Rectum limited fluid

The human rectum is 15-20 cm long. It is normally empty and contains 2-3 ml of mucous fluid with pH 7-8. There are no villi and only a limited surface area of 200-400 cm is available for absorption. 

The amount of liquid in the rectum has been reported to be about 3 ml. This is small compared to the volume of fluid available throughout the GI tract when a drug is administered orally. Such a small volume of fluid can limit dissolution of drugs, particularly those with low aqueous solubility. It also may be a constraint to the rapid dissolution and release of compounds from water-soluble vehicles where dissolution of the vehicle is considered to be the rate-determining step in drug release from the vehicle. 

Glucocorticoid enemas are useful in patients whose disease is limited to the rectum (proctitis) and left colon. Hydrocortisone is available as a retention enema (100 mg/60 mL), and the usual dose is one 60-mL enema per night for 2 or 3 weeks. When administered optimally, the drug can reach up to or beyond the descending colon. Patients with distal disease usually respond within 3—7 days. Hydrocortisone also can be given once or twice daily as a 10% foam suspension (CORTIFOAM) that delivers 80 mg hydrocortisone per application this formulation can be useful in patients with very short areas of distal proctitis and difficulty in retaining fluid. 

The rectum is the lowest part of the large intestine. It is 15-20 cm long with a diameter of about 5 cm. In the rectum 1-5 mL of viscous fluid with a pH between 6.4 and 7.4 and a small buffer capacity is present. The temperature (under physiological conditions) is 36.2—37.6 °C. The rectum is a flat tube, because of the pressure of the bowels. After administration of a fluid into the rectum the Uquid will spread due to this pressure. Larger volumes (enemas) are spread into the colon as well. A defecation reflex will occur when volumes exceeding 100 mL are applied, which limits the volume of enemas. 

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