Лако-красочные материалы — производство

Most recently administered drugs for either local or systemic therapy are given in suppository form. Systemic availability of rectally administered drugs is maximal when the dosage form is close to the anus [51]. Normally, after insertion, suppositories tend gradually to migrate and rest in the upper portion of the rectum. Drugs that are absorbed through this area into the bloodstream enter the hepatic-portal system and are subject to first-pass metabolism, which in turn degrades many susceptible drugs and leaves them ineffective. The lower rectum’s blood flow, however, drains directly into the general circulation, and first-pass metabolism of a drug can be avoided if the delivery system can be maintained in the lower region [52,53]. Suppositories containing bioadhe­sives can reduce this migration toward the upper rectum and hence improve drug bioavailability.

Penetration enhancers that improve the uptake of compounds into the epithelium can also be incorporated into such a delivery system. These enhancers are often used for hydrophilic compounds (especially peptides and proteins), which show low permeability through the barrier membrane. Although penetration enhancers have obvious benefits in absorption of drugs through the epithelium, they may also cause adverse effects to the tissue as well as local or systemic side effects [54]. Yet because of the delivery system’s localization, the concentration of enhancers can be minimized, thus reducing adverse effects. Indeed, promising results were shown in using enhancers in the rectum for com­pounds that normally show poor bioavailability. For example, insulin uptake into the bloodstream has been shown to increase when enhancers are used in rectal administration [55,56]. Controlled release of antipyrine and theophylline using cross-linked hydroxyethyl methacrylate (HEMA) as a bioadhesive was shown to sustain the availability of rectally applied drug in humans [57]. The combination of permeability enhancement and localiza­tion by bioadhesives has the potential to increase drug bioavailability significantly via the rectal route of administration.