How Medications Get Absorbed By Your Body

Summary

The script discusses the process of medication absorption, highlighting that oral drugs are absorbed primarily in the small intestine, undergoing the first-pass effect in the liver, which can reduce bioavailability. Intravenous and other non-oral routes bypass this effect, ensuring full bioavailability. Factors influencing absorption include dissolution rate, surface area, blood flow, lipid solubility, and pH differences, with formulations like sustained-release impacting the rate and extent of absorption.

Takeaways

• 💊 Medication absorption involves the movement of a drug from its administration site into the bloodstream.
• 🧬 Oral drugs may dissolve in the stomach or pass undissolved to the small intestine, the primary site for absorption.
• 🛡️ Drugs that pass through the small intestine enter the liver through the portal venous system, where they undergo the first-pass effect.
• 🔄 The first-pass effect in the liver can metabolize some of the drug, reducing its active amount in the bloodstream.
• 💉 Intravenous (IV) drugs bypass the GI tract and liver, entering directly into the bloodstream with 100% bioavailability.
• 🦵 Drugs administered via intramuscular or subcutaneous injection enter muscle or tissue and reach the bloodstream without GI absorption.
• 📉 Bioavailability of oral drugs is less than 100% due to the first-pass effect in the liver.
• 🕒 Different drug formulations affect bioavailability, as they are absorbed at different rates and extents.
• 🏃 The rate of drug absorption is influenced by factors like dissolution rate, surface area, blood flow, lipid solubility, and pH partitioning.
• 🌡️ Highly lipid-soluble drugs are absorbed more easily, and absorption is faster when the pH difference between the administration site and plasma favors ionization in the plasma.

Q & A

What is medication absorption?

Medication absorption is the process by which a drug moves from its site of administration into the bloodstream.

How do oral drugs typically enter the body?

Oral drugs enter the body through the stomach, where they either dissolve and pass through the cell membranes of epithelial cells or travel undissolved to the small intestine for absorption.

Why is the small intestine the most common site for drug absorption?

The small intestine is the most common site for drug absorption because it is where most drugs dissolve and pass through the intestinal wall due to its large surface area and rich blood supply.

What is the first pass effect and how does it affect oral drugs?

The first pass effect is the process where the liver metabolizes some of the drug after it enters the bloodstream from the gastrointestinal tract, either inactivating it or excreting it into bile. This reduces the bioavailability of oral drugs.

How does intravenous injection bypass the first pass effect?

Intravenous injection bypasses the first pass effect because the drug is directly introduced into the bloodstream, avoiding the liver and gastrointestinal tract.

What are the two other common methods of drug administration that bypass the gastrointestinal tract absorption?

Intramuscular and subcutaneous injections are two other common methods that bypass gastrointestinal tract absorption, as the drug enters muscle or subcutaneous tissue and then into general circulation.

What is bioavailability and why is it important?

Bioavailability is the net amount of a drug dose that is actually absorbed into the bloodstream. It is important because it determines the effectiveness and potency of the drug in the body.

Why is the bioavailability of oral drugs less than 100 percent?

The bioavailability of oral drugs is less than 100 percent due to the first pass effect of the liver, which can inactivate or excrete a portion of the drug before it reaches general circulation.

How do different drug formulations affect bioavailability?

Different drug formulations affect bioavailability because they may not be absorbed at the same rate or to the same extent due to varying dissolution rates and other factors.

What are some factors that can affect the rate of drug absorption?

Factors affecting drug absorption include the rate of dissolution, surface area, blood flow, lipid solubility, and pH partitioning.

How do sustained-release formulas impact drug absorption?

Sustained-release formulas contain tiny spheres that dissolve at different rates, resulting in a steady drug release throughout the day but also leading to variable absorption.