Dexketoprofen/tramadol 25/75 mg (DKP/TRAM) is a fixed-dose combination of a cyclooxygenase inhibitor and opioid receptor agonist. To better understand the efficacy and safety of DKP/TRAM in the treatment of moderate to severe acute lower back pain (LBP) with or without radiculopathy, we carried out a large explorative phase IV international, multicenter, prospective, randomized, double-blind, parallel group, placebo-controlled study (DANTE). A total of 538 patients with or without a history of LBP and experiencing acute LPB of moderate to severe intensity [Numerical Rating Scale-Pain Intensity (NRS-PI) score > 5] were randomized 4:4:1:1 to DKP/TRAM 25/75 mg every 8 h (n = 211), tramadol (TRAM) 100 mg (n = 207), placebo-matched DKP/TRAM (n = 59), or placebo-matched TRAM (n = 61). The proportion of patients achieving the primary endpoint, defined as the time to first achieve NRS-PI score < 4 or pain intensity reduction ≥ 30% from drug intake up to 8 h after the first dose, was higher in the DKP/TRAM arm than in the placebo group, but the difference was not statistically significant (46.1% vs. 42.6%, respectively; hazard ratio 1.11; 95% confidence interval 0.775, 1.595; p = 0.566). DKP/TRAM achieved superiority over TRAM in total pain relief at 4, 6, and 8 h (p < 0.05). Conversely, in relation to the secondary endpoints, a significantly greater reduction in NRS-PI score was seen with DKP/TRAM versus placebo starting from 1 h, and this reduction remained numerically lower throughout 8 h. Summed pain intensity difference values were also significantly lower at 4, 6, and 8 h with DKP/TRAM compared to TRAM (p < 0.05). Overall, DKP/TRAM was well tolerated. Although the primary endpoint was not met, secondary efficacy analyses suggest the superiority of DKP/TRAM over placebo and TRAM alone in terms of total pain relief. DKP/TRAM can be considered to be an effective and safe option for the treatment of moderate to severe acute LBP. EudraCT number: 2019-003656-37; ClinicalTrials.gov Identifier: NCT05170841.