Abstract

A 7-year-old, 33.5 kg, captive hatched male green sea turtle with no prior medical concerns presented acutely for intermittent episodes of abnormal erratic behavior lasting approximately one minute in duration followed by extreme lethargy. These unpredictable episodes were observed regardless of the presence or absence of known stimuli and occurred both in and out-of-the-water. The episodes included a series of the following behaviors: fast paddling of the front flippers, becoming vertical in the water column until the animal flipped over onto its back, swimming into objects or swimming in tight circles. When out-of-the-water during staff evaluation, the episodes were accompanied by urination. Thorough diagnostics including serial physical examinations, complete blood counts, plasma biochemistry analysis, blood cultures, radiographs, ultrasound, computed tomography, and magnetic resonance imaging could not definitively identify a cause for the acute onset of erratic episodes. Empirical treatment with broad-spectrum antibiotics, anti-inflammatories, thiamine, antifungals, and diazepam did not alleviate these symptoms.

There are no reports in the peer-reviewed literature describing the clinical appearance or management of suspected seizures in sea turtles. Empirical treatment with phenobarbital was utilized in this case. Initial administered doses were conservative and were increased slowly in response to serum drug concentrations and changes in clinical signs. There are no published doses or therapeutic serum levels available for phenobarbital in reptiles, but serum concentrations considered therapeutic in mammals (15–45 µg/mL) were achieved in this turtle (25.8–46.3 µg/mL) at a dose of 1.5 mg/kg orally twice daily. Clinical signs decreased in frequency after 1 month of phenobarbital treatment but continued to occur intermittingly; therefore, gabapentin was added as adjunct therapy. Plasma gabapentin concentrations above the therapeutic range in humans (2–20 µg/mL) were achieved in this sea turtle (27–33.6 µg/mL) at a dose of 9 mg/kg orally once a day. The erratic episodes ceased in this sea turtle after receiving this combined therapy for approximately 1 month. No adverse effects of the medications or obvious signs of sedation were noted. The characterization of the individual drug effects on the clinical signs is hard to determine since this sea turtle was on a multidrug treatment regimen. However, if no further erratic episodes are observed, the next goal is to taper and possibly discontinue treatment with gabapentin followed by phenobarbital while closely monitoring animal behavior and blood concentrations.

This case report suggests that long-term seizure management may be possible in affected sea turtles. Monitoring of serum and plasma drug concentrations suggest that oral phenobarbital and gabapentin are well absorbed in green sea turtles and achieve concentrations considered therapeutic in mammals. Over the course of 3–4 months, blood concentrations steadily increased indicating that both phenobarbital and gabapentin concentrations accumulate slowly over time. When utilizing these medications long-term in reptiles, it is recommended to monitor serum and plasma drug concentrations followed by an appropriate adjustment in dose if needed. This case emphasizes the need for pharmacokinetic studies of anticonvulsant medications in reptiles and the challenge associated with the diagnosis and management of suspected seizures in sea turtles.

Acknowledgements

The authors wish to thank the aquarists at SeaWorld California for their dedication in providing care for this green sea turtle and the Veterinary Specialty Hospital of San Diego for their assistance in acquiring advanced diagnostic imaging.

* Presenting author