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Cross-Linked Polymers for Drug Delivery Systems
Published in Munmaya K. Mishra, Applications of Encapsulation and Controlled Release, 2019
The rectal route of administration of drugs is an effective route for the administration of drugs in infants who have difficulty in swallowing orally administered medicine [43]. This route is usually used in patients who are uncooperative or unconscious or when the intravenous route is compromised [44]. The length and circumference of the human rectum are in the range of 10–15 and 15–35 cm, respectively. The pH of its fluid content is in the range of 7–8 [44, 45]. The surface area is small, in the range of 200–400 cm2. It is drained by three veins: the superior, middle, and inferior rectal veins. The superior rectal vein drains the upper part, while the middle and inferior rectal veins drain the lower part of the rectum [ [44, 45]. The rectal wall is composed of epithelium, and it contains cells that secrete mucus. It is usually empty, and its filling results in the defecation reflex under voluntary control45]. Drugs are absorbed from the rectum by passive diffusion. The rate of drug absorption from the rectum is lower than from the oral route due to the small surface area of absorption [45]. The lower and middle rectal veins drain into the inferior vena cava, and the blood flows directly to the heart and to the general circulation. In contrast, the upper rectal vein drains into the portal vein, and the blood flows through the liver before reaching the heart [45]. This indicates that drug molecules from the rectum can be transported either directly to the general circulation or through the liver. Drug absorbed in the middle and lower parts of the rectum avoids the first-pass metabolism in the liver and is transported directly to the general circulation (Figure 5.5).
Evaluation of the Macy Catheter®: a rectal catheter for rapid medication and fluid administration
Published in Expert Review of Medical Devices, 2018
Kim Marie C. Macygin, Erik Kulstad, Robert K. Mokszycki, Morgan Goldsmith
The rectum itself is pH neutral, 7–8. It has a small surface area, 200–400 cm2, compared to that of the small intestines with 200 m2. Circulation through the rectum is performed by three vessels: the superior, middle, and inferior rectal veins (see Figure 2). The lower two avoid first-pass metabolism, increasing the bioavailability of drugs that do not need to be activated by processes in the liver [28,29].