Vagina absorption

Few, if any, products are administered via the vagina that are intended for systemic absorption. Thus, this route has not been as widely studied and characterized as others. On the other hand, large numbers of different products (douches, spermicides, antiyeast agents, etc.) have been developed that require introduction into the vagina in order to assert their localized effects. Increased research into different birth control and antiviral prophylaxis will result in more vaginal products in the future. All these must be assessed for vaginal irritation potential, and this serves as an example of the other tissue tolerance issues. 

The vagina offers a substantial area for drug absorption, beeause numerous folds in the epithelium inerease the total surfaee area. A rieh vaseular network surrounds... 

Pharmacokinetics Absorption from vagina is variable and unreliable. Primarily metabolized by acetylation. Excreted in urine. Half-life Unknown. 

Macht, D. 1918. The absorption of drugs and poisons through the vagina. J Pharmacol Pathol 10 509. 

Daneshmend, T.K. 1986. Systemic absorption of miconazole from the vagina. J Antimicrob Chemother 18 507. 

Monkeys, in particular Rhesus macaque and squirrel monkey, have been considered as models for vaginal drug absorption because of the similarities between nonhuman primate and human anatomy. The vagina of rhesus macaques is characterized by connective tissue attachments, localization of steroid hormone receptors, duration, and cyclic changes in vaginal physiology similar to that of humans [119]. 

Compare the vagina with other absorptive sites for drugs in the body... 

The systemic absorption of these drugs had previously been considered only from the standpoint of toxicity. However, in addition to local delivery, there has recently been considerable interest in the possibility of vaginal delivery for the systemic delivery of drugs, via the mucous membranes of the vagina. 

The vagina offers a relatively large surface area (approximately 60 cm2) for drag absorption. However, it is much smaller than that offered by the nasal (150 cm3), rectal (200-400 m2), pulmonary (75-700 m2) and intestinal (200 m2) routes. 

Although, as described above, the vagina is permeable to many peptides and proteins, in most cases the bioavailability is insufficient for systemic therapy and is also highly variable. Penetration enhancers may be used to promote peptide absorption across the vaginal epithelium. However, less extensive investigations on the use of penetration enhancers for the vaginal route have been carried out in comparison to other routes, such as intranasal and transdermal (see Sections 9.7.1 and 8.6.1). 

The vagina is a possible site for the systemic administration of various drugs. However, the low and erratic bioavailability of biopharmaceuticals via this route necessitates the use of absorption enhancers. Until safe, non-toxic absorption enhancers can be found, the route is of limited potential. A further major limitation of this route is the lack of reproducibility resulting from cyclic changes in the reproductive system. Finally, no matter what degree of optimization can be achieved via this route, it can only ever benefit approximately 50% of the population ... 

Absorption of drugs through the vagina is an important parameter to be evaluated, particularly when a systemic effect is required. Also, assessment of the absorption potential of drugs intended to locally exert their effects needs to be evaluated, as this event can lead to unwanted systemic effects. The evaluation of both formulated and unformulated drugs can be performed by in vitro or in vivo methods. 

Robinson, G. D. (1925), Absorption from the human vagina, BJOG, 32,496-504. 

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