16-11-2012, 10:42 AM
Vaginal Drug Delivery System
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Introduction
The vagina, unlike other systems like buccal or gastrointestinal, is highly dynamic with respect to its physiology, which renders the vaginal environment an uncertainty factor with respect to retention of vaginal dosage forms, absorption of drugs, their metabolism and their elimination from the vagina. This review brings out the factors that contribute to the vaginal dynamism and its influence on the fate of the administered drug.
Anatomy & Physiology of Vagina
The vagina in the adult premenopausal female is approximately 7-8 cm in length and 2 cm wide, shrinking in the postmenopausal female to approximately 4.5-6 cm in length and 1-1.5 cm in width.
Normal pH of the vagina in premenopausal women ranges from 4 to 5, and rises to almost 7 in the post menopausal female.
The vagina is characterized by an exceptional elasticity and the surface area of the vagina is increased by numerous folds by microridges covering the epithelium cell surface.
Vagina as a site for drug delivery
The vaginal defense micro-biology and vascularity make it ideal for absorbing drugs.
The anatomical position of vagina in human favours secures retention of vaginal formulations.
Vaginal delivery can be used for systemic as well as local action.
However, several drawbacks like cultural sensitivity, personal hygiene, gender specificity, local irritation and influence on sexual intercourse need to be addressed during the design of a vaginal formulation.
Advantages of vaginal drug delivery
Vaginal route can be used for local as well as systemic effect, attaining sustained therapeutic levels compared to conventional oral route.
Vaginal administration permits use of prolonged dosing, with continuous release of medicaments, and hence, longer interval between doses, improving user compliance.
Avoiding the fluctuations resulting from daily intake may also lower the incidence of side effects. For example, vaginal delivery of bromocriptine reduces the incidence and severity of its gastrointestinal (GI) side-effects if administered orally.
Alleviating the inconvenience caused by pain, tissue damage and probable infection, it serves as a better alternative to parenteral route.
Physiological factors affecting vaginal drug delivery
The vaginal epithelium undergoes cyclic changes, under the influence of hormones such as oestrogen, progesterone, luteinizing hormone, follicle stimulating hormone.
These cyclic changes drastically affect the epithelial thickness and porosity, pH and amount and composition of vaginal secretions.
The vaginal absorption of steroids is affected by the thickness of the vaginal epithelium.
Vaginal absorption of oestrogen is reported to be higher in postmenopausal women compared to premenopausal women.
The volume, viscosity and pH of vaginal fluid have a considerable influence on vaginal drug absorption
The variations in the enzyme activity with cyclic and hormonal changes affect vaginal drug delivery.