Salts of an anti-migraine indole derivative

The present invention relates to hydrobromide salts of 3-(N-methyl-2(R)-pyrrolidinylmethyl)-5-(2-phenylsulphonylethyl)-1H-indole having the formula (I): ##STR1##

The present invention relates to hydrobromide salts of 
3-(N-methyl-2(R)-pyrrolidinylmethyl)-5-(2-phenylsulphonylethyl)-1H-indole 
having the formula (I): 
##STR2## 
In a preferred aspect, the invention relates to a particular polymorphic 
form, hereinafter referred to as the .alpha.-form, of the hydrobromide 
salt identified above. In addition it relates to an intermediate 
polymorphic form, hereinafter referred to as the .beta.-form, of the said 
hydrobromide salt, to processes for the preparation of the .alpha.- and 
.beta.- forms, to pharmaceutical compositions containing the .alpha.-form, 
and to uses of the .alpha.-form in medicine. 
WO-A-92106973 relates to a series of 3,5-disubstituted indoles and 
pharmaceutically acceptable salts thereof useful in the treatment of 
migraine and other disorders. Examples cited therein of such salts are the 
hydrochloride, hydrobromide, hydroiodide, nitrate, sulphate or bisulphate, 
phosphate or acid phosphate, acetate, lactate, citrate or acid citrate, 
tartrate or bitartrate, succinate, maleate, fumarate, gluconate, 
saccharate, benzoate, methanesulphonate and pamoate. Specifically 
disclosed therein is 
3-(N-methyl-2(R)-pyrrolidinylmethyl)-5-(2-phenylsulphonylethyl)-1H-indole 
and its hemisuccinate salt, the latter being characterised as a 
noncrystalline foam. Further studies have confirmed that this salt is 
unsuitable for pharmaceutical formulation, as numerous attempts to obtain 
it in a form which has the properties required for formulation have been 
unsuccessful. 
Thus the problem addressed by the present invention is the provision of a 
pharmaceutically acceptable salt of 
3-(N-methyl-2(R)-pyrrolidinylmethyl)-5-(2-phenylsulphonylethyl)-1H-indole 
which can be efficiently processed to provide stable and effective 
formulations of the drug, in particular solid and compressible dosage 
forms. Such dosage forms include conventional-release oral tablets, 
controlled-release (matrix) tablets, fast-dissolving tablets (e.g. 
freeze-dried), sublingual tablets, buccal tablets, oral powder- and 
granule-filled capsules, powders for reconstituted suspensions, 
conventional and controlled-release multiparticulate systems filled into 
capsules or compressed into tablets, lozenges, dragees, suppositories, 
pessaries, solid implants, lyophile plugs, nanoparticles and 
microparticles and powder for suspension and nasal delivery, and dry 
inhalation systems. 
Important criteria to be satisfied are, inter alia, that the selected salt 
should be crystalline, of suitable melting point, non-hygroscopic, 
compressible and possess solid-state stability, coupled with acceptable 
solubility and dissolution behaviour. 
This problem has been solved by the surprising finding of a novel 
.alpha.-form of the hydrobromide salt of formula (I) which meets the above 
requirements; thus it is pre-eminently suitable for providing 
pharmaceutical formulations in solid dosage form, in particular for oral, 
buccal and sublingual administration. 
The first step in approaching the solution to the problem was the 
generation of an acid addition salt of the monoacidic base, 
3-(N-methyl-2(R)-pyrrolidinylmethyl)-5-(2-phenylsulphonylethyl)-1H-indole, 
which is both crystalline and of high enough melting point (&gt;ca. 
130.degree. C.) to have the potential to undergo pharmaceutical processing 
during solid dosage form manufacture and compaction. 
