Retention and distribution of two 99mTc-DTPA labelled vaginal dosage forms

To objectively evaluate the performance of new vaginal dosage forms, it is important to determine their time of residence and their distribution. This paper describes the in vivo characteristics of a reference and test product in this situation.

A randomised cross-over study was performed in the same phase of the menstrual cycle in eight pre-menopausal women. The retention and distribution of a commercially available vaginal clotrimazole cream and a test gel product, each "labelled" with 99mTc-DTPA was assessed by gamma scintigraphy for 24 h after administration of the products. Mass balance analysis was attempted by collecting and counting sanitary napkins worn for the study time.

Within individuals there was little variation in the clearance of the formulations, but wide variation between individuals with a range between 81 and 1% of the administered doses retained by 24 h. The losses appeared to occur mainly at times of urination with 12 +/- 8% (cream) and 20 +/- 23% (gel) collected on the sanitary napkins, but 46 +/- 34% (cream) and 38 +/- 22% gel activity not accounted for by 24 h. The intravaginal distribution of activity was similar for each product.

Radioactive tracer methods are useful in assessing and comparing vaginal dosage forms.