ADIS DRUG EVALUATION
`
`Drugs 1999 Sep; 58 (3): 553-578
`0012-6667/99/0009-0553/$26.00/0
`7298
`© Adis International Limited. All rights reserved.
`
`Deferiprone
`A Review of its Clinical Potential in Iron Overload
`in β-Thalassaemia Major and Other
`Transfusion-Dependent Diseases
`
`Julia A. Barman Balfour and Rachel H. Foster
`Adis International Limited, Auckland, New Zealand
`
`Various sections of the manuscript reviewed by:
`M.B. Agarwal, Department of Haematology, LTMG Hospital and LTM Medical College, Bombay, India; C.
`Giardini, Divisione di Ematologia, Centro Trapianti Midollo Osseo di Muraglia, Pesaro, Italy; A.V. Hoffbrand,
`Department of Haematology, Royal Free Hospital, London, England; G. Koren, Division of Clinical
`Pharmacology and Toxicology, Hospital for Sick Children, Toronto, Ontario, Canada; A. Piga, University of
`Turin, Turin, Italy; M.H. van Weel-Sipman, Department of Paediatrics/BMT Unit, Leiden University Medical
`Centre, Leiden, The Netherlands; B. Wonke, Department of Haematology, Whittington Hospital, London,
`England.
`
`Data Selection
`Sources: Medical literature published in any language since 1966 on deferiprone, identified using AdisBase (a proprietary database of Adis
`International, Auckland, New Zealand) and Medline. Additional references were identified from the reference lists of published articles.
`Bibliographical information, including contributory unpublished data, was also requested from the company developing the drug.
`Search strategy: AdisBase search terms were ‘deferiprone’ or ‘1-2-Dimethyl-3-hydroxypyrid-4-one’ or ‘CGP-37391’ or ‘CP-20’ or ‘L-1’.
`Medline search terms were ‘deferiprone’ or ‘CGP 37391’ or ‘CP 020’ or ‘CP 20’. Searches were last updated 28 Jul 1999.
`Selection: Studies in patients with iron overload who received deferiprone. Inclusion of studies was based mainly on the methods section
`of the trials. When available, large, well controlled trials with appropriate statistical methodology were preferred. Relevant pharmacodynamic
`and pharmacokinetic data are also included.
`Index terms: deferiprone, thalassaemia, iron-overload, pharmacodynamics, pharmacokinetics, therapeutic use.
`
`Contents
`
` . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
`Summary
`1.
`Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 557
`2. Pharmacodynamic Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558
`2.1 Binding of Iron and Other Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558
`2.1.1 Promotion of Iron Excretion in Vivo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559
`2.1.2 Source of Iron Chelated by Deferiprone . . . . . . . . . . . . . . . . . . . . . . . . . . . 559
`2.2 Oxidant/Antioxidant Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 560
`2.3 Cytotoxic and Antiproliferative Effects
` . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
`2.4 Other Effects
` . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
`3. Pharmacokinetic Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
`3.1 Absorption and Plasma Concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
`3.2 Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 562
`3.3 Metabolism and Elimination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563
`4. Therapeutic Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563
`4.1 Urinary Iron Excretion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565
`4.2 Serum Ferritin Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 566
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`554
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`Barman Balfour & Foster
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` . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567
`4.3 Hepatic Iron Content
`4.4 Other Effects
` . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568
`4.5 Comparisons with Deferoxamine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568
`4.6 Use in Combination with Deferoxamine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569
`4.7 Compliance with Therapy and Quality of Life . . . . . . . . . . . . . . . . . . . . . . . . . . . 569
`5. Tolerability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 570
`5.1 Arthropathy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 570
`5.2 Neutropenia/Agranulocytosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 570
`5.3 Gastrointestinal and Liver Enzyme Disturbances . . . . . . . . . . . . . . . . . . . . . . . . . . 571
`5.4 Immunological Abnormalities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 571
`5.5 Zinc Deficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 571
`5.6 Hepatic Fibrosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 572
`5.7 Other Effects
` . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 572
`6. Dosage and Administration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 572
`7. Potential Place of Deferiprone in the Management of Iron Overload in
`β-Thalassaemia Major and Other Transfusion-Dependent Diseases . . . . . . . . . . . . . . . . . . 573
`
`Summary
`Abstract
`
`Patients with β-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 com-
`pliance 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 β-thalassaemia have demon-
`strated 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 defer-
`oxamine; 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 arthrop-
`athy and neutropenia/agranulocytosis. Other adverse events include gastrointes-
`tinal 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 de-
`
`© Adis International Limited. All rights reserved.