Attempts were made to obtain a suitable form of the following salts: 
hydrochloride, hydrobromide, hemisulphate, bisulphate, nitrate, acid 
phosphate, phosphate, methanesulphonate, benzenesulphonate, 
p-toluenesulphonate, (+)-camphorsulphonate, acetate, benzoate, citrate, 
hemifumarate, fumarate, hemimaleate, maleate, hemisuccinate, succinate, 
hemi-L-tartrate, L-tartrate, hemi-D-tartrate, D-tartrate, L-lactate, 
(R)-(-)-mandelate, hippurate, hemiphthalate, phthalate and 
hemiterephthalate. 
Of these thirty possible salts, only four could be obtained as crystalline 
solids, namely the hemisulphate, hydrochloride, hydrobromide and 
benzenesulphonate; the remainder were obtained as non-crystalline/low or 
non-sharp melting/sticky solids, gums, glasses, froths, resins or oils. 
Moreover, of the four crystalline salts, the benzenesulphonate proved to 
have an insufficiently high melting point (m.p.) of 74-75.degree. C. Thus 
only the hemisulphate, hydrochloride and hydrobromide salts were 
progressed to more detailed studies. 
Hemisulphate Salt 
The hemisulphate salt initially isolated (m.p. 145-147.degree. C.), 
designated the .beta.-form, does not show a clean single-melting endotherm 
when examined by differential scanning calorimetry (DSC) but rather a 
complex trace indicative of polymorphic transition. Indeed, this 
.beta.-form is very hygroscopic at relative humidities (RH) higher than 
50% and, under certain conditions, water uptake can cause polymorphic 
conversion to an alternative form, designated the .alpha.-form, of m.p. 
185.degree. C., or even degradation. Furthermore, the .beta.-form 
undergoes a colour change on compression and causes punch-filming during 
tabletting and thus, for a variety of reasons, its physicochemical 
properties render it unsuitable for the development of solid dosage forms. 
Whilst the .alpha.-form of the hemisulphate salt does not display solid 
state instability associated with water uptake, it is extremely 
hygroscopic nevertheless and therefore also unsuitable for development 
because of consequential difficulties with variable flow properties, and 
bulk and dosage form instability which precludes, inter alia, accurate 
assignment of drug activity. 
Hydrochloride Salt 
Depending on the solvent used as reaction medium and for crystallisation, 
either of two forms of the hydrochloride salt can be obtained. The first 
of these to be isolated and characterised, designated the .beta.-form, of 
m.p. 125-129.degree. C. (broad endotherm at 135.degree. C. at a scan rate 
of 20.degree. C./min. by DSC, but no dehydration endotherms apparent), was 
found to have a water content of 4.42% (1.08 mol) by Karl Fischer 
titrimetry (KFT). However, although hygroscopicity studies revealed that 
the .beta.-form does not display solid state instability, it was excluded 
from further development by its behaviour during compression studies in 
which melting and sticking of the disk to the punches were observed, thus 
reinforcing the requirement for a higher melting solid. 
The alternative hydrochloride salt, designated the .alpha.-form, showed a 
major, sharp endotherm at 165.degree. C. by DSC (scan rate 20.degree. 
C./min.). Determination of its hygroscopicity profile revealed that after 
seven days at a temperature (T) of 40.degree. C. and RH of 75%, unlike the 
.beta.-form, a significant amount of water had been taken up. This water 
uptake was found to be associated with changes in the DSC trace which 
demonstrated that, at least under these humidity conditions, the anhydrous 
.alpha.-form converts to the hydrated .beta.-form. Thus pharmaceutical 
development of the .alpha.-form is also precluded by inadequate physical 
stability. 
Hydrobromide Salt 
The hydrobromide salt is also isolable in one of two forms, depending on 
the preparative conditions employed. The lower melting form, designated 
the .beta.-form, was found not to be a viable option for the development 
of a solid dosage form because, when attempts are made to improve its 
quality, it undergoes polymorphic conversion to a higher melting form, 
designated the .alpha.-form. 
However, by contrast, the novel .alpha.-form of the hydrobromide salt of 
formula (I) was found to be unique in unexpectedly possessing the 
combination of properties required to enable the efficient development of 
solid dosage forms, namely those of crystallinity, sufficiently high m.p., 
lack of hygroscopicity, solid-state stability, compressibility and lack of 
polymorphic conversion, together with satisfactory solubility and 
dissolution rate profiles. 
