Deferiprone in iron overload

Deferiprone: a review of its clinical potential in iron overload in beta-thalassaemia major and other transfusion-dependent diseases

Patients with beta-thalassaemia and other transfusion-dependent diseases develop iron overload from chronic blood transfusions and require regular iron chelation to prevent potentially fatal iron-related complications. The only iron chelator currently widely available is deferoxamine, which is expensive and requires prolonged subcutaneous infusion 3 to 7 times per week or daily intramuscular injections. Moreover, some patients are unable to tolerate deferoxamine and compliance with the drug is poor in many patients. Deferiprone is the most extensively studied oral iron chelator to date. Non-comparative clinical studies mostly in patients with beta-thalassaemia have demonstrated that deferiprone 75 to 100 mg/kg/day can reduce iron burden in regularly transfused iron-overloaded patients. Serum ferritin levels are generally reduced in patients with very high pretreatment levels and are frequently maintained within an acceptable range in those who are already adequately chelated. Deferiprone is not effective in all patients (some of whom show increases in serum ferritin and/or liver iron content, particularly during long term therapy). This may reflect factors such as suboptimal dosage and/or severe degree of iron overload at baseline in some instances. Although few long term comparative data are available, deferiprone at the recommended dosage of 75 mg/kg/day appears to be less effective than deferoxamine; however, compliance is superior with deferiprone, which may partly compensate for this. Deferiprone has additive, or possibly synergistic, effects on iron excretion when combined with deferoxamine. The optimum dosage and long term efficacy of deferiprone, and its effects on survival and progression of iron-related organ damage, remain to be established. The most important adverse effects in deferiprone-treated patients are arthropathy and neutropenia/agranulocytosis. Other adverse events include gastrointestinal disturbances, ALT elevation, development of antinuclear antibodies and zinc deficiency. With deferiprone, adverse effects occur mostly in heavily iron-loaded patients, whereas with deferoxamine adverse effects occur predominantly when body iron burden is lower.

CONCLUSION

Deferiprone is the most promising oral iron chelator under development at present. Further studies are required to determine the best way to use this new drug. Although it appears to be less effective than deferoxamine at the recommended dosage and there are concerns regarding its tolerability, it may nevertheless offer a therapeutic alternative in the management of patients unable or unwilling to receive the latter drug. Deferipone also shows promise as an adjunct to deferoxamine therapy in patients with insufficient response and may prove useful as a maintenance treatment to interpose between treatments.

Aluminium distribution and excretion: a comparative study of a number of chelating agents in rats

The present study was conducted to assess in rats the comparative effects of a number of chelating agents on the urinary excretion and tissue distribution of A1. Adult male Sprague-Dawley rats received a single intraperitoneal dose of aluminium (A1) nitrate nonahydrate (0.24 mmol/kg). Ten min. after A1 injection 1,2-dimethyl-3-hydroxypyrid-4-one, 2,3-dihydroxybenzoic acid, picolinic acid, methylmalonic acid, ethylenediamine-di(o-hydroxyphenylacetic) acid, 1-benzyl-2-methyl-3-hydroxypyrid-4-one, 1-(p-methylbenzyl)-2-methyl-3-hydroxypyrid-4-one, 1-(p-methoxy-benzyl)-2-methyl-3-hydroxypyrid-4-one, 1-(p-chlorobenzyl)-2-methyl-3-hydroxypyrid-4-one, 1-benzyl-2-ethyl-3-hydroxypyrid-4-one, 1-(p-methyl-benzyl)-2-ethyl-3-hydroxypyrid-4-one, 1-[3-hydroxy-2-methyl-4-oxopyridyl]-2-ethanesulfonic acid and 1-benzyl-(4-carboxylic acid)-3-hydroxy-2-methyl-4-oxopyridine were given by gavage at 1.79 mmol/kg. A control group received similar volumes of distilled water. An additional group of rats received a subcutaneous injection of desferrioxamine at 1.79 mmol/ kg. Urine samples were collected daily for three consecutive days and the animals were killed after this period. Samples of brain, bone, liver, kidney and spleen were collected. Although desferrioxamine, 1,2-dimethyl-3-hydroxypirid-4-one, 1-(p-methylbenzyl)-2-methyl-3-hydroxypyrid-4-one, 1-(p-methoxybenzyl)-2-methyl-3- hydroxypyrid-4-one, 1-(p-methylbenzyl)-2-ethyl-3-hydroxypyrid-4-one, 1-[3-hydroxy-2-methyl-4-oxopyridyl]-2-ethanesulfonic acid and 1-benzyl-(4-carboxylic acid)-3-hydroxy-2-methyl-4-osopyridine significantly enhanced the total excretion of A1 into urine, only treatment with 1-(p-chlorobenzyl)-2-methyl-3-hydroxypyrid-4-one and 1-benzyl-2-ethyl-3-hydroxypyrid-4-one significantly reduced A1 concentrations in all analyzed tissues. No beneficial effects of the remaining chelators on Al mobilization were observed. Further studies on the effects of some 3-hydoxrypyrid-4-ones on A1 removal can be of interest for the treatment of A1 accumulation and toxicity.

The pharmacokinetics and blood-brain barrier permeation of the chelators 1,2 dimethly-, 1,2 diethyl-, and 1-[ethan-1'ol]-2-methyl-3-hydroxypyridin-4-one in the rat

The 3-hydroxypyridin-4-ones (HPs) are iron and aluminum chelators. Their ability to enter the brain had not previously been directly determined. To determine whether they cross the blood-brain barrier (BBB), three HPs possessing a wide range of lipophilicity were examined: 1-[ethan-1'ol]-2-methyl-HP (CP40), 1,2-dimethyl-HP (CP20, L1, deferiprone), and 1,2-dimethyl-HP (CP94, EL1NEt). Their pharmacokinetics were determined in rats to establish dosing parameters for microdialysis studies of BBB permeation. Studies were then conducted with microdialysis probes in the blood, frontal cortex, and lateral ventricle to determine the rate and extent of HP BBB permeability. All three HPs were detectable in brain dialysate samples collected 0-7 min after HP injection, demonstrating rapid entry into the brain. The extent of unbound distribution (an indicator of the mechanism of BBB permeation) was 0.9 and 1.2 for the frontal cortex and lateral ventricle for CP20, and was 1.1 and 1.6 for CP94, suggesting diffusion across the BBB. The extent of unbound distribution of CP40 was 0.2 for both the frontal cortex and lateral ventricle, suggesting the presence of a transporter moving it out of brain extracellular fluid. Introduction of cyanide into the brain did not affect the brain to blood CP40 ratio, suggesting that the transporter is not energy-dependent. Both CP94 and CP40 caused death due to respiratory failure, whereas CP20 did not. The ability of less toxic bidentate HP chelators, such as CP20, to enter the brain may enable their use in the treatment of metal-induced diseases and iron-facilitated oxidative injury involving the central nervous system.