Pharmacokinetics - What your body does to the med - Quick Review - Pharmacology Series

Summary

In this engaging and informative video, the speaker delves into the essential concepts of pharmacokinetics in anesthesiology. From explaining ADME (Absorption, Distribution, Metabolism, Excretion) to the differences between lipid and water-soluble drugs, the video breaks down complex topics with humor and relatable examples. The content covers how drug properties affect their movement through the body, their metabolism, and how factors like pH and ionization impact drug absorption and excretion. With practical insights into anesthesia management and drug interactions, this video is a valuable resource for healthcare professionals looking to understand the pharmacology behind effective anesthesiology practices.

Takeaways

• 😀 Hypothermia complications can lead to delayed wound healing, infections, blood loss, and other serious issues, especially in anesthesia patients.
• 😀 Pharmacokinetics (ADME) explains how the body processes drugs, including absorption, distribution, metabolism, and excretion.
• 😀 Lipid-soluble drugs require plasma proteins for transport, while water-soluble drugs can travel freely in the blood.
• 😀 The 'like reabsorbs like' rule in pharmacology determines how drugs are reabsorbed or excreted based on their acidity or alkalinity.
• 😀 Drug ionization depends on the pK of the drug and the pH of the environment; this affects absorption and excretion.
• 😀 A drug can have both an ionized and non-ionized fraction, and the ionized fraction is less likely to be absorbed or reabsorbed.
• 😀 The blood-brain barrier and lipid solubility influence how drugs, like anesthetics, affect the brain and body during surgery.
• 😀 When drugs are administered intravenously, they bypass the liver's first-pass metabolism, making them more bioavailable than oral drugs.
• 😀 Redistribution of drugs, especially anesthetics, can lead to fast onset and offset, requiring careful dosing and continuous infusions.
• 😀 Metabolism converts drugs from active to inactive forms, often making them more water-soluble for easier excretion by the kidneys.

Q & A

What are the main components of pharmacokinetics in anesthesiology?

The main components of pharmacokinetics in anesthesiology are absorption, distribution, metabolism, and excretion (ADME). These describe what the body does to the drug after it is administered.

How does hypothermia affect patients in the context of anesthesiology?

Hypothermia increases the risk of delayed wound healing, wound infections, blood loss, nitrogen loss, cardiac morbidity, hospitalization, and postoperative complications. To prevent these, patients should be kept warm with forced air warming blankets and warm IV fluids.

What is the difference between pharmacokinetics and pharmacodynamics?

Pharmacokinetics refers to what the body does to the drug, including absorption, distribution, metabolism, and excretion. Pharmacodynamics, on the other hand, is what the drug does to the body, particularly its effect on receptors and cellular systems.

What is the significance of lipid-soluble vs. water-soluble drugs in pharmacokinetics?

Lipid-soluble drugs can pass through cell membranes more easily and are often transported by plasma proteins, while water-soluble drugs cannot pass through cell membranes without the help of receptors on the outside of cells. Lipid-soluble drugs tend to be more inactive physiologically but are more active pharmacologically.

What happens to a drug in the body if it is lipid-soluble?

A lipid-soluble drug can pass through cell membranes, including the blood-brain barrier. It is typically metabolized in the liver and may have a slower excretion process, as it is reabsorbed in the kidneys.

How does pH influence drug ionization and its pharmacokinetic behavior?

The pH of the surrounding environment affects whether a drug is ionized or non-ionized. Drugs are more likely to be absorbed when they are non-ionized, as ionized drugs cannot pass through membranes. The pH at which the concentration of ionized and non-ionized forms are equal is called the pKa of the drug.

How do changes in urine pH affect the excretion of aspirin?

If the urine is alkaline, aspirin, which is an acid, becomes ionized and is excreted in the urine, rather than being reabsorbed into the bloodstream. In an acidic urine environment, aspirin remains non-ionized and is more likely to be reabsorbed.

What are the main factors that affect drug absorption?

Key factors that affect drug absorption include concentration gradient, surface area, temperature, molecular size, and the thickness of the membrane. Drugs are absorbed more efficiently when the surface area is larger, the temperature is higher, and the membrane is thinner.

What is first-pass metabolism, and how does it affect drug bioavailability?

First-pass metabolism refers to the process where drugs taken orally are absorbed into the liver before reaching systemic circulation. This can significantly reduce the bioavailability of the drug, as the liver metabolizes it before it reaches the bloodstream. Intravenous drugs avoid first-pass metabolism and have higher bioavailability.

Why is thiopental, a barbiturate, used in anesthesia, and what are its pharmacokinetic properties?

Thiopental is a barbiturate that is rapidly metabolized in the liver and has slow redistribution from poorly perfused tissues back into the bloodstream. This results in its rapid onset, but it can also leave the brain quickly, causing patients to wake up during surgery. To counter this, it is administered as an IV infusion to maintain anesthesia.