Morning stiffness and nightime pain in ankylosing spondylitis. A comparison between enteric-coated and plain naproxen tablets.

Thirty-nine patients with ankylosing spondylitis participated in a randomized, double-blind, double-dummy, multi-cross-over study with enteric-coated (ECT) and plain (PT) naproxen tablets. The duration of the study was 24 days with 6 treatment periods of 4 days. The majority of the patients were taking 750 mg naproxen daily. The mean plasma concentration of naproxen in the morning was 36% higher with ECT (p < 0.001). No significant differences regarding duration of morning stiffness and night time pain were found in this patient category. The mean duration of morning stiffness was 116 minutes (ECT) and 125 minutes (PT). We were not able to show correlation between plasma concentration of naproxen and duration of morning stiffness.