Intrathecal administration of Ziconotide: does single-shot injection predict efficacy?

Introduction: Though a trial of intrathecal (IT) therapy should always be performed before implantation of a definitive intrathecal pump, there is no agreement as to how this test should be performed. Ziconotide is trialed in most of cases with continuous IT administration using implanted catheters. Unlike other intrathecal drugs, there is little experience with single bolus IT injections of ziconotide. The aim of the study is to assess the feasibility of single-shot IT trialing with ziconotide. Patients and methods: Eleven consecutive patients with chronic neuropathic intractable pain were trialed with a single IT bolus of 2.5 mcg of ziconotide. Pain and side effects are monitored for at least 72 hours after the injection. Depending on the response, a second injection is given a week later, with either the same dose (if VAS decreased ≥50% without side effects), a higher dose of 3.75 mcg (if VAS decreased 50% without side effects after the first or the second dose, the result is confirmed by one more injection of the same dose one week later. The trial is considered positive if two successive injections provide a VAS decreased more than 50% without side effects. Results: Eleven patients (6 females and 5 males) were included. Nine patients experienced modest or no pain relief. Four of these had significant side effects (dizziness, nausea, vomiting or abdominal pain) and had no further injection. In the others 5, one patient retired from study and four received a second injection of 3.75 mcg. The trial was negative in all 5 cases because of side effects (dizziness, drowsiness, weakness, muscle cramps), the pain decreased in only 2 patients. Two patients experienced profound pain relief with an IT injection of 2.5 mcg. One patient had no side effects and the other had dizziness and drowsiness that disappeared with an injection of 1.25 mcg. Pain relief without adverse effects was confirmed with the second injection. The trial was considered positive for those two patients. Discussion and conclusion: The response rate of 18% (2/11) is consistent with the success rate of a continuous infusion trialing with an implanted catheter. Single-shot injection of ziconotide may therefore predict efficacy.