The present invention therefore provides a crystalline, polymorphic 
.alpha.-form of a hydrobromide salt of formula (I), whose infra-red (IR) 
spectrum as a mull in nujol shows significant absorption bands at 
.nu.=3371, 3293, 2713, 2524, 1419, 1343, 1307, 1264, 1151, 1086, 1020, 
1008, 999, 922, 900, 805, 758, 740, 728, 689, 672, 652, 640, 598, 581, 
573, 531, 498, 465, 457, 443, 428, 422, 414 and 399 cm.sup.-1. 
The .alpha.-form is further characterised by its powder X-ray diffraction 
(PXRD) pattern obtained using copper radiation filtered with a graphite 
monochromator (.lambda.=0.15405 nm) which shows main peaks at 9.7, 10.7, 
15.9, 16.5, 17.8, 18.3, 19.3, 19.8, 20.1, 21.2, 24.4, 25.5, 25.8, 26.7, 
27.6 and 29.4 degrees 2.theta.. 
The .alpha.-form is yet further characterised by its differential scanning 
calorimetry (DSC) trace which shows a sharp endotherm at 176.5.degree. C. 
at a scan rate of 20 .degree. C./min. 
The invention also provides a crystalline, polymorphic .beta.-form of a 
hydrobromide salt of formula (I), which can be used as an intermediate in 
the preparation of the .alpha.-form. Its IR spectrum as a mull in nujol 
shows significant absorption bands at .nu.=3239, 2672, 2656, 2632, 1409, 
1366, 1351, 1334, 1303, 1293, 1152, 1138, 1122, 1098, 1086, 791, 771, 746, 
688, 634, 557, 528, 484, 476, 469, 463, 455, 432, 424, 413 and 401 
cm.sup.-1. 
The .beta.-form is further characterised by its PXRD pattern obtained using 
copper radiation filtered with a graphite monochromator (.lambda.=0.15405 
nm) which shows main peaks at 11.0, 17.2, 19.2, 20.1, 21.6, 22.6, 23.6 and 
24.8 degrees 2.theta.. 
The .beta.-form is yet further characterised by its DSC trace which shows a 
sharp endotherm at 154.8.degree. C. at a scan rate of 20.degree. C./min. 
The invention further provides processes for the preparation of the 
.alpha.-form of a compound of formula (I), as illustrated by the 
following. 
(A) Treatment of a solution of 
3-(N-methyl-2(R)-pyrrolidinylmethyl)-5-(2-phenylsulphonylethyl)-1H-indole 
in a suitable solvent, preferably acetone, at room temperature, with an 
aqueous solution of hydrogen bromide, followed by crystallisation of the 
isolated crude oil from a suitable solvent, preferably 2-propanol, affords 
the .alpha.-form of the required hydrobromide salt. 
(B) Treatment of a solution of 
3-(N-methyl-2(R)-pyrrolidinylmethyl)-5-(2-phenylsulphonylethyl)-1H-indole 
in a suitable solvent, preferably acetone or an ether solvent such as 
tetrahydrofuran or 1,2-dimethoxyethane, more preferably 
1,2-dimethoxyethane, at from 0 to 10.degree. C., with an aqueous solution 
of hydrogen bromide, furnishes the .beta.-form of the required 
hydrobromide salt. 
Crystallisation of the .beta.-form from a suitable solvent, preferably 
aqueous acetone, followed by slurrying of the resulting mixture, gives the 
desired .alpha.-form. 
(C) Treatment of a solution of 
3-(N-methyl-2(R)-pyrrolidinylmethyl)-5-(2-phenylsulphonylethyl)-1H-indole 
in a suitable solvent, preferably acetone, at from 0 to 5.degree. C. with 
an aqueous solution of hydrogen bromide and then slurrying of the reaction 
mixture, optionally followed by heating under reflux, cooling and further 
slurrying, provides the required .alpha.-form. 
