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Bioavailability of norethindrone in human subjects
European Journal of Clinical Pharmacology
|March 17, 1978
Summary
A new assay measures norethindrone plasma levels, revealing higher concentrations in women than men. Pharmacokinetic analysis showed similar half-lives and bioavailability across different formulations.
Area of Science:
- Pharmacology
- Endocrinology
- Analytical Chemistry
Background:
- Norethindrone is a synthetic progestin used in hormonal therapies.
- Accurate measurement of norethindrone plasma levels is crucial for understanding its pharmacokinetics and therapeutic effects.
- Existing methods may have limitations in sensitivity or practicality for routine clinical use.
Purpose of the Study:
- To develop and validate a competitive protein binding assay for quantifying norethindrone in human plasma.
- To investigate the pharmacokinetic profile of norethindrone, including plasma levels, dose-dependency, and half-life in human subjects.
- To compare the bioavailability of norethindrone from different manufacturers.
Main Methods:
- Development of a competitive protein binding assay (CPBA) for norethindrone.
- Measurement of plasma norethindrone concentrations in male and female human subjects following oral administration.
- Pharmacokinetic analysis including determination of plasma half-life.
- Comparative bioavailability study of norethindrone from two different manufacturers.
Main Results:
- The developed CPBA enabled reliable measurement of plasma norethindrone levels.
- Plasma norethindrone levels were significantly higher in women compared to men, particularly at lower doses.
- Dose-dependent increases in plasma levels were observed in men, while women exhibited greater inter-individual variability.
- The plasma half-life of norethindrone was approximately 5 hours in both sexes for doses ranging from 5 to 20 mg.
- No significant differences in absorption characteristics were found between the two norethindrone formulations, indicating comparable bioavailability.
Conclusions:
- The competitive protein binding assay is a suitable method for measuring norethindrone plasma levels.
- Sex-based differences in norethindrone pharmacokinetics exist, with women showing higher plasma concentrations.
- Norethindrone exhibits predictable pharmacokinetics with a consistent half-life across a therapeutic dose range.
- The bioavailability of norethindrone is comparable between different manufacturers when formulated similarly.