SPECIAL FEATURE SECTION: Polymorphism and Crystallization
`
`Apotex Exhibit 1015.001
`
`

`

`Organic Process
`Research &
`Development
`
`A publication of the
`American Chemical Society
`and the
`Royal Society of Chemistry
`
`Orgallic Process Research & Developmelll (IS'SN'
`1083-6 160) is copublished bimonthly by the
`American Chemical Society at 1155 16th St.,
`N.W., Washington, DC 20036, and the Royal
`Society of Chemistry at Thomas Graham House,
`Science Park, Milton Road, Cambridge CB4 OWF,
`UK. Periodicals postage pending at Washington,
`DC, and additional mailing offices. POSTMAS(cid:173)
`TER: Send address changes to Orgallic Process
`ResearciJ & Developmellt, Member & Subscriber
`Services, P.O. Box 3337, Columbus, OH 43210.
`
`Copyright Permission: See copyright status . form for certain rights (http://pubs.acs.org). Repro(cid:173)
`graphIc copymg beyond that permItted by SectIon 107 or 108 of the U.S. Copyright Act is allowed
`provided that $19.00 per article is paid to the Copyright Clearance Center, 222 Rosewood Drive'
`Danvers, MA 01923 . Republication or reproduction for sale of articles or abstracts in this journal i~
`permitted only by written permission from the Copyright Office, ACS, Washington, DC. Tel: (202)
`872-4368. Fax: (202) 776-8112. E-mail: copyright@acs.org.
`
`Subscription Donations: Members may donate/share their personal subscriptions to/with libraries but
`only after 5 years from publication.
`
`Editorial Information
`
`Instructions for Authors and Copyright Status Form: See the first issue of each volume or visit
`the Publications Division Web site (http://pubs.acs.org). Please conform to these instructions When
`submitting manuscripts.
`
`Manuscript ,Submission: Send manuscripts to the Editor, Trevor Laird, or to the Associate Editors,
`Richard Pariza and Christopher Schmid, at the addresses given.
`
`Accepted Papel's and Proofs: Direct correspondence to Publishing Operations, Columbus, OH. Tel:
`(614) 447-3665. Fax: (614) 447-3745. E-mail: acsproof@acs.org.
`
`Journal Policies: The American Chemical Society, the Royal Society of Chemistry, and their Editors
`assume no responsibility for the statements and opinions advanced by contributors. Registered names
`and trademarks, etc., used in this publication, even without specific indication thereof, are not to be
`considered unprotected by law.
`
`Document Number: At the end of each document is a 9-character code that serves as a link between
`the printed and electronic products and facilitates retrieval of the document in electronic form.
`
`MANAGEMENT BOARD
`American Chemical Society
`Anne C. O'Melia
`Mary E. Scanlan
`Digital Object Identifier (001): The DOl identification system for digital media has been designed
`to provide persistent and reliable identification of digital objects. Information on the DOl and its gov(cid:173)
`Royal Society of Chemistry
`erning body, the International DOl Foundation, can be found at http://www.doi .org. In the Web edi(cid:173)
`Robert J. Parker
`Harpal Minhas
`..4...,
`tions of ACS journals, the DOl appears at the top of the HTML version of an article and at the bot(cid:173)
`tom of the first page in its PDF version; in the print editions, the DOl appears in the same location
`Publishing Operations
`as in the PDF version.
`American Chemical Society ~
`V
`2540 Olentangy River Road
`P.O. Box 3330, Columbus, OH 43210
`(6 14) 447-3665
`Fax (614) 447-3745 ; Telex 6842086
`E-mail acsproof@acs.org
`Manager: Anne C. O'Melia
`Journals Editing Manager: Debora Ann Bittaker
`Assistant Editor: Mary Ellen Nesham
`Information Services ~
`~~~~Ia~~::~;f ;o~:~stry ~
`Web Edition'
`$117
`$117
`$ 86
`Members
`Print/V" eb Combination'
`Science Park, Milton Road
`t For Institutional rates, call Member & Subscriber Services. 1 For subscriptions in the UK and Europe CO Il (cid:173)
`Cambridge CB4 OWF, UK
`tact the Royal Society of Chemistry, Turpin Distribution Services Ltd., Blackhorse Road, Letchworth, Herts.
