Advantage And Disadvantage Of Rectal Medication

Medications administered per rectum (PR) are ideal for local or systemic treatment, as the rectal mucosa has a blood and lymph supply that is capable of effective systemic absorption. Medication intended for rectal administration often comes in the form of a suppository or an enema. Suppositories are small, torpedo-shaped pellets that melt at body temperature, whereas enemas are substances in liquid form designed for rectal administration.

Rectal Medication

The rectum constitutes the final 20cm or so of the terminal gastrointestinal tract; approximately 2-3cms of this is the anal canal. Absorption from within the anal canal is via its highly vascular mucous membrane that is divided into folds or pillars, known as anal columns. Rectal epithelium is composed of non-keratinized and villi-free cells. This provides approximately 200 - 400 cm³ surface area for absorption.

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The anal canal is divided into areas above and below the pectinate line; the area below (distal) is sensitive to pain, touch and temperature, whereas the area above (proximal) is only sensitive to stretch.

Therefore, once carefully inserted into the rectum, medication should not cause pain.

Within the anal canal are two areas to control the opening of the anus – the internal and external sphincters. The internal sphincter functions involuntarily, whereas the external sphincter is under the control of the individual. This is important and underlines the need to ensure a patient receiving drugs via the rectal administration route is sufficiently relaxed and cooperative, to enable both insertion and retention of the drug.

Also, the superior hemorrhoidal vein joins the mesenteric circulation, which feeds into the portal vein and from there to the liver. Location of the drug in the rectum affects drug absorption as some may suffer first pass metabolism.

Advantage Of Rectal Medication

1. Have a faster onset of action than oral formulation

2. Higher bioavailability when we look at oral dosage form

3. Shorter peak compare to oral administration

4. Shorter duration than oral administration

5. Use in nausea and vomiting

6. Can be self administered

7. Some of the drug don't go through the first pass effect

8. Not expensive

9. Not affected by food or other digestive tract content including condition that reduce absorption

10. Can be administered to unconscious patient

11. Localised action reduce systemic distribution

12. Lower dose in localised condition leading to less toxicity

13. No pain

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Disadvantage Of Rectal Medication

1. Discomfort

2. Patient adherence may be a problem.

3. Microorganisms may degrade the drug

4. It can trigger defecation which can interrupt treatment

5. Irritation of the mucosa

6. Unpredictable and undesirable absorption as placement too high in the rectum will lead to first pass effect