Have you ever wondered how your body breaks down the chemicals in medications when you take them orally? Drug metabolism has a mechanism known as the first-pass effect.
As a result, the concentration of a drug drops dramatically before it enters the systemic circulation when taken orally.
To find out why and how only a tiny part of the tablet dose that passes through your digestive system reaches the target organ in the human body, read this article.
The main purpose of metabolism in the human body is to change the chemical composition of substances consumed so that the body can absorb the necessary elements and get rid of the rest. Therefore, the effectiveness of a drug may increase or decrease due to metabolismaffecting an individual’s health.
Therefore, understanding the therapeutic effect or toxicity of a drug is essential to predict the variation in drug response and elimination caused by metabolism in individuals.
Oral administration of drugs requires passage from the colon to the liver before reaching the general circulation, which is contrary to intravenous, intramuscular, sublingual or transdermal administration. Thus, before reaching the tissues, a large part of the dose of many drugs is lowered by metabolism.
First-pass metabolism, also known as the first-pass effect, refers to the combined impact of metabolism by the liver and gut, as certain drugs are digested by gut flora or digestive enzymes.
Retracing the pathway after oral administration of a drug
Oral drugs are modified by enzymes, pH, and motility of the stomach and intestine before being delivered through the portal vein.
The portal vein is a vein that carries blood from the gastrointestinal tract to the liver. In addition, the portal vein helps the arteries supply the intestine with oxygen and blood.
The sinusoids in the liver, where blood can flow, absorb the drug so that the hepatic artery can carry it to the liver cells. The hepatic artery is the artery that carries oxygen to the liver.
The drug in the blood is released into the hepatic vein after passing through the sinusoids, which return deoxygenated blood from the liver to the heart. The drug will eventually go from the heart through both lungs and into the systemic circulation.
Note from The Fitness Freak
One way to lessen the effects of first-pass metabolism is to administer the drug intravenously. Another way to do this is to administer the drug rectally. The first-pass effect is not always undesirable, however. In some cases, it may be beneficial for the liver to biotransform the drug. These types of drugs are called “prodrugs.” They go from an inactive state to an active state. For example, codeine is supplied before being biotransformed into morphine in the liver.
First-pass metabolism has several health implications, as a significant amount of the absorbed drug may be lost before it reaches the bloodstream due to “biotransformation” in the stomach, intestine, liver or the lungs, as pictured above.
In other words, the bioavailability of the drug decreases considerably during this initial passage through many organs.
It helps to understand drug responses.
According to research, patients should adhere to the correct dosage of the appropriate medication. In addition, the pharmacological dosage must take into account the regular changes in human metabolism.
Each individual has a different level of first-pass metabolism, which helps explain why patients respond differently to medications and why some patients are more likely than others to experience adverse drug reactions.
Reduces drug bioavailability
If a drug has high first-pass metabolisms, the liver breaks it down before it reaches the rest of the body. As a result, this limits the bioavailability of the drug or the amount of it that enters the bloodstream.
One can change the mode of administration or increase the dosage to circumvent this problem. With intravenous administration, the liver is bypassed, so a lower dose is usually needed.
It helps in the proper administration of medication.
The first-pass effect is important for drugs like morphine. These medications need to be taken in larger amounts by mouth because the body digests them quickly when taken by mouth.
Therefore, the correct administration and continued maintenance of drug therapy depends on understanding the clinical importance of the first-pass effect.
Summary
The first-pass effect is one of the things that can cause the response to medications to vary from person to person. This is when the liver breaks down a drug before it can enter the bloodstream.
Some people’s liver does this more than others. If a person’s first-pass metabolism is severe, it may be necessary to use a different method of administration or give a higher dose to avoid the first-pass effect.
Your health care provider will decide what is best for you based on your medical history and your body’s needs.