`+44 (0)1223 420066
`SG6IHN, U.K.
`Fax +44 (0)1223 420247
`E-mail OPRD @rsc.org
`Web Edition: This journal is available to subscribers via the Internet. Contact Member & Subscriber
`Services [Tel: (614) 447-3776 or (800) 333-9511. Fax: (614) 447-3671. E-mail: service@acs.org] or
`General Manager: Robert J. Parker
`visit the Publications Division Web site (hUp://pubs.acs.org) for additional details.
`Managing Editor: Harpal Minhas
`
`2000 Subscription and Ordering Information
`
`Printed Edition
`
`Members
`Student Members
`Nonmembers
`Institutional
`
`Members
`
`North
`America
`
`$ 61
`$ 46
`$203
`$483
`
`$ 25
`
`UK and
`Europe
`
`£ 381
`£ 281
`£ 140"
`£3221
`$ 25
`
`All Other
`Countries
`
`$ 92
`$77
`$234
`$5 14
`
`$ 25
`
`American Chemical Society
`1155 16th St. , N.W.
`Washington, DC 20036
`(202) 872-4614
`TDD (202) 872-6076; Fax (202) 776-8264
`
`Sales & Marketillg
`Justin R. Spence, Director
`Dean J. Smith, Manager, Institutional Sales
`
`Member & Subscriber Services
`American Chemical Society
`P.O. Box 3337, Columbus, OH 43210
`(614) 447-3776; (800) 333-9511
`Fax (614) 447-3671
`E-mail service@acs.org
`Advertising Office except for UK and Em'ope
`Centcom, Ltd.
`676 East Swedes ford Road
`Suite 202, Wayne, PA 19087-1612
`(6 10) 964-8061
`Advertising Office for UK and Europe
`Royal Society of Chemistry
`Advertising Department
`Thomas Graham House
`Science Park, Milton Road
`Cambridge CB4 OWF, UK
`+44 (0)1223 420066
`
`Canadian GST Reg. No. 127571347
`Printed in the USA
`
`New and Renewal Subscriptions: RSC members send with payment to the Royal Society of Chem(cid:173)
`istry, Membership Department, Thomas Graham House, Science Park, Milton Road, Cambridge CB4
`OWF, UK. ACS members and all institutional subscribers except those noted below send with pay(cid:173)
`ment to American Chemical Society, Department L-OOII , Columbus, OH 43268-0011. For nonmem(cid:173)
`ber subscriptions in the UK and Europe, contact the Royal Society of Chemistry, Turpin Distribution
`Services Ltd., Blackhorse Road, Letchworth, Herts SG6 I HN, UK. E-mail: custservturpin@rsc.org.
`Institutional subscribers in Japan must enter subscription orders with Maruzen Company Ltd., 3- 10
`Nihonbashi 2-chome, Chuo-ku, Tokyo 103, Japan. Tel : (03) 272-7211.
`
`Change of Address: Notify Member & Subscriber Services, ACS , Columbus, OH. Tel: (614) 447-
`3776 or (800) 333-9511. Fax: (614) 447-3671. E-mail: address@acs.org. Include both old and new
`addresses and a mailing label from a recent issue.
`
`Microfilm, Microfiche, Back Issue, and Printed Edition Single Issue Orders: Send requests to
`Publications Support Services, ACS, Washington, DC. Tel : (202) 872-4376. Fax: (202) 872-6325.
`E-mail: pss@acs.org.
`
`Bulk Reprint Orders: For quotes and information, contact CJS Reprint Services. Tel: (888) 257-
`2134 or (4 10) 819-3991. Fax: (410) 820-9765.
`
`Claims fot Issues Not Received: Claims will be honored only if submitted within 90 days of the
`issue date (subscribers in North America) or within 180 days of the issue date (all other subscribers).
`Send requests to Member & Subscriber Services, ACS, Columbus, OH. Tel: (6 14) 447-3776 or (800)
`333-9511. Fax: (614) 447-3671. E-mail: service@acs.org.
`
`Supporting Information (SI): SI from 1995 to present is available free of charge via the Internet
`(http://pubs.acs.org) from the journal 's home page. For information on electronic access, send E-mail
`to si-help @acs.org. SI prior to 1995 is available, for a fee, from Publications Support Services. Tel:
`(202) 872-4376. Fax: (202) 872-6325 . E-mail : pss@acs.org.
