A small clinical trial comparing AstraZeneca’s Seroquel with Johnson & Johnson’s Risperdal has shown the two antipsychotics have equivalent efficacy but that Seroquel is better tolerated than its rival.

The study, published in the European Archives of Psychiatry and Clinical Neuroscience, demonstrates that Seroquel (quetiapine) and Risperdal (risperidone) were equally effective in treating schizophrenic patients with negative symptoms – such as emotional withdrawal and loss of drive – that tend to be much harder to treat than positive symptoms like delusions and hallucinations.

But Seroquel showed superior tolerability especially with respect to extrapyramidal symptoms, such as akathisia (restlessness and inability to remain motionless) and parkinsonism, according to the researchers.

Existing drugs have been shown to treat these negative symptoms, but one of the key issues that impacts positive treatment outcome is patient adherence to medication, which is often influenced by side effects, according to the authors of the study, from Ludwig-Maximilian-University in Munich, Germany.

Risperdal posted sales of $3 billion in 2004 but is jostling for market share in an increasingly crowded segment with Seroquel and other drugs such as Eli Lilly's top-selling Zyprexa (olanzapine), Pfizer's Geodon (ziprasidone) and Bristol-Myers Squibb's Abilify (aripiprazole). Seroquel had sales of $2 billion in the first nine months of 2005.

Last month, J&J filed for a successor antipsychotic drug, paliperidone, in the USA. The new agent uses a drug delivery technology designed to smooth out blood levels of the active drug over 24 hours. In addition to bolstering J&J’s schizophrenia franchise against its current rivals, the new product will also help the firm weather the upcoming patent expiry on Risperdal in the USA.

Seroquel is also facing a patent challenge from Israeli generic drugmaker Teva Pharmaceutical Industries in the USA.