Sales of schizophrenia drug treatments are set to decline in seven major markets to 2014, but the launch of premium-priced emerging agents will drive new growth to 2021, according to new research.

Sales of these drugs will drop from $7.4 billion in 2011 to $6.5 billion in 2014 in the US, UK, France, Germany, Italy, Spain and Japan, says the study, from Decision Resources. 

But after that, the launch of premium-priced emerging therapies, coupled with an increase in the prevalent population - as a result of population growth - will drive the market to a value of $8 billion by 2021, it forecasts.

Polypharmacy rates will increase with the launch of a treatment for negative symptoms that will be used as an adjunctive to antipyschotics, says the report. Also, three of the most highly-prescribed atypical antipsychotics - Eli Lilly's Zyprexa (olanzapine) products, AstraZeneca/Astellas' Seroquel (quetiapine) and Bristol-Myers Squibb/Otsuka Pharmaceutical's Abilify (aripiprazole) - will have lost patent protection early in the forecast period, resulting in substantial sales losses to 2016.

The report also discusses Eli Lilly's recent decision to discontinue development of pomaglumetad methionil, after clinical trials failed to show efficacy for the drug as monotherapy treatment of schizophrenia and for adjunctive treatment of negative symptoms. As a result of this decision, there remains substantial need for a therapy to treat patients who experience suboptimal response to current therapies, it says.

Atypical antipsychotic depot sales will more than double, from $1.4 billion in 2011 to $3 billion in 2021, the report forecasts. This growth will be driven primarily by the launches of Otsuka/Lundbeck's aripiprazole depot - which offers a better-tolerated option to the depot market - and Janssen's three-month formulation of paliperidone palmitate, which provides meaningful delivery advantages to physicians and patients. These new depot formulations will command premium pricing, and Decision Resources is forecasting peak-year sales of at least $500 million in schizophrenia for aripiprazole depot and at least $1 billion in post-2021 peak-year sales for paliperidone palmitate three-month depot. 

The report expects patient share for depot therapies to grow slightly, as new and more favourable options become available, but also points out that resistance by psychiatrists and patients to injections remains a substantial barrier to their growth of patient share.

Moreover, as a result of the plethora of available antipsychotics, most of which will become generically available over the next five years - new entrants to the schizophrenia market will have to differentiate themselves effectively in order to establish a foothold.

"While the unpredictability of patients' individual responses to drugs drives frequent switching, a crowded market provides less opportunity for late-to-market entrants and greater barriers to market access, as generics become increasingly entrenched on favourable formulary tiers," comments Decision Resources' analyst Anne-Elise Tobin.

"Interviewed experts are most interested in drugs with novel mechanisms of action - which include Roche/Chugai's bitopertin - that have the potential to treat symptoms that are not well-controlled by current therapies, such as negative symptoms," she adds.

Decision Resources expects bitopertin, a glycine transporter 1 inhibitor, to be the first approved treatment for negative symptoms of schizophrenia. Given that approximately two-thirds of schizophrenia patients experience significant negative symptoms, and that experts interviewed for the report say they welcome a treatment for these symptoms, bitopertin is expected to achieve blockbuster status, it adds.

Nevertheless, opportunity will remain for additional treatments providing a variety of mechanisms of action to sufficiently address this top unmet need in this large and diverse patient population, the report concludes.