Sigma Pharmaceuticals (Australia) Pty Ltd v Wyeth
[2011] FCAFC 132
At a glance
Source factsCourt
Federal Court of Australia (Full Court)
Decision date
2011-10-28
Before
Yates JJ
Source
Original judgment source is linked above.
Judgment (23 paragraphs)
Background 133 I have had the advantage of reading the reasons for judgment of Bennett J and Yates J. I generally agree with their reasons and I also agree with the orders they propose. However, I wish to explain in my own terms why I do not think the relevant claims are entitled to a priority date of 25 March 1996 and why they are not fairly based on matter described in the specification. For the purpose of doing so I shall use the definitions adopted by Bennett J to identify parties and relevant documents.
The Priority Document 134 The Priority Document is entitled "Extended Release Formulation". The specification embarks upon its description of the background to the invention with a discussion of extended release drug formulations. 135 The specification then explains that such formulations are conventionally produced as compressed tablets by hydrogel tablet technology. When the tablets made by compounding the active ingredient with various cellulose ethers are introduced to the digestive system, the latter gradually leach away, making the active ingredient available for the absorption by the body. These formulations are referred to as "extended" or "sustained" release formulations. The specification explains that where the production of tablets is not feasible, it is conventional in the drug industry to prepare encapsulated formulations which provide extended release properties. This is achieved by mixing the active ingredient with binding agents from which an extrudable cylindrical mass is created which is then chopped into small lengths that are then transformed into spheroids. These are then film coated (if so desired) to varying degrees to retard dissolution of the active ingredient at different rates in order to obtain the desired therapeutic effect. Gelatin capsules can then be filled with the film coated spheroids. 136 The specification then explains that venlafaxine is an important drug used in the treatment of depression. Venlafaxine hydrochloride is administered to adults in compressed tablet form in doses ranging from 75 to 350 mg/day in divided doses two or three times a day. The specification explains that rapid dissolution of venlafaxine results in a rapid increase in blood plasma levels of the drug shortly after dosing followed by a decrease in those levels over several hours until sub-therapeutic levels are approached after twelve hours. It is these fluctuations in the blood plasma levels of the drug that give rise to the need for multiple dosing. However, nausea is said to be a common side effect of the multiple dosing. 137 There follows what is entitled "Brief Description of the Invention" which is the part of the Priority Document that describes the invention in the broadest terms. It states: In accordance with this invention, there is provided an extended release (ER), encapsulated formulation containing venlafaxine hydrochloride as the active drug component, which provides in a single dose, a therapeutic blood serum level over a twenty four hour period. Through administration of the venlafaxine formulation of this invention, there is provided a method for obtaining a flattened drug plasma concentration to time profile, thereby affording a tighter plasma therapeutic range control than can be obtained with multiple daily dosing. In other words, this invention provides a method for eliminating the sharp peaks and troughs (hills and valleys) in blood plasma drug levels induced by multiple daily dosing with conventional immediate release venlafaxine hydrochloride tablets. In essence, the plasma levels of venlafaxine hydrochloride rise, after administration of the extended release formulations of this invention, for between about five to about eight hours (optimally about six hours) and then begin to fall through a protracted, substantially linear decrease from the peak plasma level for the remainder of the twenty four hour period, maintaining at least a threshold therapeutic level of the drug during the entire twenty-four [hour] period. In contrast, the conventional immediate release venlafaxine hydrochloride tablets give peak blood plasma levels in 2 to 4 hours. Hence, in accordance with the use aspect of this invention, there is provided a method for moderating the plural blood plasma peaks and valleys attending the pharmacokinetic utilization of multiple daily tablet dosing with venlafaxine hydrochloride which comprises administering to a patient in need of treatment with venlafaxine hydrochloride, a one-a-day, extended release formulation of venlafaxine hydrochloride. The use of the one-a-day venlafaxine hydrochloride formulations of this invention reduces by adaptation, the level of nausea and incidence of emesis