Arthritis happens as we age and giant Galapagos tortoises are no exception! For animals known to live over 100 years old and weigh 215-415 lbs., they can definitely experience the pain of joint disease for many years or even decades. Managing that pain and discomfort in our animal patients is an integral part of clinical veterinary medicine. As a zoo veterinarian, this can be quite difficult, due to a lack of knowledge of how many medications work in different species with varying anatomy and physiology. Additionally, it can be tough to assess pain in different animals, as some species are very good at hiding signs of discomfort.

These were the problems the veterinary team faced when Ms. B, one of the Zoo’s female Galapagos tortoises, was diagnosed with arthritis in her limbs. At over 90 years of age, Ms. B is one of the oldest animals at the Zoo but Galapagos tortoises can live well over 100 years of age! In order to manage Ms. B’s arthritic discomfort through her golden years, the veterinary team started treating her with tramadol, a medication frequently used in humans to treat pain, but rarely used in tortoises.  As there were no dosages reported in tortoises, we extrapolated a tramadol dose from aquatic turtles. However, it soon became clear that there were some important differences in the way turtles and tortoises metabolize this drug, as Ms. B became very sleepy and sedate after administration. We decreased the dose to optimize Ms. B’s comfort and she returned to normal behavior, but we were left with a very important question – what is the ideal tramadol dose for Galapagos tortoises?

In order to bridge this knowledge gap, we decided to perform a pharmacokinetic study to determine how this medication is metabolized by Galapagos tortoises. Three of our adult tortoises and eight juvenile tortoises were used in the study. Each tortoise was given an oral dose of tramadol. We then collected blood from each tortoise at set time points after administration.  A similar study in a mammal would have frequent blood samples collected in a 24-hour window, but as tortoises have very slow metabolisms, we were collecting blood samples for four days after drug administration to determine when the last remnants of the tramadol left their system.  After waiting three weeks, we then repeated the study, this time with a different tramadol dose. The blood we collected was then sent to a pharmacology laboratory to have the drug concentrations measured.

The information collected from this study was able to determine the appropriate dose of tramadol for Galapagos tortoises and how frequently it should be given.  For Ms. B, this pharmacokinetic knowledge will help us optimize her pain management and comfort level as she ages and improve her overall quality of life.  We hope that our study will aid in the treatment of pain in giant tortoises and other closely related species in the wider zoo community.

-Daniela Y., OKC Zoo’s veterinary resident