publicatlon o~ th’e American Phd~’maeeUtieal
`
`AUGUST 1969
`
`-¢odeni Je~.SA
`
`" " "
`
`’
`
`I_upin l~x. ’103’1 (Page ’1 of
`
`

`

`Journal of
`Pharmaceutical
`Sciences
`
`AUGUST 1969
`VOLUME 58 NUMBER 8
`
`EDWARD G, FELDMANN
`Editor
`
`MARY HUDSON FERGUSON
`
`Associate Editor
`SYLVIA R. SLOANE
`Production Editor
`DDRWARD F. DOD~EN
`Contributing Editor
`
`SAMUEL W. GOLDSTEIN
`
`Contributing Editor
`
`LINDA A. LAFONTAINE
`Contributing Editor
`
`EDITORIAL ADVISORY BOARD
`
`JOSEPH P, BUCKLEY
`
`W. LEWIS NOBLES
`
`JACK COOPER
`
`GORDON H. SVOBODA
`
`EDWARD ’R. GARRETT
`
`JOSEPH V. SWINTOSKY
`
`COMMITTEE ON PUBLICATIONS
`
`ROBERT C. JOHNSON~
`Chairman
`
`GROVER C. BOWLES~ JR.
`
`CLIFTON J. LATIOLAIS
`
`WILLIAM S. APPLE
`
`JOHN H. NEUMANN
`
`The Journal of Pharmaceutical Sciences is published
`monthly by the American Pharmaceutical Association at
`20th ~’Northampton Sis., Easton, PA 18042. Seco~d-
`class j~ostage paid at Easton, Pa, and at additional mail-
`ing emcee.
`All expressions of opinion and statements of supposed
`fact appearing in articles or editorials carried in this
`journal are published on the authority of the writer over
`whose name they appear, and are not to be regarded as
`necessarily expressing the policies or views of the American
`Pharmaceutical Association.
`Ottices--Editorial, Advertising,. and Subscription
`Offices: 2215 Constitution Ave., N. W., Washington,
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`institutions. $30, indlviduals. ~f°r personal use onl.y $20’,
`tangle copies $3. Subscription rates are subject to
`chango without; no~ice. Members of the American
`Pharmaceutical Association may elect to receive the
`Journal of Pharmaceutical Hciences as a part of their
`annual $30 AI?HA membership dues.
`Claims--Missing numbers will not be supplied if
`dues or subscriptions are in arrears for more thar~ 60 days,
`or if claims are received more than 60 days a~ter the date
`of the issue, or if loss was due to faiiure ~o gi~e notice of
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`sponsibility for foreign delivery when i~s records indicate
`shipment has been made.
`Change of Address--Members and subscribers should
`notify at once both the Post Office and the American
`Pharmaceutical Association, 2215 Constitution Ave.,
`DG 20037, Of any change of address.
`American Pharmaceutical As~oeia-
`Ave., N. W., Washington, DC
`20037; all rights reserved.
`
`IN THE PUBLIC AND
`PROFESSIONAL INTEREST
`
`Historically pharmacy has fostered and participated in public
`spirited programs designed and intended to benefit the general
`population or to inform people how to cope with some of the
`problems of our complex society. The leading role played by
`pharmacy during the past decade in poison prevention activities
`is one good illustration of such endeavors.
`More recently individual pharmacists, as well as the organized
`profession, liave been devoting an increasing amount of time
`and attention to programs pertaining to drug abuse. Such activ-
`ities have ranged from speaking appearances bef6i’e local groups,
`including civic organizations and higl~ school classes, to major
`involvement by AP~A in programs of a national character. A
`striking example of the latter was the recent election of AP~A
`to the Board of Trustees of the National Coordinating Council
`on Drug Abuse Education and Information, Inc., and of George
`B. Griffenhagen as Council Secretary.
`Beyond the very considerable public service that pharmacy is
`rendering through these activities, we believe that there is a
`secondary benefit to the profession itself which is not readily
`apparent. Drug abuse is one of the most major threats which
`exist today to the mental, physical, and moral health of the
`nation and especially its youth. Moreover, the public at large is
`in a position both to comprehend this problem and to take effec-
`tive action at a personal level toward its solution--in contrast
`to other major problems such as national defense and security,
`environmental pollution, urban decay, and mass transportation.
