a way that would allow it to be administered by less invasive means. However, this must be weighed against the high level of pain management, both in terms of degree and length, and the apparent lack of tolerance and other signs of dependence even after extended treatment along with the need for alternatives to other therapies that have not worked for the patient. Ziconotide is also contraindicated for patients with certain preexisting mental disorders (e.g. psychosis) due to evidence that they are more susceptible to certain severe side effects. Adverse reactions The most common side effects are dizziness, nausea, confusion, nystagmus, and headache. Others may include weakness, hypertonia, ataxia, abnormal vision, anorexia, somnolence, unsteadiness on feet, vertigo, urinary retention, pruritus, increased sweating, diarrhea, nausea, vomiting, asthenia, fever, rigors, sinusitis, muscle spasms, myalgia, insomnia, anxiety, amnesia, tremor, memory impairment, and induced psychiatric disorders. Other side effects which are less frequent but still clinically significant include auditory and visual hallucinations, thoughts of suicide, acute kidney failure, atrial fibrillation, cardiovascular accident, sepsis, new or worsening depression, paranoia, disorientation, meningitis, and seizures. Therefore, it is contraindicated in people with a history of psychosis, schizophrenia, clinical depression, and bipolar disorder. Recent incidents suggesting a link between intrathecal ziconotide treatment and increased risk of suicide have led to calls for strict and ongoing psychiatric monitoring of patients to avoid suicide occurring in vulnerable individuals. There is no known antidote. Structure Ziconotide is a peptide with the amino acid sequence H-Cys-Lys-Gly-Lys-Gly-Ala-Lys-Cys-Ser-Arg-Leu-Met-Tyr-Asp-Cys-Cys-Thr-Gly-Ser-Cys-Arg-Ser-Gly-Lys-Cys-NH2 (CKGKGAKCSRLMYDCCTGSCRSGKC-NH2) and contains 3 disulfide bonds (Cys1-Cys16, Cys8-Cys20, and Cys15-Cys25). Patents The drug was patented by Neurex Corp., a U.S. company purchased in 1998 by Élan Corporation, plc of Ireland. U.S. patents assigned to Elan include , , , and . References External links Analgesics Calcium channel blockers Peptides