The Purinergic System and Glial Cells: Emerging Costars in Nociception

Table 1

Summary of past and current clinical trials evaluating purinergic ligands in pain.

Name of ligand	Company	Clinical trial number	Type of pain	Main outcomes
AF219; (P2X3 antagonist)	Afferent Pharmaceuticals	NCT01554579	Osteoarthritis of the knee	No published results yet
		NCT01569438	Interstitial cystitis/bladder pain syndrome	No published results yet
CE-224,535; (P2X7 antagonist)	Pfizer	NCT00628095	Rheumatoid arthritis	CE-224,535 was not efficacious, compared with placebo, for the treatment of RA in patients with an inadequate response to metotrexate [72]
		NCT00418782	Osteoarthritis of the knee	CE-224,535 failed to demonstrate efficacy in a 2-week study of knee pain in osteoarthritis patients
AZD9056	AstraZeneca	NCT00520572	Rheumatoid arthritis	AZD9056 does not have significant efficacy in the treatment of RA [73]
GSK1482160; (P2X7 antagonist)	GlaxoSmithKline	NCT00849134	“First-in-human” study to assess the pharmacokinetic profile of the drug	No major safety or tolerability concerns were identified in this study. Nevertheless, monitoring the release of IL-1β in subjects led to the decision to discontinue drug development for inflammatory pain conditions [74]
Adenosine; (e.v.)	Wake Forest School of Medicine	NCT00349921	Neuropathic pain (comparison with clonidine)	No published results yet
	Xsira Pharmaceuticals	NCT00298636	Perioperative pain (hysterectomy/myomectomy)	No published results yet
GW493838	GlaxoSmithKline	NCT00376454	Neuropathic pain as a result of postherpetic neuralgia or nerve injury	No published results yet