Brit. J. Pharmacol. (1961), 17, 358-371.
`
`STUDIES ON A NEW INTRAMUSCULAR HAEMATINIC,
`IRON-SORBITOL
`
`BY
`
`S. LINDVALL AND N. S. E. ANDERSSON
`
`From the Research Laboratories of AB Astra, Sodertalje, and the Medical Department,
`Centrallasarettet, Danderyd, Sweden
`
`(Received May 31, 1961)
`
`A new iron preparation for intramuscular use is described.
`It contains a complex
`Its properties in comparison with several other
`of iron, sorbitol and citric acid.
`complexes, particularly iron-dextran, have been studied. The preparation is stable
`in serum, is hypertonic, does not produce haemolysis, and affects coagulation only
`Absorption from
`at very high concentrations, such as are reached only in vitro.
`muscle takes place very rapidly; two-thirds of the iron is removed within 3 hr, and
`there is a very rapid increase in the serum-iron concentration.
`In experimental
`animals, the maximum level is reached after about 20 min and in man after about
`2 hr. Disappearance from the serum takes place rapidly. The preparation contains a
`small amount of a fraction which reacts with transferrin and is dialysable.
`In man,
`about 30% of the total dose of iron is excreted through the kidneys during the first
`24 hr after injection, the greater part of the excretion taking place during the first
`few hours.
`
`Parenteral iron therapy has been increasingly used since Nissim (1947) discovered
`that saccharated oxide of iron could be used for intravenous administration.
`This
`preparation produces severe local
`side-reactions and cannot be administered
`intramuscularly (Slack, 1949).
`Agner, Andersson & Nordenson (1948) studied an
`iron preparation for intravenous use in which the iron was present as a special
`ferri-dextrin complex in colloidal form.
`Later investigations by Andersson &
`Bergstr6m (1956) demonstrated that this iron compound could also be administered
`intramuscularly in man.
`Complex compounds of the iron-dextran type (Fletcher & London, 1954), ferric
`disodium-N-hydroxyethyl-ethylene-diamine-triacetate (Seven & Peterson, 1958) and
`ferric choline citrate (Virtanen & Hartiala, 1958) have also been investigated, and
`of these the iron-dextran complex is used clinically (Baird & Podmore, 1954;
`Cappell, Hutchison, Hendry & Conway, 1954; Scott & Govan, 1954; Jennison &
`Ellis, 1954).
`This compound is said to be a low molecular dextran-iron complex
`and has a low toxicity.
`Its pharmacology has been studied by Martin, Bates,
`Beresford, Donaldson, McDonald, Dunlop, Sheard, London & Twigg (1955).
`Beresford, Golberg & Smith (1957) investigated the absorption mechanism and the
`local effect of the compound on muscle, and Norden (1957), Grimes & Hutt (1957)
`and Karlefors & Nord6n (1958) studied in man the metabolism of an intramuscu-
`larly administered iron-dextran complex labelled with 59Fe.
`
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`
`IRON-SORBITOL
`
`359
`
`According to these more recent investigations 50% to 80% of the dose of iron
`given was absorbed from the site of injection within 20 to 100 days while the
`residual iron remained in the muscle for a long period. A search has therefore
`been made for an iron preparation for intramuscular injection which can be absorbed
`more rapidly and completely.
`Sorbitol is known to improve the absorption of oral ferrous sulphate (Hemdon,
`Rice, Tucker, van Loon & Greenberg, 1958). The possibility of producing new iron
`complexes for intramuscular injection, containing sorbitol or even other substances,
`has been studied by Lindvall & Hogberg (unpublished observation). The resulting
`preparations have been tested, and the product with the best properties is described
`here.
`
`METHODS
`Characterization of the preparations used
`This is a complex of iron, sorbitol and citric acid, containing, in addition, dextrin.
