Tablets have been designed for vaginal administration in the treatment oflocal infections as well as for systemic absorption and absorption into thevaginal tissue. The vaginal wall consists of highly vascular tissue providing the potential for- excellent absorption across the membrane lining.The venous circulation from this area drains through the hypogastic veindirectly into the 'inferior vena cava thus bypassing .the portal vein andavoiding the rapid destruction of those drugs which are susceptible tofirst-pass metabolism in the liver.Only those compounds that have specific use in treating the femal reproductive system are usually administered by the vaginal route, althoughmany drugs are well absorbed this way and would give effective bloodlevels. The absorption of compounds used to treat local vaginal infectionsis not necessarily desirable, since this could lower the effective concentration of the drug directly in contact with the infecting organism. Manytypes of products have been designed for vaginal administration includingcreams, gels, suppositories, powders, solutions, suspensions, and spongesas well as tablets, which are the subject of this discussion. Estrogenshave been administered to increase the level in the vaginal tissue in thetreatment of atropic vaginitis and further absorption into the system isnot seen as beneficial. Progesterones such as flugestone acetate havebeen administered intravaginally on sponges to syncronize estrus in sheepand other domestic animals [60]. Tablets could also be used but are notconsidered the dosage form of choice for this purpose.Vaginal absorption follows first-order kinetics and has been describedas two parallel pathways, a lipoidal and an aqueous pore pathway. Thisis based on a study of absorption of aliphatic acids and alcohols in therabbit [61]. The plasma level of propranolol in women after vaginal administration has been shown to be much higher than when the product isgiven orally [62]. Cyclodextran formulations of hydrophilic drugs such asamino glycosides , B-Iactam antibiotics, and peptides are reported to bemore readily absorbed from the nasal cavity, vagina, and rectum thanwhen the drug is administered alone [63].Despite the demonstrated effectiveness of systemic absorption throughthe vaginal wall, the most frequent use of vaginally administered medication and especially tablets is in the treatment of localized vaginal infectionssuch as Candida albicans, yeast. and Haemophilus vaginalis. The mostcommonly used drugs in the treatment of these infections are nystatin.clotrimazole, and sulfonamides. The formula and design of vaginal tabletsshould aim for the slow dissolution or erosion of the tablet in the vaginal secretions, as a rate sufficient to provide an effective level of medicationfor as long a time as possible. The same approach is also used in the formulation of buccal tablets and troches. The tablet should remain in onepiece during dissolution and not break into fragments. Vaginal tabletsweigh from 1 to 1-1/2 g, are flat with an oval-. pear-, or bullet-shapedsilhouette, and are usually not coated. They can be inserted with the aidof an applicator that is provided by the manufacturer. The treatment forthese infections usually is one to two tablets once or twice daily for 2weeks.Since these tablets are not subject to peristaltic action. a method oftesting tablet disintegration under static conditions has been devised thatshould give a more realistic measure of what could be expected in actualuse and also serve as a quality control test [64]. The apparatus is simpleand consists of two pieces of no. 9 mesh screen wire. The tablet isplaced on a screen and covered with the second screen and placed in distilled water at 37°C in the horizontal position. The disintegration time isdefined as the time when the two screens touch. This method has beenused for both effervescent and noneffervescent tablets.Sustained release-type formulations that were previously describedunder buccal tablets also include references to and examples of vaginaltablets using HPMC or vegetable gumsSublingual Tablet
đang được dịch, vui lòng đợi..