Anurse has been administering a drug to a client intramuscularly (im). the health care provider discontinued the im dose and wrote an order for the drug to be given orally. the nurse notices that the oral dosage is considerably higher than the parenteral dose and understands that this due to:

First-pass effect.

  
The first-pass effect involves drugs that are given PO and absorbed from the small intestine directly into the portal venous system, which delivers the drug molecules to the liver. Once in the liver, enzymes break the drug into metabolites; they may become active or may be deactivated and readily excreted from the body. A large percentage of the oral dose is usually destroyed and never reaches tissues. Oral dosages account for this phenomenon to ensure an appropriate amount of the drug in the body to produce a therapeutic action. Passive diffusion is the major process through which drugs are absorbed into the body. Active transport is a process that uses energy to actively move a molecule across a cell membrane and is often involved in drug excretion in the kidney. Glomerular filtration is the passage of water and water-soluble components from the plasma into the renal tubule.