Two antipsychotic agents have been launched in the last two years: olanzapine in the 4th quarter of 1996 and quetiapine in the 4thquarter of 1997. The rates of uptake of each of these two drugs illustrate many of the factors that affect the rate of uptake of a new antipsychotic agent.
As shown in Exhibit VI-11, the rate of uptake of olanzapine has been remarkably fast. From launch in the 4th quarter of 1996, olanzapine gained 8% market share within four full quarters. At the end of the second full year on the market, olanzapine attained a market share of 16% in the 45 Medicaid jurisdictions included in the analysis. This change represents a doubling of the number of prescriptions dispensed over the previous year. In contrast, quetiapine obtained only 4% market share within its first four quarters on the market, only half that of olanzapine.
These results indicate that Medicaid has increasingly accepted atypical antipsychotics, and in recent years has done so rather quickly. These gains in market share for olanzapine and quetiapine occurred in a Medicaid market that was transitioning from typical to atypical antipsychotics. This trend is further evidenced by the fact that from the time of the launch of olanzapine, risperidone market share increased from 17% to 22%, while the number of risperidone prescriptions increased nearly 50%.
There are likely many reasons for the slow uptake of quetiapine relative to olanzapine. First, the uptake of olanzapine was extremely fast by most standards. Furthermore, quetiapine was the third entrant in to the field of second generation, relatively undifferentiated atypical antipsychotics. As a result, clinicians may have been reluctant to learn to use a third new agent that did not offer any clear advantages over familiar therapies (i.e., risperidone, and olanzapine). Finally, the fact that the manufacturer of quetiapine, Zeneca (now AstraZeneca) was relatively inexperienced at marketing pharmaceuticals to the mental health services sector likely slowed diffusion of quetiapine even further.
Exhibit VI-11. Uptake of Newer Antipsychotic Medications in Medicaid and Growth of Prescription Volume 1996-1998
Source: The Lewin Group analysis of HCFA(now known as CMS) Medicaid Drug Rebate Program Data, 1998. 45 States Reporting.