<p>Naproxen is available as a free acid and sodium salt.<sup class="text-reference-group"><a class="reference-popover-link" data-content="Todd PA, Clissold SP: Naproxen. A reappraisal of its pharmacology, and therapeutic use in rheumatic diseases and pain states. Drugs. 1990 Jul;40(1):91-137. doi: 10.2165/00003495-199040010-00006. (PubMed ID 2202585)" href="#reference-A179098">5</a></sup> At comparable doses, (naproxen 500 mg = naproxen sodium 550 mg) they differ slightly in their rates of absorption, but otherwise they are therapeutically and pharmacologically equivalent.<sup class="text-reference-group"><a class="reference-popover-link" data-content="Todd PA, Clissold SP: Naproxen. A reappraisal of its pharmacology, and therapeutic use in rheumatic diseases and pain states. Drugs. 1990 Jul;40(1):91-137. doi: 10.2165/00003495-199040010-00006. (PubMed ID 2202585)" href="#reference-A179098">5</a></sup> Naproxen sodium achieves a peak plasma concentration after 1 hour, while peak plasma concentration is observed after 2 hours with naproxen (free acid).<sup class="text-reference-group"><a class="reference-popover-link" data-content="Todd PA, Clissold SP: Naproxen. A reappraisal of its pharmacology, and therapeutic use in rheumatic diseases and pain states. Drugs. 1990 Jul;40(1):91-137. doi: 10.2165/00003495-199040010-00006. (PubMed ID 2202585)" href="#reference-A179098">5</a></sup> There are no differences between the 2 forms in the post-absorption phase pharmacokinetics.<sup class="text-reference-group"><a class="reference-popover-link" data-content="Todd PA, Clissold SP: Naproxen. A reappraisal of its pharmacology, and therapeutic use in rheumatic diseases and pain states. Drugs. 1990 Jul;40(1):91-137. doi: 10.2165/00003495-199040010-00006. (PubMed ID 2202585)" href="#reference-A179098">5</a></sup> The difference in initial absorption should be considered when treating acute pain, since naproxen sodium may offer a quicker onset of action.<sup class="text-reference-group"><a class="reference-popover-link" data-content="Todd PA, Clissold SP: Naproxen. A reappraisal of its pharmacology, and therapeutic use in rheumatic diseases and pain states. Drugs. 1990 Jul;40(1):91-137. doi: 10.2165/00003495-199040010-00006. (PubMed ID 2202585)" href="#reference-A179098">5</a></sup></p><p>The mean Cmax for the various formulations (immediate release, enteric coated, controlled release etc.) of naproxen are comparable and range from 94 mcg/mL to 97.4 mcg/mL.<sup class="text-reference-group"><a class="reference-popover-link" data-content="Naprelan FDA Label" href="#reference-L6582">12</a></sup><sup class="text-reference-group"><a class="reference-popover-link" data-content="Naprosyn FDA Label" href="#reference-L6583">13</a></sup> In one pharmacokinetic study, the mean Tmax of naproxen 500 mg (immediate release) given every 12 hours over 5 days was 3 hours, compared to a mean Tmax of 5 hours for Naprelan 1000 mg (controlled release) given every 24 hours over 5 days.<sup class="text-reference-group"><a class="reference-popover-link" data-content="Naprelan FDA Label" href="#reference-L6582">12</a></sup> In this same study, the AUC<sub>0-24hr</sub> was 1446mcgxhr/mL for naproxen immediate release and 1448 mcgxhr/mL for the controlled release formulation.<sup class="text-reference-group"><a class="reference-popover-link" data-content="Naprelan FDA Label" href="#reference-L6582">12</a></sup> A separate study comparing the pharmacokinetics of Naprosyn tablets and EC-Naprosyn observed the following values: Tmax and AUC<sub>0-12hrs</sub> of EC-Naprosyn were 4 hours and 845 mcgxhr/mL respectively, and Tmax and AUC<sub>0-12hrs</sub> values of Naprosyn were 1.9 hours and 767 mcgxhr/mL respectively.<sup class="text-reference-group"><a class="reference-popover-link" data-content="Naprosyn FDA Label" href="#reference-L6583">13</a></sup> </p><p>When given in combination with sumatriptan the Cmax of naproxen is roughly 36% lower compared to naproxen sodium 550 mg tablets, and the median Tmax is 5 hours.<sup class="text-reference-group"><a class="reference-popover-link" data-content="Treximet FDA Label" href="#reference-L7309">15</a></sup></p><p>Based on the AUC and Cmax of naproxen, Vimovo (naproxen/esomeprazole combination product) and enteric-coated naproxen may be considered bioequivalent.<sup class="text-reference-group"><a class="reference-popover-link" data-content="Vimovo FDA Label" href="#reference-L7312">16</a></sup></p><p>Overall, naproxen is rapidly and completely absorbed when administered orally and rectally.<sup class="text-reference-group"><a class="reference-popover-link" data-content="Davies NM, Anderson KE: Clinical pharmacokinetics of naproxen. Clin Pharmacokinet. 1997 Apr;32(4):268-93. doi: 10.2165/00003088-199732040-00002. (PubMed ID 9113437)" href="#reference-A179110">6</a></sup><sup class="text-reference-group"><a class="reference-popover-link" data-content="Todd PA, Clissold SP: Naproxen. A reappraisal of its pharmacology, and therapeutic use in rheumatic diseases and pain states. Drugs. 1990 Jul;40(1):91-137. doi: 10.2165/00003495-199040010-00006. (PubMed ID 2202585)" href="#reference-A179098">5</a></sup> Food may contribute to a delay in the absorption of orally administered naproxen, but will not affect the extent of absorption.<sup class="text-reference-group"><a class="reference-popover-link" data-content="Todd PA, Clissold SP: Naproxen. A reappraisal of its pharmacology, and therapeutic use in rheumatic diseases and pain states. Drugs. 1990 Jul;40(1):91-137. doi: 10.2165/00003495-199040010-00006. (PubMed ID 2202585)" href="#reference-A179098">5</a></sup></p>