• Drug administration via the rectal route is preferred for certain drugs that may be destroyed in the GI tract or when oral administration is not possible because of vomiting or difficulty swallowing PO medications.
• The rate (speed) of rectal drug absorption is often lower than the oral route, due to the relatively small surface area available for drug uptake.
• Some drugs have an increased extent of absorption even when the rate of absorption not increased. This is because per rectum drugs avoid the hepatic first-pass effect. For this reason, rectal doses are frequently lower than PO doses.
• Bleeding is not a common disadvantage of the rectal route.
• Hypersensitivity is no more likely by this route than others.
• Constipation is not a common result of administration via the rectal route unless the drug itself has that side effect.