A high-performance liquid chromatographic method for the measurement of the iron chelator 1,2-dimethyl-3-hydroxypyridin-4-one in human plasma

Development of a fast LC-MS/MS assay for the determination of deferiprone in human plasma and application to pharmacokinetics

A fast and accurate liquid chromatography/tandem mass spectrometric (LC-MS/MS) assay was first developed and validated for the determination of deferiprone in human plasma. The analytes were extracted with acetonitrile from only 50 μL aliquots of human plasma to achieve the protein precipitation. After extraction, chromatographic separation of analytes in human plasma was performed using a Synergi Fusion-RP 80A column at 30 °C. The mobile phase consisted of methanol and 0.2% formic acid containing 0.2 mM EDTA (60:40, v/v). The flow rate of the mobile phase was 0.8 mL/min. The total run time for each sample analysis was 4 min. Detection was performed using electrospray ionization in positive ion multiple reaction monitoring mode by monitoring the precursor-to-parent ion transitions m/z 140.1 → 53.1 for deferiprone and m/z 143.1 → 98.1 for internal standard. A linear range was established from 0.1 to 20 µg/mL. The limit of detection was determined as 0.05 µg/mL. The validated method was estimated for linearity, recovery, stability, precision and accuracy. Intraday and interday precisions were 4.3-5.5 and 4.6-7.3%, respectively. The recovery of deferiprone was in the range of 80.1-86.8%. The method was successfully applied to a pharmacokinetic study of deferiprone in six thalassemia patients.

Iron chelating agents with clinical potential

Iron is a critically important metal for a wide variety of cellular events. The element holds this central position by virtue of its facile redox chemistry and the high affinity of both redox states (iron II and iron III) for oxygen. These same properties also render iron toxic when levels exceed the normal binding capacity of the cell. As a result of this potential toxicity, selective iron chelators are finding an important role in the treatment of iron overload associated with many forms of thalassaemia. In addition, they appear to have potential in treating situations where a local increase in iron concentration causes an unfavourable pathology, for instance, in reperfused tissue (heart disease and stroke) and in Parkinsonian brain. There is also evidence that iron chelators may minimise the toxicity of paraquat and the side effects of bleomycin and doxorubicin.

Non-haem iron enzymes can also be inhibited by iron chelators and consequently such enzymes as ribonucleotide reductase and lipoxygenase can be selectively inhibited. Such inhibitory action is being investigated for the treatment of malaria, neoplastic disease, psoriasis and asthma.

Recent developments in these areas are discussed in the present overview.

Contractile and morphological properties of hamster retractor muscle following 16 h of cold preservation

INTRODUCTION

Cold hypoxia is a common factor in cold tissue preservation and mammalian hibernation. The purpose of this study was to determine the effects of cold preservation on the function of the retractor (RET) muscle of the hamster in the non-hibernating state and compare these with previously published data (van der Heijden et al., 2000) on the rat cutaneus trunci (CT) muscle.

MATERIALS AND METHODS

After cold storage (16 h at 4 degrees C), muscles were stimulated electrically to measure maximum tetanus tension (P(0)) and histologically analyzed. The protective effects of addition of the antioxidants trolox and deferiprone and the calcium release inhibitor BDM to the storage fluid were determined.

RESULTS

After storage, the twitch threshold current was increased (from 60 to 500 microA) and P(0) was decreased to 27% of control. RET morphology remained unaffected. RET muscle function was protected by trolox and deferiprone (P(0), resp., 43% and 59% of control). Addition of BDM had no effect on the RET.

CONCLUSIONS

The observed effects of cold preservation and of trolox and deferiprone on the RET were comparable to those on CT muscle function, as reported in a previously published study (van der Heijden et al., 2000). Both hamster RET and rat CT muscles show considerable functional damage due to actions of reactive oxygen species. In contrast to the CT, in the RET cold preservation-induced functional injury could not be prevented by BDM and was not accompanied by morphological damage such as necrosis and edema. This suggests that the RET myocytes possess a specific adaptation to withstand the Ca(2+) overload induced by cold ischemia.

