From the Research
Rectal Absorption Time
The rectal absorption time for a substance can vary depending on several factors, including the type of substance, the formulation of the suppository, and the individual's physiology.
- The rate of rectal drug absorption is often lower than with oral absorption, possibly due to the relatively small surface area available for drug uptake 1.
- The composition of the rectal formulation (solid vs liquid, nature of the suppository base) appears to be an important factor in the absorption process by determining the pattern of drug release 1.
- Coadministration of absorption-promoting agents (surfactants, sodium salicylate, enamines) represents another approach towards manipulating rectal drug absorption 1.
Factors Affecting Rectal Absorption
Several factors can affect the rectal absorption of a substance, including:
- The nature of the suppository base, with some bases allowing for faster or more complete absorption than others 2.
- The use of surfactants or other additives, which can enhance absorption 2.
- The particle size of the active ingredient, with smaller particles potentially allowing for faster absorption 2.
- The site of drug administration in the rectum, with the upper part of the rectum being connected to the portal system and the lower part being directly connected to the systemic circulation 2.
Specific Substances
The rectal absorption time for specific substances has been studied, including:
- Salicylic acid, which was found to have higher levels in the blood after rectal administration of a 600-mg suppository compared to oral administration of a 162-mg tablet 3.
- Nalbuphine, which was found to have a mean time to achieve maximum plasma concentration of 25 minutes after rectal administration in children undergoing general anesthesia 4.
- Methadone, which was found to have a mean absolute rectal bioavailability of 0.76 and a rapid absorption rate after rectal administration in healthy subjects 5.