`It is pre-
`pared by adding an aqueous solution of ferric chloride in portions to a solution of 60' C
`temperature containing sorbitol, citric acid and dextrin. The pH of the solution is adjusted to
`weakly alkaline after the addition of each portion. After cooling, the complex is precipitated by
`adding alcohol to the mixture. The iron content of the complex is 14±2%. A solution of
`it is sterilized by autoclaving and contains 50±2 mg/ml. elemental iron and has a pH of
`7.5±0.2 [Jectofer, Astra]. This solution is referred to as iron-sorbitol.
`Electrophoretic investigations with a paper-strip electrophoresis apparatus from L.K.B.
`Produkter Fabriks A.B., Sweden, in a 0.1 M phosphate buffer at pH 7.6 show that the compound
`contains at least two iron-containing components which migrate towards the anode (Fig. 1).
`Furthermore, about 6% of the iron is found in a more rapidly moving form in investigations
`with a Spinco continuous-flow paper electrophoresis using 0.07 N acetate buffer of pH 5.0
`(Fig. 2). This part of the compound is of lower molecular weight and dialysable.
`Moreover,
`it will be seen from Fig. 2 that the dextrin can be separated from the iron-containing fractions.
`It is presumed that dextrin acts as a stabilizer (Eriksson, unpublished observation).
`Ultracentrifugation of the poly-dispersed iron compound gives an upper limit for the
`sedimentation constant of 8 to 9 Swedberg units. As the density of the molecule is unknown,
`it is not possible to calculate the exact molecular weight.
`With certain assumptions, the
`probable average molecular weight is estimated to be below 5,000 (Eriksson, 1962).
`A solution of iron-dextran containing Fe 50 mg/ml. and with a pH of 5.8 [Imferon, Benger]
`was used as a basis of comparison. In some of these experiments, solutions of the iron-dextrin
`complex containing Fe 20 mg/ml. and with a pH of 7.4. [Astrafer, Ferrigen, Astra], as well
`as solutions of saccharated oxide of iron containing Fe 20 mg/ml. and with a pH of 10.9
`[Intrafer, Pharmacia]. were also used.
`Stability at different pH
`The pH of the preparations in aqueous solutions was regulated within the range 1 to 8,
`with 0.1 and 1.0 N hydrochloric acid, in accordance with the method of Nissim & Robson
`After the addition of the hydrochloric acid the iron concentration in all the solutions
`(1949).
`was Fe 1 mg/ml. After the solutions had been standing for 24 hr at room temperature the
`precipitate was removed by centrifugation and the iron content and pH in the supernatant
`determined. The iron was estimated calorimetrically by means of ammonium thiocyanate.
`Haemolytic effect
`This was studied by mixing 1.0 ml. of solutions of the iron complexes containing Fe 0.04
`to 20.0 mg/ml. of 0.9% sodium chloride solution with 0.43 ml. of blood corpuscle suspension
`consisting of 1.0 ml. of rabbit blood in 25 ml. of physiological saline.
`After the mixture
`N
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`
`360
`
`S. LINDVALL and N. S. E. ANDERSSON
`
`Saccharated oxide of iron
`
`0 c0 ma
`
`.
`
`0 u0 4
`
`.,
`0
`
`-C
`
`._
`
`0
`
`13i
`
`Paper electrophoresis of iron-sorbitol, iron-dextran, iron-dextrin and saccharated oxide of
`Fig. 1.
`iron in phosphate buffer at pH 7.6. The fractions are stained for iron by using potassium
`ferrocyanide in 1 N hydrochloric acid.
`
`had been standing for 3 hr at room temperature the non-haemolysed corpuscles were removed
`by centrifugation.
`After having been washed twice with 3.5 ml. of physiological saline the
`blood cells were haemolysed with 5 ml. of 0.05% ammonium hydroxide solution (5 ml./100
`ml. of concentrated ammonia). The extinction was read at 576 my.
`Anticoagulant activity
`This was measured in vitro by the method of Nissim (1954).
`1 ml. of blood was taken from
`the carotid artery of a rabbit and transferred directly to tubes containing 0.32 ml. of iron
`solutions with an iron content of 0.045 to 25 mg/ml. Fe of physiological saline.
