Rectal delivery forms

Drug Delivery Rectal Route Table 2 Rectal dosage forms marketed in the United States for systemic indications ... 

Rectal delivery, depending on the position of the dosage form in the rectum, can be used to target either the systemic circulation or the liver. For systemic targeting, the dosage form should be placed and located directly behind the internal rectal sphincter, whereas targeting the liver requires the dosage form to be placed in the ampulla recti (about 12-15 cm up the rectum) (50). 

Some additives can suppress dissociation of CyD complexes. Morphine occurs naturally in the opium poppy. It is a potent narcotic analgesic, and its primary clinical use is in the suppression of moderately severe pain. In patients with vomiting, a rectal dosage form such as a suppository should be usefiil, especially a prolonged-release-type suppository. We have demonstrated that a combination of a-CyD and xanthan gum, a polysaccharide-type polymer with high swelling capacity, enhanced rectal absorption of morphine in rabbits, when administered to rabbit s rectum in the form of Witepsol H-15 [81] hollow-type suppositories. The combination of CyDs and viscous polymers may be useful for optimizing the trans-mucosal delivery of morphine [81]. 

Other rectal dosage forms may be used other than fat-based suppositories. One study describes a liquid suppository that immediately after administration forms a gel with strong adhesion to the rectal mucosa [14]. The gelling at body temperature is caused by a poloxamer. Adhesion to the rectal mucosa is provided by carbomers and cellulose derivates. Compared to a fatty suppository, this delivery system is expected to spread less far into rectum and colon, thereby avoiding the hepatic portal system (see also Sect. 11.3). 

Buur, A., Bundgaard, H., Prodrugs of 5-fluorouradl V. 1-alkoxycarbonyl derivatives as potential prodrug forms for improved rectal and oral delivery of 5-fluorouradl, ]. Pharm. Sci. 1986, 75, 522-527. 

In the caudal form of extradural anesthesia, the agent is introduced through the sacral hiatus above the coccyx. It is particularly applicable to perineal and rectal procedures. Anesthetization of higher anatomical levels is not easily obtained, because the required injection volume can be excessive. Although caudal anesthesia has been used extensively in obstetrics, lumbar epidural blockade is now more commonly used because of the lower dose of drug required in addition, the sacral segments are spared until their anesthesia is required for the delivery. 

The rectal milieu is quite constant as its pH is about 7.5, and the temperature is usually 37°C. It is normally empty and the pressure varies between 0 and 50 cm. This makes this route suitable for the (controlled) delivery of drugs by applying adequate (controlled release) dosage forms such as osmotic pumps and hydrogels, since the classical suppositories are, in general, not the most suitable dosage form to achieve a reproducible rate and extent of drug absorption. 

Carbopol resins also have been used in controlled-release dosage forms. Especially, the resins Noven AA-1 USP and Carbopol 934P NF are being extensively developed in bioadhesive drug delivery systems for topical, bucal or nasal, ocular, and rectal applications (e.g., Fentanyl ). Noven CA-1 USP and CA-2 USP are used as oral laxative and antidiarrheal products in swallowable and chewable tablets. 

Polymethacrylate polymers may additionally be used to form the matrix layers of transdermal delivery systems and have also been used to prepare novel gel formulations for rectal administration. ... 

The vaginal delivery system for dinoprostone (Propess 10 mg) is even more different from the classical dosage forms for rectal or vaginal use. It is a thin, flat polymeric matrix of crosslinked macrogols forming a hydrogel in the vagina. Dinoprostone is... 

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