Interaction Between Phenylbutazone and Thiopental Sodium in Female Stray Dogs: The Effect on the Recovery from Anesthesia

Summary Anesthesia often involves administration of several drugs from different classes. Drug–drug interactions may affect the duration of action of anesthetic agents. The purpose of this research was to investigate interaction between phenylbutazone and thiopental sodium in dogs. Twenty-six female stray dogs were randomly divided into two groups. Each group subdivided into two subgroups <18kg and ≥18kg. Equivalent doses of thiopental sodium were intravenously administered following the injection of 0.9% normal saline in control group and phenylbutazone via the same route in experimental group. After anesthesia, time intervals needed for the return of palpebral reflex, opening of eyes, tongue movement, stretching of limbs, head and neck movements, sitting position, trying to stand, imbalanced walking and normal walking were recorded. Results showed the average time periods in the experimental group were generally more than those in the control group. It was shown the duration of the above chronological parameters were significantly higher in heavier dogs compared to the lighter. Females generally have a larger proportion of body fat content than males. This may cause a higher volume of distribution and a longer elimination half-life for thiopental in female dogs. This interaction with phenylbutazone may be due to an increase in the unbound form of thiopental sodium and its quicker distribution into the brain and a longer duration of anesthesia.