Standardizing 8-methoxypsoralen plasma profiles by using an emulsion form.

Uniform 8-methoxypsoralen (8-MOP) absorption from the gastrointestinal tract is necessary to avoid day-to-day variations in 8-MOP plasma levels when treating patients with psoriasis by photochemotherapy. Because of its low water solubility, particle size and crystal form of the 8-MOP can significantly influence its bioavailability. The presentation form is also important, as is shown by the present study in which 8-MOP plasma levels were compared in thirty patients after oral administration in three different forms: formulation A consisted of gelatin capsules containing 8-MOP with a mean particle size of 200 mu; formulation B consisted of gelatin capsules containing 8-MOP in microcrystalline form with particle size between 20 mu and 30 mu; formulation C contained the same microcrystalline 8-MOP but in an emulsion base. Significantly higher plasma levels were found with formulations B and C than with formulation A. Furthermore, the individual differences in plasma profiles were markedly less with the emulsion base than with the capsule forms. Therefore, the clinical use of 8-MOP in emulsion form would constitute a major step in 8-MOP dose standardization and could lead to better control of subjective side effects and better therapeutic results.