Rapid Responses to:
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Rapid Responses: Rapid Responses published:
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![[Read Rapid Response]](/icons/misc/sectionDOWN.gif)
Burns After Photodynamic Therapy
- David Horrobin (7 February 2001)
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Re: Burns After Photodynamic Therapy
- David Kessel (28 February 2001)
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Re: Burns After Photodynamic Therapy
- Richard Bryce (15 March 2001)
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David Horrobin, Research Director Laxdale Research, Stirling, FK7 9JQ
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Dear Editor, BURNS AFTER PHOTODYNAMIC THERAPY The letter from Scotia proffers more confusion than light. Most pharmaceutical scientists would not call a mix of polyethylene glycol, ethanol and water “aqueous”. This type of solvent is used for materials, like Foscan, which do not readily dissolve in water. The explanation for Dr Dow’s use of the terms “aqueous” and “water” is therefore not persuasive. It seems more likely that a simple error was made and that this error led to Foscan being administered via an injection port which had already been flushed with saline. Scotia pointedly do not say whether or not their instructions to Dr Hettiaratchy et al suggested or allowed Foscan to be injected after saline flushing or whether Foscan was in fact administered after saline flushing. Please could we have a clear response from the company on this issue? In the description of the clinical trial, it is not clear whether the saline flushing was given to the five patients before or after Foscan. Flushing after Foscan would not be expected to cause venous precipitation since by then the Foscan would have been dispersed in the blood. Only flushing before Foscan would cause the problem. Please can we know clearly which was the case? Many of the patients in the clinical trial were Indian and such patients would be much less susceptible to Foscan burns. How many of the five patients were Indian? I hope that Scotia will now give clear answers to these questions. Yours faithfully D.F. Horrobin Competing interests: DFH was formerly chief executive of Scotia. |
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David Kessel, Professor of Pharmacology and Medicine Wayne State University School of Medicine
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It is not clear to me how the precipitation of Foscan in a blood vessel might lead to a photodynamic response. This could occur if there was solubilization of the drug by plasma and a resulting penetration into tissues. In order to rule this in or out, it is necessary to examine the solubility of Foscan in plasma. Otherwise, it's all speculation. |
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Richard Bryce, Medical Director Scotia Pharmaceuticals Ltd,. Stirling
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Dear Editor BURNS AFTER PHOTODYNAMIC THERAPY In his letter of 20 January(1) and his Rapid Response of 7 February, Dr Horrobin comments upon references by Dr Dow to the terms "aqueous" and "water" and whether, if there is a view in Scotia that Foscan is water soluble, this might have led to erroneous injection instructions being given to the doctors performing the volunteer study(2). On 26 July 2000, Dr Dow wrote to the editor of this journal to correct any misunderstanding caused by Dr Dow's application in his letter of 1 July 2000(3) of the term "water" in the description of the solvent used in the formulation of Foscan. Furthermore, this simplified description was not used in protocols or written drug administration instructions issued by Scotia to investigators in its patient and volunteer studies. The doctors at the clinical research unit conducting the volunteer study followed their own drug administration and flushing procedure, rather than instructions issued by Scotia. However, Scotia does not consider that flushing instructions or other simplistic suggestions will easily explain these unusual events. Scotia continues to consider what additional in-vitro and in-vivo work could usefully contribute to reaching a clear understanding of the cause of the unusual frequency and severity of reactions seen in the volunteer study. Dr Horrobin also states that Indian patients would be much less susceptible (than white patients) to Foscan burns. In fact, the clinical database shows no differences in incidence or severity of photosensitivity reactions (including burns) between ethnic or racial groups. Yours sincerely Dr Richard Bryce
1. Horrobin DF. BMJ 2001;322:171 2. Hettiaratchy S, Clarke J, Taubel J, Besa C. BMJ 2000;320:1245 3. Dow RJ. BMJ 2000;321:53 |
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