that attend the administration of multiple daily dosing. In clinical trials of venlafaxine hydrochloride ER, the probability of developing nausea in the course of the trials was greatly reduced after the first week. Venlafaxine ER showed a statistically significant improvement over conventional venlafaxine hydrochloride tablets in two eight-week and one 12 week clinical studies. Thus, in accordance with this use aspect of the invention there is provided a method for reducing the level of nausea and incidence of emesis attending the administration of venlafaxine hydrochloride which comprises dosing a patient in need of treatment with venlafaxine hydrochloride with an extended release formulation of venlafaxine hydrochloride once a day in a therapeutically effective amount. 138 What is described in this passage is an extended release, encapsulated formulation containing venlafaxine hydrochloride as the active ingredient and a method of obtaining a particular drug plasma concentration to time profile. Significantly, however, the method so described is said to be obtained "[t]hrough the administration of the venlafaxine formulation of this invention." Similarly, the description of the variations in plasma levels of venlafaxine occurring over a twenty four hour period are also said to be obtained after administration of the extended release formulation of this invention. 139 The general description of the invention is followed by a detailed description. After referring to the two forms of venlafaxine hydrochloride isolated and characterised to date, the detailed description continues: The extended release formulations of this invention are comprised of [venlafaxine] hydrochloride in admixture with microcrystalline cellulose and hydroxpropylmethylcellulose. Formed [as] beads or spheroids, the drug containing formulation is coated with a mixture of ethyl cellulose and hydroxypropylmethyl cellulose to provide the desired level of coating, generally from about two to about twelve percent on a weight/weight basis of final product or more preferably from about five to about ten percent (w/w), with best results obtained at from about 6 to about 8 percent (w/w). Thus, the specification contains a very clear statement that the formulations of the invention are comprised of venlafaxine hydrochloride in admixture with microcrystalline cellulose (MC) and hydroxpropylmethylcellulose (HPMC), formed into beads or spheroids, and coated with ethyl cellulose (EC) and more HPMC. 140 After further describing the ingredients and methods used to make the spheroids and the coatings the following statement appears: It was completely unexpected that an extended release formulation containing venlafaxine hydrochloride could be obtained because the hydrochloride of venlafaxine proved to be extremely water soluble. Numerous attempts to produce extended release tablets by hydrogel technology proved to be fruitless because the compressed tablets were either physically unstable (poor compressibility or capping problems) or dissolved too rapidly in dissolution studies. Typically, the tablets prepared as hydrogel sustained release formulations gave 40-50% dissolution at 2 hrs, 60-70% dissolution at 4 hrs and 85-100% dissolution at 8 hrs. And later: Thus, the desired dissolution rate of a sustained release dosage form of venlafaxine hydrochloride, impossible to achieve with hydrogel tablet technology, has been achieved with the film-coated spheroid compositions of this invention. 141 Each of the claims 1 to 8 of the Priority Document is to an encapsulated extended release formulation of venlafaxine hydrochloride that comprises encapsulated spheroids made from venlafaxine hydrochloride, MC and HPMC coated with EC and HPMC. However, claims 9 and 10 are as follows: 9. A method for providing a therapeutic blood plasma concentration of venlafaxine over a twenty four hour period with diminished incidences of nausea and emesis which comprises administering orally to a patient in need thereof, an encapsulated, extended release formulation that provides a peak blood plasma level of venlafaxine in from about four to about eight hours, said formulation containing venlafaxine hydrochloride as the active ingredient. 10. A method for eliminating the troughs and peaks of drug concentration in a patients blood plasma attending the therapeutic metabolism of plural daily doses of which comprises administering orally to a patent in need thereof, an encapsulated, extended release formulation that provides a peak blood plasma level of venlafaxine in from about four to about eight hours, said formulation containing venlafaxine hydrochloride as the active ingredient. Each of these claims is for a method that provides, among other things, a peak blood plasma concentration of venlafaxine in from about four to eight hours. And each of them involves the administration of an encapsulated, extended release formulation containing venlafaxine hydrochloride.