Page 1157 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

Ionophores Chapter | 78 1089

VetBooks.ir as α-tocopherol acetate at 17 IU/kg) prior to a single oral factors influence the severity and outcome of the toxic
exposure. Results of controlled studies and confirmed field
dose of 50 mg monensin/kg (LD 50 16.7 6 3.57 mg/kg). A
reports of toxicity indicate that the greatest risk of intoxica-
similar regimen in cattle administered toxic doses of mon-
ensin provided only partial protection but clinical signs in tion is upon initial exposure to ionophore-containing feed
pigs with tiamulin-induced salinomycin toxicity were or supplement. Following sublethal exposure, consumption
ameliorated following administration of vitamin E. of culprit feed or supplement is negligible because of
The protection against the toxicoses was theorized to be anorexia. Animals that die acutely after high levels of
produced by stabilization of cellular membranes since exposure often will have few or no lesions. Those that die
selenium and vitamin E are known to prevent and control later have profound striated (cardiac and/or skeletal) mus-
peroxidation-mediated cellular injury (Tappel, 1981; Van cle lesions and changes secondary to CHF in some animals
Vleet, 1986). Similarly, the antioxidant property of zinc that survive the acute toxic episode.
prevented adverse effects of salinomycin in chickens Confirmatory diagnosis requires efficient laboratory
(Kamashi et al., 2004). Monensin, like all polyether assays to determine the identity and amounts of the iono-
carboxylic ionophores, is lipophilic and may produce phore involved and a thorough consideration of differen-
dose-dependent membrane perturbations and increased tial diagnosis. These cannot be overemphasized. There is
lipid peroxidation, which could lead to degradative pro- no known antidote or specific treatment for ionophore
cesses. Further studies are needed to determine whether toxicoses and treatment is largely supportive. Judicious
antioxidants, such as vitamin E and selenium, or zinc use, avoidance of overdosing, and adherence to species
administration may have important roles in the prevention recommendation will enhance livestock production and
and treatment of ionophore toxicoses. help prevent the occurrence of adverse effects associated
Until proper and effective therapy is available, preven- with this class of compounds.
tion of ionophore toxicoses by (1) proper use from the
implementation of good feed manufacturing and feeding
practices at the feed mill and farm level; (2) avoidance of REFERENCES
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Adovelande, J.B., Schrevel, J., 1996. Carboxylic ionophores in malaria
carry over to feeds for nontarget species; and (3) adher-
chemotherapy: the effects of monensin and nigericin on Plasmodium
ence to species restrictions will help prevent the adverse
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effects associated with this class of compounds.
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Agaoglu, Z.T., Akgul, Y., Keles, I., et al., 2002. Accidental salinomycin
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AND FUTURE DIRECTIONS Amend, J.F., Mallon, F.M., Wren, W.B., Ramos, A.S., 1981. Equine
monensin toxicosis: some experimental clinicopathologic observa-
Seven ionophores—monensin, lasalocid, salinomycin, tions, Comp. Cont. Ed., 11. pp. S173 S183.
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uses continue to be investigated and applied in many
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Becker, J.A., Speare, D.J., Daley, J., Dick, P., 2002. Effects of dose and
these versatile compounds could lead in the future to treatment time on xenoma reduction in microsporidial gill disease in
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Generally, these feed additives have been found to be efficiency and mode of action. J. Anim. Sci. 58, 1465 1483.
safe and effective in target animal species, but toxic syn- Bertini, S., Feirrero, S., Berny, P., 2003. A new improved high perfor-
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adverse effects are observed. Consumption of complete Susceptibility of Mycobacterium avium sbsp paratuberculosis to
feed containing the maximum approved use levels of mon- monensin sodium or tilmicosin phosphate in vitro and resulting
ensin, lasalocid, or laidlomycin is harmless. Dose and time infectivity in a murine model. Can. J. Vet. Res. 88, 175 181.