Inadvertent Administration Of Ivermectin To Two Spurred Tortoises, Geochelone sulcata, Without Apparent Toxic Effects
Assoc Reptilian Amphibian Vet 7[1]:4 Jan/Apr'97 In My Experience (unrefereed material) 4 Refs

- Two spurred tortoises, Geochelone sulcata, one male and one female of unknown age, were presented for examination. The male weighed 5.7 kg and presented with a dry epidermal excoriation on the right craniolateral carapace. Fecal examination was positive for flagellates and spirurid ova. The female weighed 7.7 kg and was presented for a strong urine odor and some bubbling noted from the nares for several days. A cloacal wash was positive for flagellates. Both tortoises were treated with metronidazole for the flagellates at 130 mg/kg PO. Both tortoises were also inadvertently given ivermectin: the male was administered 1.25 mg (0.22 mg/kg) SC, and the female 1.5 mg (0.19 mg/kg) SC in their forelegs. The mistake was realized immediately after treatment and the owners were instructed as to the potential toxic effects of the drug. No treatment or medication was given following the ivermectin injections. We were not able to contact the owners until 14 days after ivermectin administration. At that time, the owners reported the tortoises never exhibited any depression or weakness, and were eating and acting normally. Ivermectin has been shown to be toxic in several species of chelonians and it has been suggested that either it may cross the blood-brain barrier or that GABA is a peripheral neurotransmitter in some species of chelonians. The toxic effects in chelonians include paresis or paralysis, with death occurring due to paralysis of respiratory muscles; tortoises appear to be more sensitive to ivermectin's toxic effects than other chelonians, and leopard tortoises, Geochelone pardalis, seem to be the most sensitive. Many veterinarians and experienced herpetoculturists believe the use of ivermectin in chelonians is dangerous and can lead to neurological disease and death. Anecdotal reports have shown this not to always be the case and, in my opinion, further research needs to be done before we condemn the use of ivermectin in all chelonian species. Until such research is done, it is still ill-advised to use ivermectin in chelonians when an alternative treatment exists. Keep in mind that the relatively small volume of the typical dosage for the commercially available injectable ivermectin makes overdosing smaller species even easier and hence more dangerous.