Sales of drugs to treat Parkinson's disease in seven major markets will decline slightly, from a total $2.7 billion in 2010 to $2.6 billion in 2020, as key treatments lose patent protection, say new forecasts.

The major therapies on which patents are set to expire by 2020 are Novartis/Orion Pharma's Comtan/Comtess/Stalevo (carbidopa/levodopa/entacapone) and Teva/Lundbeck's Azilect/Agilect (rasagiline), according to the study, from Decision Resources.

Also facing increasing generic competition will be ropinirole (GlaxoSmithKline's Requip and GSK/SkyePharma's Requip XL/LP/RP/Modutab/Prolib) and pramipexole (Boehringer Ingelheim's Mirapex/Mirapexin/Sifrol/BI-Sifrol and Mirapex ER/Mirapexin ER/Sifrol Retard), it adds.

Sales in the seven markets - US, France, Germany, Italy, Spain, the UK and Japan - will continue to be driven by the leading dopamine agonists, pramipexole and ropinirole, and by increasing use of the monoamine oxidase B (MAO-B) inhibitor Azilect/Agilect, as well as by the re-entry of UCB/Schwarz Pharma's Neupro/Leganto (rotigotine) to the US market and its wider use in Europe, says the study.

Despite some key current therapies experiencing increased uptake during the forecast period and the launch of three new agents by 2020, sales of current products and the market impact of emerging therapies will be offset by generic competition, it forecastss.

The three emerging therapies set to launch through 2020 are Impax Laboratories/GSK's IPX-066, a reformulation of levodopa, the mainstay of Parkinson's therapy, plus Merck Serono/EMD Serono/Newron Pharmaceuticals' MAO-B inhibitor safinamide and Kyowa Hakko Kirin's adenosine A2A receptor inhibitor antagonist istradefylline. 

Decision Resources expects IPX-066, and to a lesser extent safinamide, to contribute moderately to market growth, as both will contend with established agents within the same respective drug classes - which are often generically valuable - and which are commonly used in the patient populations targeted by the emerging therapies.

While the first-in-class agent istradefylline will benefit from use in the management of motor response complications arising from levodopa treatment, its overall impact will be modest as it is currently expected to launch only in Japan, says the report.

"As we do not expect major shifts in the treatment paradigm of Parkinson's disease over the next 10 years, by 2020 the generalisation of several key Parkinson's disease therapies will depress market growth," comments Decision Resources analyst  Nadja Rodovsky. "Future therapies will need to clearly demonstrate superiority over current therapies to gain a competitive edge in this mature market," she adds.