Generic drug trials: more transparency needed

The New York Times reported a couple of days ago that "Federal regulators and the generic drug industry are putting the final touches on an agreement that would help speed the approval of generic drugs in this country and increase inspections at foreign plants that export generic drugs and drug ingredients to the United States." The generic drug manufactures will pay an annual fee of 299$ million dollars, so that the FDA will be able to hire more reviewers and speed up approval of applications for marketing of generic drugs. The question is: what do we know about the generic drugs marketed today?

Van der Meesch et al. (2011) published in PLoS One a methodological systematic review about Bioequivalence trials which compared generic to brand-name drugs published between 2005 and 2008. They searched Medline for appropriate papers, as well as journals which regularly publish bioequivalence trials. Out of 134 papers that reported bioequivalence trials between brand-name drug and generic drug, 55 didn't include the reference drug name and were excluded. The final sample consisted of 79 papers which dealt with assessment of the bioequivalence of generic and brand-name drugs.

What do the FDA and the EuropeanMedicine Agency (EMA) demand from a generic drug?

The FDA wants to know three things:

Cmax - maximum plasma drug concentration

Tmax - time required to achieve a maximal concentration

AUC - total area under the plasma drug concentration-time curve

The 90% confidence intervals for the ratios (test:reference) have to be between 80% and 125%. The EMA wants to know only the Cmax and the AUC.

Source: Generics – equal or not? (Birkett, 2003)

Experiments of bioequivalence are usually randomized crossover trials. They are conducted on healthy volunteers by administrating one dose of the drug. Seventy-three (92%) of the trials were indeed single-dose trials (6 (8%) were multiple-dose) and 89% of the single-dose trials reported bioequivalence. About a third didn't report CIs for all the FDA criteria, and 20% didn't report the required EMA criteria. Only 41% of the papers reported funding, 25% had private funding.

As always, the study has limitations: it included only papers from the years 2005-2008 and relied on FDA guidelines from 2003 and EMA guidelines from 2001 (updated 2008). It's also possible that they researchers' search in Pubmed didn't retrieved all the relevant papers.

In conclusion, there is a serious lack of available data about generic drugs. The authors point out that while 1,661 generic drugs were approved by the FDA during the study period, there weren't any data available about trials assessing generic drugs on the FDA and/or EMA sites. The authors also hypothesize that such a small percent (10%) of failed bioequivalence trials seem unlikely and suggested a possibility of publication bias.

van der Meersch, A., Dechartres, A., & Ravaud, P. (2011). Quality of Reporting of Bioequivalence Trials Comparing
Generic to Brand Name Drugs: A Methodological
Systematic Review PLoS One : 10.1371/journal.pone.0023611