CMYKP
`
`ORIGINAL ARTICLE
`
`Port J Nephrol Hypert 2011; 25(3): 219-224
`Advance Access publication 13 September 2011
`
`Assessment of dextran antigenicity
`of intravenous iron products
`by an immunodiffusion assay
`
`Susann Neiser, Maria Wilhelm, Katrin Schwarz, Felix Funk, Peter Geisser, Susanna Burckhardt
`
`Vifor (International) Inc. St. Gallen, Switzerland.
`
`Received for publication:
`Accepted:
`
`26/07/2011
`30/08/2011
`
` (cid:132)
`ABSTRACT
`
`The antigenicity of a number of different intrave-
`nous iron preparations was tested by reverse single
`radial immunodiffusion with antidextran antibodies.
`The tested products are low molecular weight iron
`dextran, ferumoxytol, iron isomaltoside 1000, sodium
`ferric gluconate, iron sucrose, and ferric carboxymalt-
`ose. Dextran-induced anaphylactic reactions have
`been clinically observed with low molecular weight
`iron dextran and with ferumoxytol, which contains
`a dextran derivative as ligand, whereas no dextran-
`induced anaphylactic reactions have been reported
`since its introduction in 2010 with iron isomaltoside
`1000, which contains a ligand based on dextran 1.
`The results of the immunoassay confirmed that the
`dextran-free preparations sodium ferric gluconate,
`iron sucrose, and ferric carboxymaltose do not cross-
`react with antidextran antibodies. In contrast, low
`molecular weight iron dextran and ferumoxytol react-
`ed with the antibodies, as demonstrated by the
`formation of a precipitation ring. As expected, dex-
`tran 1 did not cross-react with antidextran antibod-
`ies. Iron isomaltoside 1000 formed a precipitation
`ring, which suggests that if dextran 1 surrounds the
`polynuclear iron core, it can act as a polyvalent,
`higher molecular weight dextran and thus cross-react
`with the antibodies. Because of the limited number
`of patients and the exclusion criteria selected for
`clinical registration studies, e.g. previous hypersen-
`sitivity to iron dextran or other iron complexes, rare
`adverse events such as dextran-induced anaphylac-
`tic reactions often do not occur in controlled studies,
`
`as was the case with ferumoxytol. However, the
`presented immunodiffusion assay yielded results in
`agreement with post-marketing experience for five
`preparations, including ferumoxytol. Thus, this meth-
`od could be a valuable tool for the determination
`of antidextran reactivity of new intravenous iron
`preparations.
`
`Key-Words:
`Iron dextran; iron isomaltoside 1000; iron sucrose;
`ferric carboxymaltose; ferumoxytol; sodium ferric
`gluconate.
`
` (cid:132)
`INTRODUCTION
`
`Intravenous (IV) iron preparations are effectively
`used for the treatment of iron deficiency especially
`in patients with chronic diseases with an inflamma-
`tory component such as chronic kidney disease,
`chronic heart failure, cancer, or inflammatory bowel
`disease1. Long-known IV iron preparations include
`iron dextran and iron sucrose. Iron dextran com-
`plexes are kinetically robust and have a low toxicity2,
`but they carry the risk of inducing life-threatening
`dextran-induced anaphylactic reactions (DIAR)3,4.
