Enzymatic assay of medroxyprogesterone acetate in plasma

An enzyme linked immunosorbent assay (ELISA) for plasma medroxyprogesterone acetate (MPA)

A single extraction fixed antigen enzyme-linked immunosorbent assay (ELISA) that can be completed in less than 24 h is described for the measurement of medroxyprogesterone acetate (MPA) in plasma. MPA is covalently coupled to bovine thyroglobulin and passively adsorbed in guanidine hydrochloride to a standard 96-well microtitre plate where it competes with MPA in the extracted plasma sample for goat anti-MPA. Antibody binding to the solid phase is determined via binding of a horse-radish peroxidase second antibody which reacts colorimetrically with its substrate. The reaction is stopped by addition of 1.25 M H2SO4 and absorbance read at 492 nm. All steps except for sample addition and extraction can be performed on an automatic ELISA processing machine. The assay is sensitive, specific and precise, with intra- and inter-assay coefficients of variation of less than 10 and 15%, respectively. Assay sensitivity is 0.08 ng/ml. The assay follows established methodology for other assays in this laboratory which assists standardization, cost structure and sample throughput and thus is a useful alternative to radioimmunoassays for the determination of MPA in plasma.

Comparison of mass spectrometry and radioimmunoassay to measure medroxyprogesterone acetate in patients with endometrial cancer

Serum medroxyprogesterone acetate (MPA) was measured by radioimmunoassay (RIA) and gas chromatography-mass spectrometry (GC-MS) in patients with endometrial cancer. Samples were obtained 3, 6 and 24 h after the oral administration of 100 or 200 mg MPA once a day. The levels obtained by GC-MS were lower (median 16-29%) than those obtained by RIA, which is probably attributable to the presence of metabolites interfering with the RIA. Two commercial MPA formulations gave different MPA serum levels by both RIA and GC-MS. The levels obtained by GC-MS were so low that frequently only partial saturation of the endometrial progesterone receptor may be achieved which may explain why high oral doses are needed to produce optimum therapeutic response.

Plasma concentrations of megestrol acetate and medroxyprogesterone acetate after single oral administration to healthy subjects

Plasma concentrations of megestrol acetate (MA) were measured by radioimmunoassay (RIA) after a single oral dose of 60 mg either in the form of one tablet, or four 15 mg tablets, to 10 women 21-40 years old using a cross-over design. No statistically significant difference between the two preparations was observed with respect to plasma concentrations, the area under the curve from 0 to 24 h or the maximum concentration (c(max)). For comparison, data are presented on the plasma level of medroxyprogesterone acetate (MPA) following a single oral dose of 100 mg given using a cross-over design in two different tablet forms to 10 healthy men, when no significant difference was observed for these parameters. The mean c(max) for MA after 2.6 h was 43.9 ng/ml (range 21.7-87.7 ng/ml), whereas that for MPA at 3.1 h was 13.1 ng/ml (range 4.4-29.5 ng/ml) despite the higher dose. After 24 h immunoreactive MA and MPA ranged from 9.6 to 29.0 ng/ml and from 0.2 to 4.0 ng/ml respectively. Moreover, it was found that petroleum ether extraction gives the most specific result by RIA, although considerable amounts of metabolites are still co-estimated. By comparison with selected ion monitoring using GC-MS, metabolite interference in RIA increases with time after administration of the steroids and is considerably greater for MPA than for MA. It is concluded that after oral administration the relative bioavailability of MA is significantly better than that of MPA.