High-performance liquid chromatographic determination of etretinate and all-trans- and 13-cis-acitretin in human plasma.

A high-performance liquid chromatographic procedure is described for the simultaneous determination of etretinate (Tigason), all-trans-acitretin (Neotigason) and 13-cis-acitretin in human plasma. The compounds are extracted from the plasma with n-hexane under acidic conditions. Quantification is performed on a normal-phase column (CP-Spher Si, 5 microns), followed by UV detection at 350 nm. The limit of quantification is 3 ng/ml. The day-to-day precision was 6.7, 13.6 and 9.1% for etretinate (means = 53 ng/ml), all-trans-acitretin (means = 95 ng/ml) and 13-cis-acitretin (means = 149 ng/ml), respectively (n = 13 for each compound). The within-day precision of nine determinations was 3.2, 11.7 and 6.5%, respectively, with mean concentrations of 128.53 and 261 ng/ml, respectively. The method was also applied to the study of the long-term pharmacokinetic behaviour of etretinate in psoriatic patients previously treated with etretinate but now on therapy with all-trans-acitretin.