Rectal Administration, Suppositories & Rectal Liquids (Enemas)
7. Rectal Administration:
Rectal administration is an important route that can be used for both local (e.g. laxative and anti-inflammatory) and systemic effects (e.g. antipyretic and anticonvulsive) in all age groups. This route of administration is especially valuable when oral administration is not possible because of the condition of the child and palatability issues. In certain cases it is possible to obtain immediate systemic effect by rectal administration of solutions. There is, however, limited absorption and bioavailability for many APIs. Erratic absorption due to faecal contents in the rectum may unpredictably delay absorption.
Dosage forms for rectal administration are primarily suppositories, rectal capsules and rectal liquids (enemas). Other dosage forms are available, e.g. rectal foams provided in pressurized containers.
When suppositories and rectal capsules are administered to paediatric patients there is a risk of premature expulsion, especially when the dosage form constituents have an irritating effect. Rectal dosage forms should be used with extreme caution in premature infants, as they can tear very delicate tissues and, thus, introduce infection.
Adherence for rectal preparations may be lower than for oral dosage forms. There are barriers to rectal administration for both caregivers and patients in some regions and cultures. Generally their acceptability among children of any age is poor.
7.1 Suppositories:
Suppositories for use in paediatric patients must be tailored to the age or size of the child. Cutting of suppositories into halves should be avoided unless they are designed to be cut. The majority of suppositories contain APIs as solid particles, which may be unevenly distributed in the suppository base as a result of the manufacturing technique of moulding a molten formulation. However, it is also possible to prepare suppositories which can be cut in smaller portions, ensuring delivery of an appropriate dose. Information on acceptability of cutting suppositories should be provided. When designed to be cut, information on the technique should be provided in the patient leaflet.
Two types of suppository base are available: one is insoluble in water, e.g. hard fat, which melts below body temperature. With suppository melt formulations, special consideration has to be given to storage temperature. The other type of suppository is soluble or miscible with water, e.g. macrogols, which
are dissolved in or mixed with the rectal liquid. Both types may be irritants.
7.2 Rectal Liquids (Enemas):
Rectal liquids are solutions, suspensions or emulsions based on water or vegetable oil. Any volume to be administered should be appropriate to the size of the child. For systemic therapy, the volume to be administered should be as small as possible to achieve accurate delivery, good absorption and to avoid irritation. Volumes of 1–5 ml may be acceptable.
The rectal tube should be of a length appropriate to the size of the child and should not cause injury. Use of pre-filled syringes equipped with a rectal tube facilitates individual dosing and may reduce the need for several strengths of the formulation.
Formulation of aqueous rectal liquids is similar to the formulation of other aqueous liquids regarding use of stabilizing agents, including surfactants and antimicrobial agents. Non-ionic surfactants are preferred because ionic surfactants are frequently irritating to the rectal mucosa. The need for stabilizing agents, in particular antimicrobial agents, may be reduced by the formulation of rectal tablets to be dispersed or dissolved in water immediately before administration.
Development of Paediatric Medicines: points to consider in formulation,
(Annex 5, WHO Technical Report Series 970, 2012)