`
`© Copyright 2000 American Chemical Society and The Royal Society of Chemistry
`
`Apotex Exhibit 1015.002
`
`

`

`Organic Process Research & Development 2000, 4, 427-435
`
`Salt Selection and Optimisation Procedures for Pharmaceutical New Chemical
`Entities
`
`Richard J. Bastin,t Michael J. Bowker,*,t,§ and Bryan J. Slater'
`Pre formulation Department, Pharmaceutical Sciences, Aventis Phanna, Dagenham Research Centre (DR C), Rainham
`Road South, Dagenham, Essex RM10 7XS, UK, and World-Wide Physical Chemistl), Department, Discovel)' Chemistl)"
`Aventis Pharma, Dagenham Research Centre (DR C), Rainham Road South, Dagenham, Essex RMlO 7XS, UK
`
`Abstract:
`Selection of an appropriate salt form for a new chemical entity
`provides the pharmaceutical chemist and formulation scientist
`with the opportunity to modify the characteristics of the
`potential drug substance and to permit the development of
`dosage forms with good bioavailability, stability, manufactur(cid:173)
`ability, and patient compliance. Salts are most commonly
`employed for modifying aqueous solubility, however the salt
`form selected will influence a range of other properties such as
`melting point, hygroscopicity, chemical stability, dissolution
`rate, solution pH, crystal form, and mechanical properties.
`Where possible, a range of salts should be prepared for each
`new substance and their properties compared during a suitable
`preformulation program. Since it is normally possible to fully
`develop only one salt form, its properties should be appropriate
`to the primary route of administration and dosage form. An
`understanding of the influence of drug and salt properties on
`the finished product is essential to ensure selection of the best
`salt. The drug properties required for one dosage form may
`be quite different from those required for another. A well
`designed salt selection and optimisation study provides a sound
`base on which to build a rapid and economic product develop(cid:173)
`ment programme.
`
`Introduction
`Modem drug discovery processes involve the screening
`of vast numbers of compounds that may have been made by
`the Company's research laboratories over many years, Added
`to these may be the many thousands of compounds that have
`been manufactured as libraries of structurally related series
`by "combinatorial chemistry" techniques. All of these
`compounds are generally dissolved in dimethylsulphoxide
`(DMSO) solution and screened in an enzyme- or receptor(cid:173)
`based assay system. If the number of "hits" produced is large,
`the numbers are usually refined by further screening and
`selection until a manageable number of "leads" is available.
`Many of these leads will show only weak or moderate
`activity and further refinement and optimisation is invariably
`necessary. These optimisation procedures usually involve
`numerous structural modifications, aided by computational
`techniques, until a small number (usually 1-5) of highly
`active "candidates" remain.
`* To whom correspondence should be sent.
`t Preformulation Department, Pharmaceutical Sciences.
`t World-Wide Physical Chemistry Department, Discovery Chemistry.
`§ Current address: M. J. Bowker Consulting Ltd., 36, Burses Way, Hutton,
`Brentwood, Essex CM13 2PS, UK
`
`These candidates are usually free bases, free acids, or
`neutral molecules, rather than their salts. Also, because of
`the generally higher molecular weights of modem drug
`substances and the increased use of DMSO solutions in the
`screening processes, it is becoming apparent that there is a
`tendency towards ever more lipophilic candidates being
`presented. Frequently, when first proposed as potential
`development candidates, they are often amorphous or
`partially crystalline as little effort has been made to
`investigate formal crystallisation procedures. The need for
`water-soluble candidates has been recognised l - 4 for many
`years before the advent of 'combinatOlial chemistry.
