Table 2.

D1-selective DAs with available clinical evidence in PD.

Name of DA	Dopamine receptor selectivity	Current clinical statusa	Evidence of motor control
ABT-431	D1/D5 full [43], [45]	Discontinued after pilot clinical study [45]	Clinically and statistically significant difference relative to placebo in motor subsection of the UPDRS score in pilot study in advanced PD [45]
Dihydrexidine	D1/D5 full [46], [47]	Discontinued after pilot clinical study [46]	3 of 4 patients did not have motor improvement; 1 patient had motor response similar to levodopa, as assessed by UPDRS motor score immediately after dosing in pilot study in mild/moderate PD [46]
PF-06412562	D1/D5 partial [48]	Discontinued after phase 1 study [115]	Clinically meaningful motor improvement relative to placebo, as assessed by LSM MDS–UPDRS Part III motor score in phase 1 study in all patients with PD [48]
Tavapadon	D1/D5 partial	Phase 3, ongoing [108], [109], [110]	Significantly greater improvement in mean MDS-UPDRS Part III score at 15 weeks relative to placebo in phase 2 study in early-stage PD [50]

^aAs of July 2022. DA, dopamine agonist; LSM, least-squares mean; MDS, Movement Disorder Society; PD, Parkinson’s disease; UPDRS, Unified Parkinson's Disease Rating Scale.