`By providing the leadership in efforts directed at solving the
`problem of drug abuse, and by throwing its full support behind
`these efforts, pharmacy cannot help but enhance its professional
`image in the public eye. Interestingly enough, this was largely
`the experience of dentistry when that profession and its prac-
`titioners, took the lead in endorsing and advocating fluoridation
`of public water supplies. There is an interesting further paralle!
`here in that pharmacy involvement in drug abuse, and dentistry
`involvement in fluoridation, are both quite obviously devoid
`of any personal gain. On the contrary, if successful, both cam-
`paigns serve to reduce potential income for the respective prac-
`titioners. Hence, it should be apparent to the public that such
`involvement by the professions is completely altruistic and with-
`out any possible selfish motivations.
`But if the practic.ing pharmacist can make an important con-
`tribution to the public health through involvement in drug
`abuse prevention, it would seem that the pharmaceutical
`scientist can do much more. With his additional trgining in the
`various biological and physical sciences, he should be in even
`better position to lnake a most effective contribution in this
`activity.
`For example, some years ago the APnA Academy of Pharma-
`ceutical Sciences prodnced a slide talk presentation on the haz-
`ards associated with Slnoking. This slide talk was very well
`prepared and presented its message in a convincing manner to
`the layman.
`Now the pharmaceutical scientific community might well
`consider deeper individual and group involvement in the drug
`abuse problem, since it would seem that pharmaceutical scien-
`tists could do nmch here to help the general welfare as well as
`to enhance professional prestige. Many resource materials are
`available to draw upon, such as the APr~A booklet "A Guide for
`the Professions...Drug Abuse Education;" and the extensive,
`eight-unit "Drug Abuse Edudation Slide Resource Kit," just
`developed by the APHA under the sponsorship of the Bureau
`of Narcotics and Dangerous Drugs of the U.S. Department of
`Justice. ~E.G.F.
`
`Lupin Ex. 1031 (Page 2 of 21)
`
`

`

`Journal of
`Pharmaceutical
`Sciences
`
`AUGUST 1969
`
`VOLUME 58 NUMBER 8
`
`REVIEW ARTICLE
`
`Pharmaceutical Applications of Polymorphism
`
`JOHN~I=IALEBLIAN and WALTER McCRONE
`
`Keyphrases [] Polymorphism--pharrnaceutical applications [] Sta-
`bility, chemical--polymorphorphism[] Methodology--polymor-
`phism determination [] Metastable polymorphs--preparation
`
`A polymorph is a solid crystalline phase of a given
`compound resulting from the possibility of at least two
`different arrangements of the molecules of that com-
`pound in the solid state. The molecule itself may be of
`different shape in the two polymorphs, but that is not
`necessary and, indeed, certain changes in shape (involv-
`ing dynamic isomerism or tautomerism) involve forma-
`tion of different molecules and hence do not constitute
`polymorphism. Geometrical isomers or tautomers, even
`though interconvertible and reversibly so, cannot be
`called polymorphs although they may behave in a con-
`fusingly silnilar manner. Shape changes, permissible in
`the molecule crystallizing in two or more polymorphic
`forms, include resonance structures, rotation of parts of
`the molecule about certain bonds, and minor distortions
`of bond distances and angles. These distortions of
`molecular shape result from polarizability effects of
`one molecule on another due to the change in relative
`positions of adjacent molecules in the two different
`crystalline arrangements.
`A safe criterion for classification of a system as po!y-
`morphic is the following. Two polymorphs will be
`different in crystal structure but identical in the liquid
`and vapor states. Dynamic isomers will melt at different
`temperatm’es, as do polymorphs, but will give melts of
`different composition. In time each of these melts
`changes to an equilibriuln mixture of the two isomers
`with temperature-dependent composition. Some re-
`ported cases of polymorphism are undoubtedly dynanfic
`isomerism, since the two behave quite similarly, espe-
`
`dally if the equilibrium between the two isomers is very
`rapidly established.
