Pharmacokinetics I, II and III

Questions and Answers

What is the primary purpose of drug metabolism?

To detoxify drugs and decrease their activity (correct)

To facilitate the absorption of drugs

To convert drugs into similar endogenous compounds

To enhance the pharmacological activity of drugs

Which of the following is NOT a consequence of drug metabolism?

Inactivation of drugs

Promotion of renal excretion

Increased drug toxicity (correct)

Activation of prodrugs

What role does the liver play in drug metabolism?

It eliminates all toxins from the body before drug metabolism occurs

It metabolizes hydrophilic drugs exclusively

It is the site where all drugs are absorbed into the bloodstream

It is the principal site responsible for drug metabolism (correct)

What is the 'first-pass effect'?

The initial metabolism of orally administered drugs by the liver Signup and view all the answers

Which of the following correctly describes prodrugs?

Compounds that are inactive until metabolized into an active form Signup and view all the answers

What is the primary reason weakly basic drugs, such as tetracycline, are more soluble in acidic solutions?

Weakly basic drugs remain unionized and more soluble at low pH. Signup and view all the answers

How does lipid solubility affect drug absorption?

Highly lipid-soluble drugs can easily cross biological membranes. Signup and view all the answers

What determines the degree of ionization of a drug?

The pH of the solution the drug is in. Signup and view all the answers

Which factor is NOT mentioned as affecting drug absorption?

Environmental temperature. Signup and view all the answers

What type of drugs are more likely to be absorbed from the stomach rather than the small intestine?

Weakly acidic drugs. Signup and view all the answers

Study Notes

Drug Absorption

Weakly basic drugs, such as tetracycline, demonstrate higher solubility in acidic environments like the stomach.
Drugs with high lipid solubility are absorbed more rapidly because they can easily cross lipid-rich biological membranes.
Body membranes are selectively permeable, allowing only unionized particles to pass through.

pH Partitioning

Drug ionization influences absorption and diffusion through membranes based on the local pH of the solution.
Charged drug forms (positively or negatively charged) are less likely to diffuse across membranes compared to their uncharged counterparts.

Factors Influencing Drug Absorption

Surface Area: Increased surface area enhances absorption; drugs are typically absorbed better in the small intestine than in the stomach.
Blood Flow: Enhanced blood flow to absorption sites leads to quicker drug uptake.
Transport Mechanisms: Includes various channels and pores, specialized transport systems, and direct membrane penetration.

Drug Metabolism

Main function of drug metabolism is to detoxify drugs and reduce their pharmacological activity.
Some metabolites may exhibit increased activity (prodrugs) or toxicity while others may be carcinogenic.
Delayed metabolism can result in drug accumulation within the body.

Sites of Drug Metabolism

The liver is the primary site for drug metabolism, with additional sites in the gut, lungs, skin, and kidneys.
Metabolism following oral administration involves the liver first-pass effect, intestinal processing, and interactions with gut microorganisms.

Consequences of Drug Metabolism

Drug inactivation may occur alongside promoting renal excretion by increasing drug polarity.
Metabolism can activate prodrugs, making them pharmacologically active.

Cytochrome P450 System

Humans possess 18 families of Cytochrome P450 genes, with numerous subfamilies driving the metabolism of drugs and steroids.
CYP2 family is particularly significant for drug and steroid metabolism.

Oxidative Reactions in Metabolism

Not all oxidation reactions are catalyzed by Cytochrome P450; alternative systems include flavin-containing monooxygenase and aldehyde dehydrogenase.
Monoamine oxidase (MAO) plays a role in the oxidative deamination of catecholamines.

Phase I and Phase II Reactions

Phase I reactions include oxidation and are often necessary before Phase II conjugation can take place.
Phase II reactions involve conjugation with endogenous molecules to produce more water-soluble metabolites for easier excretion.

Glucuronidation

The glucuronidation pathway is the most critical Phase II metabolic process, utilizing UDP-glucuronosyltransferase enzymes.
Enterohepatic recycling may lead to the reactivation of certain drugs within the gastrointestinal tract.

Drug Excretion

Excretion refers to the elimination of drugs and metabolites from the body, primarily through renal routes where drugs may be unchanged or metabolized.
Non-renal excretion routes include bile, feces, lungs, sweat, saliva, and breast milk.

Renal Excretion Processes

Glomerular filtration allows free drugs under a molecular weight of 5000 to enter the filtrate.
Passive tubular reabsorption favors drug absorption back into circulation, influenced by urinary pH adjustments for ionized versus non-ionized forms.
Active tubular secretion for drugs not filtered occurs through energy-dependent transport systems.

Alternative Routes for Drug Clearance

Intestinal excretion primarily involves unabsorbed substances, while the lungs eliminate inhaled anesthetics.
Breast milk can also serve as a route for drug clearance in nursing mothers.

Description

This quiz focuses on the pharmacokinetics of drugs, specifically the solubility of weakly basic drugs and the impact of lipid solubility on drug absorption. It explores how these properties influence drug effectiveness and absorption in the body. Test your knowledge on these crucial pharmacological concepts.