BACKGROUND: Naproxen sodium/paracetamol (acetaminophen) is a combination for the treatment of symptomatic pain and fever marketed both as a prescription and an over-the-counter product in Mexico. OBJECTIVE: The aim of these 2 studies was to compare the bioavailability and to determine the bioequivalence of 2 test formulations (an oral-tablet formulation containing the combination of naproxen sodium/paracetamol 275/300 mg and an oral-suspension formulation containing the combination of naproxen sodium/paracetamol 375/300 mg per 15 mL) with their corresponding listed reference-drug formulations in Mexico (a list issued by Mexican health authorities). METHODS: Two separate, single-dose, randomized, open-label, 2-period crossover, postmarketing studies were conducted. For each study, a different set of eligible subjects was selected comprising healthy Mexican adults of either sex, and subjects were randomly assigned to receive 1 test formulation of the combination of naproxen sodium/paracetamol followed by the corresponding reference-drug formulation, or vice versa, with a 1-week washout period between doses. After a 12-hour overnight fast, subjects received a single dose of naproxen sodium/paracetamol 275/300-mg tablet or naproxen sodium/paracetamol 375/300 mg per 15 mL suspension, depending on the study. For the analysis of pharmacokinetic parameters, including C(max), AUC from time 0 (baseline) to 48 hours (AUC(0-48)), and AUC from baseline to infinity (AUC(0-infinity)), blood samples were drawn at baseline and at 0.16, 0.33, 0.5, 0.75, 1, 1.25, 1.5, 2, 2.5, 3, 4, 6, 8, 12, 24, and 48 hours after administration. The formulations were considered bioequivalent if the geometric mean ratios (test/reference) of the C(max) and AUC were within the predetermined range of 80% to 125%. Tolerability was determined by clinical assessment, monitoring vital signs, laboratory analysis results, and subject interviews regarding adverse events. RESULTS: A total of 26 subjects (15 men, 11 women; mean [SD] age, 29 [8] years [range, 20-50 years]; weight, 63.1 [9] kg [range, 51.4-84.4 kg]; height, 164 [9] cm [range, 149-179 cm]; and body mass index [BMI], 23.53 [2.18] kg/m(2) [range, 18.54-26.82 kg/m(2)]) were enrolled to receive the suspension-dosage formulation; 13 subjects received the suspension-test formulation first. A total of 26 subjects (13 men, 13 women; mean [SD] age, 29 [8] years [range, 18-43 years]; weight, 64.3 [7.7] kg [range, 50.6-80.7 kg]; height, 165 [9] cm [range, 151-181 cm]; and BMI, 23.64 [2.43] kg/m(2) [range, 18.02-26.42 kg/m(2)]) were enrolled to receive the tablet-dosage formulation; 13 subjects received the tablet-test formulation first. No significant period or sequence effects were detected based on analysis of variance. For the suspension-dosage formulation, the 90% CIs for naproxen C(max), AUC(0-48), and AUC(0-infinity) were 93.06% to 104.00%, 93.50% to 98.44%, and 92.14% to 98.99%, respectively, and were 90.09% to 105.90%, 88.58% to 99.34%, and 91.43% to 101.55%, respectively, for paracetamol. For the tablet-dosage formulation, the 90% CIs for naproxen C(max), AUC(0-48), and AUC(0-infinity) were 102.83% to 117.15%, 96.59% to 104.26%, and 96.01% to 102.90%, respectively, and were 94.04% to 121.09%, 95.48% to 105.64%, and 96.64% to 105.42%, respectively, for paracetamol. CONCLUSIONS: In these 2 small studies in healthy Mexican adult subjects, a single dose of naproxen sodium/paracetamol 275/300 mg of the test formulation of the tablet-dosage formulation or a single dose of naproxen sodium/paracetamol 375/300 mg per 15 mL of the test formulation of the suspension-dosage formulation was found to be bioequivalent to the corresponding reference formulations according to the regulatory definition of bioequivalence based on the rate and extent of absorption. All formulations were generally well tolerated.