`
`Drugs 1999 Sep; 58 (3)
`
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`2 of 26
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`Taro Pharmaceuticals, Ltd.
`Exhibit 1017
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`Deferiprone in β-Thalassaemia: A Review
`
`555
`
`Pharmacodynamic
`Properties
`
`Pharmacokinetic
`Properties
`
`velopment 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. Deferiprone 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.
`Deferiprone is an oral bidentate iron chelator which binds to iron in a 3 : 1 ratio.
`It also binds other metals including aluminium, gallium, copper and zinc, but not
`calcium or magnesium.
`Deferiprone reduces body iron content in iron-overloaded animals and hu-
`mans. Iron excretion is related to dosage and the degree of iron overload, and
`occurs largely by the renal route. Deferiprone appears to mobilise iron from both
`reticuloendothelial and hepatocellular pools, from transferrin, ferritin and
`haemosiderin and from pathological iron deposits in intact red blood cells from
`patients with thalassaemia or sickle-cell anaemia.
`Depending on concentration, deferiprone has been reported to promote (at low
`concentrations, in vitro), and conversely to protect against (at high concentra-
`tions), oxidative damage caused by oxygen free radicals.
`As with deferoxamine, deferiprone inhibits proliferation of several cell lines
`in vitro and may induce apoptosis. It has also shown myelosuppressive effects in
`animals and humans. Although in vitro data suggest that deferiprone is markedly
`less toxic than deferoxamine to bone marrow myeloid progenitors, the clinical
`relevance of this is unclear, as deferiprone-induced myelosuppression may occur
`via a reactive metabolite-induced event mediated by the immune system.
`Peak plasma concentrations (Cmax) are reached within approximately 1 hour after
`oral administration of deferiprone. Food intake reduces the rate, but not the extent,
`of absorption of the drug. Administration of deferiprone 75 mg/kg/day at 12-
`hourly intervals produced a Cmax of 34.6 mg/L and area under the plasma con-
`centration-time curve (AUC) of 137.5 mg/L • h in patients with β-thalassaemia.
`Coadministration of iron (ferrous sulfate 600mg) reduced the AUC by about 20%
`in healthy volunteers.
`It is not clear whether deferiprone induces its own metabolism in vivo. This
`has been demonstrated in vitro. Trough plasma concentrations of deferiprone
`decreased during long term treatment with the drug in 1 study, but this was not
`corroborated by other studies.
`The volume of distribution after administration of deferiprone 75 mg/kg/day
`was 1.55 or 1.73 L/kg at steady state (depending on the dosage schedule) in
`patients with β-thalassaemia. Deferiprone was found to accumulate (≈3-fold) in
`thalassaemic, but not normal or sickle, red blood cells in vitro.
`Deferiprone is metabolised predominantly (>85%) to a glucuronide conjugate
`that lacks chelating properties. The drug, its conjugate and the deferiprone-iron
`complex are mainly excreted by the kidney and approximately 80% of a dose is
`recovered in the urine. Deferiprone is rapidly eliminated, with an elimination
`half-life (t1⁄2β) of approximately 1 to 2.5 hours in patients with β-thalassaemia.
`The t1⁄2β of deferiprone glucuronide was significantly correlated with creatinine
`clearance and this metabolite was found to accumulate in a patient with renal
`dysfunction. Although deferiprone is metabolised by the liver, the effects of he-
`patic impairment on the pharmacokinetics of the drug are yet to be determined.
`
`© Adis International Limited. All rights reserved.
`
`Drugs 1999 Sep; 58 (3)
`
`
`3 of 26
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`Taro Pharmaceuticals, Ltd.