`
`Investigations into the Possibilities of Salt Formation
`When first presented for initial preformulation investiga(cid:173)
`tions, normally the amount of drug substance available from
`Discovery Chemistry rarely exceeds 1 g. To maximize the
`amount of data gained from such small quantities, semi-micro
`techniques have been developed and are used regularly within
`our groups. Invariably, the first information generated for
`each candidate is the calculated pKa value of each ionisable
`group in the molecule.s- s This is quickly checked against
`the value determined experimentally on 1-2 mg of sample
`by potentiometric titration (e.g., Sirius Model GLpKa ap(cid:173)
`paratus, Sirius Analytical Instruments Ltd.). Knowledge of
`the pKa value enables potential salt forming agents (coun(cid:173)
`terions) to be selected, for each candidate, based on lists that
`are available in the literature.2,9-11 For the formation of a
`stable salt, it is widely accepted that there should be a
`minimum difference of about 3 units between the pKa value
`
`(I) Hirsch, C. A.; Messenger, R. J.; Brannon, J. L. 1. Phal'm. Sci. 1978,67,
`231.
`(2) Gould, P. L. Int. 1. Phal'm. 1986, 33, 201.
`(3) Morris, K R.; Fakes, M. G.; Thakur, A. B.; Newman, A. W.; Singh, A.
`K; Venit, J. J.; Spagnuolo, C. J.; Serajuddin, A. T. M. lnt. 1. Phal'm. 1994,
`105,201.
`(4) Anderson, B. D.; Flora, K P. In The Practice of Medicinal Chemist!),;
`Wermuth, C. G., Ed.; Academic Press Ltd., 1996; Chapter 34.
`(5) Remington: The Science and Practice of Pharmacy, 19th ed.; Gennaro,
`A. R., Ed.; Mack Publishing Co.: Easton, Pennsylvania, 1993; Vol. II, p
`1456.
`(6) Hammett, L. P. Chem. Rev. 1935, 17, 125.
`(7) Perrin, D. D.; Dempsey, B.; Serjeant, E. P. pK" Prediction for Organic
`Acids and Bases; Chapman and Hall: London, 1981.
`(8) Albert, A. A.; Serjeant, E. P. Ionization Constants of Acids and Bases;
`Wiley: New York, 1984.
`(9) Wells, J. 1. Pharmaceutical Preformulation, 2nd ed.; Ellis Horwood:
`Chichester, 1993; p 29.
`(10) Martindale, W. In The Extra Pharmacopoeia, 30th ed.; Reynolds, J. E. F.,
`Ed.; The Pharmaceutical Press: London, 1993.
`(\1) Berge, S. M.; Bighley, 1.. D.; Monkhouse, D. C. 1. Pharm. Sci. 1977, 66,
`1.
`
`10.102110p000018u CCC: $19.00 © 2000 American Chemical SOCiety and The Royal Society of Chemistry
`Published on Web 0711912000
`
`Vol. 4, No.5, 2000 1 Organic Process Research & Development
`
`427
`
`Apotex Exhibit 1015.003
`
`

`

`Table 1. Classification of common pharmaceutical salts
`
`salt class
`
`inorganic acids
`sulfonic acids
`carboxylic acids
`anionic amino acids
`hydroxyacids
`fatty acids
`insoluble salts
`
`organic amines
`insoluble salts
`metallic
`cationic amino acids
`
`examples
`
`Anions
`hydrochloride, hydrobromide, sulfate, nitrate, phosphate
`mesylate,b esylate," isethionate,d tosylate,e napsylate/besylateg
`acetate, propionate, maleate, benzoate, salicylate, fumarate
`glutamate, aspartate
`Citrate, lactate, succinate, tartrate, glycollate
`hexanoate, octanoate, decanoate, oleate, stearate
`pamoate (embonate), polystyrene sulfonate (resinate)
`Cations
`triethylamine, ethanolamine, triethanolamine, meglumine, ethylenediamine, choline
`procaine, benzathine
`sodium, potassium, calcium, magnesium, zinc
`arginine, lysine, histidine
`
`a Based on data from various sources.9- 11 b Methane sulfonate. C Ethane sulfonate. d 2-Hydroxyethane sulfonate. C Toluene sulfonate. fNaphthalene sulfonate. g Benzene
`sulfonate.
`
`of the group and that of its counterion, especially when the
`drug substance is a particularly weak acid or base. Occasion(cid:173)
`ally, exceptions may be found where a salt has an acceptable
`stability, despite there being a smaller difference in the pKa
`values.
