Steady-state pharmacokinetics of enteric-coated naproxen tablets compared with standard naproxen tablets

In this open-label, randomized, cross-over study, 24 healthy volunteers (12 men and 12 women) received either enteric-coated (EC) naproxen tablets 500 mg twice daily or standard naproxen tablets 500 mg twice daily for 7 days. In each of the two study periods, blood sampling began on day 8, after one last dose of the study drug was administered, to determine and compare steady-state pharmacokinetics for each of the two naproxen formulations. The plasma half-life of naproxen averaged 16.3 and 16.9 hours following EC naproxen and standard naproxen treatments, respectively. Mean time to maximum plasma concentration (Tmax) was greater for EC naproxen than for standard naproxen (4.0 vs 1.9 hours), while the maximum observed plasma concentration (Cmax) was slightly, but not significantly, smaller (94.9 vs 97.4 micrograms/mL, respectively). The mean values for average plasma concentration (Cave) and minimum plasma concentration for EC naproxen were 70.4 and 60.6 micrograms/mL, respectively, compared with 63.9 and 44.1 micrograms/mL for standard naproxen. The mean plasma fluctuation about the mean was greater for standard naproxen than for EC naproxen (85.3% vs 49.3%), while the mean area under the plasma concentration-time curve (AUC) was smaller for standard naproxen (766.8 vs 845.0 micrograms x h/mL). At steady state, EC naproxen was similar to standard naproxen tablets with respect to Cmax, Cave, Cmax:Cave, 0- to 12-hour AUC, and half-life but differed in Tmax. In addition, fluctuations about Cave in plasma levels were considerably lower with EC naproxen than with standard naproxen.