Use of Intrathecal SNX-111, a Novel, N-Type, Voltage-Sensitive, Calcium Channel Blocker, in the Management of Intractable Brachial Plexus Avulsion Pain

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Abstract
The objective was to assess the analgesic, antihyperesthesic, and antiallodynic properties of SNX-111 in neuropathic pain. We describe a patient with refractory, severe deafferentation pain successfully treated with SNX-111 in an open-label, baseline-controlled Phase I/II trial. The patient was hospitalized for treatment and observation. The patient was a 43-year-old man with intractable deafferentation pain of 23 years' duration secondary to brachial plexus avulsion. SNX-111, the first neuron-specific, N-type, voltage-sensitive calcium channel blocker developed for clinical use, was administered by continuous, constant-rate, intrathecal infusion via an indwelling cervical catheter. The primary outcome measures were the Visual Analog Scales of Pain Intensity (VASPI) and Pain Relief (VASPR). The patient experienced complete pain relief (VASPI = 0.0 cm and VASPR = 10.0 cm) with elimination of hyperesthesia and allodynia. SNX-111, administered intrathecally by continuous, constant-rate infusion, produced dose-dependent pain relief in a 43-year-old male patient with a 23-year history of intractable deafferentation and phantom limb pain secondary to brachial plexus avulsion and subsequent amputation. Dizziness, blurred vision, and lateral-gaze nystagmus were dose-dependent side effects that resolved with decreasing dose levels. Complete pain relief was achieved in this patient without side effects after dose adjustment. We conclude that SNX-111 is a potent analgesic, antihyperesthesic, and antiallodynic agent. Controlled studies of SNX-111 in patients with malignant and nonmalignant pain syndromes are warranted and are under way.