A Randomized, Double-Blind, Placebo-Controlled, Crossover Study of the T-Type Calcium Channel Blocker ABT-639 in an Intradermal Capsaicin Experimental Pain Model in Healthy Adults.

Objective: This randomized, double-blind, placebo-controlled, crossover trial evaluated the pharmacodynamic effects of a single 100-mg dose of ABT-639, a peripherally active, selective T-type Ca3.2 channel blocker, with the intradermal capsaicin pain model using pregabalin 300 mg as a positive control.

Subjects: Healthy adult males (aged 21 to 55 years) were randomly assigned to receive single oral doses of ABT-639, pregabalin, and placebo.

Methods: Serial measurements for area (cm) of hyperalgesia, allodynia, and flare response were performed over a 20-minute period after each capsaicin injection at 1 and 4 hours post-dose. Capsaicin injections were administered in different arms as determined by random assignment. Serial measurements for spontaneous pain and elicited pain were performed over a 60-minute period at 1 and 4 hours post-dose using a 100-mm visual analog scale. Standard safety evaluations were performed.

Results: Nineteen participants were randomized and included in the analysis. No significant differences were observed between ABT-639 and placebo in spontaneous pain, elicited pain, and areas of allodynia, hyperalgesia, and flare after intradermal capsaicin injection at 1 and 4 hours post-dose. In contrast, pregabalin demonstrated significant reductions in spontaneous pain at 1 and 4 hours post-dose, and elicited pain and areas of allodynia and hyperalgesia at 4 hours post-dose compared with placebo. ABT-639 demonstrated acceptable safety and tolerability; somnolence and euphoric mood were the most commonly reported adverse events.

Conclusions: These data indicate that a single 100-mg dose of ABT-639 had no effect on experimental pain induced by intradermal capsaicin injection.