A Cochrane review included 29 studies with a total of 5 247 subjects. Participants randomised to a dopamine agonist were less likely to develop dyskinesia (OR 0.51, 95% CI 0.43 to 0.59), dystonia (OR 0.64, 95% CI 0.51 to 0.81) and motor fluctuations (OR 0.75, 95% CI 0.63 to 0.90) than levodopa-treated participants. However, various 'non-motor' side-effects, including oedema (OR 3.68, 95% CI 2.62 to 5.18), somnolence (OR 1.49, 95% CI 1.12 to 2.00), constipation (OR 1.59, 95% CI 1.11 to 2.28), dizziness (OR 1.45, 95% CI 1.09 to 1.92), hallucinations (OR 1.69, 95% CI 1.13 to 2.52) and nausea (OR 1.32, 95% CI 1.05 to 1.66) were all increased in agonist-treated participants (compared with levodopa-treated participants). Agonist-treated participants were also significantly more likely to discontinue treatment due to adverse events (OR 2.49, 95% CI 2.08 to 2.98). Finally symptomatic control of Parkinson's disease was better with levodopa than with agonists, but data were reported too inconsistently and incompletely to meta-analyse.
Comment: The quality of evidence is downgraded by study quality (unclear allocation concealment and unclear intention-to-treat adherence). The balance of risks and benefits remains unclear; data on patient-rated overall quality of life is lacking.