The pharmacology and safety profile of ferric carboxymaltose (Ferinject®): structure/reactivity relationships of iron preparations

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 ABSTRACT
Ferric carboxymaltose (FCM, marketed as Ferin-
ject®) is a new intravenous iron preparation. It
combines the positive characteristics of iron dextran
and iron sucrose but is not associated with dextran-
induced hypersensitivity reactions and can be given
in much higher doses than iron sucrose or iron
gluconate. The chemical characteristic of the iron-
carbohydrate complex means that iron is released
slowly, avoiding toxicity and oxidative stress. Up to
1000 mg iron can be given in a single administration
of FCM, and this can be given by rapid infusion over
15 minutes. The reduced administration time, cou-
pled with the fact that a test dose is not required
(in contrast to iron dextran and iron sucrose) and
the fact that a large amount of iron can be given in
one dosage, offer convenience for patients and
potential cost savings for healthcare providers.
Key-Words:
Antianaemic drug; iron carboxymaltose; metabolism;
pharmacokinetics; reactivity.
 INTRODUCTION
A new form of intravenous iron, ferric carboxy-
maltose (FCM, marketed as Ferinject®) has been
developed to combine the positive characteristics of
iron dextran and iron sucrose. There was a need for
such an iron preparation because of the problems
and limitations associated with iron dextran and iron
sucrose. FCM was therefore developed to have a
better safety and tolerability profile than existing
products. Specifically, it avoids dextran-induced
hypersensitivity reactions (DIAR) and overcomes the
low-dosage limitations of iron sucrose and iron
gluconate. It has a neutral pH and a physiological
osmolarity and can be given by rapid infusion. FCM
exhibits low reactivity with molecules in blood and
living cells and therefore causes little toxicity. It has
a structure similar to ferritin and causes iron to be
deposited in the reticuloendothelial system (RES) of
the liver. It can therefore provide iron without induc-
ing oxidative stress.
 CHEMICAL CHARACTERISTICS
AND METABOLISM OF FCM
The active pharmaceutical ingredient (API) of FCM
is water soluble and the final product (FP) Ferinject®
is a colloidal solution. FCM comprises a macro-
molecular iron-hydroxide complex of polynuclear iron
(III) hydroxide in a carbohydrate shell. The complex has
a molecular weight of around 150,000 Daltons. This
means that little of the product is lost through renal
elimination, unlike other smaller iron complexes.
Once in the body, iron is released gradually, avoid-
ing the acute toxicity of many other iron compounds
The pharmacology and safety
profile of ferric carboxymaltose
(Ferinject®): structure/reactivity
relationships of iron preparations
Peter Geisser
Vifor (International) Inc. St. Gallen, Switzerland.
Port J Nephrol Hypert 2009; 23(1): 11-16
Advance Access publication 17 December 2008
Received for publication: 25/11/2008
Accepted: 12/12/2008
EDITORIAL
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12 Port J Nephrol Hypert 2009; 23(1): 11-16
but allowing large amounts of iron to be delivered.
This results in a much wider therapeutic window. For
example, the LD50 (i.e. the dose that kills 50% of
experimental mice) is just 11 mg Fe/kg for intravenous
administration of the common salt, iron sulphate
(FeSO4), around 50 for oligonuclear complexes such
as Fe(III)EDTA and Fe(III) gluconate, >200 for iron
sucrose, >2500 for iron dextrin and iron dextran1. For
FCM the LD50 is >1000 mg Fe/kg body weight.
Due to the stability of the complex, FCM does not
release ionic iron under physiological conditions.
The iron hydroxide is tightly bound within a carbo-
hydrate cage (Fig. 1).
Therefore the iron hydroxide core, with its carbohy-
drate shell, is taken up by macrophages and enters the
lysosomes where Fe3+ can be converted into Fe2+ as
required. The Fe2+ is released by a divalent metal
transporter (DMT1) then by ferroportin and taken up by
transferrin after oxidation by ceruloplasmin (Fig. 2).
In less stable complexes, iron is released rapidly
from the complex causing high levels of transferrin
saturation (60-100%) and therefore non-transferrin-
bound iron (NTBI). This NTBI, outside the mac-
rophage, is highly toxic. Small amounts of iron in
the serum (about 3 mg/l) can result in almost com-
plete transferrin saturation.