`Exhibit 1017
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`556
`
`Barman Balfour & Foster
`
`Therapeutic Potential
`
`Tolerability
`
`Clinical studies, mostly in patients with β-thalassaemia, have demonstrated that
`deferiprone 75 to 100 mg/kg/day is capable of reducing iron burden in regularly
`transfused iron-overloaded patients. Factors affecting response to deferiprone
`appear to include the degree of iron overload and duration, dosage and degree of
`compliance with therapy.
`Serum ferritin levels (an indirect indicator of body iron load) are generally
`decreased in patients with very high pretreatment levels. In patients who are
`already adequately chelated at baseline, serum ferritin levels frequently remain
`stable. However, increases or inadequate decreases in serum ferritin and/or he-
`patic iron content were seen in some patients, especially after long term treatment.
`In some instances, this may reflect suboptimal dosage and/or severe degree of
`iron overload at baseline. Beneficial effects noted in some long term studies
`include lightening of the skin and decreased serum ALT and non-transferrin-
`bound iron levels.
`It should be noted that long term clinical trials reported to date have generally
`been noncomparative and conducted in small numbers of patients, who differed
`greatly with regard to baseline chelation status and underlying disease. Moreover,
`in many studies, the proportion of patients who were adequately chelated on
`deferiprone was not reported.
`Short term comparative studies have demonstrated that deferiprone ≤75
`mg/kg/day is less effective than deferoxamine in increasing iron excretion. How-
`ever, compliance during clinical use is superior with deferiprone, which may
`compensate for this to some degree. Few data from long term prospective ran-
`domised studies comparing deferiprone with deferoxamine have been reported.
`In these studies, deferiprone appeared to be slightly less effective than deferoxam-
`ine in reducing serum ferritin and less effective in controlling hepatic iron levels.
`Preliminary data suggest that deferiprone can be used successfully in combi-
`nation with deferoxamine, with additive or synergistic effects on urinary iron
`excretion and substantial reductions in serum ferritin levels being achieved.
`
`The most common adverse events in deferiprone-treated patients have been ar-
`thropathy (musculoskeletal stiffness and pain, accompanied by effusion in severe
`cases) and gastrointestinal disturbances (anorexia, nausea, vomiting). Arthropa-
`thy occurred in up to 39% of patients in clinical trials and generally resolves on
`dosage reduction or drug withdrawal.
`The most serious adverse effect associated with deferiprone is severe neu-
`tropenia/agranulocytosis (approximately 2% of patients each). This appears to be
`reversible.
`Other adverse events include elevated ALT and immunological abnormalities
`(development of antinuclear and antihistone antibodies). Deferiprone also pro-
`motes increased urinary excretion of zinc, particularly in patients with diabetes
`mellitus. This may occasionally lead to clinical signs of zinc deficiency (e.g.
`dry/itchy skin), which respond to zinc supplementation.
`Progression of existing liver fibrosis in 5 of a series of 14 patients treated with
`deferiprone was attributed to the drug, but this conclusion was subsequently
`questioned on the basis of methodological flaws in the study concerned. Long
`term follow-up of deferiprone-treated patients by other investigators implicates
`chronic hepatitis C infection and iron overload, rather than deferiprone, in pro-
`gression of hepatic fibrosis in transfusional iron-overloaded patients.
`
`© Adis International Limited. All rights reserved.
`
`Drugs 1999 Sep; 58 (3)
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`Deferiprone in β-Thalassaemia: A Review
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`557
`
`Dosage and
`Administration
`
`The recommended dosage of deferiprone is 25 mg/kg 3 times daily, although
`some investigators recommend use of dosages up to 100 mg/kg/day and/or twice
`daily administration. Special monitoring is required in all patients. Particular
`caution is recommended (with monitoring of renal or hepatic function) when
`treating patients with impaired renal or hepatic function. Deferiprone is contra-
`indicated in patients with neutropenia or a history of agranulocytosis or recurrent
`episodes of neutropenia, those taking drugs known to cause neutropenia, and in
`pregnant or lactating women. Women of childbearing potential should use con-
`traceptives while taking deferiprone. Weekly monitoring of neutrophil count is
`recommended and patients should be advised to report immediately any symp-
`toms of infection, such as fever, sore throat or flu-like symptoms.
