THE PATENT
16 The complete specification is entitled "Reconstitutable parenteral composition containing a COX-2 inhibitor".
17 The patent identifies that the field of the invention is as follows:
The present invention relates to water-soluble selection cyclooxygenase-2 (COX-2) inhibitory drugs and salts and prodrugs thereof and in particular to parecoxib, for example in the form of its sodium salt (parecoxib sodium). Parecoxib is a water-soluble prodrug of the selective COX-2 inhibitory drug valdecoxib. More particularly, the invention relates to parenterally deliverable, for example injectable, formulations of water-soluble selective COX-2 inhibitory drugs and salts and prodrugs thereof. Even more particularly, the invention relates to such formulations that are prepared as powders for reconstitution in an aqueous carrier prior to parenteral administration. The invention also relates to processes for preparing such reconstitutable formulations, to therapeutic methods of use of such formulations and to use of such formulations in manufacture of medicaments.
18 Under the heading "Background of the Invention", the specification identifies that:
(1) inhibition of COX enzymes is believed to be at least the primary mechanism by which nonsteroidal anti-inflammatory drugs, or NSAIDs, exert their characteristic anti-inflammatory, antipyretic and analgesic effects through inhibition of prostaglandin synthesis;
(2) inhibition of COX-1, which produces prostaglandins that are necessary for normal cell function, appears to account for certain adverse side effects that had been associated with use of conventional NSAIDs. By contrast, selective inhibition of COX-2 without substantial inhibition of COX-1 leads to anti-inflammatory, antipyretic, analgesic and other useful therapeutic effects while minimising or eliminating such adverse side effects;
(3) selective COX-2 inhibitory drugs are formulated in a variety of orally deliverable dosage forms. However, parenteral routes of administration offer numerous benefits over oral delivery for a wide variety of drugs;
(4) relatively few NSAIDs are commercially available in injectable form. It would therefore represent a further significant advance in the art if a parenterally deliverable formulation of a selective COX-2 inhibitory drug could be provided;
(5) it is known to prepare parenteral formulations by a process of lyophilisation (freeze-drying) of an aqueous solution of a therapeutic agent and excipients are often added to the therapeutic agent to increase the amount of solids so that the resulting powder is more readily visible when the amount of therapeutic agent is very small. Amongst the substances found most useful for this purpose is mannitol; and
(6) parecoxib is one of a class of water-soluble prodrugs of selective COX-2 inhibitory drugs which rapidly converts to the substantially water-insoluble selective COX-2 inhibitory drug valdecoxib following administration to a subject. However, there is a problem (described by the primary judge at [228] J1 as the conversion problem) in that parecoxib converts to valdecoxib upon exposure to water, for example upon dissolution in water. There has been interest in developing parecoxib for parenteral use because of its high water solubility. However, no pharmaceutically acceptable injectable formulation of drugs or prodrugs such as parecoxib has hitherto been described and problems have beset the formulator attempting to prepare such a formulation, illustratively of parecoxib. It is said that the present invention provides a solution to these problems.
19 The specification provides a summary of the invention, commencing with the consistory clause for claim 1, namely: in one embodiment, a pharmaceutical composition comprising, in powder form, (a) at least one water-soluble therapeutic agent selected from selective COX-2 inhibitory drugs and prodrugs and salts thereof, in a therapeutically effective total amount constituting about 30% to about 90% by weight, (b) a parenterally acceptable buffering agent in an amount of about 5% to about 60% by weight, and optionally (c) other parenterally acceptable excipient ingredients in a total amount not greater than about 10% by weight, of the composition. The specification states that the composition is reconstitutable in a parenterally acceptable solvent liquid, preferably an aqueous liquid, to form an injectable solution.
20 The specification states that the composition can be prepared by a process comprising a step of lyophilisation of an aqueous solution comprising the therapeutic agent, the buffering agent and optionally other excipient ingredients to form a readily reconstitutable powder; such process representing a further embodiment of the present invention. The specification also describes further embodiments and states that an especially preferred therapeutic agent is a water-soluble salt of parecoxib.
21 The specification identifies a list of selective COX-2 inhibitory drugs or selective COX-2 inhibitor components which includes valdecoxib of which parecoxib is a prodrug.
22 The specification states that one or more therapeutic agents selected from those disclosed in the specification are present in a reconstitutable powder composition of the invention in a total amount of about 30% to about 90%, preferably about 40% to about 85%, and more preferably about 50% to about 80%, by weight of the composition.
23 It further states that the buffering agent, which is present in an amount of about 5% to about 60%, preferably about 10% to about 60%, and more preferably about 20% to about 50%, by weight of the composition, is typically the predominant excipient ingredient. It is stated that the buffering agent is selected to provide a pH of the composition, upon reconstitution in a physiologically acceptable volume of a parenterally acceptable solvent liquid, that (a) is parenterally acceptable, (b) is consistent with the therapeutic agent being entirely in solution in the solvent liquid, and (c) provides a medium wherein the therapeutic agent exhibits acceptable chemical stability for at least about one hour following reconstitution. The specification identifies that preferred buffering agents are dibasic sodium and potassium phosphates and tromethamine. It further states that an especially preferred buffering agent is dibasic sodium phosphate, for example dibasic sodium phosphate anhydrous, heptahydrate, dodecahydrate etc.
24 The specification continues to state that, in one embodiment, the pH of the composition can be at certain levels upon reconstitution and that, if desired, the pH can be adjusted by including, in addition to the buffering agent, a small amount of an acid and/or a base. These were referred to as the pH adjusters in the reasons of the primary judge and they are included to adjust the pH to within an appropriate range.
