Absence of an interaction between iron and mycophenolate mofetil absorption

Abstract

Aim

To determine whether concomitant iron affects the absorption of mycophenolate mofetil.

Methods

An open-label, single centre, randomized, crossover trial was conducted in 16 healthy males. Fasting subjects received mycophenolate mofetil alone (treatment A) or co-administered with iron (treatment B).

Results

The mycophenolic acid AUC(0,24 h) for treatments A and B were 42.5 ± 10.5 and 44.7 ± 12.4 µg ml⁻¹ h, respectively. anova modelling showed the relative bioavailability of mycophenolate mofetil to be similar for the two treatments (90% confidence interval 0.92, 1.19).

Conclusions

There was no interaction between mycophenolate mofetil and iron supplements administered concomitantly to healthy fasting subjects.

Introduction

Mycophenolate mofetil (MMF) is an effective immunosuppressive agent indicated for the prevention of acute rejection in adult recipients of renal, cardiac or hepatic transplants, as well as paediatric recipients of renal transplants [1]. Following oral administration, the drug is rapidly absorbed and hydrolyzed to form the active metabolite mycophenolic acid (MPA) [1].

Iron supplements are routinely given to renal transplant recipients to treat anaemia. A previous study suggested that, in the fasted state, concomitant administration of a sustained-release ferrous sulphate formulation resulted in decreased MPA bioavailability [2]. This would mean that patients receiving MMF and iron may not have adequate exposure to MPA, and thus, may be at risk of acute rejection.

The current study was performed to confirm the previously published results regarding the potential interaction of iron with MMF.

Methods

Subjects

Healthy males (18–45 years) with a body mass index between 18 and 28 kg m⁻² were enrolled in the study after providing written informed consent. The subjects gave a detailed medical history and received a complete physical examination within 28 days of the start of the study. Subjects were excluded if they had a history or current evidence of clinically significant haematological, renal, cardiac, bronchopulmonary, vascular, gastro-intestinal, allergic, neurological, psychiatric, metabolic, immunodeficiency or hepatic disorders. Heavy smokers (> 5 cigarettes/day) were also ineligible for inclusion. Subjects retained the right to withdraw from the study at any time and for any reason. The study was conducted in full compliance with the principles of the Declaration of Helsinki, and performed according to Good Clinical Practice Guidelines. The protocol was reviewed and approved by the Comité Consultatif de Protection des Personnes dans la Recherche Biomédicale d’Alsace Strasbourg, France.

Materials

Mycophenolate mofetil in the form of 250 mg capsules (CellCept®, lot W1200, Roche, France) and the sustained release iron preparation Ferro-Gradumet (lot 70357VA, Abbott Laboratories Ltd, UK), providing 325 mg of ferrous sulphate per tablet (105 mg elemental ferrous ion), were used in this study.

Study design

This was an open-label, single centre, randomized, 4-way crossover study, with a washout period of at least 7 days between treatments.

The treatment sequences were 1 g of MMF administered alone (treatment A) or concomitantly with two iron tablets (treatment B) in the fasting state. As part of the overall study design, two other treatments (co-administration of MMF and iron with food, and a 3 h interval between MMF and iron administration) were also investigated, but the results are not included in this report.

Eligible subjects were admitted to the study centre on the evening before each treatment period and remained there for 24 h blood after dosing. Subjects were fasted from midnight before each dosing. All subjects received a light lunch approximately 5 h after dosing, and supper approximately 10 h after dosing. Smoking and the consumption of alcohol or caffeine-containing beverages were not permitted while the subjects were resident in the study centre or during the 48 h after dosing. No concomitant medication was permitted, with the exception of medications to treat adverse events.

Blood sampling and analysis of mycophenolic acid

Blood samples were collected immediately prior to drug administration and at 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, 6, 8, 10, 12, 16 and 24 h postdose in each period. Venous blood (5 ml) was collected into lithium heparinized vacuum collection tubes. Following centrifugation, plasma was stored at −20 °C until assay.