`Deferiprone may interact with concomitantly administered medications con-
`taining metallic cations, including aluminium-based antacids.
`
`1. Introduction
`
`Thalassaemia major is one of the most common
`worldwide causes of iron overload. The thalas-
`saemias are a heterogeneous group of hereditary
`haemolytic anaemias characterised by inadequate
`synthesis of one or more haemoglobin polypeptide
`chains. They are classified according to which chain
`is involved (α, β or δ). In β-thalassaemia, de-
`creased β-chain production leads to a relative ex-
`cess of α-chains, which are unstable.
`Patients with β-thalassaemia major (or Cooley’s
`anaemia; the most severe form of the disease) usu-
`ally manifest symptoms at 4 to 6 months of age,
`developing severe anaemia with a haematocrit of
`<20%. They require regular blood transfusions in
`order to avoid the complications of anaemia and
`ineffective erythropoiesis, allow normal growth
`and development and prevent early death. How-
`ever, iron from the transfused blood accumulates
`in the reticuloendothelial system and parenchymal
`cells.
`Iron toxicity begins when the load of iron in a
`particular tissue exceeds the binding capacity of
`ferritin in the cell and of transferrin in the plasma.
`This results in accumulation of free or non-trans-
`ferrin-bound iron (NTBI), which can participate in
`free radical formation, leading to peroxidation and
`damage in various tissues. As reviewed by Olivieri
`and Brittenham[1] the degree of clinical iron toxic-
`ity in iron-overloaded patients is determined by:
`• the amount of excess iron
`
`• the rate of iron accumulation
`• the duration of exposure to elevated iron levels
`• the distribution of iron between highly hazard-
`ous and less hazardous body sites
`• ascorbate status (which influences body distri-
`bution of iron)
`• presence of viral hepatitis
`• alcohol intake.
`The sequelae of iron overload include hepatic
`fibrosis and cirrhosis, multiple endocrinopathies
`(diabetes mellitus, hypogonadism, hypopara-
`thyroidism, hypothyroidism), immunological dys-
`function, growth and bone abnormalities, short
`stature, cardiac disease (congestive heart failure,
`arrhythmias), pulmonary dysfunction and hyper-
`pigmentation of the skin. Progressive organ dys-
`function, affecting the heart, liver and endocrine
`system in particular, ultimately leads to death in the
`second or third decade of life if left untreated.
`A high proportion of regularly transfused tha-
`lassaemic patients have hepatitis C acquired via
`transfused blood, whereas vaccination has drasti-
`cally decreased the incidence of hepatitis B in this
`population.
`The management of thalassaemia and iron over-
`load has been reviewed by other authors.[1-6]
`The iron-chelating agent deferoxamine has been
`available for over 2 decades. Effective chelation
`with this agent maintains body iron stores in pa-
`tients with thalassaemia major at 5 to 10 times the
`levels found in healthy individuals.[7] Neverthe-
`less, with this level of control of body iron, patients
`
`© Adis International Limited. All rights reserved.
`
`Drugs 1999 Sep; 58 (3)
`
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`

`558
`
`Barman Balfour & Foster
`
`are protected against impaired glucose tolerance,
`diabetes mellitus, cardiac disease and early death.
`However, the high cost of deferoxamine pre-
`cludes its use in many parts of the world where
`β-thalassaemia is endemic (e.g. Asia). Addition-
`ally, many patients, particularly adolescents, fail to
`comply adequately with deferoxamine therapy be-
`cause of the onerous administration schedule (sub-
`cutaneous infusion over 8 to 24 hours 3 to 7 times
`weekly or intramuscular injection daily plus intra-
`venous infusion at the time of blood transfu-
`sion[8,9]). This noncompliance can allow iron-re-
`lated complications to develop. Serious adverse
`effects of deferoxamine include sensorineural
`hearing loss, retinal/visual damage, abnormal car-
`tilage metabolism and stunted linear growth. Other
`adverse effects include increased susceptibility to
`Yersinia, and more rarely other, infections. The risk
`of adverse effects increases when serum ferritin
`levels fall below 1000 μg/L (i.e. when body iron
`burden is only very modestly elevated or becomes
`normalised).[1] Deferoxamine-associated toxicity
`is less likely to occur at dosages ≤40 mg/kg/day in
`patients with thalassaemia (the recommended sub-
`cutaneous dose is 20 to 40 mg/kg/day in the US[8]
`and 20 to 50 mg/kg in the UK[9]).