Following a 100mg iron dose from FCM (Ferin-
ject®), iron sucrose (Venofer®) or iron gluconate
(Ferrlecit®) different patterns of transferrin saturation
are observed. With FCM, unbound apo-transferrin
predominates, with iron sucrose, more monoferric
transferrin (Fe-Tf) is observed, whereas with iron
gluconate, both Fe-Tf and diferric transferrin (Fe2-Tf)
is observed after 4 hours incubation (Fig. 3).
Following a 1000mg iron dose, iron sucrose and
gluconate cause oversaturation of transferrin, while
with FCM a balance of apo-transferrin, Fe-Tf and Fe2-
Tf is observed. This higher reactivity of iron sucrose
and gluconate is reflected in the clinical characteristics
and recommended doses, since the maximum single
dose for iron gluconate is 62.5-125mg iron, that for
iron sucrose is 200-500mg iron, while for FCM up to
1000 mg iron can be given in a single dose.
Figure 1
Iron carboxymaltose (FCM) showing the iron oxyhydroxide core contained
in the carbohydrate shell.
Figure 2
Metabolism and toxicity of iron-hydroxide carbohydrate complexes (ICC).
Figure 3
Reactivity of iron carboxymaltose (FCM, Ferinject®), iron sucrose (Venofer®)
and iron gluconate (Ferrlecit®) with transferrin (incubation time 4 hours).
Peter Geisser
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Port J Nephrol Hypert 2009; 23(1): 11-16 13
 SAFETY AND TOLERABILITY
OF IRON PREPARATIONS
Oversaturation of transferrin following rapid
administration of iron sucrose (faster than the recom-
mended rate) leads to transient adverse events such
as hypotension, nausea, vomiting, abdominal pain,
oedema and metallic taste2.
Hutchinson et al.3 and Dresow et al.4 have shown
that giving oral iron therapy with ferrous salts, at
dosages of only 60-100mg iron per dose, leads to
transferrin saturation of up to 80% with resultant
NTBI at each administration. They also observed
similar side effects to those seen in the Chandler
study. The most common side-effects associated
with oral iron therapy (according to the Summaries
of Product Characteristics) include: epigastric pain,
indigestion, nausea, vomiting, diarrhoea, constipa-
tion, perforation of duodenal or jejunal diverticulum,
urticaria, rash, exanthema and anaphylaxis5.
Table 1 shows the properties of various iron
preparations. The tolerability of iron compounds
depends not only on the reactivity of the iron and
how easily it is released from the carbohydrate but
also on the size of the iron-carbohydrate complex
and the nature of the carbohydrate moiety. The
release rate of iron from polynuclear iron hydroxide-
carbohydrate complexes is inversely related to the
molecular weight of the complex1 (Fig. 4).
Table I
Classification of iron complexes
Type I Type II Type III Type IV
Example Iron dextran
BP/USP
Iron dextrin
Iron sucrose Iron (III)-gluconate
Iron (III)-citrate
Iron (III)-sorbitol
Iron (III)-citrate + iron (III)-sorbitol + iron dextrin
Iron (III)-gluconate + iron sucrose
Preparations Ferinject®
InFeD®
Dexferrum®
Venofer®
Fesin®
Jectofer®
Ferrlecit®
Characteristic Robust and strong Semi-robust and mod-
erately strong
Labile and weak Mixtures containing at least 2 different iron com-
plexes
Molecular mass [Dalton] >100,000 30,000-100,000 <50,000 <50,000
Reactivity
degradation kinetics
k •103 • min-1
at θ = 0.5
15-50 50-100 >100 >100
with transferrin
[μg iron/dL]
52.7 a 140.7 c 251.7 d
redox-active iron
[μM]
0.57 b 1.11 c 1.52 d
redox potential
[mV]
-475 a
-390f
-526 c -200 d
Toxicity
*LD50 1013 a,e 359 c not available 155 d
Oral >2500 >2500 429-1000
Intravenous >2500 >200 13-16.5
BP = British Pharmacopoiea, USP = US Pharmacopoiea, a = iron dextran, b = iron dextrin, c = Venofer®, d = Ferrlecit®, e = Martin et al.13, f = Ferinject®, * = LD50 in white
mice in mg Fe/kg body weight.
