Early clinical experience with the novel NMDA receptor antagonist CNS 5161

Aims: To investigate the safety, tolerability and pharmacokinetics of the novel NMDA antagonist CNS 5161 in humans. Excessive activation of glutamate receptors, especially of the N-methyl-d-aspartate (NMDA) subtype has been associated with neuropathic pain, and brain damage caused by focal ischaemia in mature brain or hypoxia-ischaemia (HI) in neonates. CNS 5161 is a novel NMDA ion-channel antagonist that interacts with the NMDA Receptor/ion channel site to produce a noncompetitive blockade of the actions of glutamate. Pre-clinical studies have demonstrated neuroprotective effects of CNS 5161 in the adult rat model of focal cerebral ischaemia, as well as anticonvulsant and analgesic effects. This study reports the first administration of CNS 5161 to man. Its objectives were to investigate the haemodynamic effects of the compound, to assess its safety and tolerability in healthy male volunteers, and to provide some preliminary human pharmacokinetic data.

Methods: We performed a randomized, double-blind placebo controlled phase 1 dose escalation study of CNS 5161. Volunteers were randomized to receive CNS 5161 or placebo in a ratio of 3:1. Twenty-four of 32 healthy volunteers received intravenous infusion of CNS 5161 over 15 min, followed by serial measurements of plasma drug concentration and haemodynamic observations over 24 h. A dose escalation design was adopted and the volunteers were stratified into eight dosage groups, ranging from 30 microg to 2000 microg.

Results: The drug was well tolerated by recipients. Side-effects were dose-related, self limiting and comprised minor subjective sensory symptoms. A dose dependent rise in systolic, mean arterial and diastolic blood pressure was seen in subsequent dosage groups, reaching 23/19 mmHg. Maximal effects were seen between 60 and 120 min after commencement of infusion. All subjects returned to baseline haemodynamic values within 24 h. Putative neuroprotective concentrations of CNS 5161 were achieved transiently, although these levels were not sustained. The pharmacokinetic data were best described by a two compartment model. The mean half-life was 2.95 h (s.d. 0.75). Mean clearance was 106 l h(-1) (s.d. 17.8) mean volume of distribution was 296 l (s.d. 69). These parameters were not significantly affected by body weight.

Conclusions: This study suggests that CNS 5161 is well tolerated in healthy volunteers within the dose range studied. In addition, information concerning the pharmacokinetics of the compound has been acquired. Studies to investigate the efficacy of the compound in man may now be justified.