`Therefore, before administration of the first dose of
`a dextran-containing iron preparation to a new patient,
`a test dose must be administered. The rate of life-
`threatening adverse drug events is reported to be
`higher for high molecular weight than for low molec-
`ular weight iron dextran complexes5. The dextran-free
`
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`Pharmacosmos, Exh. 1028, p. 1
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`Susann Neiser, Maria Wilhelm, Katrin Schwarz, Felix Funk, Peter Geisser, Susanna Burckhardt
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`CMYKP
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`alternatives iron sucrose and sodium ferric gluconate
`obviously do not carry the risk of DIAR, and they
`showed the lowest risk for life-threatening and total
`adverse drug events4–6. On the other hand, because
`of the lower complex stability2,7 the maximum sin-
`gle infusion dose of iron sucrose (100-500 mg iron)
`and especially of sodium ferric gluconate (62.5-125
`mg iron) is lower than that of iron dextran (up to
`20 mg iron/kg body weight)1. The newest generation
`of IV iron complexes, ferric carboxymaltose, feru-
`moxytol, and iron isomaltoside 1000 can be admin-
`istered relatively quickly with high maximal doses
`(1000 mg iron such as ferric carboxymaltose, 510
`mg iron such as ferumoxytol1, and 20 mg iron/kg
`body weight as iron isomaltoside 10008). Being
`dextran-free, ferric carboxymaltose cannot induce
`DIAR, whereas the other two preparations were
`developed to minimise the risk of DIAR9,10. Never-
`theless, iron isomaltoside 1000 is based on a very
`low molecular weight dextran11, and ferumoxytol on
`a carboxymethylated dextran10.
`
`Dextran is composed of α(1→6)-linked polyglucose
`and is produced by bacteria, whereas animal- or
`plant-derived polysaccharides such as glycogen and
`starch consist of mainly α(1→4)-linked polyglucose.
`Since dextran is produced not only by the industri-
`ally relevant leuconostoc mesenteroides strains but
`also by caries-inducing streptococcus species and
`intestinal bacteria, a sensibilisation often results from
`naturally occurring dextran, and most people have
`dextran-reactive antibodies12,13. Immune reactions to
`dextran may therefore occur at the first clinical admin-
`istration of dextran as well as after subsequent
`doses. It has been shown that the titer of dextran-
`reactive antibodies correlates positively with the
`severity of DIAR, but does not allow to predict wheth-
`er a reaction will occur in an individual patient12,13.
`
`Dextran has also been used in plasma replacement
`therapy and thromboprophylaxis14. In this context,
`it has been shown that severe DIAR are caused most
`importantly by IgG antibodies which suggests an
`immune complex anaphylaxis as underlying mecha-
`nism for severe DIAR13,15,16. It is known that most
`antidextran antibodies bind to the linear α(1→6)
`glucose-sequence12,17, which explains the cross-
`reactivity of pre-existing antidextran antibodies with
`synthetic, linear dextran fractions15. The immunoge-
`nicity of dextran depends on its size, with low
`molecular weight dextrans being less immunogenic
`
`than high molecular weight dextrans18. Very low
`molecular weight dextran of molecular weight of
`about 1000 Da (dextran 1, Promit®) was success-
`fully used as hapten: dextran 1 blocks the binding
`sites of antidextran antibodies and can thus mini-
`mise13–15, though not entirely prevent19, DIAR if
`injected prior to higher molecular weight dextrans.
`
`An in vitro antibody test, the reverse single radi-
`al immunodiffusion assay, has been shown to indi-
`cate the existence of an antigenic dextran structure
`with an immunogenic potential in dextran-containing
`preparations20,21. In the present study, the same
`assay was used to investigate the antidextran reac-
`tivity of currently available IV iron preparations. The
`tested preparations were low molecular weight iron
`dextran (CosmoFer®), dextran 1-based iron isomalto-
`side 1000 (MonoFer®), the iron dextran derivative
`ferumoxytol (Feraheme®), and three preparations free
`of dextran and dextran derivatives, i.e. iron sucrose
`(Venofer®), sodium iron gluconate (Ferrlecit®), and
`ferric carboxymaltose (Ferinject®).
`
` (cid:132)
`MATERIALS AND METHODS
` (cid:132)
` Dextran detection by reverse single radial
`immunodiffusion
`
`The method is based on that described by Rich-
`ter20,21 and employs monoclonal dextran antibodies
`deposited in a well punched into an agar plate that
`contains test substance. If immunologically active
`dextran or a cross-reacting dextran derivative is pres-
`ent in the test substance, it forms a precipitate with
`the antibody upon its diffusion into the agar. Prep-
`aration of agar plates: The supporting gel was pre-
`pared from 1% agarose (m/v) (Fluka, art. no. 05065,
`lot 1098455) and 1% polyethylene glycol 6000 (m/v)
`(Fluka, art. no. 03394, lot 146875) in phosphate
`buffer (pH 8.0 aqueous solution of 1.725% (w/v)
`Na2HPO4 • 2H2O and 0.055% (w/v) NaH2PO4 • 2H2O).