`A microplate technique has been developed for the
`screening of salts; this involves dissolving approximately 50
`mg of sample in a suitable, volatile solvent and adding a
`fixed volume of this solution, containing about 0.5 mg of
`sample, into each microplate well. Concentrated solutions
`of each potential counterion in equimolar propOliion, or other
`appropriate stoichiometric ratio, are prepared and a few
`microlitres of each is added sequentially to each well. Thus,
`all of the wells in line 1 (x-direction) will contain the same
`combination of sample and counterion 1; all of the wells in
`line 2 contain the same combination of sample and counte(cid:173)
`rion 2, etc. Different, potential crystallising solvents can be
`investigated methodically in the y-direction. The wells are
`inspected using an inverted microscope (Leica, Model
`DMIRB) at regular intervals for the appearance of crystals.
`Occasionally, crystallisation can be promoted by evaporation
`of any excess solvent in some wells using a slow stream of
`dry nitrogen gas.
`Once the combinations of counterion and solvent(s) are
`identified, studies at a slightly larger scale (usually 10-50
`mg, occasionally up to 500 mg) can be initiated to confirm
`the suitability and viability of the crystals. These studies can
`help identify problems with low melting points, determined
`by hot-stage microscopy, and hygroscopicity, if processed
`on a suitable apparatus (e.g., Dynamic Vapour Sorption
`Analyser, model DVS-l, Surface Measurement Systems
`Ltd.). Frequently these studies can also give preliminary
`information on the existence of solvates and hydrates,
`especially if differential scanning calorimetry (DSC, Mettler
`Toledo DSC, model 820), thermal gravimetric analysis
`(TGA, Mettler Toledo TGA, model 850) and hot-stage
`microscopy are also used in the evaluation process.
`In parallel with these studies, a preliminary high perfor(cid:173)
`mance liquid chromatographic (HPLC) method is quickly
`developed to give an estimate of the purity of the sample,
`whilst infrared and other spectroscopic techniques may be
`
`428
`
`Vol. 4, No.5, 2000 I Organic Process Research & Development
`
`used to define the salt and the stoichiometry. Knowledge of
`the approximate purity is important at this stage as the
`presence of high levels of some impurities can often hinder
`crystallisation or alter the polymorphic form obtained.
`Therefore, from these preliminary, small-scale studies, a
`range of potential salt formers and recrysallisation solvents
`can be quickly identified. Following further scale-up to gram
`quantities, more comprehensive data can be obtained to
`evaluate their suitability for use in formulations.
`
`Choice of the Salt Former
`Although the choice of salt is governed largely by the
`acidity or basicity of the ionisable group, safety of the
`counterion, drug indications, route of administration and the
`intended dosage form must also be considered. Toxicological
`and pharmacological implications of the selected salt former
`must be considered as well as the effects of the parent drug.
`Salt formers can be subdivided into a number of categories,
`depending upon their functionality and purpose. Some of the
`most frequently used examples are listed in Table 1.
`The vast majority of salts are developed to enhance the
`aqueous solubility of drug substances. For weakly basic drug
`substances, salts of an inorganic acid (e.g., hydrochlOlide,
`sulphate, or phosphate), a sulphonic acid (mesylate or
`isethionate), a carboxylic acid (acetate, maleate or fumarate),
`a hydroxyacid (citrate or tartrate), or possibly an amino acid
`(arginine or lysine) could be considered. Hydrochloride salts
`have often been the first choice for weakly basic drugs, since
`as a consequence of the low counterion pKa, salts can nearly
`always be formed, and recrystallisation from organic solvents
`is normally straightforward. However, the potential disad(cid:173)
`vantages of hydrochloride salts may include unacceptably
`high acidity in formulations (e.g., parenteral products), the
`risk of corrosion, less than optimal solubility due to the risk
`of salting out and the potential for poor stability if the drug
`is acid labile and hygroscopic.2
`Occasionally, salts may be also prepared to decrease drug
`substance solubility for use in suspension formulations where
`very low solubility is necessary to prevent "Ostwald ripen(cid:173)
`ing", for taste-masking, or to prepare an extended release
`product. Embonate salts have been used in suspension
`
`Apotex Exhibit 1015.004
`
`

`

`Table 2. a Preformulation studies that are normally considered for comparison of salt forms and parent compound for oral
`dosage forms
`
`test
`
`suitable techniques
`
`comments
`
`dissociation constant and
`basic physico-chemical
`properties
`melting point
`
`aqueous solubility
`
`pH of solution
`
`cosolvent solubility
`
`common ion effect on solubility
`
`hygroscopicity
`
`potentiometry, solubility,
`UV spectroscopy
`
`capillary m.pt., hot stage microscopy,
`differential scanning calorimetry
`overnight equilibration at 25 DC; analysis
`by UV spectroscopy or HPLC
`
`overnight equilibration at 25 DC, analysis
`by UV spectroscopy or HPLC
`
`overnight equilibration at 25 DC
`in suitable media and analysis
`by UV spectroscopy or HPLC
`use DVS apparatus or expose
`to various RH values and
`measure weight gain after 1 week
`
`intrinsic dissolution rate
`
`use Wood's apparatus 14
`
`crystal shape and appearance
`
`SEM or optical microscopy
`
`particle size
`polymorphismJpseudopolymorphism
`powder properties
`stability
`
`SEM and laser diffraction
`recrystallizations, HSM, DSC, TGA
`bulk density measurement
`various
`
`determine pKa for parent drug
`
`perform on each salt and
`compare to parent
`Perform on each salt and
`compare to parent
`Examine pH of saturated solution
`if quantities permit.