`Polymorphism is the ability of any element or com-
`pound to crystallize as more than one distinct crystal
`species (e.g., carbon as cubic dialnond or hexagonal
`graphite). Different polymorphs of a given compound
`are, in general, as different in structure and properties
`as the crystals of two different compounds. Solubility,
`melting point, density, hardness, crystal shape, optical
`and electrical properties, vapor pressure, etc., all vary
`with the polymorphic form. In general, it should be
`possible to obtain different crystal forms of a drug and
`thus modify the performance properties for that com-
`pound. To do so requires a kriowledge of the behavior of
`polymorphs.
`Mitscherlich (1) is generally given credit for first using
`the term polymorphism during his work on the iso-
`morphous sulfates of iron (ferrous), coba.lt, nickel,
`magnesium, copper,, zinc, and manganese. It is, however,
`obvious that the idea was not new at that time, since
`Humphrey Davy in 1809 pointed out that diamond and
`graphite are both carbon and that the two differ only in
`their arrangement of carbon atoms in the solid phase.
`Indeed, Klaproth may have been the first to be aware of
`polymorphism when he observed (1788) that calcium
`carbonate crystallizes both as calcite and as aragonite.
`Since that tilne a very large number of compounds,
`organic and inorganic, as well as the elements them-
`selves, have been shown to crystallize in two or more
`different crystalline arrangements--chemically identical,
`physically different. Besides graphite and diamond there
`are, to name a few in the mineral field, wurtzite and
`sphalerite (ZnS); calcite, aragonite, and vaterite
`(CaCOs); rutile, brookite, and anatase (TiO~). Most
`polymorphs, especially those of organic compounds, do
`not have special names; instead they are referred to as a,
`
`Vol, 58, No. 8, August 1969 [] 911
`
`Lupin Ex. 1031 (Page 3 of 21)
`
`

`

`0, % etc., or I, II, III, etc. Many compounds exist in
`five, six, and even ten, eleven, or more different crystal
`forms. Ammonium nitrate has five fo!’ms, progesterone
`also has five, water has eight or nine, tripalmitin has
`seven, and some drugs have been found to have ten or
`more different crystal forms. It is now apparent, that
`most, if not all, compounds and elements show a
`rarity of different crystal forms. Deffet (2) has sum-
`marized the properties of a number of organic systems
`exhibiting polymorphism.
`The subject of polymorphism has also been covered
`in several texts including those by O’Connor (3),
`Hartshorne and Stuart (4), Kofler and Kofler (5),
`McCrone (6, 7), and Verma and Krishna (8).
`The scientific literature also included numerous
`indications of its importance in pharmaceuticals.
`Several authors have systematically studied different
`classes of drug compounds. In Austria Kuhnert-
`Brandst~itter et al., using thermomicroscopic methods,
`have reported on the polymorphism of steroids (9=12),
`barbiturates (13-15), and antihistamines (16), Their
`work probably represents the most intensive study of
`polymorphism and drugs. Similarly, in England, Mesley
`et al., using IR spectroscopy, have described the poly-
`morphism of steroids (17, 18), barbiturates (19, 20), and
`sulfonamides (21). While the subject of polymorphism
`is extensively covered in the scientific literature, there
`are relatively fewer reports regarding its importance in
`the area of pharmaceutics. The following reviews the
`available literature and includes a discussion of how the
`principles of crystal chemistry can be applied to solve
`various dosage form problems arising from misuse or a
`lack of understanding of how the solid state properties
`of a drug substance can affect its stability and availa-
`bility:
`In a 1965 survey, Kuhnert-Brandstiitter (22) reported
`that (see Table I), of 48 steroids studied with m.p.’s
`less than 210°, 67 70 exhibited polymorphism. Out of 40
`sulfonamides studied, 4070 exhibited polymorphism,
`,and out of 38 barbiturates studied, 6370 existed in
`different polymorphic forms. When checking marketed
`products she found that 17 70 of the steroids, 23 70 of the
`sulfonamides and 11 70 of the barbiturates were un-
`stable, as a result of polymorphic changes in the system.
