What is the impact of depot binding on drug efficacy?

High binding reduces free drug availability, potentially requiring higher doses for effect.

What is the relationship between drug competition and side effects?

can displace each other at binding sites, leading to higher-than-expected blood levels and increased side effects.

What is the physiological basis for withdrawal symptoms?

The body becomes accustomed to the drug, leading to adverse symptoms when the drug is no longer present.

What is the role of the liver in drug metabolism?

contains microsomal enzymes that primarily metabolize drugs, influencing their bioavailability and effects.

zero-order kinetics

removes a constant amount regardless of concentration.

intramuscular (IM) injections

provides slower and more even absorption.

Phase 1 of Biotransformation

enzymes modify drug drugs by making it more charged. Resulting metabolite is less lipid soluble and less active

Phase 2 of Biotransformation

enzymes conjoin drugs to small molecules making it too big to pass easily AND more charged. The resulting metabolite is less lipid soluble and inactive.

antagonists in drug action

block activity without triggering a response.