CP-101606 is a potent, selective NMDA receptor (NR2B subunit) antagonist under development by Pfizer for its potential as a neuroprotectant in head injury and neurodegenerative disease. It is in phase II trials in the US and in phase I in Japan for the potential treatment of head injury [267139], [320737], [378812]. As of March 2000, CP-101606 had completed US phase I trials successfully and was well tolerated with a good safety profile. Results of an open-label study in patients treated with CP-101606 (24 to 72 h infusion) following severe head trauma showed that 80% of patients had good recovery at the 3-month follow-up stage [360864]. In August 2000, Merrill Lynch predicted that the phase II trials program could be complete by the end of 2000 with the possibility of a filing based on its results if positive [379892]. The drug lacks the amnesic side effects of other NMDA receptor antagonists and it has no effects on long-term potentiation (LTP) [347642]. According to presenters at the 1999 Society for Neuroscience meeting, this may result from a novel activity-dependent or NR2B-selective mechanism of action [345079]. It is thought to act by inhibiting the damaging influx of Ca2+ across neuronal cell membranes following glutamate release triggered by tissue injury, e.g., stroke [300847]. CP-101606 prevents glutamate-induced toxicity in cultured hippocampal neurons when given during or immediately after glutamate perfusion, (IC50 = 11 and 35 nM, respectively). In contrast, CP-101606 does not protect against glutamate-induced neurotoxicity in cultured cerebellar neurons, up to a dose of 10 microM. These results are consistent with CP-101606 being a potent NMDA antagonist, selective for the type of NMDA receptor associated with the hippocampus [195435]. CP-101606 is a single isomer analog of CP-98113 (Pfizer Inc) [254010]. CP-101581 (Pfizer Inc) is an isomer of CP-101606 [254010]. In December 1998, Morgan Stanley Dean Witter predicted sales of US $5 million in 2001, rising to US $80 million by 2005 [315350].