Rectal drug delivery
Rectal administrationuses the rectum as a route of administration for medication and other fluids, which are absorbed by the rectum’s blood vessels, and flow into the body’s circulatory system, which distributes the drug to the body’s organs and bodily systems.
Rectal administration provides rapid absorption of many drugs and is an alternative when oral administration is inconvenient because of the inability to swallow or because of GI side effects such as nausea, vomiting, and irrigation. More importantly, rectal drug administration has the advantage of minimizing or avoiding hepatic first-pass metabolism. The rectal bioavailability of lidocaine in human is 65%, as compared with an oral bioavailability of 30%.
Rectal route is used to administer diazepam to children who are suffering from epileptics, in whom it is difficult to establish IV access. However, rectal administration of drugs is inconvenient and has irregular drug absorption. Moreover, rectal administration should be avoided in immunosuppressed patients in whom even minimal trauma could lead to the formation of an abscess.
Methods of rectal drug delivery
Rectal administration of medication may be performed with any of the following:
- A suppository, a drug delivery system inserted into the rectum.
- A micro-enema, a small amount (usually less than 10 millilitres) of a liquid-drug solution injected into the rectum.
- A large volume enema to inject liquid into the colon either to cleanse as much of the colon as possible of feces as well to deliver a drug solution.
- A specialized catheter designed for rectal administration of medications and liquids, that can be placed safely and remain comfortably in the rectum for repeated use.
Drugs administered PR have a faster action than via the oral route and a higher bio-availability – that is, the amount of effective drug that is available is greater as it has not been influenced by upper gastrointestinal tract digestive processes. Rectal absorption results in more of the drug reaching the systemic circulation with less alteration on route. As well as being a more effective route for delivering medication, rectal administration also reduces side-effects of some drugs, such as gastric irritation, nausea and vomiting
There are occasions when the administration of medication PR is contraindi-cated, for example:
- Lack of consent (verbal, written or implied);
- Recent rectal or anal surgery – this can include tissue changes caused by pelvic radiation;
- Abnormalities or trauma involving the perineal or perianal areas;
- When a prescriber has specifically instructed that it not take place;
- Suspected paralytic ileus or colonic obstruction – this should be discussed first with relevant medical or other prescribing staff.