The efficacy of oral deferiprone in acute iron poisoning

Due to its high cost and need for parenteral administration, the standard iron chelator deferoxamine is not used in many individuals with acute and chronic iron poisoning worldwide. Deferiprone is the first oral iron chelator to be shown to be effective in chronically iron overloaded thalassemia patients. Its efficacy, by oral administration, in acute iron poisoning has not been tested. Our objective was to determine whether orally administered deferiprone can reduce the mortality of rats following acute, toxic, oral doses of iron. Rats were administered 612 mg/kg elemental iron orally, corresponding to LD50 in the species tested. Two other groups received the same oral dose of iron followed by oral deferiprone: 800 mg/kg and 800 mg/kg, followed by another dose of 800 mg/kg 2 hours later. Coadministration of 800 mg/kg deferiprone with the iron decreased mortality from 30% to 6.6% after 2 hours (P = .02), from 40% to 16.6% after 12 hours (P = .04), and from 53.3% to 20% after 24 hours (P = 0.007). Mortality was also significantly decreased among animals coadministrated 2 repeated doses of deferiprone of 800 mg/kg with iron, to 0%, 9%, and 18%, and 2, 12, and 24 hours postdrug administration, respectively (P = .04, .05, .04, respectively). Histologically, there was a dose-dependent decrease in iron accumulation in the gastrointestinal tract. Orally administered deferiprone can decrease morbidity and mortality caused by acute iron overdose in rats. Oral deferiprone holds promise in the treatment of iron poisoning in humans.

An investigation into variability in the therapeutic response to deferiprone in patients with thalassemia major

Data suggest a large variability in the effectiveness of the orally active iron chelator, deferiprone, in inducing a sustained decrease in body iron to concentrations compatible with the avoidance of complications from iron overload. We analyzed 19 patients with thalassemia major who were undergoing long-term therapy with deferiprone (75 mg/kg/day every 8 hours). In seven of the 19 patients, hepatic iron concentration had been reduced or maintained at less than 7 mg/g of dry weight liver tissue, associated with no evidence of iron-induced toxicity (group A). In the remaining 12, hepatic iron concentration had either stabilized at higher than 7 mg/g of dry weight liver tissue, or increased to such concentrations during therapy with deferiprone (group B). We studied in these patients determinants that may explain such variability, including initial hepatic iron concentrations, compliance, transfusion index, pharmacokinetic characteristics of deferiprone, and plasma vitamin C status. Patients in group B showed significantly decreased plasma vitamin C concentrations compared with those in group A, who demonstrated normal levels (0.04 mg/dl [0.04-0.19 mg/dl] and 0.62 mg/day [0.44-1.05 mg/day], respectively; p = 0.02). A significant difference in apparent volume of distribution (Vd/F) had developed between the groups over time, with a higher Vd/F in group B (1.66 [0.681, group A] and 3.16 [0.811, group B]; p = 0.006). Group B had started with hepatic iron concentrations that were significantly higher than those of group A, a difference that became more pronounced over time. In the initial analysis, serum ferritin concentrations were also higher in group B. The two groups did not differ in the remaining factors. The initial hepatic iron concentrations predicted the slope of change in this value. Regression analysis suggested that patients with initial hepatic iron concentration of less than or equal to 7.22 mg/g of dry weight liver tissue are unlikely to further decrease while taking deferiprone 75 mg/kg/day. Vitamin C deficiency developed in patients in group B over time. Vitamin C is an important biologic cofactor that plays a role in the distribution of iron. The trend of increase in Vd/F of deferiprone over time may imply a compartment shift of iron stores to one less accessed by deferiprone. This study confirmed the effectiveness of deferiprone in heavily iron-loaded patients and provided evidence that its effectiveness decreases in proportion to liver iron load.

Salivary measurement of deferiprone concentrations and correlation with serum levels

Deferiprone (L1) is the first clinically available oral iron chelator and it has been proven to be effective for the treatment of transfusional iron overload in thalassemic patients. Because many of these patients have impaired compliance with their medications, effective means of continuous monitoring of compliance are crucial. Saliva drug monitoring has the potential advantage of an easy, noninvasive approach, assuming that it represents serum levels. However, drugs have variable correlations between saliva and serum concentration. We compared serum and saliva levels of L1 at various time points after ingestion of a 75 mg/kg/day dose in nine thalassemic patients. A highly significant correlation between serum-free L1 and saliva levels (r = 0.97, p = 0.0003) was found. Pharmacokinetic profiles were similar using serum and saliva monitoring. We conclude that saliva can be substituted for serum in monitoring L1 levels.

