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BACKGROUND OF THE INVENTION
The present invention relates to a novel drug delivery system. More
particularly, the present invention relates to a product in which a
biologically active material is present in a multiphase system, i.e., (a)
captured in multilamellar lipid vesicles (MLV); (b) dissolved in the
solvent components of the system; and (c) in a solid crystalline or
amorphous state.
Liposomes are lipid vesicles composed of membrane-like lipid layers
surrounding aqueous compartments. Liposomes are widely used to encapsulate
biologically active materials for a variety of purposes, but particularly
they are used as drug carriers. Depending on the number of lipid layers,
size, surface charge, lipid composition and methods of preparation various
types of liposomes have been utilized.
Multilamellar lipid vesicles (MLV) were first described by Bangham, et al.,
(J. Mol. Biol. 13: 238:252, 1965). A wide variety of phospholipids form
MLV on hydration. MLV are composed of a number of bimolecular lamellae
interspersed with an aqueous medium. The lipids or lipophilic substances
are dissolved in an organic solvent. The solvent is removed under vacuum
by rotary evaporation. The lipid residue forms a film on the wall of the
container. An aqueous solution generally containing electrolytes and/or
hydrophilic biologically active materials are added to the film. Agitation
produces larger multilamellar vesicles. Small multilamellar vesicles can
be prepared by sonication or sequential filtration through filters with
decreasing pore size. Small unilamellar vesicles can be prepared by more
extensive sonication. An improved method of encapsulating biologically
active materials in multilamellar lipid vesicles is described in U.S. Pat.
No. 4,485,054.
Unilamellar vesicles consist of a single spherical lipid bilayer entrapping
aqueous solution. According to their size they are referred to as small
unilamellar vesicles (SUV) with a diameter of 200 to 500 .ANG.; and large
unilamellar vesicles (LUV) with a diameter of 1000 to 10,000 .ANG.. The
small lipid vesicles are restricted in terms of the aqueous space for
encapsulation, and thus they have a very low encapsulation efficiency for
water soluble biologically active components. The large unilamellar
vesicles, on the other hand, encapsulate a high percentage of the initial
aqueous phase and thus they can have a high encapsulation efficiency.
Several techniques to make unilamellar vesicles have been reported. The
sonication of an aqueous dispersion of phospholipid results in
microvesicles (SUV) consisting of bilayer or phospholipid surrounding an
aqueous space (Papahadjopoulos and Miller, Biochem. Biophys. Acta., 135:
624-238, 1968). In another technique (U.S. Pat. No. 4,089,801) a mixture
of a lipid, an aqueous solution of the material to be encapsulated, and a
liquid which is insoluble in water, is subjected to ultrasonication,
whereby liposome precursors (aqueous globules enclosed in a monomolecular
lipid layer), are formed. The lipid vesicles are then prepared by
combining the first dispersion of liposome precursors with a second
aqueous medium containing amphiphilic compounds, and then subjecting the
mixture to centrifugation, whereby the globules are forced through the
monomolecular lipid layer and forming the bimolecular lipid layer
characteristic of liposomes.
Alternate methods for the preparation of small unilamellar vesicles that
avoid the need of sonication are the ethanol injection technique (S.
Batzri and E. D. Korn, Biochem. Biophys. Acta. 298: 1015-1019, 1973) and
the ether injection technique (D. Deamer and A. D. Bangham, Biochem.
Biophys. Acta. 443: 629-634, 1976). In these processes, the organic
solution of lipids is rapidly injected into a buffer solution where it
spontaneously forms liposomes--of the unilamellar type. The injection
method is simple, rapid and gentle. However, it results in a relatively
dilute preparation of lipsomes and it provides low encapsulation
efficiency. Another technique for making unilamellar vesicles is the so
called detergent removal method (H. G. Weder and O. Zumbuehl, in "Liposome
Technology" ed. G. Gregoriadis, CRC Press Inc. Boca Raton, Fla., Vol. I,
Ch. 7, pg 79-107, 1984). In this process the lipids and additives are
solubilized with detergents by agitation or sonication yielding defined
micelles. The detergents are then removed by dialysis.
