The effect of levodopa on pulmonary function in Parkinson's disease: a systematic review and meta-analysis

Levodopa is considered the gold standard therapy for Parkinson's disease (PD). Aspiration pneumonia is the most frequent cause of death among PD patients. Asymptomatic respiratory impairment can be detected even in the initial stages of the disease course; however, there is no conclusive evidence regarding the efficacy of levodopa, the main therapeutic drug for PD, to enhance pulmonary function in these patients.

The aim of this systematic review and meta-analysis was to evaluate the effects of levodopa therapy on respiratory parameters in patients with PD.

After a comprehensive and systematic literature search in the electronic databases MEDLINE, Embase, the Cochrane Library, and Web of Science, all trials referring to levodopa and respiratory function that met the eligibility criteria were included in the analysis. Considered outcomes were forced vital capacity (FVC), forced expiratory volume in 1 second (FEV(1)), the ratio between FEV(1) and FVC (FEV(1)/FVC), and peak expiratory flow (PEF). The fixed effects model was used to assess the weighted mean difference, and heterogeneity between studies was calculated with the I(2) test.

Four clinical trials comprising 73 patients and assessing the effects of levodopa on pulmonary function in patients with PD were included in the analysis. Pooled data showed that levodopa significantly improved FVC (SMD, 0.40; P = 0.02) and PEF (standard mean difference, 0.39; P = 0.03). No significant change was observed with FEV(1) (SMD, 0.34; P = 0.05) or the FEV(1)/FVC ratio (standard mean difference, -0.08; P = 0.66) after levodopa therapy.

The results of this systematic review suggest that levodopa therapy improved FVC and PEF, whereas no changes were observed in FEV(1) and FEV(1)/FVC. These findings may provide some indirect evidence regarding the efficacy of levodopa in restrictive parameters of pulmonary function.