Colloid systems and wetting agents; subcombinations thereof; pro – Compositions containing an agent for breaking ; processes of... – Continuous liquid phase colloid system and discontinuous...
Reexamination Certificate
2000-01-28
2002-12-03
Qazi, Sabiha (Department: 1616)
Colloid systems and wetting agents; subcombinations thereof; pro
Compositions containing an agent for breaking ; processes of...
Continuous liquid phase colloid system and discontinuous...
C514S171000, C514S077000, C514S078000, C514S182000
Reexamination Certificate
active
06489369
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to novel detergents or surfactants based on amphipathic phosphocholine compounds to improve pharmaceutical formulations and their use as pharmaceutical excipients. Phosphocholine surfactants are used for the aqueous solubilization of active agents which are insoluble or sparingly soluble in water. Since phosphocholine is an endogenous component of cell membranes, these surfactants are expected to be biocompatible and biodegradable. Unlike many other surfactants, these phosphocholine surfactants are solid at room temperature and therefore have improved storage properties as dried powders or lyophilized formulations.
BACKGROUND OF THE INVENTION
There is a tremendous need for biodegradable and biocompatible surfactants in the pharmaceutical industry. Current surfactants used for parenteral delivery, often elicit an anaphylactoid reaction. Most surfacants are not composed of endogenous components; therefore, the body often recognizes these molecules as “foreign” and an immune response prevails. Phosphocholine is a natural zwitterionic component of all cell membranes. Surfactants composed of phosphocholine conjugated to a hydrophobic molecule would therefore be safe and biocompatible.
Parenteral delivery of insoluble or poorly soluble drugs is problematic. For example, intravenous administration of paclitaxel or cyclosporin A is accomplished by forming emulsions with Cremophor®EL. The poly(oxyethylene)-40-castor oil in Cremophor®EL can result in hypotension, dyspnea, angioedema, or generalized urticaria. These hypersensitive reactions can lead to life-threatening conditions, and it is recommended that all patients be premedicated with corticosteroids, diphenhydramine, and H2 antagonists to avoid severe hypersensitivity.
In another example, the anesthetic, propofol, is administered commercially as an emulsion containing soy bean oil, glycerol, and egg phosphatide. Microbial contamination is one of the greatest concerns with the current formulation of propofol, which can result in life-threatening illness or death from fever, infection or sepsis. This is especially problematic for post-operative or intensive care unit (ICU) patients. Although U.S. Pat. No. 5,714,520 discloses a method to minimize microbial contamination by the addition of the preservative edeate, this formulation is not an antimicrobial preserved product by USP standards and extrinsic contamination remains problematic.
Cyclodextrins are also used in increasing the solubility of a compound 100- to 1000-fold. This is the upper limit of their usefulness and is related to the thermodynamic equilibrium binding constant, which is 10
5
. Additionally, cyclodextrins are only useful in solubilizing compounds with low molecular weights, and the compound must be partially soluble (around 1 &mgr;g/ml).
U.S. Pat. No. 5,747,066 of Pittrof and Steffen describes the formation of mixed micelles for aqueous solubilization of active substances using phosphatides which are phospholipids comprised of glycerol, fatty acids, and phosphocholine. The critical micellar concentration (cmc) of phosphatides decreases as the length of the fatty acyl chain increases (Jones and Chapman, 1995), such that for all practical purposes, there is no appreciable concentration of monomeric species of natural membrane phosphatides with C16 to C18 acyl chains. While the use of phosphatides disclosed by Pittrof and Steffen is significant, phosphatides are large molecules and since they contain two fatty acyl chains in conjunction with a zwitterionic head group (phosphocholine), they form a variety of lyotropic mesophases in aqueous media. This potentially limits the ability of phospholipids, such as the phosphatides disclosed by Pittrof and Steffen, to solublize a wide variety of pharmaceutical agents. Moreover, these mixed micellar emulsions are meta-stable and precipitation or crystallization of the insoluble drug can occur, which when administered intravenously, can increase the risk of an embolism.