Multilamellar vesicles can be reduced both in size and in number of
lamellae by extrusion through a small orifice under pressure, e.g., in a
French press. The French press (Y. Barenholz; S. Amselem and D.
Lichtenberg, FEBS Lett. 99: 210-214, 1979), extrusion is done at pressures
of 20,000 lbs/in at low temperature. This is a simple, reproducible,
nondestruction technique with relatively high encapsulation efficiency,
however it requires multilamellar liposomes as a starting point, that
could be altered to oligo- or unilamellar vesicles. Large unilamellar
lipid vesicles (LUV) can be prepared by the reverse phase evaporation
technique (U.S. Pat. No. 4,234,871, Papahadjopoulos). This technique
consists of forming a water-in-oil emulsion of (a) the lipids in an
organic solvent and (b) the substances to be encapsulated in an aqueous
buffer solution. Removal of the organic solvent under reduced pressure
produces a mixture which can then be converted to the lipid vesicles by
agitation or by dispersion in an aqueous media.
U.S. Pat. No. 4,016,100, Suzuki, et al., describes still another method of
entrapping certain biologically active materials in unilamellar lipid
vesicles by freezing an aqueous phospholipid dispersion of the
biologically active materials and lipids. All the above liposomes, made
prior to 1983, can be classified either as multilamellar or unilamallar
lipid vesicles. A newer type of liposomes is referred to as multivesicular
liposomes (S. Kim, M. S. Turker, E. Y. Chi, S. Sela and G. M. Martin,
Biochim. Biophys. Acta 728; 339-348, 1983). The multivesicular liposomes
are spherical in shape and contain internal granular structures. A lipid
bilayer forms the outermost membrane and the internal space is divided up
into small compartments by bilayer septrum. This type of liposomes
required the following composition: an amphiphatic lipid with net neutral
charge, one with negative charge, cholesterol and a triacylglycerol. The
aqueous phase containing the material to be encapsulated is added to the
lipid phase which is dissolved in chloroform and diethyl ether, and a
lipid-in-water emulsion is prepared as the first step in preparing
multivesicular liposomes. Then a sucrose solution is shaken with the
water-in-lipid emulsion; when the organic solvents are evaporated
liposomes with multiple compartments are formed.
For a comprehensive review of types of liposome and methods for preparing
them refer to a recent publication "Liposome Technology" Ed. by G.
Gregoriadis. CRC Press Inc., Boca Raton, Fla., Vol. I, II, & III 1984.
Solutions are one of the oldest type of pharmaceutical dosage forms or drug
delivery systems. A true solution is defined as a mixture of two or more
components that form a homogeneous molecular dispersion, i.e., a one phase
system. According to the United States Pharmacopeia, Twentieth Revision
(USP XX, page 1027), solutions are liquid preparations that contain one or
more soluble chemical substances usually dissolved in water. Further,
solutions are used for the specific therapeutic effect of the solute,
either internally or externally. Id.
Suspensions are preparations of finely divided, undissolved drugs dispersed
in liquid vehicles (USP XX page 1030). In this sense a suspension is a
heterogenous, two-phase system. Suspensions have been used as drug
delivery systems for centuries, for providing an insoluble bioactive
ingredient for oral, parenteral and for the topical route of
administration. In the present multicomponent, multiphase liposomal system
the biologically active substance is present in the solid form dispersed
in the aqueous medium both inside and outside the lipid vesicles.
