Veterinary care becomes qualitatively different when an animal has several clinically important conditions because the value, risk, feasibility, and timing of each intervention depend on the rest of the patient's disease and care context. Single-disease reasoning can therefore produce locally appropriate recommendations that become collectively burdensome, interacting, contradictory, or poorly aligned with patient welfare and caregiver capability. This article develops an original non-empirical, patient-centered clinical decision architecture for companion-animal multimorbidity. It distinguishes disease–disease, drug–disease, and drug–drug interactions from simple coexistence; separates physiological reserve and functional status from chronological age; and treats treatment burden, monitoring burden, caregiver capability, and patient-caregiver priorities as clinically relevant constraints rather than secondary implementation concerns. The proposed architecture does not assign numerical weights or universal thresholds. Instead, it organizes multimorbidity decisions around clinically consequential interactions, competing therapeutic goals, noncompensatory constraints, revisable prioritization, and explicit reassessment after therapeutic change. Existing veterinary evidence supports the importance of multimorbidity, frailty, caregiver burden, medication feasibility, and dynamic monitoring, but does not establish a validated integrated decision instrument. The architecture is therefore intended as a structured synthesis that makes otherwise hidden trade-offs visible and empirically testable. Its principal boundaries are the predominance of dog and cat evidence, heterogeneous disease-specific literatures, incomplete evidence on deprescribing and multimorbidity-specific outcomes, and the need for prospective validation before clinical utility can be claimed.
