Acitretin (Neotigason). A review of pharmacokinetics and teratogenicity and hypothesis on metabolic pathways

Normal phase LC-MS determination of retinoic acid degradation products

The degradation products formed when 13-cis retinoic acid (13-cis RA) and all-trans RA were exposed to fluorescent light and air were investigated. These retinoids are known to undergo Z-E isomerization (due to the existence of four unsaturated double bonds) and oxidation when exposed to light and air. Analysis by LC was carried out on a 25 cm x 4.6 mm Zorbax Rx-SIL (5 microns) with a mobile phase (1.4 ml min-1) of heptane-THF-acetic acid (96.5:3.5:0.015) and an in-line UV (365 nm) detector. The LC eluate was coupled through a Vestec universal interface to a Finnigan 4023 mass spectrometer. EI-mass spectra were obtained at 77 eV from m/z 200 to 350 with multiplier voltage of 1200 V. Solid samples of 13-cis RA and all-trans RA exposed to light and air and also solutions of these retinoids in the mobile phase exposed to the same conditions were used for the analysis. Tentative identities of the degradation products from the mass spectra suggest the isomerization of the retinoids (Z-E isomerism) and the formation of the 5,6-epoxides of these isomers. Identities of the 5,6-epoxides were confirmed with chromatographic and mass spectral data from synthetic samples of the epoxides. Isomerization occurred more readily in solution than in the solid form and the 13-cis RA isomer oxidized more readily than the all-trans isomer.

Separation of 13-cis and all-trans retinoic acid and their photodegradation products using capillary zone electrophoresis and micellar electrokinetic chromatography (MEC)

Two retinoic acid isomers; 13-cis retinoic acid and all-trans retinoic acid and their photodegradation products were resolved with capillary electrophoresis (CE) (UV detector, 345 nm) using three different mobile phases: method 1--an acetonitrile modified borate buffer (pH 8.5); method 2--borate buffer (pH 8.5) modified with acetonitrile and alpha-cyclodextrin; and method 3--borate buffer (pH 8.5) modified with SDS (MEC). Concentration of acetonitrile in the buffer was varied from 10 to 50% in method 1 and resolutions of 0-1.9 were obtained for the two retinoic acid isomers. Similarly in method 2, concentration of alpha-cyclodextrin in the buffer (with 10% acetonitrile) was varied from 0 to 40 mM, giving resolutions of 0-3.8. In method 3, concentration of SDS in the buffer was varied from 5 to 60 mM resulting in resolutions of 1.3-4.1. Optimum separation conditions for the three methods were applied to the separation of photodegradation products of the two retinoids after exposure to fluorescent light for 36 h. A buffer modified with 45% acetonitrile and the same buffer modified with 10 mM SDS gave incompletely resolved electropherograms with a 72 cm x 50 microns capillary (50 cm to the detector). A buffer containing 20 mM alpha-cyclodextrin 10% acetonitrile gave completely resolved peaks for each isomer. The buffer containing 10 mM SDS gave completely resolved peaks for the photodegradation products when a 122 cm x 50 microns capillary (100 cm to detector) was used.