Hydrogels can be any one of a wide variety of synthetic and natural
hydrophilic polymers. They are used in pharmaceutical dosage formulation
for various purposes, i.e., as viscosity inducing agents for suspensions
and ophthalmic solutions; as protective colloids to stabilize emulsions
and suspensions; as vehicles for topically applied dosage forms; as
controlled-release drug delivery systems (J. D. Andrade (ed) "Hydrogels"
for Medical and Related Applications: ACS Symposium, Series Nol. 31 ACS
Washington, D.C., 1976). A gel is generally a semisolid system of at least
two constituents, consisting of a condensed mass enclosing and
interpenetrated by a liquid. The gel mass may consist of flocculles of
small particles or macromolecules existing as twisted, intermingled,
matted strands. The polymer units are often bound together by
electrostatic, hydrogen and van der Waal forces. Gels containing water are
called hydrogels, those containing organic liquid are called organogels.
The hydrophilic polymers in aqueous media exhibit "pseudoplastic flow" due
to the effect of intermolecular entanglements and the binding of water
molecules. When the long randomly coiled polymer chain moves, their
solvation layer (water of hydration) are dragged along which increases the
resistance to flow, or the viscosity of the solution. This property is
often utilized in pharmaceutical formulation to increase the viscosity of
the preparation. Recently the hydrogels have been disclosed as useful for
a controlled drug delivery system (S. W. Kim, Pharmacy International 4:
90-91 (1983)).
PRIOR ART
A large number of liposomal preparations are known, as described above. A
method for preparing liposomal preparations using contact masses such as
glass beads to increase the surface area for liposome formation is
described in U.S. Pat. No. 4,485,054. Several publications disclose the
use of glass beads and the like to accelerate dispersion during the
addition of the aqueous phase. See, e.g., U.S. Pat. No. 4,342,826; UK
patent application No. 2,050,833; A. D. Bangham, et al., Methods in
Membrane Biology 6 (London 1974); and A. D. Bangham, et al, Chem. Phys.
Lipids 1:266 (1967).
SUMMARY OF THE INVENTION
The present invention particularly provides:
a pharmaceutical composition comprising:
(a) multilamellar lipid vesicles with a slightly water soluble biologically
active compound captured therein;
(b) a saturated solution of the biologically active compound; and
(c) the biologically active compound in solid form. The present invention
further provides:
(1) the composition described above wherein the vesicles, the solution, and
the solid form of the biologically active compound are dispersed in a
hydrocolloidal gel; and
(2) a method for preparing this latter composition comprising
(a) providing a vessel partially filled with inert, solid contact masses;
(b) providing a lipid component and the biologically active material
dissolved in a suitable organic solvent within the vessel;
(c) removing the organic solvent by evaporation so as to form a thin lipid
film on the inner wall of the vessel and on the surfaces of the contact
masses;
(d) thereafter adding an aqueous liquid solution containing the
biologically active material and possibly electrolytes and hydrocolloids
to the vessel, and agitating the vessel to form an aqueous dispersion of
lipid, gel and bioactive substances; and
(e) allowing the dispersion to stand essentially undisturbed for a time
until the formation and dispersion of the multilamellar lipid vesicles and
the hydrogen is completed.
The present invention further provides:
a method for administration of slightly water soluble biologically active
compounds comprising topically applying a composition described above.
Alternatively, where the biologically active material has a melting point
low enough to be fused together with the lipid components without any
chemical decomposition (typically less than 100.degree. C.) and the
biologically active ingredient(s) in powder form and placed in the vessel
containing the solid contact masses and fused together by rotating or
shaking the vessel.
During the above procedures, a person having experience in the art of
making liposomes can easily realize, that optimal results can be achieved,
if various temperatures are utilized, depending on the transition
temperature of the lipid component(s) and depending on the nature of the
hydrogels, the efficiency of encapsulation can be favorably affected by
selection of the appropriate types of lipids, the shape and size of the
vessel in which the procedures are carried out, the amount and size of
solid contact masses, the degree of vacuum during evaporation and the
agitation and the temperature during hydration of the lipid film. A thin,
even film is desired for optimal results.
Generally, dipalmitoyl phosphatidyl choline, pear shaped flasks, mild
heating, (up to about 60.degree. C.) and mild vacuum are preferred.
