The vagina is able to absorb drugs, even the likes of morphine and atropine, a muscle relaxant. Drugs used vaginally are most often designed to treat local conditions, but this delivery method could also be used for drugs to treat other conditions.
Some medicines generally used by mouth are used vaginally, for example misoprostol, a labour-induction drug. Another drug, oxybutynin, was marketed as an oral medicine, but is now used in a vaginal ring for treatment of overactive bladder.
The vagina is very capable in absorbing drugs, since it is raw mucous membrane with a hefty blood supply behind it. Some of the benefits of using the vagina as a drug delivery system include the digestion problems that can be encountered, like nausea, diarrhoea, poor absorption, and drug interactions. Skin patches can present problems if the patient has a lot of fat tissue, as it hampers absorption.
Skipping the digestive system means drugs avoid the first pass in the liver, which can significantly affect the absorption and distribution of drugs, as well as cause excess excretion of drugs taken orally. Lower doses, therefore, are required vaginally for the same effect. Less frequent dosing can improve side-effect profile by keeping drug levels steady for longer. Interestingly, the uterus gets a higher dose of any vaginally applied treatment compared to oral administration. This is due to the vast blood supply of the uterus.
Patient concerns with vaginal drug delivery
Women may be concerned that their treatments will ‘fall out’, however so long as the dose is applied deep enough, the vaginal rugae are quite able to hold treatments inside without effort. Additionally, like a tampon, treatments can’t be felt, due to very low innervation of most of the vaginal canal. Many patients may be unsure or reluctant to use this method, however with proper education, it can be a very beneficial delivery system. Vaginal drug delivery is very discreet.
Another concern is the effect of the drug on local flora, which may be detrimental. Trials would need to be conducted to confirm that no changes to flora occurred as a result of the vaginal drug delivery. Local irritation is also a risk.