Technical Field of the Invention
The present invention relates to nanoparticulate forms of an oxazolidinone derivative RBx 12276, methods of preparing said nanoparticulate forms and pharmaceutical compositions containing them, and in particular nanosuspensions comprising RBx 12276.
Background of the invention
RBx 12276, described in US co-pending patent application no. 60/616,964, belongs to the class of oxazolidinones, particularly, (S)-3-aryl-5- acetamidomethyl-2-oxazolidinones that are a novel class of totally synthetic antibacterial agents indicated for respiratory tract infections. Chemically, RBx12276 is N- [((5S)-3- {3-fluoro-4- [2-(1H-1, 2,4-triazol-1-yl) pyrimidin-5-yl] phenyl} -2-oxo-1, 3-oxazolidin-5-yl) methyl] acetamide.
(Formula removed)

Oxazolidinones have a number of intriguing attributes, including: (1) a unique mechanism of action that involves inhibition of protein synthesis at a very early stage, ensuring a lack of cross-resistance with existing antimicrobials; (2) a spectrum of activity that includes a number of important bacterial species involved in nosocomial infections (3) activity in animal models of human infection when administered by either oral or parenteral routes; and (4) sufficient structural latitude to allow for activity and/or toxicity modifications.
RBx 12276 is a chiraly pure (S)-isomer and has superior activity against Gram positive pathogens such as MRSA, VRE and Streptococcus pneumoniae. Additionally, it has
activity against Linezolid resistant strains and anaerobes. Linezolid is a well known oxazolidinone derivative sold under brand name of Zyvox™. The projected dose of RBx 12276 in an adult human is about 600mg/day. A characteristic but undesirable property of RBx 12276 is its extremely low water solubility (0.1 mg/ml). This low solubility would contribute to improper bioavailability when administered in the form of a pharmaceutical composition particularly as an oral composition.
Oral route of administration has numerous advantages such as being the safest route of administration, economical, convenient for the patient and there is no need of sterile equipment. The intravenous route is still preferable in some cases as it is extremely rapid, initial absorption step is bypassed, drug levels are more accurately controlled, a lesser efficacious dose is required than by oral route and is suitable for delivering large volumes. The intravenous administration is particularly useful in life threatening conditions when immediate onset of therapeutic effect is required. Moreover, the greatest advantage associated with the intravenous route is that the "first-pass effect" as a result of passage of drug through liver is minimized. Following oral administration, the absorption of drugs from the intestine is mainly dependent on their solubility in the intestinal fluids and their intestinal permeability. Poorly soluble drugs generally have low dissolution rates and exhibit only a small concentration gradient across the intestinal mucosa, which can result in low and unreliable levels of absorption. Thus, typical problems associated with low solubility drugs are a too low bioavailability and/or erratic absorption. Although parenteral administration can help administer such low solubility drugs, but in case of a too low solubility of a drug, even parenteral administration cannot solve this problem in many cases. Due to poor solubility, intravenous injection as a solution is not possible due to non-availability of a suitable vehicle, which can dissolve the drug. Parenteral administration as a micronized product does not lead necessarily to sufficiently high drug levels because the solute volume at the injection site is too low. Low intrinsic solubility combined with a low dissolution velocity is the obstacle preventing sufficiently high blood levels. Possible exceptions are only the drugs being poorly soluble but highly potent. Delivering a projected human dose of 600 mg/day is therefore only possible if the solubility of RBx 12276 is enhanced.
Various methods of solubilization are known from the literature like salt formation, prodrugs, co-solvent approach, cyclodextrin based complexation and pH adjustment. WO 02/15940 discloses the most studied approach to improve solubility of oxazolidinones i.e. complexation with cyclodextrins. The use of cyclodextrin for IV delivery has numerous disadvantages like toxicity of cyclodextrins, drug loading efficiency of the system, incomplete drug release from the formed complexes, viscosity of solution and processing of the formulation. Moreover, cyclodextrins are expensive excipients and in many cases the degree of enhancement of solubility, or other benefit obtained, has not economically justified the increased cost of a formulation arising from addition of a cyclodextrin.
A need therefore exists for a pharmaceutical composition of an oxazolidinone with low aqueous solubility, for example, RBx 12276 which can deliver the intended therapeutic dose and show an acceptable bioavailability. A particular need exists for a parenterally deliverable pharmaceutical composition of an oxazolidinone, for example RBx 12276 having a relatively high load of the drug.
