Generic Conversion of the SSRI Market and the Impact on Branded Products

Over the past three years, three major selective serotonin reuptake inhibitor (SSRI) antidepressants—Paxil^®, Celexa^®, and Zoloft^®—have all lost exclusivity, opening the door to widespread generic competition. Following introduction of generic sertraline this summer, Lexapro^® remains the only branded SSRI on the market. In this article, we examine the penetration of generics into the SSRI market as well as the impact to date on branded Lexapro use.

Methods

To investigate trends in antidepressant use, we examined retail pharmacy prescription data from January, 2002, to September, 2006. The Verispan data captures more than 1.4 billion prescriptions per year, nearly half of all prescription activity in the US. This data set includes prescriptions from a variety of US pharmacies, including those that are part of national retail chains and mass merchandisers. To smooth out monthly variation in utilization (i.e., related to number of working days in the month), prescriptions were aggregated up to obtain rolling quarterly figures (i.e., a sum of data over three months).

Results

Total branded and generic prescriptions for SSRIs are shown in Figure 1. As seen in Figure 1, for the quarter ending March, 2002, only 20 percent of SSRIs dispensed were generic (primarily fluoxetine). With introduction of generic competition for Celexa, Paxil, and Zoloft, the proportion of generic SSRIs has grown to 57 percent by the quarter ending September, 2006, and will likely increase to approximately 70 percent over the upcoming months as generic sertraline replaces branded Zoloft sales.

Figure 1.

Brand vs. generic use of SSRIs, January 2002 to September 2006 (VONA USC Class 64340; TRxs)

Quarterly SSRI market share from January, 2002, through September, 2006, is displayed in Figure 2. As can be seen in the figure, fluoxetine sales declined over the period and paroxetine sales likely would have continued to decline had Paxil^® CR not experienced a manufacturing shortage. Citalopram, however, deviated slightly from this trend by exhibiting a three percentage-point growth in share after generic competition. The growth in generic citalopram, however, did not appear to come at the expense of the branded agents. Rather, the branded agents, Lexapro and, at the time, Zoloft, seem to continue along existing trend lines. Although it is still a bit early to make conclusions about the effect of generic sertraline, the impact of the generic conversion of the SSRI market on Lexapro, the only remaining branded agent, appears minimal to date.

Figure 2.

SSRI Market Share, January 2002 to September 2006 (VONA USC Class 64340; TRxs)

Expert Commentary— Generic Conversion of the SSRI Market and the Impact on Branded Products

David V. Sheehan

There are at least two dynamics in play that lead to the results in Figure 2. First, Paxil CR and paroxetine (brand plus generic) in aggregate, have dropped more than any other SSRI. This is probably related to the net effect of three factors: a) the temporary Paxil CR withdrawal from the market because of concerns about the splitting of tablets; b) the findings in two databases suggesting that paroxetine, more than other antidepressants, may be associated with an increase in congenital cardiac defects in babies born to mothers exposed to paroxetine during pregnancy; and c) the impact of these concerns on the enthusiasm of the manufacturer to continue aggressively promoting either Paxil or Paxil CR. The data in Figure 2 suggest that the temporary withdrawal of Paxil CR resulted in a shift of most, but not all, of these patients to paroxetine (brand plus generic) and that the reintroduction of Paxil CR resulted in many, but not all, of those patients being shifted back to Paxil CR.

Second, Figure 1 shows that the biggest increases in the use of generic SSRIs occurred in the quarter immediately following the availability of generic paroxetine, citalopram, and sertraline, respectively, after which these drops leveled out over the ensuing several quarters. Some practitioners remain concerned about the quality of some generic SSRIs. They know if they write a prescription for a brand name SSRI, that in many states pharmacists can and do switch such patients to a generic equivalent. To minimize such switching and to ensure consistency in quality over time, clinicians are more likely to prescribe a brand for which there is no generic equivalent. This results in the surviving brand without generic competition (e.g., Lexapro) doing better than might otherwise be expected and to appear to be immune to the overall increase in generic alternatives. In the generation of tricyclic antidepressants, branded nortriptyline benefited in a similar way. These quality concerns about some SSRI generics are a growing concern among practitioners and cannot be lightly dismissed in the absence of good scientific data to the contrary. While switching to generics reduces costs in the pharmacy benefit managers' silo, it remains to be demonstrated whether this results in a reduction in overall total medical and psychiatric care costs, since the cost of medication is the smallest segment in the overall costs incurred by patients with depression and anxiety disorders.