OBJECTIVE: To evaluate the effect of effervescent paracetamol on office and ambulatory blood pressure (BP) compared with noneffervescent paracetamol in hypertensive patients. DESIGN: This was a multicenter open crossover randomized clinical trial. SETTING: Primary care centers in Catalonia and the Basque Country. PARTICIPANTS: Inclusion criteria were office BP 150/95¿mmHg or less and daytime ambulatory BP 140/90¿mmHg or less, stable pharmacologic or nonpharmacologic antihypertensive treatment, and concomitant chronic osteoarticular pain. INTERVENTIONS: Baseline randomized assignment to 3-week periods of effervescent paracetamol (1¿g three times a day) first and noneffervescent paracetamol later, or inversely, during a 7-week study period. At the start and end of each treatment period, 24-h ambulatory BP monitoring was performed. MAIN OUTCOME MEASURES: Differences in 24-h SBP between baseline and end of both treatment periods. The main analyses were performed according to the intention-to-treat principle. RESULTS: In intention-to-treat analysis, 46 patients were analyzed, 21 were treated with paracetamol effervescent and noneffervescent later, and 25 followed the opposite sequence. The difference in 24-h SBP between the two treatments was 3.99¿mmHg (95% confidence interval 1.35-6.63; P¿=¿0.004), higher in the effervescent paracetamol treatment period. Similarly, the per-protocol analysis showed a difference in 24-h SBP between the two groups of 5.04¿mmHg (95% confidence interval 1.80-8.28; P¿=¿0.004), higher in the effervescent paracetamol treatment period. Self-reported pain levels did not differ between groups and did not vary by treatment period. No serious adverse events were reported in either study arm. CONCLUSION: Effervescent paracetamol tablets are responsible for a significant daytime and overall increase in ambulatory 24-h SBP. TRIAL REGISTRATION: NCT: 02514538 EudraCT: 2010-023485-53.

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