`After
`thorough mixing, the time at which coagulation occurred was measured.
`Intramuscular absorption of iron from site of injection
`The iron preparations were injected deep into the glutei of rabbits.
`(Male albino rabbits
`weighing 2 to 3 kg were used consistently.) The animals were killed at different time intervals
`after injection and the gluteal muscles were dissected away from the leg. The muscles and
`skin at the site of injection were wet-oxidized with sulphuric and nitric acid and the iron
`determined colorimetrically by means of ammonium thiocyanate.
`The residual iron was
`obtained by subtracting the iron content of normal muscle.
`Iron concentration in serum
`The serum-iron was estimated according to the principles of Heilmeyer & Plo6tner (1937).
`1.0 ml. of serum was mixed with 1.5 ml. of 4 N hydrochloric acid and hydrolysed at 500 C
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`
`IRON-SORBITOL
`
`361
`
`I
`
`E
`
`2
`e20 2.0 E|
`
`~~~~~~~I
`I
`~~~~~~~~~~+
`
`~
`~~
`I0
`
`0.5~~~~~~~~~~~~~~~~~4
`
`510 1.
`
`cathode
`
`anode
`
`20
`
`25
`30
`Fraction
`
`Fig. 2.
`
`Continuous-flow paper electrophoresis of iron-sorbitol in acetate buffer at pH 5.0.
`
`After hydrolysis, the protein was precipitated with 1.5 ml. of 20% trichloro-
`for 20 min.
`Ten minutes later, the precipitate was centrifuged off at 3,500 g for
`acetic acid solution.
`30 min.
`3.0 ml. of the clear supernatant was transferred to a 5.0 ml. volumetric flask ;
`5 drops of freshly prepared 0.2% ascorbic acid solution, 4 drops of I% ortho-phenanthrolene
`in a 10% alcohol solution and I drop of a 0.2 % 2,5-dinitrophenol solution in absolute
`alcohol were added with shaking.
`The sample was -then neutralized with concentrated
`ammonia till the indicator turned yellow. The mixture was acidified with 0.4 N hydrochloric
`acid till the exact moment when the yellow colour disappeared, and the volume was adjusted
`to make 5.0 ml. The extinction was read in a Zeiss photometer at 515 mros. The analytical
`values obtained by this method include plasma-bound iron and circulating iron preparations.
`Diffusion of iron into tissue fluids
`'Me diffusion into tissue fluids was studied by the method of Nissim (1953) with the
`peritoneum of the mouse as the dialysing membrane.
`The mice were injected
`intraperitoneally with 2.0 ml.
`of physiological
`saline and
`immediately afterwards received iron-sorbitol and iron-dextran solutions by intravenous
`injection. The animals were killed with ether after different intervals, the peritoneal cavity
`was opened and the fluid in the abdominal cavity collected. Abdominal contents contami-
`nated with blood were not used.
`The concentration of iron
`wras determined with
`ortho-phenanthrolene in 3 ml. mixed samples from six mice according to the serum-iron
`method.
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`
`362
`
`S. LINDVALL and N. S. E. ANDERSSON
`
`Iron in urine
`The iron concentration was determined after the urine had been wet-oxidized with
`sulphuric acid and hydrogen peroxide in accordance with the ortho-phenanthrolene method.
`
`RESULTS
`Precipitation test
`The solution of iron-sorbitol can be diluted with 0.9% sodium chloride solution
`to concentrations between 0.001 and Fe 25 mg/ml. without giving any visual
`precipitation. Nor does any precipitation take place after dilution with rabbit serum
`and 1% bovine fibrinogen solution to the same concentrations as above, when the
`solution is kept at 370 C for 2 hr.
`The results from the studies about the stability of the iron preparations at different
`pH showed that iron-sorbitol precipitated within the pH range of 1.7 to 3.5, with
`maximum precipitation (40%) at pH 2.5. Between 3.5 and 8 there was no precipita-
`tion.
`Iron-dextran was stable between a pH of 1 and 8.