`Diethylenetetra-penta-acetic acid (DTPA), an-
`other hexadentate chelator, is also given by slow
`subcutaneous infusion. However, it also chelates
`zinc avidly, which causes difficulties in maintain-
`ing adequate levels of zinc during long term ther-
`apy. Nevertheless, it provides a possible alternative
`to deferoxamine in those who cannot tolerate the
`latter drug.[3,10]
`Bone marrow transplantation provides the pos-
`sibility of radical cure in the minority of eligible
`patients for whom a suitable donor is available and
`facilities and funds allow.
`Thus, there is a considerable need to develop an
`oral iron chelator. Deferiprone is the best studied
`oral chelator to date. It is a bidentate iron ligand
`(i.e. it has 2 binding sites per molecule for iron,
`whereas deferoxamine has 6; fig. 1). The remainder
`of this review focuses on its clinical potential in the
`management of iron overload in β-thalassaemia.
`
`O
`
`N
`
`CH3
`
`OH
`
`CH3
`
`Deferiprone (molecular weight 139)
`
`CONH
`(CH2)2
`
`H2N
`
`(CH2)5
`N C
`
`OH O
`
`(CH2)5
`N C
`
`OH O
`
`CONH
`(CH2)2
`
`CH3
`
`(CH2)5
`N C
`
`OH O
`
`Deferoxamine (molecular weight 656)
`
`Fig. 1. Comparison of structural formulae of deferiprone and
`deferoxamine.
`
`Deferiprone has also been studied in small numbers
`of iron-overloaded patients with other transfusion-
`dependent diseases,
`including myelodysplastic
`syndrome, and sickle cell or Blackfan-Diamond
`anaemia and relevant data are included in this re-
`view.
`
`2. Pharmacodynamic Properties
`
`2.1 Binding of Iron and Other Metals
`
`Deferiprone forms strong, water-soluble 3:1 com-
`plexes with the Fe+++ ion, with a binding constant
`of 37, which is markedly higher than that of
`deferoxamine.[11] It also binds aluminium,[12-16]
`gallium,[17] copper[16] and zinc, but not calcium or
`magnesium.[11] Although deferiprone appears to
`have a low affinity for zinc in vitro,[16] zinc defi-
`ciency has been reported in a small number of iron-
`overloaded patients receiving long term deferi-
`prone treatment (see section 5.5). Lead, aluminium
`and copper, but not magnesium, calcium or man-
`ganese, compete with iron for binding to deferi-
`prone in vitro.[16]
`
`© Adis International Limited. All rights reserved.
`
`Drugs 1999 Sep; 58 (3)
`
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`6 of 26
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`Taro Pharmaceuticals, Ltd.
`Exhibit 1017
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`Deferiprone in β-Thalassaemia: A Review
`
`559
`
`patients treated immediately post-transfusion,
`when haemoglobin levels are relatively high.[29]
`Other investigators found that urinary iron excre-
`tion in patients with thalassaemia was indepen-
`dently affected both by steady-state trough plasma
`concentrations[30] and AUC[31] of deferiprone.
`The amount of iron excretion promoted by
`deferiprone is also related to iron load,[20,26,32] and
`the drug does not appear to chelate iron apprecia-
`bly in healthy volunteers who are not iron-over-
`loaded.[20,32]
`The therapeutic potential of deferiprone in in-
`ducing iron excretion in iron-overloaded patients
`is discussed in section 4.
