Pharmacokinetics: Drug absorption and distribution

Summary

This video explains pharmacokinetics, the study of how a medication moves and is modified in the body. It covers four key processes: absorption, distribution, metabolism, and excretion (ADME). Absorption involves medication crossing cell membranes into the bloodstream, while distribution refers to its movement into tissues. Metabolism mainly occurs in the liver, where drugs can be activated or inactivated, and excretion happens through urine or feces. Bioavailability measures how much of the medication reaches circulation unchanged. The video also explains factors affecting these processes, such as pH, drug properties, and protein binding.

Takeaways

• 💊 Pharmacokinetics is the study of how the body affects a medication, focusing on its absorption, distribution, metabolism, and excretion.
• 🚪 Medications can be administered through various routes, including oral, intravenous, intramuscular, nasal, inhalational, and cutaneous methods.
• 🩸 After administration, medications must be absorbed into the circulation and distributed throughout the body to take effect.
• ⚖️ The process of elimination, which includes metabolism and excretion, removes the medication from the body, making it inactive.
• 🧪 Absorption can occur through passive transport, which requires no energy, or active transport, which requires ATP.
• 🌡️ Medications are absorbed more efficiently in environments where their chemical properties align with the pH level, affecting how they pass through cell membranes.
• 📊 Bioavailability refers to the fraction of a medication that reaches the bloodstream in its active form, with intravenous administration providing 100% bioavailability.
• 🧬 Distribution is influenced by factors such as blood supply, plasma protein binding, and the blood-brain barrier, impacting how well a medication reaches tissues.
• 🧪 The apparent volume of distribution (VD) indicates how extensively a medication is dispersed within body compartments, influenced by its chemical properties and conditions like liver and kidney diseases.
• 📋 The ADME acronym helps summarize the key processes in pharmacokinetics: Absorption, Distribution, Metabolism, and Excretion.

Q & A

What is pharmacokinetics?

Pharmacokinetics refers to the movement and modification of a medication inside the body, focusing on what the body does to a medication and how it processes it.

What are the main routes of medication administration mentioned in the script?

The main routes of administration include oral (swallowed), intravenous (injected into a vein), intramuscular (injected into a muscle), nasal (sprayed into the nose), and cutaneous (applied to the skin).

What are the four key processes of pharmacokinetics, and what do they stand for?

The four key processes are absorption, distribution, metabolism, and excretion, collectively referred to by the acronym ADME.

How does absorption of medication occur in the body?

Absorption is the process by which medication moves from the site of administration into the bloodstream. It can occur through passive transport (requiring no energy) or active transport (requiring ATP energy).

What factors influence the rate and extent of drug absorption?

Factors include the pH of the environment, the chemical properties of the drug, the surface area available for absorption, blood supply to the absorption site, and the presence of food or other materials in the gastrointestinal tract.

What is the first-pass metabolism or first-pass effect?

First-pass metabolism occurs in the liver, where hepatic enzymes break down medications after oral administration, reducing the concentration of active drug before it enters systemic circulation.

What is bioavailability, and how is it affected by the route of administration?

Bioavailability refers to the fraction of an administered drug that reaches systemic circulation unchanged. Intravenous administration has 100% bioavailability, while oral administration often has lower bioavailability due to first-pass metabolism.

How does the blood-brain barrier affect drug distribution?

The blood-brain barrier is a selective membrane that allows small, fat-soluble medications to pass into the brain while blocking large, water-soluble medications.

What role does plasma protein binding play in drug distribution?

Plasma protein binding limits the amount of free drug available for distribution. Only unbound drugs can diffuse into tissues, while drugs bound to plasma proteins remain in the bloodstream, acting as a reservoir.

What is the apparent volume of distribution (VD), and how is it calculated?

The apparent volume of distribution (VD) represents how extensively a drug is distributed throughout the body. It is calculated by dividing the dose administered intravenously by the plasma concentration of the drug.