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Biotech / Medical : QLT PhotoTherapeutics (QLTI)

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To: Daniel Martineau who wrote (313)	4/10/1998 10:45:00 PM
From: SC	Read Replies (2) of 1321

The subretinal neovascular membranes cause a tremendous amount of scarring when left alone. The current treatment consists of lasering membranes which are well defined on florescein angiography. In fact, if the membrane is subfoveal and well defined the current treatment is the same. The problem is that you create an immediate and permanent blindspot in the area treated (i.e. you destroy the retinal function in the area treated). In the case of subfoveal membranes you destroy the area of the retina concerned with central vision (i.e. the only area with fine enough vision to allow you to read or drive). Controlled studies have shown that patients treated in this fasion have a smaller scotoma (blindspot) 2 years later than patients who are not treated. But it is a difficult concept to convey to a patient. Imagine telling someone that they will notice an immediate worsening of vision which will be permanent after treatment in order to limit the size of the blindspot! These patients are usually referred to a retinal subspecialist and opinion is divided among retinal subspecialists as to whether it is better to let nature take its course or treat in order to limit the size of the scotoma(damned if you do and damned if you don't). Who wants a patient running around telling everyone he saw just fine until that doctor treated him with that laser (certainly not a reputation enhancer). Furthermore, the recurrence rate after treatment with laser (currently available laser without photodynamic drug treatment) is 50%. The other treatment that has been attempted is surgical removal of the subretinal neovascular membranes. This works well if histoplasmosis is the cause of the srnvm but poorly if AMD is the cause. The reason it works poorly in AMD is that the membranes are sub-retinal pigment endothelium in location and in the process of removing the membrane you remove the retinal pigment endothelium which is necessary for the support of the photoreceptors. The beauty of the photodynamic therapy is that the drug is preferentially accumulated in the neovascular cells then activated by a relatively low power high wavelength laser. The surrounding tissue is not destroyed as it is with the conventional laser treatments. Scarring should be much less with this treatment than it would if it were left untreated, or if it were treated with the current laser therapies. The completed TAP trial only dealt with well defined neovascular membranes, the VIP trial now getting under way is designed to show the efficacy of treating poorly defined membranes for which there is currently no treatment whatsoever. I think that the VIP trial is also studying srnvm secondary to myopic degeneration as well. It looks like this photodynamic treatment works better than anything currently available. The only question is whether or not repeated treatments on an ongoing basis is safe and effective in the opinion of the FDA panelists that review the data submitted. If the current trials underway don't answer this question to the satisfaction of the FDA panel that reviews the data, more money and time will need to be spent before the treatment is approved as safe and effective for general use. I don't know the details of the VIP trial design and that is why I posed the question of whether or not this trial addresses the need for repeated ongoing treatments. Could anyone enlighten us? sc

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