Pharmacokinetic analysis of ziconotide (SNX-111), an intrathecal N-type calcium channel blocking analgesic, delivered by bolus and infusion in the dog.

BACKGROUND AND PURPOSE: Ziconotide is a peptide that blocks N-type calcium channels and is antihyperalgesic after intrathecal (IT) delivery. We here characterize the spinal kinetics of IT bolus and infused ziconotide in dog. EXPERIMENTAL APPROACH: Male beagle dogs (N= 5) were prepared with chronic IT lumbar injection and cerebrospinal fluid (LCSF) sampling catheters connected to vest-mounted pumps. Each dog received the following: 1) IT bolus ziconotide (10 µg + 1 µCi (3) H-inulin); 2) IT infusion for 48 hours of ziconotide (1 µg/100 µL/hour); 3) IT infusion for 48 hours of ziconotide (5 µg/100 µL/hour); and 4) intravenous injection of ziconotide (0.1 mg/kg). After IT bolus, LCSF ziconotide and inulin showed an initial peak and biphasic (distribution/elimination) clearance (ziconotide T(1/2-α/ß) = 0.14 and 1.77 hours, and inulin T(1/2-α/ß) = 0.16 and 3.88 hours, respectively). The LCSF : plasma ziconotide concentration ratio was 20,000:1 at 30 min and 30:1 at eight hours. IT infusion of 1 and then 5 µg/hour resulted in LCSF concentrations that peaked by eight hours and remained stable at 343 and 1380 ng/mL, respectively, to the end of the 48-hour infusions. Terminal elimination T(1/2) after termination of continuous infusion was 2.47 hours. Ziconotide LCSF : cisternal CSF : plasma concentration ratios after infusion of 1 and 5 µg/hour were 1:0.017:0.001 and 1:0.015:0.003, respectively. IT infusion of ziconotide at 1 µg/hour inhibited thermal skin twitch by 24 hours and produced modest trembling, ataxia, and decreased arousal. Effects continued through the 48-hour infusion period, increased in magnitude during the subsequent 5 µg/hour infusion periods, and disappeared after drug clearance. CONCLUSIONS AND IMPLICATIONS: After IT bolus or infusion, ziconotide displays linear kinetics that are consistent with a hydrophilic molecule of approximately 2500 Da that is cleared slightly more rapidly than inulin from the LCSF. Behavioral effects were dose dependent and reversible.

Conus magus vs. Irukandji syndrome: a computational approach of a possible new therapy.

The Irukandji syndrome is caused by the sting of some small jellyfish species. The syndrome has severe life-threatening consequences. The exacerbating pain and cardiovascular symptoms (tachycardia and hypertension) are hard to control in many cases. We suggest a way to experiment a new possible therapy with an FDA approved analgesic, ziconotide, a synthetic derivative from a marine cone snail (Conus magus) venom component, which is administrated intravenously. The proposed experimental plasma concentration of ziconotide for rats is in the range of 0-6µgml(-1). Based on a molecular biological scenario of the venom action mechanism at cellular level, we suggest that the proposed method should be functional in re-establishing the normal cardiovascular parameters of the experimental animals and concomitantly it should abolish the severe pain caused by envenomation. We expect that positive experimental results in agreement with our theory will lead to the possibility of a new therapy for the Irukandji syndrome and possibly for other envenomations with similar ethyology.

Bioavailability of Ziconotide in brain: influx from blood, stability, and diffusion.

Ziconotide is a selective peptide antagonist of the N-type calcium channel currently in clinical trials for analgesia. Ziconotide reached a maximal brain concentration of between 0.003 and 0.006% of the injected material per gram of tissue at 3-20 min after i.v. injection, and this decayed to below 0.001%/g after 2 h. The structurally distinct conopeptide SNX-185 (synthetic TVIA) was considerably more persistent in brain after i.v. administration, with 0.0035% of the injected material present at 2-4 h after i.v. injection, and 0.0015% present at 24 h. Similar results (i.e. greater persistence of SNX-185) were obtained when the peptides were perfused through in vivo dialysis probes implanted into the hippocampus. Image analysis and serial sectioning showed that diffusion of Ziconotide in the extracellular fluid around the dialysis probe was minimal, with the peptide located within 1 mm of the probe after 2 h. In vitro diffusion through cultured bovine brain microvessel endothelial cells (BBMEC) verified that a close structural analog of Ziconotide (SNX-194) passed through this blood-brain barrier (BBB) model as expected for peptides of similar physical properties (permeability coefficient of 6.5 x 10(-4) cm/g). Passage from blood to brain was also verified by in situ perfusion through the carotid artery. A statistically greater amount of radioactivity was found to cross the BBB after perfusion of radioiodinated Ziconotide compared to [14C]inulin. Capillary depletion experiments and HPLC analysis defined the brain location and stability.

Elucidation of peptide metabolism by on-line immunoaffinity liquid chromatography mass spectrometry.

An immunoaffinity chromatography extraction capillary liquid chromatography separation has been coupled to electrospray ionization mass spectrometry for on-line characterization of drug metabolites of a therapeutic peptide in plasma. It is demonstrated that the selectivity, sensitivity and molecular weight data provided by immunoaffinity chromatography coupled to liquid chromatography/mass spectrometry provides a means of rapidly achieving qualitative determinations of small amounts of material in complicated biological matrices such as plasma. The ability to detect the peptide in rat plasma at a level of 10 ng/mL is demonstrated using this method. In addition, experiments to study the epitope of the peptide by enzymatic digestion and mass spectrometry are also discussed. The method is proposed as an alternative approach to studying the metabolism of therapeutic peptides.