How Your Body Metabolizes Medications

Summary

Drug metabolism is crucial for converting drugs into water-soluble compounds for excretion, primarily occurring in the liver. Lipophilic drugs cross cell membranes easily but must be made hydrophilic for kidney excretion. Drugs can be administered orally or parenterally, with the latter bypassing the digestive tract for quicker effect. The liver's first-pass effect metabolizes drugs before general circulation. Hepatic microsomal enzymes facilitate this conversion, with factors like enzyme induction and inhibition affecting the metabolic rate, which in turn influences a drug's duration and intensity of effect.

Takeaways

• 🧪 Drug metabolism is the process of converting drugs into water-soluble compounds for easier excretion by the body.
• 💊 The primary site for drug metabolism is the liver, while the kidneys are the main site for excretion.
• 🚀 Drugs must cross cell membranes, which are composed of phospholipids, to reach their site of action.
• 🔄 Lipophilic drugs are more easily absorbed through cell membranes than hydrophilic compounds.
• 💉 Parenteral administration, such as injections, bypasses the digestive tract and enters general circulation quickly.
• 🍽 Oral administration requires drugs to pass through the gastrointestinal tract and undergo first-pass metabolism in the liver.
• 🛑 The first-pass effect refers to the initial metabolism of drugs by the liver before they enter general circulation.
• 🔬 Hepatic microsomal enzymes, like the cytochrome P450 system, are crucial for converting lipophilic drugs to hydrophilic ones.
• 🔄 Enzyme induction can increase the amount of metabolic enzymes, thus speeding up drug metabolism.
• 🚫 Enzyme inhibition occurs when certain drugs compete for binding to metabolic enzymes, slowing down drug metabolism.
• 🌡️ Factors affecting metabolic rate include first-pass effect, liver disease, age, blood flow to the liver, and variations in hepatic enzymes.

Q & A

What is drug metabolism?

Drug metabolism is the process of converting drugs into water-soluble compounds that can be easily excreted by the body.

Where does drug metabolism primarily occur?

Drug metabolism mainly takes place in the liver.

How do drugs cross cell membranes?

Drugs cross cell membranes because they are lipophilic, or fat-soluble, and cell membranes are composed of phospholipids, allowing drugs to pass through.

Why is it necessary to convert drugs to water-soluble compounds for excretion?

Converting drugs to water-soluble or hydrophilic compounds is necessary for efficient excretion by the kidneys.

What are the different routes of drug administration mentioned in the script?

The script mentions oral administration and parenteral routes, which include injection, transdermal patches, lotions, inhalents, and suppositories.

What is the 'first pass effect'?

The 'first pass effect' refers to the process where the liver metabolizes some of the drug before it enters general circulation, especially when drugs are taken orally.

Which enzymes are involved in the metabolism of drugs in the liver?

Hepatic microsomal enzymes, such as the cytochrome P450 (CYP450) system, are involved in metabolizing drugs from lipophilic to hydrophilic compounds.

What is enzyme induction and how does it affect drug metabolism?

Enzyme induction occurs when the repeated use of certain drugs increases the amount of metabolic enzymes, thereby increasing drug metabolism.

What is enzyme inhibition and how does it impact drug metabolism?

Enzyme inhibition happens when certain drugs compete to bind to metabolic enzymes, which decreases drug metabolism.

How does the duration and intensity of a drug's effect relate to its metabolic rate?

A drug's duration and intensity of effect are largely determined by its metabolic rate; an increased metabolic rate decreases drug duration and intensity by facilitating excretion, while a decreased metabolic rate increases them.

What factors can affect the rate of drug metabolism?

Factors affecting drug metabolism include the first pass effect, liver disease, age (neonates and the elderly), compromised blood flow to the liver, variation in the amount and type of hepatic enzymes, poor diet, and nutrition.