`For the preparation of the agar sample plates, the
`supporting gel was completely melted on a steam
`bath, and 8 mL supporting agar were mixed with 2
`mL sample solution and poured into petri dishes.
`Circular wells of 3 mm diameter were punched with
`a steel tube into the hardened agar, and the agar
`cylinders were removed by suction with a Pasteur
`pipette.
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`Assessment of dextran antigenicity of intravenous iron products by an immunodiffusion assay
`
`CMYKP
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` (cid:132)
`Sample solutions
`
`The tested iron preparations were diluted to 40 μg
`Fe/mL in 0.9% (m/V) sodium chloride solution: Iron
`sucrose (Venofer®, lot 10674663, Vifor(International)
`Inc., St. Gallen, Switzerland), ferric carboxymaltose
`(Ferinject®, lot 10667273, Vifor(International) Inc., St.
`Gallen, Switzerland), low molecular weight iron dextran
`(CosmoFer®, lot 1009019, TEVA GmbH, Radebeul, Ger-
`many), ferumoxytol (Feraheme®, lot 09060402, AMAG
`Pharmaceuticals, Cambridge, MA, USA), iron isomalto-
`side 1000 (MonoFer®, lot 949171-1, Pharmacosmos,
`Holbæk, Denmark), and sodium ferric gluconate (Fer-
`rlecit®, lot D7A743A, Sanofi Aventis Deutschland GmbH,
`Frankfurt, Germany). Dextran 5 (Dextran 5, lot 00309,
`Serumwerke Bernburg AG, Bernburg, Germany, weight
`average molecular weight 4’500 Da) and dextran 1
`(dextran standard 1000 from leuconostoc mesenteroi-
`des for GPC, product no. 31416 from Fluka, Sigma-
`Aldrich, Buchs, Switzerland, weight average molecular
`weight of 1’270 Da) were tested in a concentration of
`3 μg dextran/mL in 0.9% (m/V) aqueous sodium chlo-
`ride solution. These solutions were mixed with the
`supporting gel as described above. Antigen test: 5 μL
`dextran antibody solution was added to each well (100
`mg/mL, Midland MCA Antibody, M9010, Kansas, USA).
`The plates were incubated at 4°C for 48 hours. The
`presence of dextran was visually detected as circular
`
`precipitate ring of antigen/antibody complex around
`the wells. All reported experiments were conducted at
`least in duplicate.
`
` (cid:132) Molecular weight determination by gel
`permeation chromatography (GPC)
`
`The method is based on permeation chromatog-
`raphy on a poly(methylmethacrylate) gel, calibrated
`with pullulan standards. The method has been
`described in detail elsewhere2 and corresponds to
`that described in the United States Pharmacopeial
`Convention for iron sucrose22.
`
` (cid:132)
`RESULTS
`
`Reverse single radial immunodiffusion was used to
`identify products with antidextran antibody reactivity
`(Figure 1, Table I). As expected, the dextran 5 positive
`control solution reacted with the antibody and formed
`a distinct precipitation ring, whereas the dextran 1
`negative control did not form a precipitate with the
`antibody. Venofer® (iron sucrose), Ferinject® (ferric
`carboxymaltose), and Ferrlecit® (sodium iron gluconate)
`did not form precipitates with antidextran antibodies.
`
`Figure 1
`
`Assessment of dextran antigenicity of different IV iron preparations by reverse single radial immunodiffusion. A positive antigen/antibody reaction is indicated
`by circular turbidity around the well. Dextran 5 served as a positive control.
