Pharmaceutical compositions for freeze drying

A pharmaceutical composition comprising a nucleotide analogue, mannitol and a modifying additive which is sodium chloride or a polyol which is suitable for freeze drying.

The present invention provides a pharmaceutical composition suitable for 
freeze-drying and a process for the preparation of the composition. 
BACKGROUND OF THE INVENTION 
Freeze drying is a well known process used to prepare storage stable 
formulations of pharmaceutical compounds which otherwise suffer 
degradation when stored in the presence of water, for example, because of 
disproportionation and/or hydrolysis. A typical freeze drying cycle 
consists of four stages. Freezing the composition of the compound to be 
freeze dried, a primary drying cycle which comprises applying a vacuum and 
sufficient heat to sublimate the ice present in the composition, a second 
drying cycle which removes any residual water and then recovery of the 
freeze dried composition. It is an expensive process because it takes a 
long time and because a low temperature and a vacuum are required. A low 
temperature is required because the vacuum needs to be applied at a 
temperature below the eutectic temperature for mixtures of crystalline 
substances or below the glass transition or collapse temperature for 
amorphous mixtures. This is to ensure that the water present is vapourised 
without passing through the liquid state and so that the amorphous 
mixtures do not collapse. A collapsed amorphous mixture is effectively 
useless because it is very difficult to reconstitute and may be unstable. 
To keep costs down it is preferable for the collapse or eutectic 
temperature not to be too low in order that the cooling cost is reduced. A 
higher collapse or eutectic temperature is also advantageous because the 
evaporation is hastened which reduces the length of time the vacuum is 
needed. Compositions suitable for freeze drying have been sought which 
produce a stable product and for which the collapse or eutectic 
temperature is not too low. 
DESCRIPTION OF THE INVENTION 
According to a first aspect of the invention there is provided a 
pharmaceutical composition comprising a nucleotide analogue, mannitol and 
a modifying additive which is sodium chloride or a polyol. 
The invention further provides a pharmaceutical composition in freeze 
dried, spray dried or vacuum dried form and in reconstituted form. 
According to the invention there is further provided a process for the 
preparation of a composition according to the invention which comprises 
mixing the ingredients of the composition, and either freezing them and 
drying the frozen mixture, or spraying them (for example into warm air). 
The use of the combination of mannitol and the modifying additive in the 
compositions of the invention has unexpectedly been found to improve the 
compositions long term stability after freeze drying. Another advantage of 
using such a combination is that vial breakage or cracking during 
freeze-drying is prevented. 
A nucleotide is a compound comprising a purine or pyrimidine base attached 
to a pentosugar wherein one or more of the hydroxy groups of the 
pentosugar are phosphorylated by a mono- or polyphosphate. A nucleotide 
analogue for use in the invention is in general a compound in which one or 
more of the three moieties of which a nucleotide is comprised is modified, 
for example, by attachment of one or more substituents and/or by 
replacement of one or more of the skeletal atoms. 
The nucleotide used in the invention is preferably a nucleotide from WO 
94/18216 , that is to say a compound of formula (I): 
##STR1## 
wherein R.sup.1 and R.sup.2 independently represent hydrogen or halogen, 
R.sup.3 and R.sup.4 independently represent phenyl, or C.sub.1-6 -alkyl 
optionally substituted by one or more substituents selected from OR.sup.5, 
C.sub.1-6 -alkylthio, NR.sup.6 R.sup.7, phenyl, COOR.sup.8 and halogen, 
R.sup.5, R.sup.6, R.sup.7 and R.sup.8 independently represent hydrogen or 
C.sub.1-6 -alkyl, and X represents an acidic moiety, or a pharmaceutically 
acceptable salt thereof. 
Compounds of formula (I) may exist in tautomeric, enantiomeric and 
diastereomeric forms, all of which are included within the scope of the 
definition. 
