Which of the following drugs undergoes the most significant first pass effect?
First pass effect
The first-pass effect is a phenomenon of drug metabolism whereby the concentration of a drug is greatly reduced before it reaches the systemic circulation. It is the fraction of lost drug during the process of absorption which is generally related to the liver and gut wall.
Examples of psychiatric drugs which undergoes a significant first pass effect include:
- imipramine
- fluphenazine
- morphine
- diazepam
- buprenorphine
Examples which undergo little to no first pass include:
- lithium
- pregabalin
Orally administered drugs undergo the most first pass effect. Routes which avoid the first pass effect include:-
- Sublingual
- Rectal (partly avoids first pass)
- Intravenous
- Intramuscular
- Transdermal
- Inhalation