`Iron-dextrin showed some
`precipitation within the 1.0 to 2.3 range immediately after the addition of hydro-
`chloric acid, but this disappeared after a few hours. No precipitation was observed
`at pH values exceeding 2.3. The saccharated oxide of iron used in this experiment
`diverged from that of Nissim.
`It was precipitated practically quantitatively at pH
`4.5 to 7.0, and at pH 7.2 it showed 50% precipitation. At pH 7.6 no precipitation
`could be observed.
`
`Osmotic properties
`These were studied after dilution with distilled water to different concentrations.
`The depression of freezing point was determined with a Beckmann thermometer,
`and it was found that a solution, isotonic with blood, was obtained when the iron
`content in the diluted iron-sorbitol solution was Fe 12 mg/ml. The corresponding
`value for the iron-dextran preparation was Fe 35 mg/ml. The result shows that
`the preparations are hypertonic, especially iron-sorbitol.
`
`Haemolytic effect
`The results showed that iron-sorbitol and iron-dextrin had no haemolytic effect,
`while iron-dextran was haemolytic at a concentration above Fe 1.75 mg/ml. and
`saccharated oxide of iron had an effect at a concentration above Fe 0.44 mg/ml.
`
`Anticoagulant activity
`As may be seen from Table 1, iron-dextran as well as sorbitol alone had little
`Iron-sorbitol and iron-dextrin, however, prolonged the
`effect on the coagulation.
`clotting time in concentrations higher than 0.2 mg/ml. Fe; at the highest concentra-
`tions, coagulation was completely inhibited.
`The effect of iron-sorbitol on coagulation was studied in vivo in 8 rabbits after
`intravenous and intramuscular doses corresponding to Fe 1.5 and 5.0 mg/kg. No
`effect on the coagulation was observed after 2 to 60 min; nor was any change in
`the clotting time noted in man, at the same times, after injection of doses correspond-
`ing to Fe 1.5 mg/kg in 3 healthy subjects.
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`
`20.-r IRON-SORBITOL
`
`363
`
`Sorbitol
`
`7777555555
`
`TABLE 1
`ANTICOAGULANT ACHVITY OF THREE IRON PREPARATIONS AND SORBITOL
`IN VITRO
`Clotting time in mi
`Iron-dextran
`Iron-dextrin
`17
`15
`-
`12
`82
`46
`12
`24
`12
`7
`17
`7
`15
`7
`12
`7
`10
`7
`10
`Absorption of iron after intramuscular injection
`Iron-sorbitol and iron-dextran solutions were injected into 50 rabbits in a dose of
`Fe 20 mg/kg (0.4 ml.). The results showed that iron-sorbitol, when administered
`intramuscularly, was absorbed very rapidly; after 3 hr about two-thirds of ihe iron
`had already been removed from the site of injection (Fig. 3). The corresponding
`100
`
`Iron-sorbitol
`
`42
`19
`13
`11
`10
`
`855
`
`Concentration of
`Fe or sorbitol
`in mg/ml.
`6-0
`30
`1-5
`075
`037
`0d18
`009
`0.045
`0-022
`0.011
`
`0Z
`
`EE0I
`
`- D
`
`-o
`5-
`
`00
`
`0-
`
`-0
`
`o-.
`
`80
`
`60
`
`I
`
`I
`
`i
`I
`
`.0
`0
`-0 40 .
`-o
`2!
`..
`
`04
`
`T'r,
`3612 24
`
`- .--.-.--.--*-*-I
`36 48
`2 4
`
`8
`
`12
`Time
`Absorption of iron-sorbitol and iron-dextran after intramuscular injection in rabbit of a
`dose corresponding to Fe 20 mg/kg.
`iron-sorbitol. -*
`- iron-dextran.
`
`I
`
`20
`
`I
`
`28
`
`hours
`32 days
`
`24
`
`16
`
`Fig. 3.
`
`figure for iron-dextran after the same interval was only about 10%.