Figure 4
Iron release rate versus molecular weight of different iron-carbohydrate
complexes showing an inverse relationship (modified from Geisser et al.1)
The pharmacology and safety profile of ferric carboxymaltose (Ferinject®):
structure/reactivity relationships of iron preparations
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14 Port J Nephrol Hypert 2009; 23(1): 11-16
These characteristics will influence the clinical
behaviour of the preparations.
In terms of the rate of elimination of the complex
from the serum, FCM is intermediate between iron
sucrose (which is eliminated more rapidly) and iron
dextran (which is eliminated more slowly) (Fig. 5).
The half-lives are 5 hours for iron sucrose, 16 hours
for FCM and over 3 days for iron dextran (at a dose
of 20mg iron/kg body weight).
The rate of iron release is reflected in the side-
effect profile, with more reactive compounds being
less well tolerated. However, iron dextran (which has
a low reactivity) has a higher incidence of side
effects due to dextran-induced anaphylactic reac-
tions6. Unlike iron dextran and iron gluconate, no
fatalities have been reported with iron sucrose
administration and the reported number of adverse
events (per million dose equivalents) is lower7.
Ionic iron, especially the hydrated form of ferrous
iron, Fe2+ and ferric hydroxide Fe(OH)3, can contrib-
ute to the processes that lead to the formation of
free and latent hydroxyl radicals8. Fe2+ can enter the
body from medicinal oral iron preparations but it is
also possible that Fe3+ compounds react with super-
oxide or NADPH to form Fe2+, depending on the
reduction potential (Fig. 6).
Moreover, the reactivity of superoxide with fully
saturated transferrin is greater than that with par-
tially saturated transferrin9. This means that the
pattern of transferrin saturation described above is
responsible for oxidative stress, which may be con-
sidered a ‘silent’ side effect of iron therapy. The
reduction potential of FCM is –390 mV, which pre-
vents reduction to Fe2+ species.
 PRECLINICAL STUDIES
Histological studies using a total dose of 200mg
iron/kg body weight have confirmed that the iron is
deposited in the RES and not in the parenchyma
and therefore does not induce oxidative stress reac-
tions. In contrast to iron gluconate, high dose FCM
did not induce necrosis in mouse liver (Fig. 7). There
was also no effect on aspartate amino transferase
(AST), alanine amino transferase (ALT) or alkaline
phosphatase following intravenous administration,
in contrast to other preparations such as iron dextran
and iron gluconate which caused increases in these
liver enzymes10.
Long-term lack of oxidative stress associated with
FCM is indicated by a number of parameters includ-
ing the glutathione ratio and catalase activity in
hepatic, cardiac and renal tissues four weeks after
Figure 5
Serum elimination of FCM, iron dextran and iron sucrose in humans. Half
life values from Crichton et al.8.Figure 6
Reduction potentials of iron(III) compounds at pH 7.0 and the correspond-
ing reactions (Crichton et al8).
Peter Geisser
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Port J Nephrol Hypert 2009; 23(1): 11-16 15
weekly i.v. iron administration. In contrast, iron
gluconate causes increased lipoperoxidation by
thiobarbituric reactive species (TBARS) and increased
glutathione peroxidase concentrations. Iron glucon-
ate and iron dextran cause significant decreases in
the glutathione ratio (GSH/GSSG). However, in all
these tests, there was no difference between FCM
and isotonic saline10. These all suggest that FCM is
less likely to cause oxidative stress than other iron
compounds.
Preclinical studies with Ferinject® confirm the
safety and tolerability predicted from the chemical
properties of the complex. While Dexferrum causes
a statistically significant decrease in systolic blood
pressure, the effects of FCM could not be distin-
guished from those of isotonic saline (Fig 8). Rapid
administration of high doses (240 mg Fe/kg bw in 2
seconds) to mice produced no changes in vital signs.
