| Popis: |
Metamizole is a non-opioid analgesic with additional antipyretic and spasmolytic properties. It was introduced nearly 100 years ago, but due to a severe but rare side-effect agranulocytosis, it has been withdrawn from the market in several countries. Metamizole is a prodrug, which is spontaneously hydrolyzed in the gastrointestinal tract to 4-methylaminoantipyrine (4-MAA). 4-MAA is rapidly and almost completely absorbed into circulation. The main fraction is oxidized to 4-formylaminoantipyrine (4-FAA) or demethylated to 4-aminoantipyrine (4-AA), which is then acetylated to 4-acetylaminoantipyrine. Other metabolites have been described, but these 4 main metabolites reflect about 65-70% of the administered metamizole dose. The two metabolites 4-MAA and 4-AA exhibit an analgesic effect, while the end metabolites 4-AAA and 4-FAA are considered inactive. Although metamizole has been available for nearly a century, there are still knowledge gaps such as the pharmacological mode of action. Furthermore, the enzymatic system responsible for the demethylation and the oxidation of 4-MAA has not been discovered yet. Participation of cytochrome P450 (CYP) has been suspected, but the specific isoforms have not been identified so far. Additionally, there is evidence that metamizole induces both CYP2B6 and CYP3A4 isoforms, the mechanism however has not been shown yet. A main focus of my thesis was to study the pharmacokinetics and metabolism of metamizole in clinical trials as well as in vitro experiments. These studies required reliable quantification of the metamizole main metabolites. In the first project, we therefore developed and validated a high-performance liquid chromatography tandem mass spectrometer (HPLC-MS/MS) method for the quantification of 4-MAA, 4-AA, 4-AAA, and 4-FAA in human plasma samples. A pentafluorophenyl analytical column resulted in a suitable retention of the polar metabolites by interacting with their aromatic structure. A gradient program with pre- and post-column infusion was applied for the retention and separation of the hydrophilic analytes. Formic acid was removed from the solvents and reintroduced after the chromatography to achieve sufficient ionization. The method was linear over the calibration range (R > 0.99), with an accuracy of 91.3% - 106.0% and an imprecision of 1 year when treated with the recommended i.v. dose. Furthermore, we were able to show the impact of metamizole on the activity of various CYP isoforms. The co-administration of CYP1A2, CYP2B6, CYP2C19 and CYP3A4 substrates and metamizole may lead to altered drug-exposure and may therefore promote adverse effects. |