Formulations of drugs with low aqueous solubility into particles having a size in the nanometer range have been proposed in the patent literature as one way of increasing the solubility.
US Patent No. 5,145,684 discloses dispersible particles consisting essentially of a crystalline drug substance having a non-crosslinked surface modifier adsorbed on the surface thereof in an amount sufficient to maintain an effective average particle size of less than about 400 nm.
US Patent application No. 20030054042 discloses methods for stabilizing chemical compounds, particularly pharmaceutical agents, using nanoparticulate compositions.
The method comprises adsorbing a cross-linked surface stabilizer onto the surface of nanoparticulate drug.
US Patent No. 5,858,410 discloses the preparation of medicament particles having a size in the nanometer range and the drug preparations called nanosuspensions were produced by high-pressure homogenization. The patent discloses multiple homegenization cycles to achieve desired particle size of the medicament.
US Patent application No. 20050147688 discloses the nanoparticulate formulations of various biologically active agents such as nutritional supplements, hormones, and a variety of pharmaceutical preparations prepared by microfluidization process.
Prior to the use of high-pressure homogenization, nanosuspensions were prepared by pearl milling process, which was a lengthy process than pressure homogenization and the technology is the subject of U.S. Patent No. 5,271,944. The first generation nano-products were ergo the result of pearl milling process. The second-generation products are the drug nanoparticles produced by high-pressure homogenization. High-pressure homogenization is a widely used technique throughout the literature. However, the preparation of nanoparticulate formulation of oxazolidinones and particularly by high-pressure homogenization has not been described in literature.
We hereby disclose nanoparticlulate forms of an oxazolidinone derivative RBx 12766 and particularly the nanosuspensions of RBx 12276 for intravenous administration.
Summary of the Invention
In one general aspect, it relates to an oxazolidinone derivative in a nanoparticulate form. In another general aspect, it relates to RBx 12276 in nanoparticulate form.
In another general aspect, it relates to RBx 12276 in nanoparticulate form having a volume average particle size (D5o) of less than about 1 micron.
In another aspect, it relates to a pharmaceutical composition for intravenous administration comprising nanoparticles of RBx 12276, said nanoparticles having a volume average particle size (D5o), of less than about 1 micron.
In another aspect, it relates to a pharmaceutical composition for intravenous administration comprising nanoparticles of RBx 12276, said nanoparticles having a volume average particle size (D50), of less than about 1 micron, and pharmaceutically acceptable excipients.
In another aspect, it relates to a pharmaceutical composition for intravenous administration comprising nanoparticles of RBx 12276, said nanoparticles having a volume average particle size (D50) of less than about 1 micron, and pharmaceutically acceptable excipients, wherein, the said pharmaceutical composition is provided as a nanosuspension.
In another aspect, it relates to a pharmaceutical composition for intravenous administration comprising nanoparticles of RBx 12276, said nanoparticles having a volume average particle size (D50) of less than about 1 micron; a stabilizer and a pharmaceutically acceptable vehicle and optionally one or more of pharmaceutically acceptable excipients.
In another aspect, it relates to a process for preparation of preparation of a pharmaceutical composition comprising an oxazolidinone derivative, wherein the process comprises subjecting a coarse dispersion of an oxazolidinone derivative and one or more of stabilizer(s) dispersed in a pharmaceutically acceptable vehicle to high-pressure homogenization such that the volume average particle size (D50) of less than about 1 micron is obtained.
In another aspect, it relates to a process for preparation of preparation of nanosuspension comprising RBx 12276, wherein the process comprises subjecting a coarse dispersion of RBx 12276 and one or more of stabilizer(s) dispersed in a pharmaceutically acceptable vehicle to high-pressure homogenization such that the volume average particle size (D5o) of less than about 1 micron is obtained.
In another aspect, it relates to a method of treating a medical condition in a human responsive to RBx 12276 therapy, wherein the method comprises administering a pharmaceutical composition comprising RBx 12276 in nanoparticulate form.
The details of one or more embodiments of the inventions are set forth in the description below. Other features, objects and advantages of the inventions will be apparent from the description and claims.
