After 5–10 years of treatment with levodopa, around half of patients with Parkinson's disease begin to oscillate between periods of decreased motor function, 'off-times', and periods where symptoms are well-controlled, 'on-times'.
Xadago is an add-on therapy indicated for use in combination with levodopa, with or without other Parkinson's disease therapies, in order to lengthen the 'on-times' of good control in patients with mid- to late-stage Parkinson's disease who are experiencing motor fluctuations.
The active ingredient of Xadago, safinamide, is a reversible monoamine oxidase B (MAO-B) inhibitor, which causes an increase in extracellular levels of dopamine in the brain. This increase helps supplement the direct replacement of dopamine by levodopa. Safinamide also modulates the opening of voltage-gated sodium channels and the release of glutamate, although the contribution of these actions to its overall effect is unknown.
Increase in 'on time'
Two randomised, placebo-controlled, double-blind trials involving a total of 1218 patients showed improvement in Parkinson's symptoms overall at 24 weeks with safinamide doses of 50mg and 100mg.
The change in on-time without troublesome dyskinesia after 24 weeks (primary endpoint), was significantly greater in the safinamide groups than in the placebo groups, with least-squares mean treatment differences of 0.5–0.9 hours (p=0.0054 to p<0.0001).
Post-hoc analysis indicated that more patients saw at least a 60-minute increase in on-time, at least a 60-minute decrease in off-time and at least a 30% decrease in the Unified Parkinson's Disease Rating Scale score with safinamide than placebo (p=0.0216 to 0.0017).
By the 2-year mark, however, the effect was lessened, with the difference in mean change in Dyskinesia Rating Scale total score during on-time between safinamide and placebo being non-significant.
Dr Arthur Roach, Parkinson's UK director of research and development, is cautious about safinamide: "The drug has been shown to have benefits for patients, but it is important to note its effects are similar to [those of] other MAO-B inhibiting drugs. We now have one more tool for managing the symptoms of Parkinson's. As more clinical experience is obtained, safinamide may emerge as a favoured choice in some situations."
Safinamide should not be taken in combination with other MAO inhibitors, and serious interactions may occur with SSRIs, SNRIs and tricyclic antidepressants. The drug is contraindicated in patients with severe hepatic impairment, or a personal or family history of retinal disease.
Common side-effects of safinamide were similar to those of placebo and included insomnia, dizziness, headache and nausea.