Rectal dosage forms

Rectal Administration. The administration of drugs by a solid rectal dosage form (i.e., suppositories) results in a wide variability in the rate and extent of absorption in children [79]. This fact, coupled with the inflexibility of a fixed dose, makes this a route that should not be promoted for pediatric patients. At least one death involving a 7-month-old infant can be directly attributed to the use of solid rectal dosage form of a therapeutic dose of morphine [80]. 

Solutions, suspensions, or retention enemas represent rectal dosage forms with very limited application. 

In certain areas of the world, particularly some European countries and Japan, rectal dosage forms are somewhat more accepted by the patient population and, hence, development of rectal dosage forms has surpassed that in the United States. According to a survey in 1970, approximately 7.5% of all prescriptions in France were formulations intended for rectal administration.Even though a few countries may find rectal dosage forms more acceptable, these still represent a small area of the world-wide market share which can be assigned to rectal drug therapy. 

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

Suppositories and other rectal dosage forms are more expensive to prepare and dispense than simple tablets. Therefore, unless there is a significant need and advantage by utilizing a rectal dosage form, suppositories are not likely to be used. Recently, techniques have been developed to prepare suppositories more efficiently which could lead to lower manufacturing costs. 

As discussed earlier, the pH of the rectal fluid can have a marked effect on the absorption of drugs from the rectum. Since the rectal fluid has a relatively low buffering capacity and the volume of the rectal fluid is small, it might be expected that the contents of the rectal dosage form largely control the pH of the rectum during administration. On this basis, one may be able to utilize the pH characteristics of the drug and incorporate suitable buffers and other excipients in the... 

Phenothiazines are available in oral, parenteral, and rectal dosage forms. The principal exposure pathway is intentional ingestion in adults or accidental ingestion in small children. 

Oral ingestion is the most common route of both accidental and intentional exposure to salicylates. Salicylates are also available in topical and rectal dosage forms. 

Mucoadhesion was already used as part of medicinal therapy in rectal dosage forms longer than 100 years ago. Viscosity-increasing polymers were used in the rectal solutions already at the beginning of the last century, so that that the preparation would adhere well and would not flow back [133]. A new achievement in this field is the development of mucoadhesive suppositories [18]. 

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]. 

Rectal dosage forms may be applied for systemic as well as for local action. Vaginal dosage forms are almost exclusively used for local action. Rectal administration of an active substance for systemic action is sometimes a good... 

When nausea and vomiting occur in patients with any illness, a chronic oral medication may be temporarily replaced by the same active substance in a rectal dosage form so a hydrocortisone suppository may replace hydrocortisone in tablet or capsule a carbamaze-pine suppository may replace carbamazepine and a valproic acid suppository sodium valproate in syrup, tablet or capsule. 

Vaginal foams Medicated vaginal tampons From the rectal dosage forms the suppositories, enemas, ointments and creams are important as extemporaneous pharmacy preparations from the vaginal dosage forms fliese are the vaginal suppositories (pessaries), solutions, creams and gels. 

An active substance is rectaUy administered for either a systemic or a local effect The biopharmaceutics of the systemic effects have been studied quite well. The outcomes of these studies support reconunendations for the formulation of rectal dosage forms, see Eig. 11.1. See also Sect. 16.2.4. 

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). 

If a rectal dosage form for the administration of a corticosteroid is prescribed, it is important to know if ... 

If the rectal form follows oral administration a systemic effect may be desired. It must be checked if the particular steroid is suitable for rectal administration, if the oral dosage may have to be adjusted, and if the rectal dosage form is appropriate. 

Moolenaar F, Koning B, Huizinga T (1979) Biopharmaceutics of rectal administration of drugs in man, part 7, absorption rate and bioavailability of phenobarbital and its sodium salt from rectal dosage forms. Int J Pharm 4 99-109... 

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