As previously mentioned, WO-A-92/06973 discloses 
3-(N-methyl-2(R)-pyrrolidinylmethyl)-5-(2-phenylsulphonylethyl)-1H-indole 
and pharmaceutically acceptable salts thereof for the treatment of 
migraine and other disorders (incorporated herein by reference). Thus the 
present invention also relates to pharmaceutical compositions containing 
the .alpha.-form of the hydrobromide salt thereof, uses of the 
.alpha.-form as a medicament and for the manufacture of a medicament for 
the treatment of migraine and said other disorders, and a method of 
treating a mammal having migraine or any of said other disorders with the 
.alpha.-form. 
The in vitro evaluation of the peripheral 5-HT.sub.1 receptor agonist 
activity of the .alpha.-form can be carried out by testing the extent to 
which it mimics sumatriptan in contracting the isolated dog saphenous vein 
strip (P. P. A. Humphrey et al., Brit. J. Pharmacol., 1988, 94, 1123). 
This effect can be blocked by methiothepin, a known 5-HT antagonist. 
Sumatriptan is known to be useful in the treatment of migraine and 
produces a selective increase in carotid vascular resistance in the 
anaesthetized dog and a consequent decrease in carotid arterial blood 
flow. It has been suggested (W. Feniuk et al., Brit. J. Pharmacol., 1989, 
96, 83) that this is the basis of its efficacy. 
The central 5-HT, agonist activity of the .alpha.-form can be measured in 
in vitro receptor binding assays as described for the 5-HT.sub.1A 
receptor, using rat cortex as the receptor source and [.sup.3 H]8-OH-DPAT 
as the radioligand (D. Hoyer et al., Europ. J. Pharmacol., 1985, 118, 13), 
and as described for the 5-HT.sub.1D receptor, using bovine caudate as the 
receptor source and [.sup.3 H]5-HT as the radioligand (R. E. Heuring and 
S. J. Peroutka, J. Neuroscience, 1987, 7, 894). 
In therapy, the .alpha.-form of the hydrobromide salt of formula (I) can be 
administered alone, but will generally be administered in admixture with 
pharmaceutically acceptable excipients, including glidants, disintegrants 
and lubricants, selected with regard to the intended route of 
administration and standard pharmaceutical practice. In particular, it may 
be administered orally in the form of tablets, dragees or lozenges 
containing excipients such as starch or lactose, or in capsules, ovules or 
implants, either alone or in admixture with excipients. For buccal or 
sublingual administration, it may be administered in the form of tablets, 
dragees or lozenges which can be formulated in a conventional manner. 
For oral, buccal or sublingual administration to patients, the daily dosage 
level of the .alpha.-form of the salt of formula (1) will be from 0.01 mg 
to 20 mg/Kg (in single or divided doses). Thus tablets or capsules will 
contain from 0.5 mg to 0.5 g of active compound for administration singly, 
or two or more at a time, as appropriate. The physician in any event will 
determine the actual dosage which will be most suitable for an individual 
patient and it will vary with the age, weight and response of the 
particular patient. The above dosages are exemplary of the average case; 
there can, of course, be individual instances where higher or lower dosage 
ranges are merited, and such are within the scope of this invention. 
Thus the invention provides a pharmaceutical composition comprising the 
.alpha.-form of a compound of formula (I) together with a pharmaceutically 
acceptable diluent or carrier. 
The invention also provides the .alpha.-form of a compound of formula (I), 
or a pharmaceutical composition thereof, for use as a medicament. 
The invention further includes the use of the .alpha.-form of a compound of 
formula (I), or a pharmaceutical composition thereof, both for the 
manufacture of a medicament for the curative or prophylactic treatment of 
migraine or an associated condition such as cluster headache, chronic 
paroxysmal hemicrania or headache associated with a vascular disorder, or 
of depression, anxiety, an eating disorder, obesity, drug abuse, 
hypertension or emesis, and also for the manufacture of a medicament for 
the curative or prophylactic treatment of a medical condition for which a 
selective agonist of 5-HT.sub.1 receptors is indicated. 