`
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`Port J Nephrol Hypert 2011; 25(3): 219-224 221
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`Pharmacosmos, Exh. 1028, p. 3
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`

`
`Susann Neiser, Maria Wilhelm, Katrin Schwarz, Felix Funk, Peter Geisser, Susanna Burckhardt
`
`CMYKP
`
`Table I
`
`Overview of the names of the tested IV iron preparations, their active ingredients, chemical classification of the ligands, weight average molecular weight of
`the complex, and their reactivity with antidextran antibodies.
`
`Active ingredient
`
`Name
`
`Ligand
`
`Dextran
`Very low molecular weight dextran (3-5 glucose units)
`Carboxymethylated, reduced dextran
`Carboxymaltose
`Sucrose
`Gluconate / sucrose
`
`Low molecular weight iron dextran CosmoFer®
`MonoFer®
`Iron isomaltoside 1000
`Feraheme®
`Ferumoxytol
`Ferinject®
`Ferric carboxymaltose
`Venofer®
`Iron sucrose
`Ferrlecit®
`Sodium ferric gluconate
`1 Weight average molecular weight of the complex according to the method described in the USP for Iron sucrose injection22, i.e. relative to a pullulan standard.
`2 This work.
`3 Ref. 28.
`
`Molecular weight
`(Da)1
`80’0002
`69’0002
`185’0003
`150’0003
`43’0003
`38’0003
`
`Dextran antibody
`reaction
`Yes
`Yes
`Yes
`No
`No
`No
`
`This result is in agreement with their chemical specifi-
`cations and was anticipated, because these complexes
`are free of dextran or dextran derivatives. CosmoFer®,
`a low molecular weight iron dextran, expectedly formed
`precipitates with the antibody. Also Feraheme® and
`MonoFer® clearly formed precipitates.
`
`The weight average molecular weights determined
`according to the method described in the USP for
`Iron sucrose injection (i.e. relative to a pullulan stan-
`dard) were 69'000 Da for MonoFer® and 80'000 Da
`for CosmoFer® (Table I).
`
` (cid:132)
`DISCUSSION
`
`All the tested IV iron products were developed
`either to minimise the risk of DIAR, by lowering the
`molecular weight of the iron dextran complex (Cos-
`moFer®), by using very low molecular weight dextran
`as a ligand (MonoFer®), by derivatization of dextran
`(Feraheme®), or to exclude the risk of DIAR by com-
`plete absence of dextran or dextran derivatives
`(Venofer®, Ferinject®, Ferrlecit®). However, all the
`dextran-based preparations tested formed precipi-
`tates with the antidextran antibody, whereas the
`three dextran-free preparations did not. CosmoFer®
`is classified by the manufacturer as low molecular
`weight iron dextran, and DIAR are known to occur4.
`The positive reaction of the immunodiffusion assay
`is therefore not surprising and is in agreement with
`clinical experience.
`
`a ligand9,10. The degree of carboxymethylation lies
`above the threshold that has been determined as non-
`immunogenic by measuring the extent of rat paw
`edema response, as an indicator of the potential to
`induce human adverse reactions upon intravenous injec-
`tion10. No DIAR were observed in the 568 patients who
`received Feraheme® during clinical registration studies
`– all of which excluded patients with known hypersen-
`sitivity to other iron preparations, and thus to iron
`dextran, or with multiple drug allergies23. However,
`shortly after the approval in the US in June 2009, the
`FDA raised safety concerns23, and, subsequently, a
`case of DIAR was reported in a patient with prior
`adverse reaction to iron dextran9, which led to a hyper-
`sensitivity warning for ferumoxytol. The positive antigen-
`antibody reaction in the immunoassay reported in this
`work clearly suggests the possibility of DIAR and thus
`confirms the clinical experience with ferumoxytol.