`For iron-
`sorbitol a rapid absorption phase was concluded after 12 hr, when the animals had
`15 to 20% of the injected iron left at the site of administration. For iron-dextran,
`this phase was not completed until after 48 hr. and about 20% of the iron was then
`
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`
`364
`
`S. LINDVALL and N. S. E. ANDERSSON
`
`still present in the muscle. At dissection it was seen that the muscle was free from
`the iron preparation after these intervals but that the fatty tissue between the muscles
`and the subcutaneous fat was stained with iron. The residual iron subsequently
`disappeared at a very slow rate; 32 days after the injection about 6% of the iron
`was still present in the specimens from the animals which had received iron-sorbitol
`and 9% in those which had received iron-dextran.
`Iron content in serum after intramuscular injection
`The iron content in serum was estimated in 20 rabbits at different time intervals
`after intramuscular injection of solutions of iron-sorbitol and iron-dextran in a dose
`corresponding to 1.5 Fe mg/kg. Blood samples were taken 6 to 8 times from the
`marginal ear vein of each rabbit. The values are given in Figs. 4 and 5; each point
`is the mean of 5 estimations.
`
`Em/
`
`600
`
`/+
`
`Iron-sorbitol
`
`+
`
`+
`
`El
`~400-
`0~~~~~~~~~~~0
`.Iron-dextran
`
`- 200
`
`Fig. 4.
`
`10
`
`50
`
`60
`
`20
`40
`30
`Time in min
`Serum-iron during the first hour after intramuscular injection in rabbit of iron-sorbitol
`and iron-dextran in doses corresponding to Fe 1.5 mg/kg.
`After iron-sorbitol there was a rapid rise in the serum-iron content; the maximum
`level was reached after about 20 min and was maintained for a further 30 min. With
`iron-dextran a definite increase was not recorded until about 3 hr after administra-
`tion, and the maximum value was reached after 6 hr (Figs. 4 and 5).
`Similar tests
`were carried out with iron-sorbitol in man, doses corresponding to 25, 50 and 100
`mg Fe being administered deep intramuscularly in the gluteal region in respectively
`4, 4 and 5 healthy subjects. As may be seen from Fig. 6, the serum-iron began to
`increase immediately after the injection, reached the maximum about 2 hr later,
`and then decreased gradually.
`Iron-binding capacity of serum
`The unsaturated iron-binding capacity of serum was determined by the method
`of Cartwright & Wintrobe (1949) after both intravenous and intramuscular injection
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`
`IRON-SORBITOL
`
`365
`
`Iron-sorbitol
`
`E 600
`
`400
`
`I-
`
`0 o
`
`El
`
`C-U-
`2L0
`:L 200-
`
`2
`
`I
`
`4
`
`6
`
`8
`
`10
`Time in hr
`Serum-iron 2 to 24 hr after intramuscular injection in rabbit of iron-sorbitol and iron-
`dextran in a dose corresponding to Fe 1.5 mg/kg.
`600
`
`I
`
`20
`
`I
`
`24
`
`500-
`
`./
`
`E 400 -
`
`8300
`
`/
`
`200
`
`100
`
`~~~~~
`
`mg
`
`.
`
`100mg
`
`N~~~~~~5Omg
`
`25 mg
`
`a
`
`I
`
`2
`
`4
`3
`5
`Hr after injection
`Serum-iron after intramuscular injection in man of iron-sorbitol in doses corresponding
`to 25, 50 and 100 mg Fe.
`
`6
`
`7
`
`8
`
`Fig. 5.
`
`Fig. 6.
`
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`
`366
`
`S. LINDVALL and N. S. E. ANDERSSON
`
`of iron-sorbitol into rabbits in doses equivalent to Fe 1.5 mg/kg.
`In these
`preliminary experiments it was established that the transferrin was saturated with
`After 24 hr the serum showed the same values for the
`iron during the first 6 hr.
`unsaturated iron-binding capacity as before the injection.