In a further aspect, the invention provides both a method of treating a 
human being to cure or prevent migraine or an associated condition such as 
cluster headache, chronic paroxysmal hemicrania or headache associated 
with a vascular disorder, or depression, anxiety, an eating disorder, 
obesity, drug abuse, hypertension or emesis, and also a method of treating 
a human being to cure or prevent a medical condition for which a selective 
agonist of 5-HT.sub.1 receptors is indicated, which comprises 
administering to said human being an effective amount of the .alpha.-form 
of a compound of formula (I), or a pharmaceutical composition thereof.

The preparation of the .alpha.-form of the hydrobromide salt of formula (I) 
and pharmaceutical compositions thereof are illustrated by the following 
Examples. 
Room temperature means 20 to 25.degree. C. and m.p. means melting point. 
IR means infra red, PXRD means powder X-ray diffraction, DSC means 
differential scanning calorimetry, T means temperature, RH means relative 
humidity, HPLC means high performance liquid chromatography, KFT means 
Karl Fischer titrimetry. 
EXAMPLE 1 
3-(N-Methyl-2(R)-pyrrolidinylmethyl)-5-(2-phenylsulphonylethyl)-1H-indole 
hydrobromide, .alpha.-form 
49% w/w Hydrobromic acid (432 mg, 0.3 ml, 2.6 mmol) was added to a stirred 
solution of 
3-(N-methyl-2(R)-pyrrolidinylmethyl)-5-(2-phenylsulphonylethyl)-1H-indole 
(1.0 g, 2.6 mmol) in acetone (10 ml) at room temperature. After a further 
15 minutes, the reaction mixture was evaporated under reduced pressure to 
give a yellow liquid; the residual water therein was then azeotropically 
removed using 2-propanol. The resulting cloudy, yellowish oil (1.55 g) was 
triturated with ether and then dissolved in hot 2-propanol (25 ml); this 
solution, on cooling, provided the title compound (1.13 g) as a pale 
yellow crystalline solid after filtration, washing with 2-propanol and 
drying In vacuo, m.p. 165-170.degree. C. Found: C,56.67; H,5.78; N,5.82. 
C.sub.22 H.sub.26 N.sub.2 O.sub.2 S; HBr requires C,57.02; H,5.87; 
N,6.04%. 
EXAMPLE 2 
3-(N-Methyl-2(R)-pyrrolidinylmethyl)-5-(2-phenylsulphonylethyl)-1H-indole 
hydrobromide, .alpha.-form 
(a) 
3-(N-Methyl-2(R)-pyrrolidinylmethyl)-5-(2-phenylsulphonylethyl)-1H-indole 
hydrobromide, .beta.-form 
49% w/w Hydrobromic acid (27.86 ml, 0.25 mol) was added over 1 hour to a 
stirred solution of 
3-(N-methyl-2(R)-pyrrolidinylmethyl)-5-(2-phenylsulphonylethyl)-1H-indole 
(92.86 g, 0.24 mol) in 1,2-dimethoxyethane (2.08 1) at about 5.degree. C. 
The cooling bath was removed and the resulting slurry was allowed to 
granulate by stirring at room temperature for a further 18 hours. 
Filtration, followed by washing with 1,2-dimethoxyethane and drying in 
vacuo, afforded the required product (97.9 g) as a solid, m.p. 
150-151.degree. C. Found: C,56.77; H,5.87; N,5.85. C.sub.22 H.sub.26 
N.sub.2 O.sub.2 S; HBr requires C,57.02; H,5.87; N,6.04%. 