Pharmaceutically acceptable salts of the compounds of formula (I) include 
alkali metal salts, e.g. sodium and potassium salts; alkaline earth metal 
salts, e.g. calcium and magnesium salts; salts of the Group III elements, 
e.g. aluminium salts; and ammonium salts. Salts with suitable organic 
bases, for example, salts with hydroxylamine; lower alkylamines, e.g. 
methylamine or ethylamine; with substituted lower alkylamines, e.g. 
hydroxysubstituted alkylamines; or with monocyclic nitrogen heterocyclic 
compounds, e.g. piperidine or morpholine; and salts with amino acids, e.g. 
with arginine, lysine etc., or an N-alkyl derivative thereof; or with an 
aminosugar, e.g. N-methyl-D-glucamine or glucosamine. The non-toxic 
physiologically acceptable salts are preferred, although other salts are 
also useful, e.g. in isolating or purifying the product. 
Alkyl groups in the definitions of compounds of formula (I) include 
straight, branched or cyclic, saturated or unsaturated alkyl groups. Aryl 
groups in the definitions of compounds of formula (I) include both 
carbocyclic and heterocyclic groups. The groups may contain rings or 
various numbers of C-atoms and may be fused ring structures. Particular 
carbocyclic aryl groups which may be mentioned are phenyl and naphthyl. 
Heteroaryl groups include nitrogen, oxygen or sulphur heterocycles and may 
contain one or more heteroatoms. Examples of heterocycles containing only 
one heteroatom include pyrrole, furan, thiophen and pyridine. Groups 
containing more than one heteroatom include pyrazole, oxazole, thiazole, 
triazole, oxadiazole, thiadiazole etc. 
Halogens which R.sup.1 and R.sup.2 may represent include F, Cl, Br and I. 
Preferably R.sup.1 and R.sup.2 are the same and more preferably represent 
Cl. 
Preferably R.sup.3 and R.sup.4 represent C.sub.1-6 -alkyl optionally 
substituted by one or more substituents selected from OR.sup.5, C.sub.1-6 
-alkylthio, NR.sup.6 R.sup.7, phenyl, COOR.sup.8 and halogen. Halogens 
with which R.sup.3 and R.sup.4 may be substituted include Cl, Br and I, 
and especially F. 
Particularly preferred are compounds in which R.sup.3 represents C.sub.1-6 
-alkyl optionally substituted by C.sub.1-6 -alkylthio. Particular alkyl 
groups that R.sup.3 may represent include propyl and butyl, and especially 
ethyl. Particular substituted alkyl groups that R.sup.3 may represent 
include 2-(methylthio)ethyl. 
Preferably R.sup.4 represents C.sub.1-6 -alkyl optionally substituted by 
one or more, e.g. three, halogen atoms. Particular groups that R.sup.4 may 
represent include propyl and 3,3,3-trifluoropropyl. 
Acidic moieties which X may represent include Bronsted-Lowry acids, i.e. 
moieties which act as proton donors. The acidic moiety may be mono- or 
poly-acidic. Specific acidic moieties which may be mentioned include 
--P(O)(OH).sub.2, --SO.sub.3 H and --CO.sub.2 H. Preferably X represents 
--P(O)(OH).sub.2. 
Most preferably, the nucleotide analogue is 
N-[2-(methylthio)ethyl]-2-[(3,3,3-trifluoropropyl)thio]-5'-adenylic acid, 
monoanhydride with dichloromethylenebisphosphonic acid or a 
pharmaceutically acceptable salt thereof, that is to say a compound of 
formula (Ia): 
##STR2## 
Most preferably the compounds of formula (Ia) is in the form of the 
tetrasodium salt. 
Compounds of formula (I) may be prepared using the methods disclosed in WO 
94/18216. The compounds of formula (I) are useful because they exhibit 
pharmacological activity in mammals. In a further aspect the invention 
provides a composition as defined herein for use in therapy, in 
particular, in the prevention of platelet aggregation. The compositions of 
the invention therefore act as anti-thrombotic agents. 
In a further aspect the invention provides a method of treating a platelet 
aggregation disorder which method comprises treating a subject suffering 
from a said disorder with a therapeutically effective amount of a 
pharmaceutical composition as defined herein. 