`The values for the unsaturated iron-binding capacity of the human subjects used
`for the determination of the iron content in serum were also examined. The values
`decreased following the injections. The decrease was most marked after the 100 mg
`dose, which produced complete saturation of the transferrin 0.5 to 6 hr after the
`injection (Fig. 7). The levels of the total iron-binding capacities of the respective
`
`600
`
`100 mg
`
`500 7
`
`5 m
`
`E 400-°
`
`m>> go
`2300X
`
`\'
`
`s ¢
`
`X~~~Sum of UIBC and
`serum-iron value
`
`~
`
`~
`
`e.*.-
`
`m
`
`---
`
`==- J level
`
`4
`
`1UIBC
`
`EI
`
`L~
`300
`
`It
`
`200
`
`l00l
`
`2
`
`3
`
`4
`5
`Hr after injection
`Unsaturated iron-binding capacity (UIEBC) and the sum of UIBC and serum-iron value
`Fig. 7.
`after intramuscular injection in man of iron-sorbitol in doses corresponding to 25, 50 and
`100 mg Fe. The levels for total iron-binding capacity (TIBC) are also shown.
`
`6
`
`7
`
`8
`
`groups are also indicated in the figure. These levels have been determined by adding
`the values of the unsaturated iron-binding capacity to the serum-iron values of the
`treated subjects prior to the injection of iron-sorbitol. The sum of the unsaturated
`iron-binding capacity and the serum-iron value has also been calculated at different
`times after the injection of iron-sorbitol.
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`
`IRON-SORBITOL
`
`367
`
`During the first 6 hr this sum, as can be seen from Fig. 7, exceeds the total iron-
`binding capacity as found before the injection. The reason for this is that the value
`of the iron content of serum after the injection includes, as mentioned above, both
`iron bound to plasma and circulating iron-sorbitol constituents not directly bound
`to plasma proteins. An attempt to remove this surplus iron, by chromatography
`with alumina by the method of Laurell, showed that the surplus was not adsorbable
`as is the case with iron-dextran (Laurell, 1958).
`In in vitro experiments, it was found that the iron-sorbitol solution could react
`with, and saturate, transferrin.
`Closer study established that this property was
`bound to the low-molecular and dialysable part of iron-sorbitol. The dialysate,
`however, needed a larger amount of iron in order to saturate the transferrin than
`a standard solution containing ferrous nitrate. The results are given in Fig. 8.
`
`0.03
`
`/175 ltg Fe
`
`Iron-nitrate
`
`Dialysable iron
`335 pg Fe
`
`0.01
`
`/
`
`Non-dialysable iron
`150
`300
`200
`100
`350
`250
`450
`400
`jtg of Fe added per 100 ml. serum
`Saturation of transferrin in vitro by adding iron-nitrate, dialysable and non-dialysable
`parts of iron-sorbitol to rabbit serum.
`
`50
`
`Fig. 8.
`
`Iron content in serum after intravenous injection
`The iron content of the serum was estimated at different intervals after intravenous
`injection of the iron preparations into rabbits in doses corresponding to 1.5 mg/kg.
`Iron-sorbitol, iron-dextran, iron-dextrin and saccharated oxide of iron were injected
`into the left ear of respectively 16, 8, 3 and 3 animals; blood specimens were taken
`from the right ear.
`The results have been assembled in Fig. 9, which shows that, about 4 hr after
`the injection of iron-sorbitol, iron-dextrin and saccharated oxide of iron, the iron
`concentration in the serum was in the neighbourhood of the normal.
`Iron-dextran,
`however, was removed from the blood stream at a very slow rate.
`Diffusion into tissue fluids
`360 male albino mice weighing 20 g received iron preparations intravenously in
`doses corresponding to Fe 5, 10 and 25 mg/kg.
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`
`368
`
`S. LINDVALL and N. S. E. ANDERSSON
`
`3,200
`
`-..
`
`Iron-dextran
`
`Saccharated oxide
`of iron
`
`1,600
`
`°E
`
`400
`
`-Iron-dextrin
`
`Iron-sorbitol
`
`Normal level
`
`3
`
`4
`
`200 -
`
`.
