Step 1: Rheumatic chorea is the movement-disorder component of acute rheumatic fever, driven by a streptococcal-triggered immune attack on the brain.
Step 2: Because antirheumatic therapy barely touches the chorea, doctors fall back on symptomatic control with anticonvulsants such as valproate and carbamazepine and neuroleptics such as haloperidol.
Step 3: The first-line, preferred agent for stubborn chorea is valproate, while probenecid (a gout drug) is irrelevant here.
\[\boxed{\text{Valproate}}\]