Repeated dose studies in rats and dogs showed no
adverse effects at a dose of 117 mg Fe/kg in both
species. The highest non-lethal dose of FCM was
found to be at least 5-times higher than that for iron
sucrose [Vifor, data on file].
Preclinical tests show that FCM does not cross-
react with dextran antibodies [Vifor, data on file].
FCM has no mutagenic potential, does not damage
chromosomes and is not associated with bone mar-
row cell toxicity [Vifor, data on file]. At high doses
(corresponding to between 1.2x and 12x the human
overdose level) there were no signs of embryo-foetal
or maternal toxicity in experimental animals; there
was also no pre- or post-natal toxicity and no effects
on fertility or embryonic development.
 CLINICAL PHARMACOKINETICS
Pharmacokinetic studies show a dose-proportion-
al elimination of FCM from the serum, showing no
signs of saturation at doses of up to 1000mg iron
per patient.
Radiolabelling studies in patients with iron-defi-
ciency anaemia or renal anaemia have shown that
the iron from FCM is distributed in the liver and
spleen and taken up predominantly by the bone
marrow from within 60 minutes after administration
while levels in the liver and spleen fall steadily after
about 30 minutes. In all patients, the RBC utilisation
increased rapidly up to days 6-9, then increased at
a much slower rate (Fig. 9). Within 2-3 weeks of FCM
administration, iron utilisation rates were 91-99% in
the iron-deficient patients, and 61-84% in the
patients with functional iron deficiency11.
Repeat dose pharmacokinetic studies giving 500
or 1000mg iron as FCM weekly for 4 weeks showed
no signs of saturation with multiple doses. This
means that the elimination curve for repeated doses
was the same as with a single dose8,12 (Fig. 10).
Use of FCM offers potential savings in terms of adminis-
tration time and considerable advantages to patients
compared to other intravenous iron preparations.
Liver histotoxicity: microscopic pictures of mouse liver 4 hours after injection
Iron gluconate1
Typical medium-sized and large necroses
FCM
No necroses
Geisser et al.1
Figure 7
Histopathology: effects of intravenous iron gluconate and FCM on mouse
liver (micrographs taken 4 hours after injection). Note the typical medium-
to-large necrotic areas induced by iron gluconate compared with the lack
of necrosis with FCM.
Figure 8
Effects of various iron-carbohydrate preparations on systolic blood pressure
in rats. (Toblli10)
The pharmacology and safety profile of ferric carboxymaltose (Ferinject®):
structure/reactivity relationships of iron preparations
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16 Port J Nephrol Hypert 2009; 23(1): 11-16
A dose of up to 1000 mg iron may be given in 15
minutes. This compares with a maximum dose of
500 mg iron as iron sucrose which requires a 3.5
hour infusion following a test dose, or a 6-hour
infusion and test dose for iron dextran.
In conclusion, FCM offers convenient administra-
tion and permits high doses of iron to be given in
a short period. FCM also offers considerable benefits
in terms of safety and tolerability compared with
iron gluconate and iron dextran. This is due to the
fact that FCM does not cross-react with dextran
antibodies, is a highly stable complex, does not
release ionic iron under physiological conditions,
and does not provoke oxidative stress reactions.
Conflict of interest statement. Peter Geisser PhD is Scientific Direc-
tor of Vifor (International) Ltd.
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11 Beshara S, Sorensen J, Lubberink M, Tolmachev V, Langstrom B, Antoni G, Danielson
BG. Lundqvist H. Pharmacokinetics and red cell utilization of 52Fe/59Fe-labelled iron
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12 Rumyantsev V. A multi-centre, open-label, phase I/II pharmacodynamic and safety
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Correspondence to:
Peter Geisser PhD
Scientific Director
Vifor (International) Inc
Rechenstrasse 37
CH-9001, St Gallen
Switzerland
Figure 9
Red cell utilisation of 52Fe/59Fe labelled ferric carboxymaltose following a
single i.v. administration in patients with iron deficiency, renal anemia or
functional iron deficiency (modified from Beshara et al.11)
Figure 10
Mean total serum iron over time after weekly administration of 500 or
1000 mg iron as FCM showing identical elimination curves following
repeated doses (from Rumyantsev et al.12, in Crichton8)
Peter Geisser
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