Pharmacokinetics part 1: Overview, Absorption and Bioavailability, Animation

Summary

The video script delves into pharmacokinetics, the study of a drug's journey from administration to excretion, encompassing absorption, distribution, metabolism, and excretion. It highlights how factors like age, kidney, and liver function can affect drug clearance rates. The importance of understanding pharmacokinetics for determining optimal dosages and administration routes is underscored. The script also discusses the impact of drug properties, patient factors, and administration routes on drug absorption and bioavailability, using nitroglycerin as an example to illustrate varying therapeutic effects.

Takeaways

• 💊 Pharmacokinetics is the study of how a drug moves through the body from administration to excretion.
• 🔍 It is one of two main branches of pharmacology, alongside pharmacodynamics which studies the drug's effects on the body.
• 🔄 The drug journey in the body involves four key processes: absorption, distribution, metabolism, and excretion.
• 🚀 Absorption is the movement of the drug from the site of administration into the bloodstream.
• 🌐 Distribution refers to the drug spreading from the bloodstream to the body's tissues.
• 🧪 Metabolism is the body's chemical alteration of the drug.
• 🚰 Excretion is the elimination of the drug from the body, often after metabolism, which is why they are sometimes called clearance.
• 👶 Pharmacokinetics can be influenced by patient factors, including age and organ function, affecting drug clearance rates.
• 💉 Intravenous drug administration results in immediate absorption and rapid peak plasma concentration.
• 🌡 The maximum plasma concentration and the time it takes to reach it are indicators of the drug's absorption rate.
• 🚫 Oral administration is common but not suitable for all drugs, especially those sensitive to stomach acid and enzymes.
• 🛡️ Cell membranes, being hydrophobic, allow passage of small non-polar and uncharged molecules but not large polar or charged ones.
• 🧬 Drugs in their un-ionized form are lipid-soluble and can cross cell membranes, while ionized forms cannot.
• 💧 All drugs must be in solution to be absorbed, with the rate of dissolution potentially limiting absorption.
• 💻 Bioavailability measures the extent and rate of drug absorption, with intravenous administration having 100% bioavailability.
• 📉 Bioavailability can vary based on the route of administration and patient-specific factors.
• 🌰 Nitroglycerin's different routes of administration (sublingual vs. oral) result in different bioavailabilities and therapeutic effects.

Q & A

What is pharmacokinetics?

Pharmacokinetics is the study of how a drug moves through the body from the time it is administered until it is excreted. It describes the processes of absorption, distribution, metabolism, and excretion, and what the body does to a drug.

What is the difference between pharmacokinetics and pharmacodynamics?

Pharmacokinetics focuses on what the body does to a drug, including absorption, distribution, metabolism, and excretion. In contrast, pharmacodynamics looks at the effects a drug has on the body.

What are the four processes involved in the journey of a drug through the body?

The four processes are absorption (drug moves to the bloodstream), distribution (drug is spread to body tissues), metabolism (body chemically modifies the drug), and excretion (drug is eliminated from the body).

Why is drug metabolism often paired with excretion in discussions about pharmacokinetics?

Drug metabolism and excretion are often referred to as clearance because a drug typically needs to be metabolized before it can be excreted from the body.

How do patient-related factors influence the pharmacokinetics of a drug?

Factors such as age, kidney or liver function can affect drug clearance rates, potentially causing some drugs to remain in the blood for longer periods in certain patients.

What is the significance of determining the optimal drug dosage for individual patients?

Knowledge of pharmacokinetics helps to determine the optimal drug dosage for individual patients to ensure the most suitable therapeutic effect with minimum toxicity.

How does the route of administration affect drug absorption?

Different routes of administration affect the rate and extent of drug absorption. For example, intravenous administration results in immediate absorption, while oral administration requires the drug to pass through the intestinal wall and may be subject to liver elimination before reaching systemic circulation.

What is the peak plasma concentration and why is it significant?

The peak plasma concentration is the maximum drug concentration in the blood plasma, which occurs when the drug absorption rate equals the clearance rate. It is significant as it indicates the effectiveness and potential toxicity of the drug at its highest level.

Why is oral administration the most common route for drugs, and what are its limitations?

Oral administration is common due to its convenience. However, it may not be suitable for all drugs, as they must survive stomach acid and digestive enzymes, and some drugs, like peptide drugs, are degraded in these conditions and cannot be given orally.

How do cell membranes act as a barrier to drug absorption?

Cell membranes, being mainly lipid, are permeable to small non-polar and uncharged polar molecules but not to large polar molecules and charged particles. Drugs must overcome this barrier to enter the bloodstream, typically by diffusing in their un-ionized, lipid-soluble form.

What is bioavailability and how is it measured?

Bioavailability refers to the fraction of the administered drug that is absorbed into the bloodstream and available to the target tissue. It is usually measured by calculating the area under the plasma concentration versus time curve, known as the AUC.

How does the bioavailability of a drug differ between intravenous and oral administration?

A drug given intravenously has a bioavailability of 100% as it immediately enters the systemic circulation. In contrast, an orally-administered drug has lower bioavailability due to the need to pass through the intestinal wall and potential elimination by the liver before reaching systemic circulation.

Can you provide an example of how different routes of administration can result in different therapeutic effects?

Nitroglycerin used for angina management illustrates this. Sublingual administration provides fast, strong, but short-lived action for immediate relief, while oral administration results in slower absorption and more sustained effects, suitable for preventive purposes.