A drug that is administered rectally will in general (depending on the drug) have a faster onset, higher
bioavailability, shorter peak, and shorter duration than
oral administration.[1][2] Another advantage of administering a drug rectally, is that it tends to produce less
nausea compared to the oral route and prevents any amount of the drug from being lost due to
emesis (vomiting). In addition, the rectal route bypasses around two-thirds of the
first-pass metabolism as the rectum's venous drainage is two-thirds
systemic (
middle and
inferior rectal vein) and one-third
hepatic portal system (
superior rectal vein). This means the drug will reach the circulatory system with significantly less alteration and in greater concentrations.[Note 3] Finally, rectal administration can allow patients to remain in the home setting when the oral route is compromised. Unlike
intravenous lines, which usually need to be placed in an
inpatient environment and require special formulation of
sterile medications,[3] a specialized rectal
catheter can be placed by a clinician, such as a
hospice nurse or home health nurse, in the home. Many oral forms of medications can be crushed and suspended in water to be given via a rectal
catheter.
The rectal route of administration is useful for patients with any digestive tract motility problem, such as
dysphagia,
ileus, or
bowel obstruction, that would interfere with the progression of the medication through the tract. This often includes patients
near the end of life (an estimated 1.65 million people are in
hospice care in the US each year).[4] Because using the rectal route enables a rapid, safe, and lower cost alternative to administration of medications,[5] it may also facilitate the care of patients in
long-term care or
palliative care, or as an alternative to
intravenous or
subcutaneous medication delivery in other instances.
Methods
Rectal administration of medication may be performed with any of the following:
A
suppository, a solid
drug delivery system inserted into the rectum, where it dissolves or melts to exert local or systemic effects.
A
micro-enema, a small amount (usually less than 10 millilitres) of a
liquid-drug
solution injected into the rectum.
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.
^The rectum has numerous blood vessels available to absorb drugs: upwards 2/3rds of the dose bypasses
first-pass metabolism through systemic distribution and the rest is taken through the liver and metabolized via the hepatic portal system .
^De Boer AG, Moolenaar F, de Leede LG, Breimer DD. (1982) "Rectal drug administration: clinical pharmacokinetic considerations." Clin Pharmacokinetics. 7(4):285–311
^Moolenaar F, Koning B, Huizinga T. (1979) "Biopharmaceutics of rectal administration of drugs in man. Absorption rate and bioavailability of phenobarbital and its sodium salt from rectal dosage forms." International Journal of Pharmacaceutics, 4:99–109
^Plumer AL. 2007. Plumer's Principles and Practices of Intravenous Therapy. Lippincott Williams & Wilkins. 753 pp.
^"high enema". Medical Dictionary. Merriam-Webster. Retrieved 2021-04-18.
^Rhodora Cruz.
"Types of Enemas". Fundamentals of Nursing Practice. Professional Education, Testing and Certification Organization International. Retrieved 2021-04-18.