Ziconotide, an intrathecally administered N-type calcium channel antagonist for the treatment of chronic pain. 
Ziconotide is a novel peptide that blocks the entry of calcium into neuronal N-type voltage-sensitive calcium channels, preventing the conduction of nerve signals.  N-type calcium channels are present in the superficial laminae of the dorsal horn of the spinal cord.  In various animal models of pain, intrathecal administration of ziconotide blocked nerve transmission and nociception.  The United States Food and Drug Administration recently approved ziconotide intrathecal infusion for the management of severe chronic pain in patients who require intrathecal therapy and who are intolerant of or refractory to other treatment, such as systemic analgesics, adjunctive therapies, or intrathecal morphine.  The drug has a narrow therapeutic window and a lag time for the onset and offset of analgesia and adverse events.  In early clinical trials, frequent and severe psychiatric and central nervous system adverse effects were associated with rapid intrathecal infusion (0.4 microg/hr) and frequent up-titration (every 12 hrs).  Therefore, patients with psychiatric symptoms are not candidates for this drug.  Drug trials of external intrathecal catheters and microinfusion devices demonstrated a 3% risk of meningitis.  A low initial infusion rate of 0.1 microg/hour and limiting infusion rate increases to 2-3 times/week are now recommended.  Patients responsive to intrathecal ziconotide require an implanted infusion system to receive long-term therapy.