Olanzapine is an atypical antipsychotic medicine used in the management of schizophrenia and related psychoses. It has been widely available internationally since 1996, and in NZ since 1999. Before Eli Lilly’s patent expired on the originator drug, Zyprexa, in 2011, olanzapine was a relatively expensive medicine and in NZ singly accounted for more expenditure than any other medicine in 2010 (approximately NZ$30 million/year).

Charon Lessing and co-authors used data from the national pharmaceutical claims database (PHARMS), to conduct a retrospective study of all adult patients (aged 14 years or older) in NZ who had been dispensed olanzapine tablets at least five times during the six months prior to the introduction of generic olanzapine (1 June 2011) and also for the six-month period prior to 1 June 2010, i.e. one year earlier.

The majority of all patients (98.2%) had switched within three months of implementation of the pricing policy, with a further 1.5% switching within 12 months. In the one-year follow-up, 12.5% of study patients made a single switch from originator to generic drug, whilst 86% made multiple switches among generics.

This study found no increase in hospitalizations, use of the emergency department or specialist outpatient services, or untoward health events in patients following switching from Zyprexa to generic olanzapine. The study also found no changes in dosage and no increase in the mean use of additional oral or injectable antipsychotic medicines. The rate of spontaneous adverse event reporting was similar to the rate of reports for risperidone during the same 2008–2013 period and there was no increase in the expected number of deaths in this population of patients with psychotic disorders.

There was no increase in the use of healthcare services as a consequence of switching in the NZ setting. The authors therefore concluded that ‘the study suggests that a switch can be made safely from originator olanzapine to one of the available generic brands’.

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Reference
1. Lessing C, Ashton T, Davis PB. The impact on health outcome measures of switching to generic medicines consequent to reference pricing: the case of olanzapine in New Zealand. J Prim Health Care. 2015;7(2):94-101.

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