(b) 
A stirred mixture of the previous product (20 g), acetone (140 ml) and 
water (6 ml) was heated under reflux until complete dissolution of the 
.beta.-form was achieved. The solution was then allowed to cool to room 
temperature, stirred for 1 hour and then acetone (460 ml) added to the 
resulting slurry. After a further 1 hour, the slurry was cooled to 
0-5.degree. C. and stirring continued for up to 18 hours. The colourless, 
crystalline solid was collected by filtration, washed with acetone and 
dried in vacuo to furnish the title compound (13.22 g), which was 
identical to that of Example 1. 
EXAMPLE 3 
3-(N-Methyl-2(R)-pyrrolidinylmethyl)-5-(2-phenylsulphonylethyl)-1H-indole 
hydrobromide, .alpha.-form 
62% w/w Hydrobromic acid (1.706 g, 13.07 mmol) was added over 1 hour to a 
stirred solution of 
3-(N-methyl-2(R)-pyrrolidinylmethyl)-5-(2-phenylsulphonylethyl)-1H-indole 
(5.0 g, 13.07 mmol) in acetone (112 ml) at 0-5.degree. C. After slurrying 
of the reaction mixture at 0-5.degree. C. for 3 hours, heating under 
reflux for 2 hours was effected followed by cooling to 0-5.degree. C. and 
further slurrying for 1 hour at this temperature. Filtration, followed by 
washing with acetone and drying in vacuo, furnished the title compound 
(5.18 g), which was identical to that of Example 1. 
In Examples 4 to 6, "active ingredient" means the .alpha.-form of the 
hydrobromide salt. 
EXAMPLE 4 
Tablets for Oral Administration 
______________________________________ 
A. Direct Compression 
mg/tablet 
for 50 g mix 
______________________________________ 
Active ingredient 12.12 6.06 g 
Microcrystalline cellulose 25.00 12.50 g 
Ph Eur 
Lactose Ph Eur 60.88 30.44 g 
Croscarmellose sodium NF 1.00 0.50 g 
Magnesium stearate Ph Eur 1.00 0.50 g 
______________________________________ 
The active ingredient is sieved and blended with the other components. The 
resultant mix is compressed into tablets using a rotary tablet press 
(Manesty Betapress) fitted with 6 mm normal concave punches. The resultant 
tablets can be film coated with an appropriate film coating material. 
______________________________________ 
B. Wet Granulation 
mg/tablet 
for 50 g mix 
______________________________________ 
Active ingredient 1.21 0.76 g 
Lactose Ph Eur 56.03 35.02 g 
Maize starch Ph Eur 18.68 11.67 g 
Polyvinylpyrrolidone 1.60 1.00 g 
(2% w/v soln) 
Colloidal anhydrous silica 0.08 0.05 g 
Ph Eur 
Croscarmellose sodium NF 1.60 1.00 g 
Magnesium stearate Ph Eur 0.80 0.50 g 
______________________________________ 
The polyvinylpyrrolidone is dissolved in purified water to an appropriate 
concentration. The active ingredient is sieved and blended with all of the 
other components except the magnesium stearate. Suitable volumes of the 
polyvinylpyrrolidone solution are added and the powders are granulated. 
After drying, the granules are screened and blended with the magnesium 
stearate. The granules are then compressed into tablets using suitable 
diameter punches. 
Tablets of other strengths may be prepared by altering the ratio of active 
ingredient to excipients or the compression weight and using punches to 
suit. 
EXAMPLE 5 
______________________________________ 
Capsules 
mg/capsule 
______________________________________ 
Active ingredient 18.18 
Lactose Ph Eur 208.89 
Maize starch Ph Eur 69.63 
Colloidal anhydrous silica Ph Eur 0.30 
Magnesium stearate Ph Eur 3.00 
Fill weight 300.00 
______________________________________ 
The active ingredient is sieved and blended with the other components. The 
mix is filled into size No 2 hard gelatin capsules using suitable 
machinery. Other doses may be prepared by altering the fill weight and, if 
necessary, changing the capsule size to suit. 