`Determine solubilities in ethanol,
`poly(ethylene glycol), propylene glycol
`and glycerol and compare to parent.
`compare solubility in demineralized
`water with 1.2% NaCI for salts and parent
`
`perform at 53, 93, and 97% RH,
`and other values of interest;
`assign hygroscopicity
`classification to each salt13
`compare dissolution rates at various pHs
`(can provide data on wettability)
`Compare crystal habits and
`levels of agglomeration
`Examine particle size distributions.
`preliminary exploration
`determine Can's compressibility index
`perform on parent drug and undertake
`preliminary tests on appropriate salts
`
`formulations to increase the duration of action (e.g., chlor(cid:173)
`promazine embonate). On some occasions, the selection of
`a salt with only modest aqueous solubility may be more
`suitable for use in tablet products prepared by wet granulation
`since the use of highly soluble salts can be detrimental to
`the granulation process. Depending on the dose required,
`aqueous solubilities in the range 0.1-1.0 mg/mL will
`normally be sufficient to satisfy the dissolution requirements
`for standard, solid, oral dosage forms of drugs with good to
`moderate potency. However, for parenteral solution products,
`higher solubilities, perhaps 10 mg/mL or greater, depending
`on the required dose and dose volume, may be required. For
`parenteral formulations, the pH of solution (normally within
`an acceptable range of 3-10 for intravenous solution) should
`be monitored to help ensure that the formulation will be well
`tolerated.
`Salts are also frequently prepared for the reasons other
`than solubility modification; it is frequently necessary to
`prepare a specific salt to either achieve adequate physical
`stability or for taste masking (e.g., dextropropoxyphene
`napsylate suspension). Manipulation of drug substance
`solubility by selection of salts may also be employed to
`modify the pharmacokinetic profile of the drug (e.g.,
`benzathine penicillin and insulin zinc complexes used in
`parenteral formulations). Salt formation may be alsoadvan(cid:173)
`tageous where the melting point of the active moiety is low,
`and it is necessary to mill or micronise the active ingredient
`to achieve adequate homogeneity. A suitably stable salt may
`have a melting point that is 50-100°C higher than the free
`acid or free base. Also, being more ionic, the crystals are
`
`likely to be less plastic and more easily deformed by brittle
`fracture.
`
`Scale-up of the Formation of Salts
`The information from the preliminalY crystallisation
`studies is communicated to the Process Chemistry group,
`who by this time will have started their investigations into
`possible manufacturing routes for each of the candidates
`remaining. At this stage in the development process, Process
`Chemistry usually aim to quickly manufacture 50-200 g of
`the one or two candidates that may remain to progress them
`towards initial clinical evaluation. The manufacturing route
`may be the same as used by the Discovery Chemistry group
`but usually is significantly different. The aims of both the
`Process Chemistry and Preformulation groups for the fol(cid:173)
`lowing 12-18 months is to collaborate extensively to ensure
`that, for the chosen candidate, there will be a viable synthetic
`route to the chosen form of the drug substance.
