Part Deux: Estimating sales of Viracept -LMoss
"Let's now consider events that are more evenly balanced between different outcomes. One is whether Viracept will be about equal in desired characteristics to other PIs (I label this case VE) or whether it will be better (VB). In comparing it to the three PIs already approved by the FDA, only Viracept has all of the following desired attributes: High effectiveness, relatively high bioavailability, relatively simple dosing regimen, no serious
side effects (and the less serious ones easily managed), lack of cross-resistance with other PIs, and an ability to penetrate to possible hidden reservoirs of the virus (Viracept crosses the blood-brain barrier). In this comparison, I would give VB a p=0.9. There is a bit of a wild card, however, in the Vertex/Glaxo PI (VX-478). It is a year behind Viracept in testing and possible approval, and the data is not yet available to compare it to
Viracept. It is premature to say that it is the equal of Viracept; in fact, in early testing, evidence of rash and gastrointestinal toxicity has emerged. But this uncertainty should be recognized, so I give VB a p=0.7, which in turn gives VE a p=0.3 (i.e. 1.0 minus 0.7). I also estimate that VB will produce three times the sales of Viracept than will VE.
A second event for which there is uncertainty is whether the standard therapy in FY99 (in developed countries) will be delayed treatment (DT) or early treatment (ET). Under DT, combination therapy is generally not given until the patient's immune system is in a state of collapse. Under ET, it is given to all HIV-positive people who are willing and able to adhere to the dosing regimen. The probable advantages of ET include: Better patient
outcomes, public health benefits (patients with no detectable concentrations of virus are likely less of a threat to others), lower total cost of treatment (less hospitalization at over $100,000/year), and possibly, for some patients, a cure. For these reasons, I give ET a p=0.6. It would be higher, but there are other situations where decisionmakers have been penny-wise and pound-foolish, so I want to recognize the considerable uncertainty in
this outcome. Note that there are about five times as many people who are HIV-positive than there are people with immune system collapse, but to be conservative I will estimate a three-fold increase in patients treated for the ET case."
LMoss-AOL post....Continued-next post |