The present invention thus provides a liposomal product which contains a
biologically active material in a higher concentration than its water
and/or lipid solubility. The active material is dispersed in the product
in (a) liposome encapsulated form (b) in super-saturated solution form and
(c) in solid form. Further objectives of this invention are: (a) to
provide a process that ensures maximum encapsulation of the biologically
active material in the lipid vesicles; (b) to efficiently accommodate both
lipophilic and hydrophilic substances; and (c) to provide a process of
preparation which is applicable for large scale production.
A product composed of the multicomponent system of this invention is
suitable for various routes of drug administration, i.e., oral, rectal,
parenteral and particularly local administration to the skin, eye and
mucous membranes. This multicomponent system, in which the active
ingredient is present in two states, i.e., in solution and in solid form
within and outside the lipid vesicles provides a unique biopharmaceutical
system, where the absorption and disposition of the biologically active
material can be optimized. It is especially useful for local activity
because of the different rates of absorption, distribution (clearance) and
metabolism, due to its various states, (i.e., in the "free" form in
solution, as solid particles, in the liposome-encapsulated form, and as
dissolved molecules and particles).
These and other objectives are achieved by utilizing the method for
preparing multilamellar lipid vesicles described in U.S. Pat. No.
4,485,054, and is expressly incorporated herein by reference, to formulate
a biologically active ingredient in a concentration above its water and
lipid solubility.
The process is characterized by the following steps:
(a) providing a vessel partially filled with inert, solid contact masses;
(b) providing a lipid component and the biologically active material
dissolved in a suitable organic solvent within the vessel;
(c) removing the organic solvent by evaporation so as to form a thin lipid
film on the inner wall of the vessel and on the surfaces of the contact
masses;
(d) thereafter adding an aqueous liquid containing the biologically active
material and/or other substances to the vessel and agitating the vessel to
form an aqueous dispersion of lipid and bioactive substance; and
(e) allowing the dispersion to stand essentially undisturbed for a time
until the formation and dispersion of the multilamellar lipid vesicles is
completed.
As noted above, the lipid film can be formed without using organic solvents
if the ingredients (lipids and biologically active materials) have a
melting point low enough to be fused together with the lipid components
without causing thermodecomposition.
If desired the size of the lipid vesicles and solid particles can be
reduced by ultrasonication. Dispersion of the lipid vesicles and the
bioactive material (including the gel) can be further improved by putting
the product through a homogenizer.
To manufacture the liposomal preprations of the present invention on a
larger scale. The procedure described above (and in U.S. Pat. No.
4,485,054) is modified by replacing the writs action shaker with a gyro
shaker and using an oven to provide the appropriate temperature
environment rather than a water bath. Equipment employing a container and
a shaker with gyro action could be used.
In the present invention the biologically active material is dissolved,
i.e., present in a molecular state in both the aqueous media and in the
lipid media. Its aqueous solution is present both within and outisde the
lipid vesicles. Since the present invention contains the biologically
active material also in the solid form, the solution phase should be in a
saturated state.
As used in the specification and claims, the terms(a) "biologically active
material", "biologically active substance" or "bioactive" ingredient mean
a compound or composition which, when present in an effective amount,
produces an effect in living cells or organisms. Examples of biologically
active compounds used in this invention include dermatological agents,
(i.e., triamcinolone acetonide, retinoic acid); antibacterial agents
(e.g., ampicillin); antifungal agents (e.g., econazole base, econazole
nitrate, amphotericine B); anti-convulsants (e.g., diphenylhydantoin);
antihypertensive agents (e.g., minoxidil); anticancer agents (e.g.,
methotrexate); immunomodulators (e.g., lipophilic derivatives of muramyl
dipeptide), antiviral agents (acyclovir, interferons); nonsteroidal
anti-inflammatory agents (e.g., ibuprofen); and the like. By "slightly
water soluble" is a solubility in water which is too low for the
biologically active compound to be practically used in conventional
aqueous solution formulations, i.e., the water solubility compared to the
potency of the compound is too low for an effective dose to be practically
administered in aqueous solution form or in other types of liposomal
forms. Examples of such slightly soluble biologically active compounds are
those described above.
