[1] Drexel Univ, Coll Med, Headache Clin, Dept Neurol, Philadelphia, PA 19102 USA
[2] Drexel Univ, Coll Med, Dept Physiol & Pharmacol, Philadelphia, PA 19102 USA
[3] Univ N Carolina, Dept Neurol, Chapel Hill, NC USA
[4] King Pharmaceut Inc, Houston, TX USA
[5] Houston Headache Clin, Houston, TX USA