The plasma samples were analyzed for MPA using high performance liquid chromatography. For MPA, the mobile phase consisted of acetonitrile aqueous phosphoric acid 0.05% v/v (ratio 39 : 61). Quantification was accomplished by means of the internal standard method using RS-60461-000 as the internal standard. The UV wavelength of detection was 254 nm. The validated method employed solid phase extraction (C18 column) of 0.5 ml plasma samples followed by reverse phase chromatography using a BDS-Hypersil C-18 column (5 µm) with isocratic elution and ultraviolet detection. Quantification was accomplished by the internal standard method using RS-60461-000 (E-6-[1,3-dihydro-4-(4-carboxybutoxy)-6-methoxy-7-methyl-3-oxo-5-isobenzofuranyl]-4-methyl-4-hexenoic acid). The limit of quantification was 0.1 µg ml⁻¹ (all predose plasma samples were below this concentration). The interassay precision of quality control samples ranged between 4.2% and 9.3%, and mean accuracies ranged from 99.5% to 106%.

Pharmacokinetic and statistical analysis

The area under the plasma MPA concentration-time curve from 0 to 24 h (AUC(0,24 h)) was computed using the linear trapezoidal rule. The maximum observed plasma concentration (C_max) and the time to reach C_max (t_max) were obtained directly from plasma concentrations data.

All statistical analyses were performed using SAS® version 8.2. A sample size of 16 was required to provide 80% power to detect between-group differences at the 5% level of significance. A three-way anova model with the factors treatment, period and subject was used to evaluate the potential interaction between MMF and iron using the estimated mean ratio of mycophenolic acid AUC(0,24 h) and its 90% confidence interval.

Clinical assessments

Adverse events were monitored throughout the study. Blood pressure, pulse rate and a 12-lead ECG were recorded at 4, 8 and 24 h postdose. Blood and urine samples were collected 24 h postdose for a comprehensive range of laboratory tests.

Results

A total of 16 healthy males (median age 28.5 years; median weight 73.1 kg) were enrolled and randomized to treatment. All subjects completed the study.

The mean MPA concentration-time profiles are shown in Figure 1, and pharmacokinetic parameters are summarized in Table 1. The plasma MPA concentration-time profiles were similar in the two treatment groups. The limits of the 90% confidence interval of the estimated ratio of treatment B vs. treatment A were 92% to 119%, which were well within the usual reference region (0.80, 1.25) for bioequivalence. The within–subject coefficients of variation for AUC(0,24 h) were estimated as 21.3% for MPA.

Figure 1.

Mean ± SD plasma concentration-time profiles for MPA in healthy fasting males receiving MMF alone (treatment A (○)) or MMF and iron (treatment B (•))

Table 1.

Pharmacokinetic parameters for MPA in healthy fasting males (n = 16) by treatment group

Treatment	tmax (h)a	Cmax (µg ml−1)b	AUC(0,24 h) (µg ml−1 h)b
A: MMF alone:	1.0 (0.5–2.0)	18.4 ± 7.8	42.5 ± 10.5
B: MMF + iron:	0.8 (0.6–3.0)	19.7 ± 9.1	44.7 ± 12.4

^aData are median (range) values

^bData are mean values ± SD. MMF mycophenolate mofetil; C_max, maximum observed plasma concentration; t_max, time to reach C_max; AUC(0,24 h), area under the plasma concentration–time curve from 0 to 24 h.

MMF (with or without iron) was well tolerated and the majority of adverse events were mild in intensity and none was of a serious nature, and there were no deaths during the study period. No abnormal vital signs or laboratory parameters were recorded, and all ECG readings were considered normal.

Discussion

The present study demonstrated that oral iron administration did not significantly affect MMF absorption in healthy fasting subjects, as determined by MPA AUC(0,24 h), C_max and t_max measurements.

These results contrast markedly with those previously reported by Morii et al. who concluded that concomitant administration of MMF and iron should be avoided [2]. The reason for the differences observed between the results of our study and that of Morii et al. [2] is not known. In both studies, each patient received a dose of 210 mg of elemental iron. One possible explanation for the disparity is that the bioanalytical assay used by Morii et al. was affected by the high iron content of the samples. Notably, the internal standard used by Morii et al. was indomethacin, which can potentially form iron complexes [4].

Consistent with the results of the current study and in contradiction to the findings of Morii et al. [2], two reports have shown that iron preparations do not interfere with MMF bioavailability in both non-fasting and fasting renal transplant patients [5, 6].

In conclusion, when administered in a fasting state, concomitant iron administration did not affect the pharmacokinetics of MMF in healthy subjects. The weight of evidence suggests that renal transplant patients receiving concomitant MMF and iron, at appropriate doses, should have adequate immunosuppressive coverage.