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Pain is highly prevalent, but frequently untreated or under-treated, and health care professionals are faced with a range of treatment challenges. Multimodal therapy is recommended and can be achieved using open combinations (ie, concomitant administration) of individual agents, fixed-dose combinations (FDCs), or multimodal agents (ie, single agents with multiple mechanisms of action). Co-crystallization of active pharmaceutical ingredients (APIs) offers another approach, with the potential to provide drugs with unique properties and advantages for therapeutic applications compared to combinations. API–API co-crystals are single-entity forms that offer a unique possibility of improving the physicochemical properties of both constituent APIs, as well as permitting their synchronous release. Consequently, this may positively impact on their pharmacokinetic (PK) properties and profiles, providing a potential advantage over FDCs and translating into improved clinical efficacy and safety profiles. We report here a revision of the literature concerning API–API co-crystals for the treatment of pain. It becomes apparent that identifying APIs with complementary mechanisms of action that can be adequately co-crystallized in an appropriate molecular ratio applicable for therapeutic use is challenging. In addition, API–API co-crystals normally result in a mere increased exposure of an API without defined clinical benefits (since, to maintain the benefit-risk, the dose needs to be proportionally reduced to adjust for the increased exposure). An exception to this is the co-crystal of tramadol-celecoxib (CTC), that represents a unique concept in co-crystal technology. In CTC neither of its three active components that have complementary mechanisms of action (ie, the two enantiomers of tramadol and celecoxib) show increased exposure levels versus commercially available single-entity reference products, but rather show a change in their PK profile with potential clinical advantages. CTC is in Phase III clinical development for the treatment of pain.

Aim We compared the pharmacokinetic (PK) profiles of co‐crystal of tramadol–celecoxib (CTC) vs. each reference product (alone and in open combination) after single (first dose) and multiple dosing. Methods Healthy adults aged 18–50 years received, under fasted conditions, 15 twice‐daily doses of the following treatments (separated by ≥14‐day washout): 200 mg immediate‐release (IR) CTC (equivalent to 88 mg tramadol and 112 mg celecoxib; treatment 1); 100 mg IR tramadol (treatment 2), 100 mg celecoxib (treatment 3); and 100 mg IR tramadol and 100 mg celecoxib (treatment 4). The treatment sequence was assigned by computer‐generated randomization. PK parameters were calculated using non‐compartmental analysis. Parameters for CTC were adjusted according to reference product dose. Results A total of 30 subjects (20 males, mean age 35 years) were included. Multiple‐dose tramadol PK parameters for treatments 1, 2 and 4, respectively, were 551, 632 and 661 ng ml−1 [mean maximum plasma concentration (C max)]; 4796, 4990 and 5284 ng h ml−1 (area under the plasma concentration–time curve over the dosing interval at steady state); and 3.0, 2.0 and 2.0 h (median time to C max at steady state). For treatments 1, 3 and 4, multiple‐dose celecoxib PK parameters were 445, 536 and 396 ng ml−1; 2803, 3366 and 2897 ng h ml−1; and 2.0, 2.0 and 3.0 h. Single‐dose findings were consistent with multiple‐dose data. Types of adverse events were consistent with known reference product safety profiles. Conclusion After single (first dose) and multiple dosing, PK parameters for each active pharmaceutical ingredient in CTC were modified by co‐crystallization compared with reference products alone or in open combination.

Background Co-crystal of tramadol–celecoxib (CTC), containing equimolar quantities of the active pharmaceutical ingredients (APIs) tramadol and celecoxib (100 mg CTC = 44 mg rac–tramadol hydrochloride and 56 mg celecoxib), is a novel API-API co-crystal for the treatment of pain. We aimed to establish the effective dose of CTC for treating acute pain following oral surgery. Methods A dose-finding, double-blind, randomised, placebo- and active-controlled, multicentre (nine Spanish hospitals), phase II study (EudraCT number: 2011-002778-21) was performed in male and female patients aged ≥ 18 years experiencing moderate to severe pain following extraction of two or more impacted third molars requiring bone removal. Eligible patients were randomised via a computer-generated list to receive one of six single-dose treatments (CTC 50, 100, 150, 200 mg; tramadol 100 mg; and placebo). The primary efficacy endpoint was the sum of pain intensity difference (SPID) over 8 h assessed in the per-protocol population. Results Between 10 February 2012 and 13 February 2013, 334 patients were randomised and received study treatment: 50 mg (n = 55), 100 mg (n = 53), 150 mg (n = 57), or 200 mg (n = 57) of CTC, 100 mg tramadol (n = 58), or placebo (n = 54). CTC 100, 150, and 200 mg showed significantly higher efficacy compared with placebo and/or tramadol in all measures: SPID (0–8 h) (mean [standard deviation]): − 90 (234), − 139 (227), − 173 (224), 71 (213), and 22 (228), respectively. The proportion of patients experiencing treatment-emergent adverse events was lower in the 50 (12.7% [n = 7]), 100 (11.3% [n = 6]), and 150 (15.8% [n = 9]) mg CTC groups, and similar in the 200 mg (29.8% [n = 17]) CTC group, compared with the tramadol group (29.3% [n = 17]), with nausea, dizziness, and vomiting the most frequent events. Conclusion Significant improvement in the benefit–risk ratio was observed for CTC (doses ≥ 100 mg) over tramadol and placebo in the treatment of acute pain following oral surgery. Funding Laboratorios del Dr. Esteve, S.A.U.