`
`APPLICATIONS OF POLYMORPHISM IN THE
`PHARMACEUTICAL INDUSTRY
`
`Preparation of Physically Stable Dosage Forms
`
`Suspensions--Aqueous Vehicles--Due to use of a
`wrong polymorph of a drug, a phase conversion from
`the metastable to stable polymorph may occur, This
`produces: -
`(a) Crystal growth, resulting in undesirable particle
`size distribution. This can produce serious problems
`with parenteral suspensions where syringibility of the
`product can become difficult if significant particle
`growth occurs. Biological availabilities of the drug also
`can be altered because phase transitions produce drug
`particles having different solubilities.
`(b) Caking, producing suspensions that cannot be
`uniformly resuspended by shaking. A good example of
`suspensions in aqueous vehicle is the cortisone acetate
`
`Table I~--Polymorphism of Drugs
`
`Compd.
`
`Steroids
`(m.p. less
`than 210°)
`Sulfonamides
`Barbiturates
`
`No.
`Studied
`
`Having of Unstable
`Polymorphs
`Samples
`
`48
`
`40
`38
`
`67
`
`40
`63
`
`17
`
`23
`11
`
`. Reprinted from Pure and Applied Chemistry, 10, 136~1965), by per.
`mission of the International Union of Pure and Apphed Chemistry
`and Butterworths Scientific Publications,
`
`suspension. Cortisone acetate was one of the most diffi-
`cult polymorphic problems to solve. Macek (23) ob-
`tained the first patent on stable noncaking aqueous
`suspension of cortisone acetate and methods of prepar-
`ing the same. He described the early attempts to obtain
`a stable aqueous suspension, where cortisone acetate, in
`the form of crystals stable in the dry state, was sus-
`pended in the aqueous medium and allowed to remain in
`the mediuln for a few hours. It was observed that crystal
`growth of the cortisone acetate invariably occurred with
`subsequent caking and sedimentation. A physically
`stable aqueous suspension was obtained by ball-milling
`cortisone acetate powder, referred to by Macek as
`Form 2, in the aqueous vehicle where a polymorphic
`phase transition occurred, to Form 5. In a later patent,
`Magerlein (24) described two new polymorphs of
`cortisone acetate, Form A, which is not stable in the dry
`state, and Form B, which is stable in the dry state.
`Both crystal forms when used in aqueous suspensions
`gave physically stable, noncaking aqueous suspensions.
`The cause of the growth of crystals of Form 5, in the
`early suspensions prepared by Macek, is due to greater
`solubility of Form 2 in the solution phase than Form 5.
`The concentration of Form 2 is greater in the solution
`immediately in contact with Form 5 crystals than the
`solubility of the Form 5. This happens because of the
`dissolution of more soluble Form 2 into th~ s-dlution,
`resulting in a supersaturated solution with respect to
`Form 5, the stable configuration.
`Creams--When creams are prepared with the active
`ingredient suspended in the creana base, use of the
`wrong polymorph can result in a phase inversion to a
`more stable phase. As a consequence, crystal growth can
`occur in the vehicle yielding gritty, cosmetically un-
`acceptable creanas or products in which the active
`ingredient is unevenly distributed. During the. prepara-
`tion of a topical cream it is necessary to select the
`correct polymorph of the active ingredient, which when
`suspended is least susceptible to growth in the cream
`base.
`The correct procedure is to choose the polymorphic
`phase which is least soluble in the cream base. When
`a metastable phase with high solubility is suspended in
`the cream base there is a high risk that nucleation of a
`more stable (less soluble) form will eventually occur.