Methods for increasing the bioavailability of several steroid phosphocholine conjugates are disclosed in U.S. Pat. No. 5,703,063. The surfactant properties of one steroid phosphocholine conjugate, namely cholesterol-phosphocholine, is described by Lyte, M. et al. (1979) Chem. Phys. Lipids 24, 45-55 and Ayengar, N. K. N. et al. (1979) Chem. Phys. Lipids 25, 203-208.
Therefore, a need exists for new surfactants to solubilize pharmaceutical agents for various routes of administration. Additionally, biocompatible surfactants that will not cause adverse side effects, and could be used in the delivery of pharmaceutical agents representing a plethora of therapeutic areas, including, but not limited to, proteins, peptides, nucleic acids, and small molecule drugs.
SUMMARY OF THE INVENTION
This invention relates to novel amphipathic phosphocholine derivatives which function as biodegradable and biocompatible surfactants, and their use as excipients in pharmaceutical formulation.
It is an object of the present invention to provide compositions of matter which substantially increase the aqueous solubility of pharmaceutically active agents comprising a micellar or amorphous complex of a phosphocholine surfactant and the agent. The pharmaceutically active agent may include but not limited to, antibiotics, antifungal, antiviral, antineoplastic drugs, analgesics, and anesthetics. The most preferred agents are those which are insoluble or poorly soluble and administered intravascularly, such as etoposide, paclitaxel, propofol, and cyclosporin.
DETAILED DESCRIPTION OF THE INVENTION
All patent applications, patents and literature reference cited herein are hereby incorporated by reference in their entirety.
The present invention relates to the unexpected discovery that the intrinsic aqueous solubility of various phosphocholine-conjugates varies from 1 mg/ml to greater than 500 mg/ml. This range of solubility is due in part to the formation of unique hydrated micellar structures.
This invention also relates to the unexpected discovery that many phosphocholine conjugates of sterically hindered alcohols, such as secondary and tertiary alcohols or alcohols in which neighboring groups are within van der Waals radii of the alcohol are not rapidly hydrolyzed by serum enzymes; whereas, phosphocholine conjugates of primary and phenolic alcohols are susceptible to enzymatic cleavage. This discovery predicts that phosphocholine-conjugates can function as both biodegradable and biostable surfactants, depending on the chemical nature of the phosphocholine linkage. Non-limiting examples of such sterically hindered alcohols are steroid phosphocholines and cholesterol phosphocholine.
A phosphocholine surfactant is defined herein as a compound in which phosphocholine is attached to a hydrophobic molecule by the formation of a covalent phosphoester bond. Non-limiting examples of the hydrophobic molecule are one of a number of steroids, such as cholesterol; &bgr;-sitosterol[24-ethylcholesterol]; stigmasterol[3-hydroxy 24-ethyl 5,22-cholestadiene]; ergosterol[5,7,22 ergostatrien-3-ol]; 3,7,12-trihydroxy-5-cholane; 3,12-dihydroxy-5&bgr;-cholane; or aliphatic derivatives, such as dodecanol; tetradecanol; hexadecanol; octadecanol; eicosanol; docosanol; tetracosanol; 11-hexadecenol; 9-hexadecenol; 9-octadecenol; or 9,12-octadecadienol. These compounds can be purchased from numerous commercial sources such as Sigma Chemical Co. (St. Louis, Mo.), Aldrich Chemical Co. (Milwaukee, Wis.), Acros Chemicals (Pittsburgh, Pa.) or Fluka Chemical Corp. (Milwaukee, Wis.).
The solubility of a phosphocholine-conjugate is mediated by the formation of a hydrated micellar structure. Unlike liposomes which are metastable thermodynamic structures, micelles are self-associating and thermodynamically stable. Therefore, phosphocholine-based surfactants are potentially useful as new excipients. In addition to solubilization, phosphocholine-surfactants may also function as absorption enhancers by affecting membrane stability and/or disruption. Phosphoch
Barker Peter L.
Hernandez Vincent
Morimoto Bruce H.
Piper Cass K.
Darby & Darby
Qazi Sabiha
SuperGen, Inc.
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