25 The specification then identifies that excipients other than the buffering agent, if present, constitute not more than about 10%, preferably not more than about 5%, by weight of the composition prior to reconstitution. It states that the term "excipient" embraces all non-therapeutically active components of the composition except for water. It identifies that, in one embodiment of the invention, no excipients other than the buffering agent are substantially present.
26 The specification identifies that there is a further problem to which a solution has been found (which was identified by the primary judge at [228] J1 as the stability problem).
27 The stability problem was stated in the specification in these terms, that is, where the therapeutic agent is parecoxib, for example in the form of parecoxib sodium, partial conversion to valdecoxib can occur in a composition over a period of time. The specification identifies that, as valdecoxib has extremely low solubility in water, it is desirable to minimise such conversion prior to reconstitution so that complete dissolution of the therapeutic agent is assured. It teaches that the presence of particulates, such as would result from the presence of significant quantities of valdecoxib, is generally undesirable in a solution intended for parenteral administration. The specification identifies the solution being that it was surprisingly found that conversion of parecoxib to valdecoxib in a reconstitutable powder composition can be greatly reduced by reduction or preferably elimination from the composition of bulking agents such as mannitol.
28 As to this, the specification notes that, surprisingly, it has been found important to include in the composition no more than about 10% by weight, preferably no more than about 5% by weight, and most preferably substantially no amount, of ingredients commonly used as bulking agents in reconstitutable parenteral formulations, other than buffering agents. It states that, in particular, the widely used bulking agent mannitol is preferably excluded from the composition, or if included, is present at no more than about 10%, preferably no more than about 5%, by weight of the composition. The specification identifies that, by minimising the amount of or excluding such bulking agents, especially mannitol, as components of the composition, acceptable chemical stability of the therapeutic agent can be assured.
29 The specification also identifies that a reconstitutable powder composition of the invention preferably contains less than 5%, more preferably less than 2%, and most preferably less than about 1%, by weight of water and stated that typically, the moisture content is about 0.5% to about 1% by weight. The specification identifies that it is especially important to keep the amount of water to such a low level where the therapeutic agent has a tendency to degrade or convert to a less soluble form in the presence of water.
30 As to the conversion problem, the specification states that, in the form of parecoxib sodium, partial conversion to highly insoluble valdecoxib can occur in an aqueous solution over a period of time, resulting in formation of solid particulates and that, as indicated above, the presence of solid particulates is generally undesirable in injectable formulations. The specification identifies that the rate of conversion of parecoxib to valdecoxib in an aqueous medium can be greatly reduced by maintaining the medium at a pH of about 7 or higher.
31 The final problem the specification identifies as having been solved by the invention is described as the reconstitution problem by the primary judge at [228] J1, being that parecoxib formulations containing mannitol and other excipients do not dissolve instantly. In the specification, it identifies that a powder composition in the invention preferably has sufficient porosity to permit rapid dissolution of the therapeutic agent upon reconstitution in the solvent liquid. It states that a high degree of porosity is available by using a process to prepare the powder as described in the specification, which included identified steps in a lyophilisation cycle and process. Notably, that process or cycle includes reference in the third phase of providing a powder "having a moisture content of less than about 5%, preferably less than about 2%, more preferably less than 1%, by weight".
32 The specification includes four examples which illustrate aspects of the present invention but it states that they are not to be construed as limitations.
33 The specification states that:
In the claims which follow and the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments in the invention.
34 Relevantly to this appeal and cross-appeal, the critical claims defining the invention are as follows:
1. A pharmaceutical composition comprising, in powder form:
(a) at least one water-soluble therapeutic agent selected from selective COX-2 inhibitory drugs and prodrugs and salts thereof, in a therapeutically effective total amount constituting about 30% to about 90% by weight,
(b) a parenterally acceptable buffering agent in an amount of about 5% to about 60% by weight, and
(c) other parenterally acceptable excipient ingredients in a total amount of zero to about 10% by weight of the composition;
said composition being reconstitutable in a parenterally acceptable solvent liquid to form an injectable solution.
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26. A process for preparing a reconstitutable selective COX-2 inhibitory composition, the process comprising a step of lyophilizing an aqueous solution that comprises:
(a) at least one therapeutic agent selected from selective COX-2 inhibitory drugs and prodrugs and salts thereof, in a therapeutically effective total amount constituting about 30% to about 90% by weight,
(b) a parenterally acceptable buffering agent in an amount of about 5% to about 60% by weight, and
(c) other parenterally acceptable excipient ingredients in a total amount of zero to about 10% by weight of the composition, excluding water;
said lyophilizing step resulting in formation of a readily reconstitutable powder.
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32. The process of Claim 31, wherein:
(a) in the freezing phase, temperature is lowered to a freezing temperature of about -30°C to about -60°C over a period of about 1 to about 5 hours and is held at the freezing temperature for about 0.5 to about 24 hours;
(b) in the primary drying phase, a vacuum of about 25 to about 500m Hg is drawn, and temperature is raised from the freezing temperature to about 0°C over a period of about 1 to about 5 hours; and
(c) in the secondary drying phase, under vacuum of about 25 to about 500m Hg, temperature is raised from about 0°C to a level above room temperature over a period of about 1 to about 4 hours and is held at the raised level for about 3 to about 12 hours;
to result in a powder having a moisture content of less than about 2% by weight.
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42. A pharmaceutical composition as defined in Claim 1, an injectable solution prepared by reconstituting said composition, an article of manufacture comprising said composition, a process for preparing a reconstitutable selected COX-2 inhibitory composition, or a method of treating and/or preventing a COX-2 mediated disorder in a subject, substantially as herein described with reference to any one of the Examples.