`When this happens, the crystal size distribution in the
`system is altered as the more stable form gradually
`replaces the metastable phase. The usual consequence of
`this process is a substantial increase in the mean crystal
`size of the suspended drug in the formhlation. While
`
`912 [] Journal of Pharmaceutical Sciences
`
`Lupin Ex. 1031 (Page 4 of 21)
`
`

`

`crystal growth of finely suspended drug particles can
`occur in the absence of such transformations, serious
`consideration should be given to the presence of differ-
`ent polymorphic forms when this type of problem is
`encountered with a formulation. In certain instances,
`the use of the most stable polymorph for suspension in
`liquid or semisolid dosage forms may not be the best
`procedure. For example, phase conversion may be so
`slow in certain ointment bases that a more soluble
`metastable form may be safely used. It is entirely
`possible the use of a more thermodynamically energetic
`form of the drug may result in a more efficacious thera-
`peutic formulation.
`Solutions--One of the first considerations in for-
`mulating a solution is to determine the solubility of the
`drug in its vehicle. If the solubility determination is con-
`ducted using a metastable form of the drug and the
`concentration of the drug in the system exceeds the
`equilibrium solubility of a less soluble form of the
`drug, a thermodynamically unstable formulation re-
`suits. In a sense, this is akin to emulsions which are
`also thermodynamically unstable systems. Some solu-
`tions that are supersaturated with respect to the stable
`form of the drug may remain in this state for relatively
`long periods of time. Chance nucleation of the stable
`form, however, quickly results in crystallization until
`equilibrium is reached with respect to this form. This
`is a frequent problem with sparingly water-soluble
`drugs, such as the steroids, and this phenomenon
`has been frequently encountered in these laboratories.
`Flynn (25) has reported an example of this type of
`problem in the formulation of a parenteral solution of a
`drug. In this instance, determination of the water solu-
`bility of this compound indicated the drug to be ade-
`quately soluble for the concentration required in the
`formulation. Stability studies on the formulation quickly
`turned up the presence of a precipitate. An investigation
`of the problem showed the precipitate to consist of a
`less soluble polymorph of the compound. The problem
`was solved by formulating the product in a vehicle
`containing sufficient cosolvent to solubilize the less
`soluble polymorphie form.
`Suppositories--The polymorphic changes of a sup-
`pository base could result in a product that undergoes
`a change in its melting characteristics. If the suppository
`base is of the type that depends on melting at body
`temperatures to release the active components of the
`formulations a relatively small change in its melting
`point could have severe consequences. If the melting
`point is depressed the product may melt or soften at
`shelf temperatures. If the melting point becomes
`greater than anticipated, the. suppository may not melt
`properly when administered. This point could be demon-
`strated by extemporaneous preparations of suppositories
`containing theobroma oil as their base. Theobroma
`oil, like many triglycerides, exhibits polymorphism
`(26). It exists in three different cryslal forms each with
`different melting points. Suppositories are prepared
`by fusion of theobroma oil, when they are melted
`and brought to 60-70°. The melt is then poured into
`molds and quickly chilled in a refrigerator. If sup-
`positories prepared by this method are removed from
`the refrigerator after a short time they will melt at
`
`30°, which makes their use impractical in the summer,
`and the patients will have difficulty in inserting them,
`since they liquefy in the fingers. If the suppositories are
`prepared by heating the theobroma oil just a few de-
`grees above its melting point, the suppositories will
`have a higher melting point and can be easily handled.
`This method of manufacture permits the crystalliza-
`tion nuclei of the more stable (higher melting point)
`0-forms to remain in the melt, which on chilling favors
`additional crystallization of the S-form. Fused theo-
`broma oil heated to 60-70° when chilled undergoes
`supercooling and a-form crystals develop, which have
`lower melting points. The o~-form, being a metastable
`phase, slowly changes to ~1 and to 0-form.
`
`Polymorphism and Chemical Stability
`There have been a number of instances where different
`crystalline phases of the same compound have different
`chemical stabilities. One of the authors has observed
`this while working with aqueous suspensions of an
`experimental corticosteroid, when chemical instability
`developed in some of the batches of this compound.