`A significant portion of this batch is destined for the
`preparation of 3-4 g of each of the salts that were thought
`to be viable from the smaller-scale studies. A similar sized
`portion of the free base/acid is also taken for comparison
`purposes. The combination of individual studies undertaken
`on each of these 3-4 g portions varies depending on the
`type(s) of dosage form ultimately required for marketing.
`Occasionally, it may be necessary to undertake a pharma(cid:173)
`cokinetic evaluation of each salt in comparison with the free
`acid/base. The dosage forms most commonly used for the
`drug substances encountered during preliminary clinical
`investigations are tablets/capsules, inhalation dosage forms
`and injections.
`
`Vol. 4, No.5, 2000 / Organic Process Research & Development
`
`429
`
`Apotex Exhibit 1015.005
`
`

`

`Table 3. Tests to be considered for the evaluation of
`candidate salts
`
`test to be considered
`
`amount required, mg
`
`Structural Analysis
`
`mass spectroscopya
`lHNMRa
`13CNMRa
`Ir spectrum
`UV spectrum
`fluorescence spectruma
`elemental analysis
`Physicochemical Properties
`
`melting range
`pKaa
`Clog Pllog P a
`preliminary polymorphism study
`X-ray diffraction
`aqueous solubilityb
`pH - solubility profile
`cosolvent solubilitiesC
`propellant solubilityd
`
`Physical Properties
`
`hygroscopicity
`microscopy (SEMIoptica1)
`particle size (Malvern)
`size reduction (sonication)
`Impurities (hplc)
`
`related substancesa
`degradation productsa
`chiral puritya
`
`Stability Studies
`stability to hydrolysis (pH 2, 7, lOy
`stability to oxidation (peroxide/peracidY
`stability to photolysisa
`
`1
`5
`25
`1
`1
`1
`10
`
`2
`5
`5
`200-500
`20
`100
`500
`300
`500
`
`20
`10
`100
`300
`
`10
`10
`10
`
`15
`15
`15
`
`a Determined on free acidlbase only. b Would include solubility in saline, 5%
`dextrose and some buffers C Also solubilities in complexing agents/surfactant
`systems where appropriate d Propellants and propellant/cosolvent systems for
`inhalation dosage forms.
`
`Tables 2 and 3 show the types of tests nonnally chosen,
`the information that they can produce and the amount of
`sample nonnally required for these common dosage forms.
`
`What to Develop: Salt or Free Acid/Base?
`The results obtained from each of these tests are tabulated
`for the free acidlbase, together with each of the salts, and
`discussed in detail between the Formulation Scientists,
`Preformulation Analysts, Physical Chemists, Process Chem(cid:173)
`ists, and occasionally Pharmacokineticists. The Prefonnu~
`lation Scientists assess the relative merits of each fonn for
`use in the proposed clinical formulations and whether the
`properties such as solubility are adequate to give the high
`concentrations required in the various pre-clinical formula(cid:173)
`tions. Process Chemistry need to assess the likely yield of
`each salt, as salt formation creates an additional step in the
`manufacturing process. Usually, the decision-making process
`results in the proposal of a single salt for further study,
`although occasionally it is seen that none of the salts have
`optimum properties, and two different salts can be proposed
`for in-depth study. Also, it is occasionally found that the
`overall properties of the free acidlbase are much better than
`any of the salts. This occurs more frequently where the
`
`430
`
`Vol. 4, No.5, 2000 I Organic Process Research & Development
`
`candidate has a low pKa value and the resulting salts are
`less stable than required or when the salts are particularly
`hygroscopic or when they exhibit complex polymorphism!
`pseudopolymorphism (hydration or solvation).
`These relatively simple investigations give much useful
`information very quickly; it should be noted, however, that
`the preliminary polymorphism study is far from the in-depth
`study that is always undertaken later. This preliminary study
`uses a range of protic and aprotic solvents of widely differing
`polarity and will normally show the presence of a stable
`hydrate or solvate.
`Once a decision is agreed upon within the group, a
`document that gives a precis of the discussions and the basis
`for the proposal is nonnally drafted for agreement by senior
`management. Examples of these salt selection studies are
`given below:
`
`Example No.1 (RPR 111423)
`RPR 111423 is a candidate drug substance that has been
`evaluated for the treatment of symptoms related to infection
`by AIDS. It is a crystalline, very weak base with a pKa at
`4.25. A comprehensive screening of possible salts demon(cid:173)
`strated only a monohydrochloride (RPR 111423A) and a
`mesylate (RPR 111423B) could be isolated as clystalline
`solids.
