Final answer:
The first pass effect is a pharmacokinetic phenomenon where orally administered drugs are metabolized by the liver before reaching the systemic circulation, reducing their concentration. It affects the drug's bioavailability, and to avoid this, drugs may be given by non-oral routes like intravenous or sublingual administration.
Step-by-step explanation:
The first pass effect, also known as first pass metabolism, is a pharmacokinetic phenomenon whereby the concentration of a drug, notably when administered orally, is greatly reduced before it reaches the systemic circulation. This is because the drug is metabolized at the site of administration, in the gut wall, and then in liver cells, which are very efficient at breaking down substances. Consequently, the amount of the drug that eventually enters general circulation and is available for use by the body can be greatly reduced.
This effect is significant because it influences the bioavailability of the medicine, which is the proportion of the administered dose of unchanged drug that reaches the systemic circulation. Drugs that are administered orally are commonly subject to the first pass effect because they pass through the liver via the portal vein after being absorbed in the intestines. To bypass the first pass effect, some drugs are given by other routes, such as intravenous, sublingual, or rectal, which deliver the drug directly into the systemic circulation.
The first pass effect can impact the efficacy of drugs and is carefully considered when determining the proper form and dosage of medication. Understanding this phenomenon is crucial in drug design and the development of delivery systems to ensure the optimal therapeutic effect of medications.