`The raw starting material batches were checked with
`X-ray diffraction and the presence of two different
`polymorphs was confirmed. When these polymorphs
`were further studied for their chemical stability it was
`found that one of these was light-sensitive. Batches
`containing this crystal form then decomposed with
`time and assayed lower than the other batches. This
`chemical sensitivity could be due to solvents occluded or
`absorbed mother liquor, where the latter could effect
`chemical stability, or in cases of polymorphs due to
`different light absorption patterns. The patterns would
`differ slightly and one must absorb a frequency that
`causes a photochemical decomposition. Similarly,
`Macek (27) has reported that the amorphous forms of
`the sodium and potassium salts of penicillin G obtained
`by evaporation fi’om solution, are less stable chemically
`than their crystalline counterparts. For example,
`crystalline potassium penicillin can withstand dry heat
`for several hours without significant decomposition.
`Under similar conditions, the amorphous forms lose
`considerable activity. "This property is important if one
`is interested in depositing penicillin on a solid, as in
`tablet coating. Application from solution in a volatile
`solvent obviously would lead to greater ihstability,
`whereas deposition of a suspension of the crystalline
`form, even though in a very fine state of subdivision,
`would be expected to result in greater stability" (27).
`In such cases where chemical stability is a problem,
`there obviously is a need for careful control during
`chemical manufacture to assure that the desired poly-
`morphic form is obtained.
`
`Polymorphism and Generically Equivalent Dosage
`Forms
`If the rate of absorption of the active ingredient in an
`oral preparation is dissolution-rate dependent, the use
`of a compound exhibiting polymorphism may lead to
`good or bad consequences. The successful utilization of
`a polymorph of significantly greater thermodynamic
`activity (i.e., solubility) than the stable modification
`may provide, in some instances, therapeutic blood
`
`VoL 58, No. 8, August 1969 [] 913
`
`Lupin Ex. 1031 (Page 5 of 21)
`
`

`

`.400
`
`.300
`
`.200
`
`.100
`
`CALCIUM NOVOBIO~;IN MICRONIZZD
`
`AMORPHOUS NOVOBIOCII’i ACID
`
`F.,~,~ ~--.-- ~.~ ’V-
`
`CRYSTALLINE NOVOBIOCIN ACID
`
`NICRONIZED
`
`0
`
`1
`
`2
`HOURS
`Figure 1--Absorbanee of novobiocin in O.Z N HCI at 305 m!~.
`
`3
`
`4
`
`levels from otherwise inactive drugs. On the other hand,
`when the existance of multiple crystalline modifications
`goes unrecognized in a particular formulation, this
`may possibly result in unacceptable dose-to-dose
`variations in drug availability to the patient (28).
`Mullins and Macek (29) working on pharmaceutical
`properties of novobiocin identified two forms of novo-
`biocin, one of which is crystalline and the other amor-
`phous. In tablet and capsule formulations novobiocin is
`used as the sodium salt which is active orally but it is
`unstable chemically in a solution, while the insoluble
`forms of novobiocin acid are more stable chemically.
`But the crystalline novobiocin acid is poorly absorbed
`and does not provide therapeutically adequate systemic
`levels following oral administration. The amorphous
`acid is readily absorbed and is therapeutically active.
`This difference in availability is due to differences in
`solubility in aqueous systems. When an excess of
`crystalline or amorphous novobiocin acid in less than
`10-/~ size were shaken in 0.1 N hydrochloric acid at 25°,
`the amorphous solids were at least 10 times more
`soluble than the crystalline acid (see Fig. 1). This differ-
`ence in solubility might be expected to favor the absorp-
`tion of the amorphous solid from the gastrointestinal
`tract. Data showing differences in novobiocin plasma
`levels in drug following oral administration of 12,5 mg.]
`kg. each of amorphous novobiocin and crystalline
`novobiocin acid and the sodium salt are shown in
`Table
`Unless special precautions are taken to maintain the
`solid in suspension in amorphous state by the addition
`of materials to suppress crystallization, amorphous
`novobiocin converts slowly to a crystalline form. The
`
`Table II--Novobiocin Plasma Levels in Dogs Following Oral
`Administration of Different Solid Formsa
`
`--
`
`Sodium
`Novobiocin,
`mcg./ml,
`Plasma
`
`Amorphous
`Novobiocin
`(Acid),
`mcg./ml.
