Comparison of Oral and Parenteral Heavy Metal Chelators for the Treatment of Lead Toxicosis in Cockatiels (Nymphicus hollandicus)
Lead toxicosis is a relatively common and clinically significant medical problem in both companion and wild birds.1,4 The current recommended therapy for lead toxicosis is calcium disodium edetate (CaEDTA), however, parenteral administration is required and the potential for nephrotoxicity has been reported in mammals.2-4 Identification of an oral heavy metal chelator with minimal side effects for the treatment of avian lead toxicosis is, therefore, desirable. In this study, an oral chelating agent, meso 2,3-dimercaptosuccinic acid (DMSA, Chemet®, Bock Pharmacal, St. Louis, MO, USA), was evaluated alone at two dosages (40 mg/kg and 80 mg/kg), and in combination with the parenteral chelating agent, CaEDTA at 40 mg/kg (Calcium Versenate®, 3M Pharmaceuticals, Northridge, CA, USA) at both DMSA dosages to evaluate its safety and efficacy at reducing blood lead concentrations in cockatiels. In addition, sodium sulfate salts (Anhydrous Sodium Sulfate, ACS Grade, Fisher Scientific, Fairlawn, NJ, USA) were utilized at a dose of 0.5 g/kg in conjunction with these two chelators to evaluate their effectiveness at reduction of gastrointestinal absorption of lead particles. Results from this study indicated that administration of DMSA resulted in a rapid decline in blood lead concentrations when used alone or in conjunction with CaEDTA, however, DMSA had a low margin of safety at the higher dose. The administration of DMSA at the 80 mg/kg dose in cockatiels without lead toxicosis caused death in greater than 60% of the cockatiel subjects in that group. Administration of sodium sulfate salts resulted in no significant difference in reduction of blood lead concentrations and the use of these salts would not be recommended. CaEDTA was not found to cause nephrotoxicity in cockatiels when used twice daily for 21 consecutive days. DMSA was not found to cause significant histopathologic changes in the cockatiels that survived treatment.
This work was supported by a grant from the Center for Companion Animal Health, School of Veterinary Medicine, University of California at Davis. We thank John Trupkiewicz DVM for performing the necropsies and histopathology, Don Priesler for photography, and Kirsten Dahl, Martha Needham, Shan Ikazawa, Leslie Storwick, and Todd Hughes for technical support.
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