Objective: Naproxen sodium (NAPSO) is commonly used in a variety of pain conditions. There are several strengths of NAPSO available over the counter (OTC). Most published data are based on single or multiple doses using 220 mg, hence there is a need to assess the analgesic efficacy of other strengths of NAPSO used in the OTC setting.
Materials and methods: We reviewed published and unpublished studies of naproxen (NAP) and NAPSO to establish the pharmacokinetic relationship between dosage, plasma concentration, and efficacy, and to compare the analgesic efficacy of NAPSO 220, 440, and 550 mg or NAP 500 mg versus placebo and active comparators.
Results: Increasing OTC doses of NAP are associated with linear pharmacokinetics, i.e., plasma levels of NAP increase proportionately with dosage. Accordingly, the therapeutic efficacy of higher doses of NAP or NAPSO is greater than lower doses. All OTC doses of NAP and NAPSO are significantly more effective than placebo. Higher strengths are as effective or more effective than lower strengths, and at least comparable to other active treatments.
Conclusion: The pharmacokinetic linearity associated with NAP means that data on efficacy for the lower OTC doses of NAPSO can be extrapolated to the higher OTC doses. Thus, it is given that NAPSO 275 and 550 mg will be at least as effective as or superior to the lower doses of 220 and 440 mg.