Real-World Phenobarbital Monitoring in Dogs: Serum Concentrations, Hepatic Biochemistry, Lipaemic Failure and Continuity of Care in a University Referral Hospital

Serum phenobarbital (PB) monitoring is recommended after treatment initiation and periodically thereafter, but real-world data on monitoring practice are scarce, particularly where imepitoin is not marketed and PB is a controlled substance. All in-house PB determinations performed on a point-of-care analyser reporting PB with a hepatic panel at a Romanian university referral hospital between January 2022 and August 2026 were retrieved and linked to the hospital register. A total of 143 canine runs from 66 dogs were obtained; 10 (7.0%) were suppressed by severe lipaemia. At the first valid determination, 47 of 65 dogs with a valid result (72.3%; 95% CI 60.4–81.7) were within the 15–35 µg/mL target range and 16 (24.6%; 95% CI 15.8–36.3) were below it. The median dose, given as fractionated human 100 mg tablets, was 5.62 mg/kg/day and was not associated with concentration; dogs under 10 kg received almost twice the weight-based dose of larger dogs without reaching higher concentrations. Alkaline phosphatase was increased in 36% of runs and was not associated with concentration in mixed-effects models. At least one determination was obtained in 79% of dogs in continued care and 88% of dogs with six or more prescriptions, but only 40% (95% CI 27–56%) of newly treated dogs were determined within 90 days and none of the 17 dogs seen only once or twice after initiation was determined. Monitoring therefore follows continuity of care; scheduling the first determination at initiation and coupling sampling with prescription renewal are proposed measures whose effectiveness requires prospective evaluation.