ASSESSMENT OF BIOAVAILABILITY OF ORAL MICRONIZED PROGESTERONE USING ASALIVARY PROGESTERONE ENZYME-IMMUNOASSAY

Salivary progesterone was measured sequentially by enzyme immunoassay following 1 month and 6 months of oral therapy with 100 mg of microniz ed progesterone (MOP) in 40 healthy estrogenized postmenopausal women (aged 40-68 years). MOP was administered for 23 days every month. Ther e were striking differences in the absorption of MOP between various s ubjects. Significant increases occurred in salivary progesterone conce ntrations over baseline and pretreatment levels and persisted for at l east 10 h. Levels of salivary progesterone remained higher than pretre atment levels for at least 24 h after administration of MOP. Maximum m ean concentrations of salivary progesterone of 827.2 and 888 pmol/l in the 1st and 6th months of therapy, respectively, were achieved within 2 h of administration and were above the 95th percentile of a control corridor which corresponds to the range found in the luteal phase. Th e areas under the salivary progesterone curve (AUC0-24h, pmol/l) were 7177.75 and 7388.20 respectively, in the lst and 6th months of therapy but the difference was not statistically significant. Serum and saliv ary progesterone peaked simultaneously and there was a significant cor relation between the concentrations measured concurrently (y = 233.08 + 35.575x; r = 0.89, p < 0.001) thus supporting the current concept Of a relatively rapid diffusion of steroids from plasma to saliva. Resul ts of this study confirm those of previous investigations which monito red the bioavailability of MOP with the use of serum progesterone meas urements and showed that luteal phase progesterone concentrations can be attained easily. The use of non-invasive salivary sampling and a co st-effective, direct enzymeimmunoassay showed a considerable advantage in the present study, compared with previous ones. We conclude that 1 00 mg MOP should be given at least twice-daily to maintain a stable ph ysiological luteal phase level of progesterone during clinical hormone replacement therapy.