| Popis: |
DF has a low general toxicity, perhaps because of its low lipid solubility, Kpart 0.01 (Porter et al, 1988b). This feature of the molecule may prevent it from penetrating most cells of the body. It appears that there may be a specific mechanism of uptake of the drug by hepatocytes (Porter et al, 1987), making the iron in these cells available for excretion via the bile, while the iron excreted in the urine may all come from extracellular chelation, particularly when iron leaves the reticuloendothelial cells (Hershko et al, 1978). On this hypothesis, cellular toxicity occurs only when DF penetrates sensitive cells in sufficient amounts so that some free DF remains after all the available iron in such cells has been chelated. Such a hypothesis accounts for the protection of cells by iron overload and therefore the greater sensitivity of unloaded patients. The retina and central nervous system are further protected by the blood-retinal or blood-brain barrier, and increased penetration of this barrier, mediated by high peak levels of DF, by drugs or other diseases would lead to the retinal or neurotoxic effects seen. In the ear, high levels of unliganded DF for a period of time may be necessary to cause deafness. Thus the very property that prevents its oral activity may be part of the reason for the low toxicity of DF. The severe toxic effects on vision, hearing and growth are all more likely at higher doses of DF and there appears to be partial protection against them by iron overload. These two conclusions have to be taken into account when deciding on the appropriate dosage for each patient. With care, the dosage can be adjusted to remove enough iron to prevent iron accumulation and therefore its toxic effects, whilst keeping doses low enough to prevent DF from being toxic itself. It appears that even in very iron-overloaded patients dosages higher than 125 mg kg-1 day-1 may cause visual disturbances and should be avoided. In patients on renal dialysis with aluminium toxicity great care is needed to avoid retinal toxicity even with dosages as low as 50 mg kg-1 day-1, although the drug should not be withheld if clinically indicated. The administration of DF to renal dialysis patients is described by Pogglitsch et al (1981, 1983), Pacitti et al (1983), Ihle et al (1986) and Molitoris et al (1987). DF should not be given to patients unless there is a clearly established clinical indication.(ABSTRACT TRUNCATED AT 400 WORDS) |