`
`1 2
`Time in hr
`Iron]Pn serum after intravenous injection in rabbit of iron-sorbitol, iron-dextran, iron-
`dextrin'andsaccharated oxide of iron in a dose corresponding to Fe 1.5 mg/kg.
`
`Fig. 9.
`
`500
`
`25 mg/kg
`
`/~~~4.
`
`*- 400
`s
`
`300
`
`C0 0
`
`20
`
`II-
`
`100
`
`|
`
`mu 200
`
`|*. 10mg/kg
`
`-~~
`
`25 mg/kg
`
`5 mg/kg
`
`10 mg/kg
`5 mg/kg
`
`10
`20
`IS
`5
`Min after injection of the iron preparation
`Diffusion into the peritoneal cavity of iron-sorbitol and iron-dextran after intravenous
`Fig. 10.
`iron-sorbitol.
`injection in mice in doses corresponding to Fe 5, 10 and 25 mg/kg.
`-* *-.-iron-dextran.
`In Fig. 10 each point represents the mean of 3 determinations in the case of
`It will be seen that both preparations
`iron-sorbitol and 2 in the case of iron-dextran.
`-diffused- into the pertoneum in amounts to some extent proportional to the dose
`injected, though the diffusion of iron-dextran was much less.
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`IRON-SORBITOL
`
`369
`
`Renal excretion
`The renal excretion of iron-sorbitol following intramuscular injection into 4 rats
`(Sprague-Dawley) of doses corresponding to Fe 1.5 mg/kg was studied in preliminary
`The animals were placed in metabolism cages and the urine was
`experiments.
`It was found that the rats excreted respectively 24.7, 26.1,
`collected during 24 hr.
`20.5 and 34.5% of the dose of iron injected within 24 hr.
`More detailed studies were made of the urinary excretion pattern in man. Nine
`healthy subjects received 100 mg Fe by intramuscular injection and during the first
`24 hr samples of urine were taken at different intervals after the injection. On an
`average, a total of 30% of the dose of iron given was excreted. As may be seen
`
`TABLE 2
`RENAL EXCRETION OF IRON AFTER INTRAMUSCULAR INJECTION IN MAN OF
`IRON-SORBITOL IN A DOSE EQUIVALENT TO 100 MG FE
`Renal excretion as %
`Hr after injection
`6-9
`0-3
`3-6
`Patient
`Total
`Over 9
`6P7
`1A4
`32*0
`11-1
`G. A., female
`12-8
`3.7
`H. J., male
`1-6
`4-0
`20-8
`30-1
`7.5
`I. M., female
`4.5
`15-2
`33.5
`6-3
`I. J.,
`female
`9-8
`27-6
`2-0
`2-6
`13-2
`1*9
`L. M., female
`13-0
`7-5
`2-1
`24-5
`1217
`9*7
`E. H., female
`4-8
`2-4
`29-6
`K. P., female
`15-0
`6-5
`12-5
`2-9
`36-9
`3-8
`S. L., male
`212
`11.0
`1-0
`38-0
`4.5
`9*4
`H. H., male
`3-3
`1-2
`18-4
`30*1
`Mean value
`14-5
`9 0
`3-8
`2-8
`from Table 2, the greater part of the excretion took place during the hours immedi-
`ately following the injection, and in general it had been completed within 24 hr.
`The same percentage excretion was obtained after doses corresponding to 50 and
`25 mg Fe.
`
`DISCUSSION
`According to Golberg (1958), absorption of the iron-dextran complex from the
`site of administration after an intramuscular injection takes place mainly during
`the first 72 hr. The absorption rate mentioned by Golberg for the iron-dextran
`complex has in the main been verified in the present investigation; about 80% of
`the iron was absorbed within 48 hr of an injection of iron-dextran. For iron-sorbitol,
`the first absorption phase was very short; two-thirds of the injected iron had already
`been cleared from the site of administration after 3 hr. and 12 hr after the injection
`an 80 to 85% absorption from the muscle was recorded. The rapid absorption of
`this complex is rendered possible partly because of its low mean molecular weight,
`which does not exceed 5,000, and also because, like iron-dextran, it is stable in tissue
`fluids and at a physiological pH.
