The liver enzymes are the clearest objective finding. Between Oct 2025 and Mar 2026, Darwin's ALT jumped from 65 → 409 (3.5x the upper limit) and AST from 31 → 96. Everything else — kidney, pancreas, thyroid, CBC, urinalysis, tick panel — is essentially clean. This points to a hepatocellular injury (damage to liver cells themselves), not cholestatic/obstructive disease (ALP and GGT are normal, no bilirubin spillover).
The isoxazoline connection is the most compelling thread:
- Darwin switched from the lower dose tier to the higher tier (22.1–44 lb range) in Oct 2024 — at 25 lbs he's been getting a dose sized for a dog nearly twice his weight.
- He switched from Simparica Trio to Bravecto in Oct 2025 — Bravecto has a longer half-life (12 weeks vs monthly), meaning the drug sits in the system longer.