`
`2.1.2 Source of Iron Chelated by Deferiprone
`Studies using radiolabelled iron in hyper-
`transfused rats indicated that deferiprone mobi-
`lises iron from both reticuloendothelial and
`hepatocellular pools. Iron from the reticuloendo-
`thelial pool was excreted in urine and bile, whereas
`all of the iron originating from the hepatic pool was
`excreted in the bile.[33] Similarly, when rats with
`normal iron stores were fed radiolabelled 3,5,5-
`trimethylhexanoyl-ferrocene (which delivers iron
`predominantly to hepatocytes), most of the iron re-
`
`0
`
`75
`50
`25
`Deferiprone dosage (mg/kg/day)
`
`100
`
`50
`
`40
`
`30
`
`20
`
`10
`
`0
`
`Mean urinary iron excretion (mg/24h)
`
`Fig. 2. Dose-related urinary excretion of iron in deferiprone-
`treated patients. All patients (n = 52) in this crossover study had
`thalassaemia major and iron overload and received deferiprone
`in 3 divided daily doses (duration of treatment was not
`stated).[27]
`
`2.1.1 Promotion of Iron Excretion In Vivo
`Orally administered deferiprone lowers body
`iron levels in animals and humans. Excretion of
`iron occurs mainly by the renal route.[18]
`When the 24-hour urinary iron excretion was
`divided by the amount of iron that a given oral dose
`was capable of binding, the chelation efficiency of
`deferiprone in iron-overloaded patients was calcu-
`lated to be 3.8[19] or 6.8%.[20] The iron-binding ef-
`ficiency of deferiprone was lower in animal stud-
`ies, ranging from 1.3 to 2.1% in iron-overloaded
`monkeys and rats.[21,22]
`intra-
`In rats with acute iron intoxication,
`peritoneal administration of deferiprone (400 mg/
`kg 15 minutes after iron administration, followed
`by 1 dose of 200 mg/kg and 2 doses of 100 mg/kg
`at hourly intervals) decreased mortality (from 59
`to 15% of animals at 14 hours; p = 0.013).[23] How-
`ever, a similar study found that, although concom-
`itant administration of deferiprone with a lethal
`dose of iron protected rats against iron toxicity,
`administration of deferiprone (≤9 mmol/kg) 10 to
`15 minutes after the iron dose appeared to increase
`mortality (p = 0.009).[24] For a review of preclinical
`studies with deferiprone see Al-Refaie and Hoff-
`brand.[18]
`In iron-overloaded patients, deferiprone in-
`creases urinary excretion of iron in a dose-depend-
`ent manner,[25-27] although increases in urinary iron
`excretion with increased dosage are more than pro-
`portional. Mean daily excretion ranged from 6.2
`mg/day at a dosage of 25 mg/day to 42.3 mg/day
`at a dosage of 100 mg/day (fig. 2).[27]
`More frequent administration of deferiprone,
`resulting in more sustained plasma drug concentra-
`tions but very similar 24-hour area under the
`plasma concentration-time curve (AUC24), achie-
`ved better chelation with the same total daily dos-
`age. Urinary iron excretion in 10 patients with β-
`thalassaemia was 0.59 mg/kg/day during 6-hourly,
`compared with 0.40 mg/kg/day (p = 0.0129) during
`12-hourly, administration of deferiprone 75
`mg/kg/day (for 3 days).[28] It was subsequently
`suggested that sustained plasma concentrations of
`deferiprone may achieve better iron excretion in
`
`© Adis International Limited. All rights reserved.
`
`Drugs 1999 Sep; 58 (3)
`
`
`7 of 26
`
`Taro Pharmaceuticals, Ltd.
`Exhibit 1017
`
`

`

`560
`
`Barman Balfour & Foster
`
`moved by deferiprone (200 mg/kg/day) was found
`in the faeces.[34]
`Deferiprone chelates iron bound by transferrin
`(iron transport protein),[20,35] ferritin (iron storage
`protein)[36] and haemosiderin (partly degraded fer-
`ritin),[36] as well as free iron. It has been calculated
`that up to 20% of iron excreted in the urine after a
`single dose of deferiprone may originate from iron
`bound to transferrin. Deferiprone was more effec-
`tive than deferoxamine in mobilising iron from
`transferrin and ferritin in vitro.[35]
`Deferiprone, but not deferoxamine, was able to
`chelate pathological iron deposits from intact red
`blood cells (RBCs) from patients with thalassae-
`mia or sickle-cell anaemia, both in vitro and in vivo.