Detailed Description of the Invention
RBx 12276 may be prepared by the process set forth in US co-pending patent application no. 60/616,964. RBx 12276 belongs to a novel class of totally synthetic antibacterial agents and has some inherent features which make it all the more suitable to be formulated as nanoparticulate composition particularly a nanosuspension. The intrinsic solubility/plasma solubility, plasma protein binding and volume of distribution of RBx 12276 are such that the required therapeutic dose to be delivered is less than the maximum dose that can dissolve in the blood i.e. RBx 12276 with solubility of 0.1 mg/mL can dissolve in amounts upto 600mg when the blood volume in an average human is about 6 litres. Actual dosage levels of RBx 12276 in the nanoparticulate composition may be varied to an amount that is effective to obtain a desired therapeutic response. The selected dosage level depends upon the desired therapeutic effect, the desired duration of treatment, and therapeutic index.
The particle size of the nanoparticles may be reported as an average particle size (e.g. a number average, weight average or volume average particle size). In the present
specification, the particle size is reported as a volume average particle size. Thus for example, a D50 of 1 micron indicates that 50% by volume of particles have a diameter of less than 1 micron. Alternatively, it can be said that the particles having a diameter of less than 1 micron occupy 50% of the total volume occupied by the total number of particles.
The term, "stabilizer" as used herein, refers to substance that provides steric stabilization to the nanosuspension. Without wishing to be bound by any theory, it is believed that the stabilizer hinders the flocculation and/or agglomeration of the nanoparticles by functioning as a mechanical or steric barrier between the particles, minimizing the close, interparticle approach necessary for agglomeration and flocculation. The stabilizer gets adsorbed over the surface of nanoparticles and provides long-term storage stability to the nanosuspensions.
The stabilizer(s) employed in the preparation of nanosuspensions may be selected from phospholipids and hydrophilic polymers. The phospholipids may be selected from lecithins, cephalins and the like. The hydrophilic polymers may be selected from block copolymers such as polyoxyethylene/polyoxypropylene block copolymer also known as poloxamer, polyvinyl derivatives such as polyvinyl alcohol, polyvinyl pyrrolidone and alginates and the like.
The pharmaceutically acceptable vehicle may be water suitable for parenteral use or a mixture of water and a pharmaceutically acceptable alcohol such as ethanol or glycerol.
Besides the above, the nanoparticulate suspension may further optionally comprise other pharmaceutical excipients like viscosity modifiers, tonicity adjusting agents, bulking agents and pH adjusting agents well known to the skilled in the field of drug delivery by intravenous route. The viscosity modifiers may include water soluble polymers like polyvinylpyrrolidone, hydroxypropylcellulose; tonicity adjusting agents may be dextrose, mannitol, glycerol; and pH adjusting agents may be pharmaceutically acceptable acids and bases like hydrochloric acid and sodium hydroxide.
The pharmaceutical composition may be formulated as liquid nanosuspension meant for IV administration or as dry preparations such as lyophilized product and spray dried product meant for reconstitution with a pharmaceutical^ acceptable vehicle.
The desired particle size may be achieved by processes known in the prior art like conventional dry grinding, wet grinding using ball mill or pearl mill and high pressure homogenization. Particularly suitable is high pressure homogenization. The high-pressure homogenizer works on the principle of breaking the nanosuspension by cavitation forces. The drug powder is first dispersed in a stabilizer solution by high speed stirring or sonication. The obtained "macro-suspension" is passed through a high-pressure homogenizer either continuously or in several homogenization cycles. The suspension passes through a very small homogenization gap in the homogenizer and due to the narrowness of the gap, the streaming velocity of the suspension increases tremendously. The dynamic fluid pressure is increased whereas the static pressure on the fluid decreases below the boiling point of water at room temperature. Consequently, water starts boiling at room temperature due to high pressure, gas bubbles are formed, which implode (cavitation) when the fluid leaves the homogenization gap. These cavitation forces are strong enough to break drug particles to nanoparticles. The average particle size obtained by this procedure depends on the pressure and the number of cycles applied. We have found that if homogenization is done at pressures of between about 25000 PSI to 28000 PSI, the number of cycles may be restricted.
In one embodiment, the nanosuspension for IV administration may be prepared by forming an aqueous dispersion of RBx 12276 in a pharmaceutical^ acceptable aqueous vehicle comprising one or more of stabilizer(s) under sonication and then subjecting the resulting dispersion to high pressure homogenization. The homogenization is carried out as a continuous process at a pressure of about 25000 to 28000 psi.