Pharmaceutical analysis of the oral iron chelator deferiprone (DMHP,L1)

The oral iron chelator deferiprone (1,2-dimethyl-3-hydroxy-pyrid-4-one, DMHP, LT or CP20) can be a useful drug in patients with transfusional hemosiderosis. From 1987 about 1000 patients in 16 countries have taken this drug on the base of clinical trials or compassionate use. Since this compound is only available as a raw substance, it is important to ascertain its purity before bringing the drug into a pharmaceutical formulation. Because deferiprone is administered chronically and in high doses, intake of potential toxic impurities can be substantial. In this article a proposal for the quality control of deferiprone is presented in the form of a pharmaceutical monograph. This includes the analytical methods required for identification, purity checking and assay. Furthermore the way we synthesized the drug to get hold of it in a pure form is described. This synthesis is also used in manufacturing the drug commercially. The monograph can be used as a guideline for standardization of the quality of deferiprone to be used for further study and treatment.

Efficacy of deferiprone in the treatment of acute iron intoxication in rats

BACKGROUND

Deferiprone [(1,2-dimethyl-3-hydroxypyrid-4-one) (L1)], is the first orally active iron chelating agent to reach clinical trials in patients with chronic iron overload. Its efficacy in preventing morbidity and mortality in acute iron poisoning has not been tested.

OBJECTIVE

To determine whether deferiprone can reduce the mortality of rats following toxic oral doses of iron.

METHODS

Rats were administered 612 mg/kg elemental iron by gavage, corresponding to the LD58. A parallel group received the same oral dose of iron followed by deferiprone intraperitoneally at 400 mg/kg (loading dose), followed by additional intraperitoneal injections of 200 mg/kg, 100 mg/kg and 100 mg/kg of deferiprone at one hour intervals.

RESULTS

Coadministering deferiprone with the iron decreased mortality from 58% (11/19) to 15% (3/20) (p = 0.013). The administration of deferiprone was associated with urinary excretion of iron (which did not occur with iron alone) and the production of the red deferiprone-iron complex. On histological examination there appeared to be less iron in the liver and gastrointestinal tract.

CONCLUSION

The coadministration of deferiprone can decrease morbidity and mortality caused by acute iron overdose. Deferiprone holds promise for the treatment of iron poisoning but additional study is required.

Critical comparison of novel and existing methods of compliance assessment during a clinical trial of an oral iron chelator

The assessment of compliance is critical in the evaluation of the effectiveness of a new therapeutic agent. Fifteen patients with transfusion-dependent beta-thalassemia, many of whom had previously demonstrated erratic compliance with deferoxamine, were enrolled in a clinical trial of a new oral iron chelator, 1,2-dimethyl-3-hydroxypyrid-4-one (L1). Their compliance with this medication was estimated by several existing methods and the novel Medication Event Monitoring System (MEMS). Overall compliance as assessed by the MEMS was 78.5 +/- 13.0% of prescribed doses taken, significantly lower than the corresponding rates calculated by pill counts and diaries (91.5 +/- 9.2% and 94.1 +/- 4.3%, respectively). However, several serious problems were encountered with the MEMS, mostly in the form of incorrect use of the device by the patients. Disclosure of the nature of the MEMS and the compliance monitoring process did not alter the rate of adherence with L1 therapy. Compliance as determined by pill counts did not differ between the 1st and 2nd 6-month periods. Although not reaching statistical significance, a trend towards better L1 compliance occurred in those patients in whom serum ferritin levels decreased. Patients who filled at least 50% of their diaries had significantly better compliance by pill counts than those who completed less than 50% of their diaries (95.9 +/- 4.1% and 86.5 +/- 11.1%, respectively). Steady-state L1 trough concentrations and 24-hour urinary iron excretion did not correlate with L1 compliance.(ABSTRACT TRUNCATED AT 250 WORDS)