`No free iron was detected in thalassaemic RBCs
`after 24 hours’ incubation with deferiprone 0.5
`mmol/L. After administration of deferiprone 50 or
`70 mg/kg/day for 2 weeks to thalassaemic patients,
`66 and 78% of free iron was removed from RBC
`membranes.[37] In 11 patients on long term therapy,
`deferiprone removed membrane free iron from β-
`thalassaemic erythrocytes with a reduction in KCl
`cotransport activity.[38] These findings may reflect
`the enhanced ability of deferiprone (compared with
`deferoxamine) to permeate cell membranes. Bi-
`dentate ligands are able to penetrate cells more ef-
`ficiently than hexadentate chelators on account of
`their lower molecular weight.[39]
`
`2.2 Oxidant/Antioxidant Effects
`
`Liberation of iron in vivo can catalyse formation
`of hydroxyl radicals, which are highly reactive and
`toxic to tissues.[40] Depending on concentration,
`deferiprone has been reported to promote (at low
`concentrations in vitro), and to protect against (at
`high concentrations), oxidative damage caused by
`oxygen free radicals.
`Binding of 1 atom of iron (which has 6 coordi-
`nation sites) requires 3 molecules of deferiprone
`but only 1 molecule of deferoxamine. Moreover,
`the chelates formed by deferiprone have relatively
`low stability.[41] At low deferiprone concentrations
`(relative to available iron concentrations), partially
`bound iron species (bound to only 1 or 2 deferi-
`
`prone molecules) can be formed. In some in vitro
`systems, devoid of substrates capable of ‘mopping
`up’ free radicals, the unoccupied coordination sites
`of these complexes can catalyse formation of hy-
`droxyl radical or other reactive oxygen species.[41]
`Exposure to deferiprone 1 mmol/L for 1 hour
`before exposure to hydrogen peroxide markedly
`potentiated hydrogen peroxide-mediated oxidative
`DNA damage in iron-loaded hepatic (HepG2) cells
`in vitro.[42] Deferoxamine 0.33 mmol/L had no ef-
`fect. However, when deferiprone exposure was
`maintained throughout hydrogen peroxide expo-
`sure, deferiprone protected against oxidative dam-
`age. Thus, the influence of the drug on iron-cata-
`lysed free radical formation may depend on the
`intracellular deferiprone : iron concentration ratio.
`In vitro studies investigating the effects of deferi-
`prone concentrations on iron-mediated ascorbate
`oxidation and deoxyribose degradation indicate
`that the deferiprone:iron ratio must be at least 3 : 1 to
`inhibit free radical generation. At lower deferi-
`prone concentrations, free radical generation is in-
`creased.[42]
`These findings may serve as an indication of the
`theoretical potential for generating reactive oxygen
`species in the presence of low tissue concentrations
`of deferiprone, but the nonphysiological condi-
`tions and concentrations employed in these studies
`should be taken into account.
`Deferiprone prevented oxidation of human low-
`density lipoproteins (LDL) in vitro, with complete
`inhibition at a concentration of 50 μmol/L, and at
`a concentration of >50 μmol/L protected human
`umbilical vein endothelial cells against the cyto-
`toxic action of oxidised LDL (p < 0.001 vs un-
`treated control). These effects were concentration-
`dependent.[43] It has been suggested that oxidation
`of lipoproteins may play an important role in ath-
`erogenesis. Administration of deferiprone 100 mg/
`kg/day to rabbits fed a high-cholesterol diet signif-
`icantly decreased aortic cholesterol accumulation
`(by 72% vs untreated controls; p < 0.0001).[43]
`Deferiprone 50 μmol/L attenuated methaemo-
`globin formation by 25% (p < 0.0001 vs untreated
`control) in β-thala