`Plasma
`
`Hours
`after
`Dose
`
`Crystalline
`Novobiocin
`(Acid)
`
`~. 24
`¯ 22
`~ 2o
`E 18
`
`_O 14
`~ 12
`~: l0
`
`< 6
`
`~ 2
`
`1 3
`
`5 7 9 11
`hr. AFTER DOSING
`Figure 2--Comparison of mean blood serum levels obtained with
`chloramphenicol palmitate suspensions containing varying ratios of
`A and B polymorphs, following single oral dose equivalent to 1.5 g.
`chloramphenicol. (Percent polymorph B in the suspension: M, 0%;
`N, 2S~o; O, 50~o; P, 75%; L, 100%.)
`
`24
`
`formulation becomes less and less absorbable and finally
`loses therapeutic effect entirely. To stabilize the sus-
`pensions they conducted a search for additives that
`would significantly retard or even prevent crystallization
`of aqueous suspensions of amorphous novobiocin, and
`they found that some agents provided adequate protec-
`tion against crystallization for significant periods of
`time. The best agents found were methyl ceIlulose, PVP,
`and several alginic acid derivatives such as sodium
`alginate and propylene glycol elgin.
`Chloramphenicol palmitate exists in four polymorphs,
`three crystalline (30)(A, B, and C), and an amorphous
`one (31, 32). Aguiar et aL (30) investigated the absorp-
`tion of Polymorphs A and B to determine the effect of
`varying concentrations (percent of Polymorph B was 0,
`25, 50, 75, and 100). After oral ingestion of the suspen-
`sion (equivalent to 1.5 g. chloramphenicol) blood and
`urine specimens were collected for a 24-hr. period. The
`mean blood levels obtained are shown in Fig° 2 and the
`urinary excretion data are given in Fig. 3. In these single
`dose studies the highest mean blood levels were ob-
`tained with suspensions containing only FQrm B. The
`blood levels decreased proportionately as the concentra-
`tion of Form A increased. These data demonstrate that
`absorption is influenced by the type and concentration
`of the crystal polymorph present.
`
`<z 90
`
`~o ~0
`
`~) 10 ~
`
`0.5
`5.0
`0.5
`l
`40:6
`0.5
`2
`29.5
`14.6
`3
`22.3
`22.2
`4
`23.7
`16.9
`5
`20.2
`10.4
`6
`17.5
`6.4
`¯ Dose = 12,5 mg./kg. ~ Not detectable.
`
`914 [] Journal of Pharmaceutical Sciences
`
`N.D.~
`N.D.~
`N:DP
`N.D.~
`N.D.~
`N.D)
`N.DP
`
`0-2 2-4 4-6 6~8 8-12 12-24
`URINE COLLECTION PERIODS, hr. AFTER DOSING
`Figure 3--Urinary excretion rate of total nitro compound ehloram.
`phenicol equivalent following single oral dose of chloramphenicol
`palmitate suspensions containing varying quantities of PolymotThs
`A and B. Dose equivalent to 1.5 g. ofchloramphen&ol. (PercentPoly-
`morph B in the suspension: M, 0%; N, 25~; ~0, 50%; P, 75%;
`L, 100%.)
`
`Lupin Ex. 1031 (Page 6 of 21)
`
`

`

`24
`
`E
`
`o
`
`_1
`
`Figure 4--Corre[ation of
`"peak" blood serum levels
`(2 hr.) vs. percent concentra-
`tion of Polymorph B.
`
`20
`
`40 60 80
`% FORM B
`
`i00
`
`The differences in absorption are even more evident
`in Fig. 4 where the absorption at 2 hr. ("peak" blood
`levels) is plotted versus the percent of Form B present in
`the suspension. A linear relationship apparently exists
`between the peak levels and concentration of Polymorph
`B. The blood levels increase in a direct relationship to
`the increase of Polymorph B. One year before Aguiar’s
`paper, Anderson (33) of the National Biological Stan-
`dards E~aboratory of Canberra, Australia, investigated a
`complaint that a chloralnphenicol suspension had had
`, an unsatisfactory therapeutic effect. Several commerical
`preparations and powders of ch!oramphenicol pahnitate
`were examined. Of six powders, four appeared to consist
`mainly of the Polymorph A, the inactive type, and of
`seven samples of suspensions, one contained mainly
`inactive Polymorph A.