`It was decided that the free base should be taken through
`the simple evaluation process in comparison with these two
`salts. It was expected that the drug substance could be
`required in the form of tablets or capsules, with an injection
`fonn needed for some pre-clinical studies and for the
`determination of absolute bioavailability in man. Because
`of its high activity in screening studies, there was a possibility
`that very low dose oral formulations might be needed. This
`may require micronised drug substance to enable content
`uniformity requirements to be met; this micronised material
`would also be expected to enhance dissolution.
`The results from the relatively simple studies undertaken
`are given in Table 4. The two salts clearly demonstrated the
`predictable problems associated with a relatively low pKa
`value; the salts were quite weak and dissociated to liberate
`the free base in media with pH values below the pKa. The
`very low solubility of the free base resulted in immediate
`precipitation following dissociation. There was clear evidence
`for multiple polymorphism for each of the salts, and
`establishing the existence of a stable polymorph, or a suitable
`pseudopolymorph, may have been necessary before a deci(cid:173)
`sion could be made on which of the two salts could be
`developed further.
`The corresponding results for the free base indicated that
`it appeared to be the better candidate; it showed no evidence
`of polymorphism, and it was not hygroscopic. The two major
`areas that required further investigation were whether it had
`sufficient solubility in gastrointestinal media and whether it
`could be micronised. Studies performed on samples of drug
`substance and on simple capsule formulations demonstrated
`that the dissolution rates of micronised free base were
`equivalent or superior to those of the salts under the same
`conditions.
`
`Apotex Exhibit 1015.006
`
`

`

`pale yellow, highly
`agglomerated powder
`2 x 1
`(microcrystalline laths)
`242
`at least four polymorphs detected;
`metastable forms revert to
`original on standing
`
`loss of Hel detected
`at 110-120 DC
`at 25 DC
`
`at 37 DC
`
`25.7
`2.51
`0.05
`0.01
`0.01
`0.36
`
`2.43
`
`28.2
`4.58
`0.13
`0.02
`0.02
`0.99
`
`result for
`RPR 111423B (mesylate)
`
`cream to pale yellow, highly
`agglomerated powder
`7 x I
`(microcrystalline laths)
`210
`at least six polymorphs detected;
`phase changes detected on
`grinding or micronisation;
`reverts to original form on heating
`nothing detected
`
`at 25 DC
`
`at 37 DC
`
`131.4
`6.11
`0.01
`0.03
`0.01
`0.33
`
`2.74
`
`204.1
`8.91
`0.02
`0.34
`0.02
`0.50
`
`appearance
`
`particle size
`by microscopy, !lm
`melting range, DC
`preliminary
`polymorphism study
`
`off-white to cream,
`crystalline powder
`10-100 (large
`rhombic crystals)
`241-244
`no other form detected
`
`other thermal behavior
`
`nothing detected
`
`at 25 DC
`
`at 37 DC
`
`11.6
`0.71
`0.03
`0.01
`0.01
`0.01
`
`6.50
`
`14.7
`0.89
`0.05
`0.02
`0.02
`0.02
`
`aqueous solubility,
`mg/mL
`- at pH 1
`- at pH 2
`- at pH 4
`- at pH 6
`- at pH 6,8
`- in demineralized water
`pH of saturated
`solution, at 20 DC,
`in water
`addition of
`water to concentrate
`- at pH 2
`- at pH 4
`hygroscopicity
`(hygrostat for 14 days)
`
`Table 4. Comparison of some simple properties of RPR111423 and its two salts
`result for
`RPR 111423A (hydrochloride)
`
`result for
`RPR 111423 (base)
`
`test
`
`no changes detected
`no changes detected
`non-hygroscopic
`<0.2%w/w water
`uptake at any RH
`
`some precipitation of free base
`extensive precipitation of free base
`slightly hygroscopic
`2.3% w/w uptake at 53% RH
`22% w/w uptake at 97% RH
`
`some precipitation of free base
`extensive precipitation of free base
`moderately hygroscopic
`3.7% w/w uptake at 53% RH
`32% w/