THE PATENT SPECIFICATION
14 It is apparent from a reading of the specification that the Patent relates to the use of raloxifene "in particulate form" in the preparation of formulations and compositions used in the treatment of various conditions including, relevantly, osteoporosis. Osteoporosis is a condition that is characterised by a loss of bone mass often resulting in bone fracture. It is a condition that is common in post-menopausal women.
15 According to the specification at p 1, lines 9 to 11, the raloxifene of the invention (sometimes referred to in the specification, including the claims, as "formula I") is of "a particle size range which allows enhanced bioavailability and control during the manufacturing process." The specification also notes, at p 1, lines 35 to 36, that raloxifene is generally insoluble, and that this can affect the bioavailability of the drug. The specification then explains, at p 2, line 37 to p 3, line 2, that "any improvement in the physical characteristics of raloxifene, would potentially offer a more beneficial therapy and enhanced manufacturing capability."
16 The specification includes, at p 2, line 3 to p 2a, line 33, a number of consistory statements which mirror the claims.
17 At p 2b, line 1 to p 3, line 31 the specification states:
It has now been found that by processing compounds of formula I, to bring their particle size within a specified narrow range, pharmaceutical compositions may be prepared which exhibit for their active ingredient both a consistent in vitro dissolution profile and in vivo bioavailability. In addition to bringing about these desired dissolution/bioavailability characteristics, the control of particle size to a narrow range has also resulted in significant improvements in manufacturing capabilities.
The mean particle size of the compounds of formula I, as set out by the invention, is less than about 25 microns, preferably between about 5 and about 20 microns. Further, the invention encompasses formula I compounds with at least 90% of the particles having a particle size of less than about 50 microns, preferably less than about 35 microns. More preferably, the mean particle size range is between about 5 and about 20 microns, with at least 90% of the particles having a size of less than about 35 microns.
It will of course be understood by those familiar with comminution process techniques that the limit set on the size of 90% or more of the particles is a limitation to further distinguish the particulate compounds of the invention from those exhibiting a broader size distribution, because of the wide variation in size encountered in all matter reduced in size by a process of comminution or particle size reduction, for example, by milling utilizing a variety of kinds of milling equipment now available, for example, hammer, pin or fluid energy mills.
The invention also provides pharmaceutical compositions comprising or formulated using the said particulate compound of the invention and one or more pharmaceutically-acceptable excipients or carriers.
18 At p 4, lines 1 to 5 the specification identifies raloxifene by its chemical name (which I need not set out) and indicates that references to raloxifene should be taken to include its salts and solvates including hydrochloride salt (HCl) which is said to be preferred.
19 At p 4, line 15 to p 5, line 8 the specification states:
Often, compounds which have poor solubility profiles can have their bioavailability enhanced by increasing the surface area of the formulated particles. The surface area generally increases per unit volume as the particle size decreases. Various techniques for grinding or milling a drug substance are well known in the art and each of these techniques are commonly used to decrease particle size and increase the surface area of the particle. It would seem reasonable that the best way to deal with any slightly soluble compound would be to mill it to the smallest size possible; however, this is not always practical or desirable. The milling process has an economic cost not only it [sic] the direct cost of the process, itself, but also with other associated factors. For example, very finely divided material presents difficulties and cost in capsule filling or tablet preparation, because the material will not flow, but becomes caked in finishing machinery. Such finishing difficulties generate nonhomogeneity in the final product, which is not acceptable for a drug substance. Additionally, the milling process, physically generates heat and pressure on the material, such conditions lead to chemical degradation of the compound, thus such milling techniques are usually kept to a minimum.
Therefore, there is always dynamic between the properties which yield the maximum bioavailability (particle surface area) and the practical limits of manufacture. The point of compromise which marks this "best solution" is unique to each situation and unique as to its determination.
20 The specification then refers to various methods for determining the size of particles. At p 5, line 14 to p 6, line 16 the specification states:
In preparing the particulate compound of the invention a compound of formula I, in its raw state, is first characterized for size using an instrument adapted to measure equivalent spherical volume diameter, that is to say a Horiba LA900 Laser Scattering Particle Size Distribution Analyzer or equivalent instrument. Typically a representative sample of a compound of formula I would be expected to comprise in its raw state particles having a mean equivalent spherical volume diameter of about 110-200 microns and with a broad size distribution.
After being characterized for size in its raw state, the raw compound is then milled, preferably using a pin mill under suitable conditions of mill rotation rate and feed rate, to bring the particle size value within the above mentioned limits according to the invention. The efficiency of the milling is checked by sampling using a Horiba LA900 Laser Scattering Particle Size Distribution Analyzer and the final particle size is checked in a similar manner. If the first pass through the mill does not produce the required size distribution, then one or more further passes are effected.
The compound of formula I in its particulate form within the above mentioned limits according to the invention may then be mixed with an excipient or carrier as necessary and, for example, compressed into tablets. Thus, for example, the particulate compound may be mixed with anhydrous lactose, lactose monohydrate, cross povidone and granulated in an aqueous dispersion of povidone and polysorbate 80. After drying and milling into granules the material can be terminally blended with magnesium stearate and compressed into tablets.
Because the particles in the raw state as well as after milling or other particle size reduction techniques are irregular in shape, it is necessary to characterize them not by measurement of an actual size such as thickness or length, but by measurement of a property of the particles which is related to the sample property possessed by a theoretical spherical particle. The particles are thus allocated an "equivalent spherical diameter".
21 This is followed by a description of a statistical procedure which is performed to calculate a mean spherical volume diameter (referred to in other evidence as the D[4,3] measurement) which may then be compared to a sample of particles drawn from the milled raloxifene in order to determine whether the raloxifene particles are of the desired size. Since the raloxifene particles are irregularly shaped, and seldom, if ever, truly spherical, the mean spherical volume diameter (D[4,3]) provides what is necessarily a theoretical approximation of the actual mean particle size found in a given sample.
22 The specification includes a description of 25 different formulations (the Examples) all of which include raloxifene HCl as the active ingredient. Most of these formulations are for tablets, capsules and suspensions suitable for oral administration. However, there are other examples of formulations that may be administered in different ways, including an intravenous solution (Formulation 7) comprising raloxifene HCl (50 mg) and isotonic saline (1,000 ml).
23 It is apparent from the specification that the raloxifene HCl utilised in each of the Examples is said to have been sourced from bulk raloxifene HCl that has been milled to achieve the preferred particle size distribution. Thus, at p 7, lines 8 to 13 the specification states:
In all of the Examples the compound was prepared from raw form using a pin mill and consisted of particles having a mean equivalent spherical volume diameter of between about 5 and 20 microns, at least 90% of the particles having a particle size of less than about 35 microns.
24 The specification also includes a lengthy discussion of the significance of particle size on the solubility and dissolution profile of raloxifene HCl as reflected in experimental data that is reported in Tables 7, 8, 10, 11, 13 and 15. The specification suggests this data shows that superior absorption is achieved using formulations with finer particle sizes, resulting in improved bioavailability.
25 The specification states at p 22, lines 18 to 20 that "[c]ompounds of formula I, alone or in combination with another pharmaceutical agent, generally will be administered in a convenient formulation." It also states, at p 22, lines 21 to 22, that the Examples are illustrative only and are not intended to limit the scope of the invention.