Does intramuscular injection of a drug bypass “First pass effect”?
Yes, they bypass. Hepatic first-pass effect is mainly for the drugs you take by mouth. (absorption from intestine). They will be absorbed & then carried to portal circulation & to liver. For intavenous, intramuscular, sublingulal drugs are carried to the systemic veins, then to heart. They can go to target tissue without passing through the liver. But for intramuscular, some metabolism occurs in the muscle itself. (so bio-availability is higher for I/V than the I/M) Eventually the drug in the venous blood will go through heart & then some portion will be also circulated to liver and (most of them) will be metabolized. But that is not the first pass. First pass means that the drug goes to liver after being absorbed & carried by portal circulation.