"Hydrogel", "hydrocolloid" or "gel" means any chemical substance which
exhibits the ability to swell in water, retaining a significant amount of
water within its structure; it could be inorganic, e.g., bentonite or
organic, e.g., methylcellulose; single or polymer compound. Any of the
known lipids and lipid-like substances can be used in the present
invention, both from natural or synthetic sources, such as ceramides,
lecithins, phosphatidyl ethanolamines, phosphatidyl serines, cardiolipins,
trilinoleins, phophatidic acid, and like compounds.
The present invention may be used as a vehicle for drug delivery for both
human and veterinary purposes. By "drug" is meant any biologically active
compound which is useful for human or veterinary purposes and is capable
of being captured by the vesicles of this invention.
Thus, drugs which are employed in the present invention are any slightly
water soluble drug capable of being captured by the lipid vesicles in some
way. "Captured" includes entrapment within the enclosed lipid bilayer
(either by fusing smaller vesicles around the drug or by transmission
through the membrane or forming the lipid vesicles within the solution
containing the drug), or (for lipophilic or ampophilic drugs)
incorporation into, or binding them to, the lipid membrane itself. These
drugs may be of varying degrees of lipophilicity, and their use in the
present invention would be obvious to a pharmaceutical formulator skilled
in the art of lipid chemistry when the properties of these vesicles are
described.
Advantages of this multicomponent liposomal system are:
(a) Biologically active ingredients can be incorporated into this liposomal
system in a concentration higher than their water or lipid solubility.
Consequently this system is particularly suitable for compounds with low
lipid or water solubility where purely liposomal preparations can contain
the ingredient only in low concentration, which may prevent proper dosing
for activity of the ingredient in solution or other previously known
liposomal forms.
(b) The bioactive ingredients are present in this system (i) in solution
form possibly in a supersaturated state, either encapsulated in the lipid
vesicle, or outside the lipid vesicle in both the aqueous and in the lipid
phase; and (ii) in solid state, crystalline or in amorphous form both
within or outside of the lipid vesicles.
Consequently the biopharmaceutical fate of the bioactive material will be
different according to its state, i.e., the rate of absorption and in vivo
disposition of the liposome-encapsulated, and the "free" solution, and the
solid form of the ingredient will be different. It is anticipated that
this difference will provide a sustained-prolonged action.
(c) The activity of the bioactive ingredients may be localized at or near
the site of application, i.e., skin, eye and mucocutaneous membranes
(lung, nose, and gastrointestinal tract, and vagina). The large
multilamellar lipid vesicles penetrate these organs, but, because of their
size, they are not taken up by the blood circulation. The lipid vesicles
may also act within the organ, as a slow-release vehicle. The prolonged
release and the reduced clearance rate leads to an accummulation of the
bioactive ingredient at or near the site of application, which results in
an intensification and also in prolongation of the local action, with a
reduction in systemic action. The "free" form also penetrates into these
organs at a higher rate, because of the presence of liposomes results in
an occlusive effect. The "free" form of the bioactive ingredient can also
be bound to the lipid vesicles or "dragged along" with the liposomes into
the tissue.
The hydrogels, besides influencing the structure and inter-relation of the
lipid vesicles, are particularly useful for topical application because of
their effect on the viscosity and adhesive properties of the final
product. Certain hydrogels also directly affect the absorbing biological
membranes, especially the muco-cutaneous membranes.
