Drug prescribing significantly influenced by clinical evidence and drug policy changes: study

01/10/2013

A new study by researchers at the Institute for Clinical Evaluative Sciences (ICES) shows the use of rosiglitazone and pioglitazone was significantly impacted by cardiovascular safety concerns and public drug formulary restrictions on these thiazolidinediones (TZDs).

TZDs are used for the treatment of type 2 diabetes. However, the 2007 publication of a meta-analysis that showed an increased risk of heart attack with rosiglitazone led to warnings and eventually to the removal of rosiglitazone and pioglitazone as unrestricted drug benefits on the public drug formulary in June 2009 in Canada.

“Publication of high-profile studies highlighting issues of drug safety in prominent medical journals can have significant impacts on drug utilization patterns,” says Muhammad Mamdani, senior author, ICES Scientist and Director of the Applied Health Research Centre at the Li Ka Shing Knowledge Institute at St. Michael’s Hospital.

Numerous factors affect drug utilization including clinical trials, promotional activity, drug safety signals and funding practices.

The population-based, cross-sectional time series analysis among more than 1.6 million older Ontario residents from January 2000 to September 2010 looked at prescribing of TZDs before and after formulary restrictions were introduced and found:

Rosiglitazone prescribing decreased significantly (92 per cent) from 5.32 to 0.44 prescriptions per 1,000 patients in the first three months following the publication of a meta-analysis suggesting safety concerns for rosiglitazone in 2007.
Pioglitazone prescribing continued to decline (72 per cent) from 1.89 just prior to the publication of the meta-analysis to 0.53 prescriptions per 1,000 patients just prior to the implementation of formulary restrictions.
Following the implementation of formulary restrictions for TZDs in the second-quarter of 2009, the rate of incident prescriptions for rosiglitazone fell further (85 per cent), from 0.20 prescriptions per 1,000 patients in the preceding quarter to 0.03 prescriptions per 1,000 patients in the subsequent quarter.
The rate of prescriptions dispensed for pioglitazone decreased by 80 per cent from 0.53 in first-quarter of 2009 to 0.11 prescriptions per 1,000 patients in third-quarter of 2009.

“Changes in drug policy can also have significant impacts on drug utilization patterns. The effects of these both evidence and policy may be more pronounced if viable treatment alternatives exist,” says Mamadani.

The study “The Rise and Fall of the Thiazolidinediones: Impact of Clinical Evidence Publication and Formulary Change on the Prescription Incidence of Thiazolidinediones” is in the current issue of the Journal of Population Therapeutics and Clinical Pharmacology.

Author block: Salman Hashim, Tara Gomes, David Juurlink, Chelsea Hellings, Muhammad Mamdani.

ICES is an independent, non-profit organization that uses population-based health information to produce knowledge on a broad range of healthcare issues. Our unbiased evidence provides measures of health system performance, a clearer understanding of the shifting healthcare needs of Ontarians, and a stimulus for discussion of practical solutions to optimize scarce resources. ICES knowledge is highly regarded in Canada and abroad, and is widely used by government, hospitals, planners, and practitioners to make decisions about care delivery and to develop policy.