In one aspect of the above embodiment, the dried product may be obtained by removing the aqueous vehicle from the nanosuspension by lyophilisation or spray

drying to provide nanoparticulate RBx 12276 in powder form that may be reconstituted with a pharmaceutical^ acceptable vehicle into a liquid nanosuspension prior to intravenous administration.
The following example is illustrative of the invention, and is not intended to be construed as limiting the invention.
(TABLE REMOVED)

Process:-
Lecithin and poloxamer are dissolved in water to form a solution and RBx 12276 is dispersed in the above solution under sonication. The resulting aqueous dispersion is then subjected to high-pressure homogenization in a continuous mode at a pressure of 25000 to 28000 PSI for about 20 minutes to get the desired product.
The effect of high pressure homogenization on particle size of RBx 12276 in example 1 is shown in Figures below. The particle size was determined by laser diffraction technique (Malvern).
(FIGURE REMOVED)

The particle size prior to high pressure homogenization was such that volume average particle size (D50) was about 29.35 urn and after high pressure homogenization D50 was less than 1.0pm i.e. about 0.69 pm.
A pharmacokinetic study was conducted in wistar rats comparing the RBx 12276 nanosuspension with an intravenous RBx 12276 solution. The intravenous solution was prepared in a vehicle containing dimethyl acetamide, polyethylene glycol and purified water in a ratio of 2:71:24 respectively. The PK parameters were compared and it was observed that the PK parameters i.e. Cmax, U12, AUC and clearance for the nanosuspension were similar to those of solution formulation.
The results are given in Table 1 below:
Table 1: - PK parameters of RBx 12276 solution and RBx 12276 nanosuspension in
Wistar rats.
(TABLE REMOVED)

WE CLAIM:
1). An oxazolidinone derivative in nanoparticulate form.
2). The oxazolidinone derivative according to claim 1 wherein the derivative is RBx 12276.
3). The derivative according to claims 1 or 2, wherein the derivative in nanoparticulate form has a volume average particle size (D50) of less than about 1 micron. 4). A pharmaceutical composition for intravenous administration comprising nanoparticles of RBx 12276, said nanoparticles having a volume average particle size (D50) of less than about 1 micron; a stabilizer and a pharmaceutically acceptable vehicle and optionally one or more of other pharmaceutically acceptable excipients. 5). The pharmaceutical composition according to claim 4, wherein the stabilizer is selected from one or more of phospholipids and hydrophilic polymers. 6). The pharmaceutical composition according to claim 5, wherein the phospholipid is selected from lecithins and cephalins.
7). The pharmaceutical composition according to claim 5, wherein the hydrophilic polymer is selected from block copolymers, polyvinyl derivatives, and alginates. 8). The pharmaceutical composition according to claim 7, wherein the block copolymer is poloxamer.
9). The pharmaceutical composition according to claim 4 wherein the pharmaceutically acceptable vehicle is selected from water and mixtures with alcohols thereof. 10). The pharmaceutical composition according to claim 4, wherein the other pharmaceutical excipients are selected from viscosity modifiers, tonicity adjusting agents and pH adjusting agents.
11). A pharmaceutical composition comprising RBx 12276 in nanoparticulate form, stabilizer selected from poloxamer and lecithin and combination thereof and a pharmaceutically acceptable vehicle wherein the composition is prepared by high-pressure homogenization.
12). The pharmaceutical composition according to claim 11, wherein the composition is lyophilized.
13). A process for preparation of a pharmaceutical composition comprising an
oxazolidinone derivative, wherein the process comprises subjecting a coarse dispersion
of an oxazolidinone derivative and one or more of stabilizer(s) dispersed in a
pharmaceutically acceptable vehicle to high-pressure homogenization such that the
volume average particle size (D50) of less than about 1 micron is obtained.
14). The process according to claim 13, wherein high-pressure is about 25000 to 28000
PSI.
15). The process according to claim 13, wherein the oxazolidinone derivative is RBx
12276.
16). The process according to claim 13, wherein the stabilizer is selected from
poloxamer and lecithin and combinations thereof.
17). A pharmaceutical composition of an oxazolidinone derivative prepared and
substantially exemplified herein.