1alpha, 25-Dihydroxy-22-oxacalcitriol (
maxacalcitol) is a
vitamin D3 analogue which displays approximately 10 times greater efficacy at suppressing keratinocyte proliferation in vitro than
calcipotriol and
tacalcitol. To determine clinical efficacy, a phase II double-blind, randomized, left vs. right, concentration-response study was performed with once-daily topical
maxacalcitol in patients with mild to moderate chronic plaque
psoriasis. Primary efficacy parameters were
psoriasis severity index (PSI) based on sum of scores for
erythema, scaling and induration and investigators' overall assessment of patients' response to
therapy at 8 weeks of treatment. One hundred and forty-four patients participated. All concentrations of
maxacalcitol ointment (6, 12.5, 25 and 50 microg/g) were significantly more effective at reducing PSI than placebo (P < 0.01), with greatest effect noted for
maxacalcitol 25 microg/g.
Calcipotriol ointment 50 microg/g once daily as active comparator had a similar effect. Marked improvement or clearance of
psoriasis was greatest for
maxacalcitol 25 microg/g (55% of subjects) which compared favourably with
calcipotriol (46%). Improvement continued throughout the study period, with no plateau at week 8. Investigators' and patients' side preference (secondary efficacy parameters) rated
maxacalcitol more effective than placebo and 25 microg/g
maxacalcitol better than
calcipotriol (P < 0.05 for investigators' assessment). Twelve patients withdrew from the study due to adverse events, of which four were judged to be due to study medication. This study indicates that once-daily
maxacalcitol ointment is effective in the management of plaque
psoriasis, with greatest effect noted at 25 microg/g. As no response plateau was noted at 8 weeks, these data suggest that further benefit might be obtained if
maxacalcitol ointment were applied for longer. Finally, investigators' overall assessment and side preference suggest that
maxacalcitol 25 microg/g may be more effective than once-daily
calcipotriol.