`The residual iron remaining at the site of injection after the first absorption phase
`is removed very slowly.
`Golberg (1958) observed that in the case of iron-dextran
`about 10% was still unabsorbed 15 days after administration into rabbits.
`In the
`present investigation, 9% of the iron was still present at the site of administration
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`
`370
`
`S. LINDVALL and N. S. E. ANDERSSON
`
`32 days after injection of the iron-dextran complex. For iron-sorbitol about 6%
`of the iron remained uncleared at the end of the same period. A probable reason
`why some of the iron from both of the preparations was retained at the site of
`injection is that the iron complex may have spread to the subcutaneous fat and to
`the fatty tissues between the muscles where clearance is more difficult. The large
`dose of iron given to the experimental animals is also a factor which may have
`contributed towards producing a more extensive spread of the iron from muscle to
`fatty tissue.
`The rapid absorption of iron-sorbitol from the site of injection was also apparent
`from the iron concentration in serum which, in the animal experiments, had already
`reached the maximum level after 20 min. Iron-dextran, on the other hand, produced
`no appreciable elevation of the iron content in serum during the first few hours. The
`difference between the behaviour of the two complexes in serum is due to the feature
`demonstrated by SvArd & Lindvall (1961), that iron-sorbitol is absorbed into the
`blood stream both directly and through lymphatic pathways, while iron-dextran is
`absorbed only via the lymphatic system.
`When iron-sorbitol appears in the serum, after absorption, it has no effect on the
`clotting mechanism of the blood. In vitro experiments demonstrated, however, that
`iron-sorbitol as well as iron-dextrin had a certain inhibitory effect on coagulation.
`This inhibition, however, occurred only at concentrations considerably higher than
`those reached in clinical use. The citric acid content of the preparations is the cause
`of this in vitro inhibition.
`Despite the rapid absorption that follows intramuscular injection of iron-sorbitol,
`the iron content of the serum was not as high as was expected, taking into considera-
`tion the blood volume and the amount of iron given.
`This is due to the fact that
`the absorbed iron disappears rapidly from the circulation, as was seen in the
`investigations on the clearance of intravenously administered iron preparations.
`Iron-sorbitol and iron-dextrin preparations disappeared from the blood stream at
`approximately the same rate while iron-dextran circulates for a long period.
`According to Andersson (1950), the uptake of iron-dextrin by the reticulo-endothelial
`system runs parallel to the disappearance from the blood. The iron-sorbitol is
`probably also taken up by these organs. The initial clearance of the iron-sorbitol
`preparation takes place more rapidly, however, than that of iron-dextrin, and this
`suggests that the elimination of the former is influenced by other factors as well.
`Filtration of the iron through glomeruli, which is made possible by the low molecular
`weight of iron-sorbitol, is a contributing factor in the rapid initial clearance. About
`15% of the dose of iron injected in man was excreted into the urine within the first
`3 hr of injection.
`Iron-sorbitol can, furthermore, diffuse into the tissue fluids.
`Following intramuscular administration of the new preparation, and when the
`doses are large, a temporary saturation of the iron-binding capacity of the serum
`occurs both in man and in animals shortly after the injection.
`This property of the
`preparation is bound to the low-molecular, dialysable fraction. Owing to the fact
`that this fraction reacts with transferrin it is presumably immediately available for
`erythropoeisis while the other part of the preparation is taken up by the reticulo-
`endothelial system for further transformation and metabolism.
`
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`

`
`IRON-SORBITOL
`
`371
`
`Our sincere thanks are due to Bertil Sjbgren, M.D., Director of the Research Laboratories
`of Astra, for constructive criticism, and to all who have assisted in their various ways to
`make possible the publication of this paper.
`Jectofer, Astra, is pending British patent application number 5791/61.
`
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