`
`The rationale for the development of MonoFer®
`was the creation of a stable iron dextran complex
`that, due to the non-immunologic properties of its
`ligand isomaltoside 1000, would not induce DIAR
`8,24. This carbohydrate is prepared from dextran 1,
`a linear dextran oligomer of very low molecular weight
`(with 3-5 glucose units), which has been shown to
`be nonanaphylactogenic25. Moreover, dextran 1 acts
`as a monovalent hapten and has been shown to
`minimise14,15, though not entirely prevent19, DIAR if
`injected prior to higher molecular weight dextrans.
`As expected, and in agreement to previous reports21,
`Dextran 1 did not show a precipitation ring in the
`immunodiffusion assay.
`
`Feraheme® contains polyglucose sorbitol carboxym-
`ethylether iron oxide, i.e. has a dextran derivative as
`
`The active ingredient of MonoFer®, however,
`consists of a polynuclear iron(III)-oxyhydroxide core
`
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`Assessment of dextran antigenicity of intravenous iron products by an immunodiffusion assay
`
`CMYKP
`
`surrounded by a number of dextran 1 molecules8
`with an overall molecular weight close to that of
`the low molecular weight iron dextran complex in
`CosmoFer® (Table I). Thus, iron isomaltoside 1000
`could immunologically resemble a polyvalent, high-
`er molecular weight dextran and thus cross-react
`with the antidextran antibodies. This effect has
`been proposed previously since positive in vitro
`antigen/antibody reactions were observed for sim-
`ilar iron dextran complexes composed exclusively
`of dextran 126. The positive reaction for Monofer®
`in the immunodiffusion assay shown in this work
`supports this theory. Taken together, the results
`imply that, despite the nonanaphylactogenic prop-
`erties of isomaltoside 1000, a DIAR with the iron
`complex MonoFer® is theoretically possible,
`although no clinical cases have been reported up
`to now.
`
`Ferric carboxymaltose (Ferinject®), iron sucrose
`(Venofer®), and sodium ferric gluconate (Ferrlecit®)
`do not contain dextran or dextran derivatives and
`as expected did not react in the dextran immunoas-
`say. This is in agreement with the clinical experience;
`neither preparation has been reported to evoke DIAR.
`In spite of the good safety profile of Venofer®, it
`can, similar to Ferrlecit®, only be administered at
`relatively low doses. Thus, the only IV iron prepara-
`tion on the market that does not react with dextran
`antibodies and that can be administered at high
`doses is Ferinject®.
`
`The results from reverse single radial immunodif-
`fusion in combination with the chemical characterisa-
`tion and clinical experience suggest that this meth-
`od could be used to estimate whether there is a risk
`of DIAR for a given preparation. Clearly, the assay
`may not identify all immunologically active dextrans
`and dextran derivatives. A main limitation is the
`choice of antibody for the immunoassay since a
`number of different dextran antibodies have been
`found in humans27.
`
` (cid:132)
`CONCLUSION
`
`The reported immunoassay data agree well with
`clinical observations and thus represent a possible
`approach for the evaluation of the risk of DIAR. The
`two tested products that are proven to induce DIAR
`
`showed a positive reaction (CosmoFer®, Feraheme®),
`whereas the three preparations that are free of dex-
`tran or dextran derivatives tested negative, in agree-
`ment with clinical experience (Venofer®, Ferinject®,
`Ferrlecit®). For MonoFer®, despite the nonanaphy-
`lactogenic property of the isomaltoside 1000 ligand,
`the test result was positive, which suggests the pos-
`sibility of a reaction with pre-existing antidextran
`antibodies.
`
`Conflict of interest statement. The authors are employed by Vifor
`(International) Inc. St. Gallen, Switzerland.
`
`Acknowledgments. We thank Ms. Maja Thum for technical assis-
`tance.
`
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`Susann Neiser, Maria Wilhelm, Katrin Schwarz, Felix Funk, Peter Geisser, Susanna Burckhardt
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`
`Correspondence to:
`Dr Susanna Burckhardt
`Vifor (International) Inc.
`Rechenstrasse 37
`9001 St. Gallen,
`Switzerland
`e-mail: susanna.burckhardt@viforpharma.com
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