In a still further aspect the invention provides use of a pharmaceutical 
composition as defined herein in the manufacture of a medicament for 
treating a platelet aggregation disorder. 
The modifying additive or agent is preferably a suitable polyol. This is 
because when NaCl is used as the modifying agent, the profile of 
impurities is unfavourable. 
A polyol suitable for use in the invention is in general a straight chain 
polyhydric alcohol or a cyclic molecule comprising one or more keto or 
aldehyde groups which is preferably a carbohydrate. The polyol used in the 
composition according to the invention is preferably sorbitol, lactose, 
sucrose, inositol or trehalose. More preferably the modifying agent is 
sorbitol because it has surprisingly been found that the long term 
stability of freeze dried compositions comprising sorbitol is improved 
compared to such compositions containing other modifying agents. 
The composition according to the invention preferably comprises mannitol as 
a crystallising agent. Suitably the compositions of the invention comprise 
about 1% or more by weight of mannitol, for example 20-40%. However there 
is a problem with mannitol in that on freeze drying, the vials containing 
the mixture without the modifying additive tend to crack due to an 
amorphous to crystalline phase transition. The amount of the modifying 
additive is preferably sufficient to prevent this phase transition from 
occurring, for example about 3 to 25%. A suitable amount can easily be 
determined by conventional analytical techniques such as differential 
scanning calorimetry. However the amount of the modifying agent should not 
be so much as to cause collapse of the composition. 
The water content of the formulation is preferably less than 5% by weight, 
more preferably less than 2% by weight and most preferably less than 1% by 
weight. 
The pharmaceutical composition according to the present invention 
optionally additionally comprises a pharmaceutically acceptable excipient, 
for example a chelating or sequestering agent, an antioxidant, a tonicity 
adjusting agent, a pH modifying agent and/or a buffering agent, for 
example one or more of those disclosed in "Review of Excipients and pH's 
for Parenteral Products used in the United States" Yu-Chang John Wang and 
R R Kowal, J Parenteral Drug Association, 34, 452-462 (1980). 
The process for preparing the pharmaceutical composition according to the 
present invention is suitably carried out using any lyophilisation, vacuum 
drying or spray drying technique commonly used within the pharmaceutical 
area. In a further aspect the invention provides a process for preparing a 
pharmaceutical composition as defined herein which comprises mixing a 
nucleotide analogue, mannitol and a sodium chloride or polyol modifying 
additive and subjecting the mixture to a lyophilisation, vacuum drying or 
spray drying procedure. 
A preferred process according to the invention is a vial freeze-drying 
process. Such a process comprises filling sterile vials with a sterile 
filtered solution of the composition according to the invention. A sterile 
freeze-drying stopper is partially inserted into the vial which is frozen, 
e.g. at a temperature from -30 to 40.degree. C., and thereafter vacuum 
dried in the frozen state. After drying the stopper is fully inserted 
before removing the vial from the lyophilization unit. 
Upon use but before administration, the pharmaceutical compositions 
according to the present invention are generally reconstituted in a 
pharmaceutically acceptable diluent. Examples of pharmaceutically 
acceptable diluents include water, saline and dextrose. Preferably water 
is used as the diluent. In a further aspect the invention provides a 
process for preparing a pharmaceutical composition as defined herein which 
comprises mixing a nucleotide analogue, mannitol and a sodium chloride or 
polyol modifying additive with a pharmaceutically acceptable diluent. 
Suitably a solution of the pharmaceutical composition according to the 
invention obtained after reconstitution and containing mannitol is an 
isotonic solution. 
In a preferred embodiment the pH of the composition of the present 
invention is from about 6 to about 10, more preferably from about 7 to 
about 9. 
The pharmaceutical composition according to the present invention when 
reconstituted is preferably administered by injection intravenously, 
subcutaneously or intramuscularly, preferably intravenously. 
The compositions according to the invention may be packed in suitably 
adapted pharmaceutical application devices, for example syringes, vials or 
ampoules, such that the addition of water allows the in situ preparation 
of an aqueous solution of the active ingredient in a form suitable for 
immediate adminstration to the patient. Such devices form a further aspect 
of the invention.