EXAMPLE 6 
______________________________________ 
Sublingual Tablets 
mg/tablet 
for 50 g mix 
______________________________________ 
Active ingredient 1.2 0.750 g 
Lactose Ph Eur 25.0 15.625 g 
Maize starch Ph Eur 25.0 15.625 g 
Mannitol Ph Eur 25.0 15.625 g 
Croscarmellose sodium NF 3.0 1.875 g 
Magnesium stearate Ph Eur 0.8 0.500 g 
______________________________________ 
The active ingredient is sieved through a suitable sieve, blended with the 
excipients and compressed using suitable punches. Tablets of other 
strengths may be prepared by altering either the ratio of active 
ingredients to excipients or the compression weight and using punches to 
suit. 
Characterisation of the Hydrobromide Salt .alpha.- and .beta.-forms by IR, 
PXRD and DSC Analysis 
BRIEF DESCRIPTION OF DRAWINGS 
(a) IR Spectroscopy 
The IR spectra were determined over the wave number (.nu.) range 4000 to 
400.sup.-1 as nujol mulls using a Nicolet 800 FT-IR spectrometer and are 
represented by FIGS. 1A and 1B. For identification of the .nu. of 
significant absorption bands, vide supra. 
(b) PXRD 
The PXRD patterns were obtained using a Siemens D500 diffractometer which 
was operated at 40 kV/30 mA and using copper radiation filtered with a 
graphite monochromator (.lambda.=0.15405nm) and a scintillation counter 
detector. For each form, beam intensity as a function of the angle 
2.theta. was recorded over the range 2.degree. to 45.degree. 2.theta. 
using a step scan mode counting for six seconds at step intervals of 
0.03.degree. 2.theta.. For identification of the main peaks (degree 
2.theta.) seen in each pattern, represented by FIGS. 2A and 2B, vide 
supra. 
(c) DSC 
Samples (ca 5 mg) of each form were analysed using a Perkin-Elmer 7 Series 
thermal analyser at a scanning rate of 20.degree. C. per minute. For 
identification of the respective endotherms, shown in the representative 
DSC thermograms of FIGS. 3A and 3B, vide supra. 
Hygroscopicity/Solid State Stability Studies 
Samples (ca 10 mg) were sieved (250 .mu.m) and then stored at each of the 
following conditions of temperature (T) and relative humidity (RH) for up 
to 4 weeks: 
30.degree. C. at 11, 75 and 90% RH 
and 
40.degree. C. at 11, 75 and 90% RH, 
the required humidities being achieved using the appropriate saturated salt 
solution in a dessicator. Measurements of water content changes were 
conducted by weight analysis using a microbalance and by Karl Fischer 
titrimetry (KFT), and chemical and physical stability evaluation by high 
performance liquid chromatography (HPLC) and DSC. 
HPLC analyses were performed on a LDC isocratic system under the following 
conditions: 
column--Novapak C.sub.18, 5 .mu.m, 15 cm; mobile phase--pH 6.0, 60:40 v/v 
0.02M KH.sub.2 PO.sub.4 (0.5% triethylamine): methanol; detection--UV (254 
nm); flow rate--1.0 ml/min; injection volume--20 .mu.l; sample 0.1 mg/ml 
in mobile phase. 
KFT was performed using a Mitsubishi moisturemeter and ca 10 mg of each 
sample. 
Table 1 shows hygroscopicity results for the .alpha.-form of the 
hydrobromide salt and the .alpha.- and .beta.-forms of the hemisulphate 
salt, expressed as moisture changes determined by % weight change under 
various conditions of T(.degree.C.) and RH(%). 