`Poole et al. (34) reported on physiochemical factors
`influencing the absorption of the a, nhydrous and tri-
`hydrate forms of ampicillin. They found that aqueous
`solubility of the anhydrous form was 20 % higher than
`the trihydrate at 37 o (10 and 8 mg./ml., respectively, for
`the anhydrous and trihydrate forms). They also deter-
`.mined the effect of the observed solubility differences on
`the in vitro availability of the drug. In the in vitro experi-
`ments they measured the %0 (time required for 50 % of
`
`2.1
`
`1
`
`2 3 4 5 6
`HOURS
`Figure 5--Mean blood sbrum concentrations of ampicillin in human
`subjects after oral aclministration of 250-rag. doses of the oral sus-
`pension. Key: (3, anhydrous; A-trihydrate [reproduced wtth per-
`mission from Current Therap. Res., 10, 299(1968)],
`
`Table HI--Area Under the Blood Serum Level-Time Curve Ob-
`served in Human Studies~
`
`Formu.
`lation
`
`Suspension
`
`Capsules
`
`Form of
`Ampicfllin
`
`Anhydrous
`Trihydrate
`Anhydrous
`Trihydrate
`
`Ratio,
`Anhydrous-
`/Trihydrate
`
`Area, cm. ~
`
`143.5
`119.0
`127.8
`109,0
`
`1.21
`
`1.17
`
`¯ Reproduced with permission from Current Therap. Res., 10, 302
`(1968).
`
`the labeled amount to appear in sol~t-tion)and they
`found that it was 7’.5 and 45 min for the anhydrous and
`trihydrate forms, respectively. They also designed ex-
`periments to correlate the in vitro data with in vivo drug
`availability. Their in vivo experiments were done with
`dogs and human subjects, where the anhydrous and the
`trihydrate form of the drug were given as oral suspen-
`sions or capsules. The anhydrous forln produced higher
`and earlier peaks in the blood serum than the trihydrate
`form. This was more pronounced in the suspension
`formulations. Figure 5 shows the mean blood serum
`concentration in human subjects after oral administra-
`tion of a 250-mg, dose of the suspension. With both
`formulations the area under the blood serum level
`versus time curve was greater with the anhydrous form
`(see Table III), indicating that the anhydrous form is
`more efficiently absorbed.
`Hamlin et al. (35), using two polymorphs of methyl-
`prednisolone (Forms I and II), prepared constant sur-
`face pellets and determined their dissolution rates by
`four different in vitro lllethods. These results were com-
`pared with in vivo dissolution rates obtained by implant-
`ing pellets in rats according to the method of Ballard
`and Nelson (36). They found that (see Table IV) in vivo
`the dissolution rate of Form II was 1.2 times greater
`than Form I, the thermodynamically more stable form
`at room temperature: While in the in vitro studies where
`the agitation intensity was of a low-order Form II had a
`dissolution rate 1.53 times more than Form I when
`studied with the hanging pellet method (37), and when
`studied by pellet holder method in the Wruble nlachine
`(38) at 6 r.p.m, the dissolution of Form II was 1.3 times
`more than Form I. At higher agitation intensities these
`differences disappeared. In a similar study, Ballard and
`
`Table 1V--Results of Dissolution Rate Experiments PerFormed
`with Constant Surface Pellets of Methylprednisolone Polymorphs I
`and II by an in vtvo and Several in vitro Methods
`
`Test
`
`Pellet implant in rats
`
`Hanging pellet method
`
`Pellet hoIder method
`in Wruble machine,
`6 r,p,m,
`Pellet holder method
`in Wruble machine,
`12 r.p,m,
`Pellet holder method
`in machine of Souder
`and Ellenbogen (39),
`40 r.p.m.
`
`Methyl-
`prednisolone
`P