It can be seen from Table 1 that the .alpha.-form of the hydrobromide salt 
showed relatively stable weights throughout the course of the study, with 
slight loss of moisture at low (11%) RH being observed at both 30 and 
40.degree. C., and these results were corroborated by those obtained by 
KFT analysis. Particularly noteworthy is that little change in its 
moisture content was noted at a RH of 75%, by comparison with the 
significant uptake seen at 40.degree. C. for both the .beta.-form and, 
especially, the .alpha.-form of the hemisulphate salt. Moreover, water 
uptake by the .beta.-form of the hemisulphate salt was accompanied by a 
change in colour of the sample from cream to yellow; although the 
.alpha.-form of the hemisulphate salt absorbed water even more rapidly 
than the .beta.-form, no concomitant colour 
TABLE 1 
______________________________________ 
SALT FORM 
T/RH Week 1 Week 2 Week 3 Week 4 
______________________________________ 
.alpha.-HBr 
30/11 -0.45 -0.51 +0.20 +0.09 
30/75 +0.08 +0.01 +0.17 +0.25 
30/90 +0.53 +0.46 +0.50 +0.49 
40/11 -0.48 +0.58 -0.51 -0.49 
40/75 +0.06 +0.23 0.00 +0.11 
40/90 +0.87 +1.27 +1.16 +1.23 
.beta.-1/2H.sub.2 SO.sub.4 40/75 +1.33 +3.79 +3.38 +1.69 
.alpha.-1/2H.sub.2 SO.sub.4 40/75 +6.0 +4.85 +5.46 +4.04 
______________________________________ 
TABLE 2 
______________________________________ 
(T/RH 40/75) 
SALT FORM Day 5 Week 1 
Week 2 Week 3 Week 4 
______________________________________ 
.beta.-HCl 
ND 0 +0.27 +0.23 +0.19 
.alpha.-HCl +0.56 +0.79 ND ND ND 
______________________________________ 
ND = not determined 
change was evident. As previously mentioned, the hygroscopicity of the 
.beta.-form of the hemisulphate salt leads to polymorphic conversion to 
the .alpha.-form and, eventually, to degradation. 
No change in DSC profile was apparent for the .alpha.-form of the 
hydrobromide salt in the T=40.degree. C./RH=90% samples, whilst HPLC 
analysis confirmed its stability under all of the conditions studied. 
Table 2 shows hygroscopicity results for the .alpha.- and .beta.-forms of 
the hydrochloride salt, expressed as moisture changes determined by % 
weight change at T=40.degree. C./RH=75%. 
The .beta.-form was judged to be non-hygroscopic on the basis of both the 
results displayed in Table 2 and the closely comparable results obtained 
by KFT analysis at week 4, with no solid state instability being detected. 
Although only 1 week of incubation was conducted for the .alpha.-form in 
this study, it is clear that it had picked up a significant amount of 
moisture even by this time-point and that this water uptake was associated 
with changes in the DSC trace which revealed the transformation of the 
.alpha.-form to the .beta.-form under these conditions. 
Compression Studies 
Samples (200 mg) were compressed using a bench IR press (Graseby Specac 
Model 15.011) at 5 tonnes for 1 minute using a 13 mm punch and die set, 
then assessed for colour change and evidence of melting. Further analysis 
(DSC and HPLC) was conducted after grinding of the compact using a mortar 
and pestle. 
For the .alpha.-form of the hydrobromide salt, no changes to the thermogram 
in respect of either melting point or enthalpy of fusion, after either 
compression or grinding, were observed. In addition, there was no evidence 
of a change in sample appearance or punch filming on compaction. 
As previously mentioned, the .beta.-form of the hemisulphate salt undergoes 
a colour change on compression and also causes punch filming on 
compaction, whilst the .beta.-form of the hydrochloride salt melts and 
causes sticking of the disk to the punches during compression, which 
behaviour is unsurprising given the significantly lower m.p. of the 
latter. The .alpha.-form of the hydrochloride salt did not melt on 
compaction. 
Polymorphic Conversion 
DSC was used to determine both the polymorphic conversions of the 
.beta.-forms of the hydrobromide and hemisulphate salts to their 
respective .alpha.-forms, and also the conversion of the .alpha.-form of 
the hydrochloride salt to its .beta.-form which is believed to be an 
anhydrate-hydrate transition. 
No polymorphic transitions of the .alpha.-form of the hydrobromide salt 
were observed under the conditions investigated.