The bioactive ingredient is dissolved in the aqueous solution at a
saturation level. The bioactive material is also present in the lipid film
in a concentration higher than its lipid solubility. The lipsome formation
is taking place at higher than room temperature, therefore, at the
completion of the product, the bioactive ingredient will be present in
solution in both the aqueous and lipid phase in a saturated state and also
in crystalline or amorphous solid state. No attempt is made to prepare and
separate the liposomal fraction. Instead the system is intentionally made
heterogeneous, where the bioactive material is dispersed in solution and
in solid form both within and outside the lipid vesicles, and the lipid
vesicles are dispersed in an aqueous media.
The present invention differs from previously known liposomal compositions
in that the product formed contains the biologically active material in
solid and molecular (dissolved) state in both "liposome-encapsulated" and
in "free" form.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is seen more fully by the Examples given below.
EXAMPLE 1
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Formula
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(i) DL alpha dipalmitoyl 400 mg
phosphatidylcholine (DPPC)
Cholesterol 200 mg
Minoxidil 100 mg
(ii) Minoxidil 20 mg
Ethanol (95%) 1 ml
Propylene glycol 0.7 ml
Calcium chloride (8 mM)
8.3 ml
solution
______________________________________
(i) Components of (i) DPPC, cholesterol and minoxidil were codissolved in
100 ml of chlorform-methanol solvent (2:1) in a 500 ml pear-shaped flask.
The solvent was evaporated under vacuum in a rotary evaporator; the lipid
and minoxidil residue formed a thin film on the wall of the pear-shaped
flask.
(ii) Separately 20 mg minoxidil was dissolved in 0.7 ml propylene glycol
and 1 ml ethanol in a 50 ml Erlenmeyer flask at 40-50.degree. C.; 8.3 ml
CaCl.sub.2 solution was added and the temperature of this solution was
brought up to 55-60.degree. C.
The pear-shaped flask containing the lipid-monoxidil solid film still under
vacuum was also brought up to 55.degree.-60.degree. C. The aqueous
solution (ii) was added to the lipid-minoxidil film and shaken with the
aid of a wrist shaker for 30 minutes immersed in a water bath set at
60.degree. C. The resultant liposomal suspension was allowed to stand for
one hour at room temperature.
One droplet of this preparation was examined microscopically under
polarized light with 640.times.magnification. Spherical shaped liposomes
of various sizes (between 1.mu. to 15.mu. diameters) were observed along
with minoxidil crystals.
EXAMPLE 2
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Formula
______________________________________
(i) DL alpha dipalmitoyl 400 mg
phosphatidylcholine (DPPC)
Cholesterol 200 mg
Minoxidil 100 mg
(ii) Minoxidil 20 mg
Ethanol (95%) 1 ml
Propylene glycol 0.7 ml
Calcium chloride (8 mM)
8.7 ml
solution
(iii) Methylcellulose 1500 cps
10 mg
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(i) Components of (i) DPPC, cholesterol and minoxidil were codissolved in
100 ml of chloroform-methanol solvent (2:1) in a 500 ml pear-shaped flask.
The solvent was evaporated under vacuum in a rotary evaporator; the lipid
and minoxidil residue formed a thin film on the wall of the pear-shaped
flask. (ii) Separately 20 mg of minoxidil in 1 ml of ethanol were placed
in an Erlenmeyer flask at 40.degree.-50.degree. C.; 8.3 ml CaCl.sub.2
solution was added and the temperature of this solution was brought up to
55.degree.-60.degree. C.
The pear-shaped flask containing the lipid-minoxidil solid film still under
vacuum was also brought up to 55.degree.-60.degree. C. Then the aqueous
solution (ii) and the 10 mg Methylcellulose powder (iii) were added to the
lipid-minoxidil film and shaken with the aid of a wrist shaker for 30
minutes immersed in a water bath set to 60.degree. C. The flask was then
placed in an ice-bath (approx. 4.degree. C.) and shaken there for 10
minutes. The resultant liposomal suspension was allowed to stand for one
hour at room temperature.
One droplet of this preparation was examined microscopically under
polarized light with 640.times.magnification. Sperical and tubular shaped
liposomes of various sizes (between 1.mu. to 15.mu. diameters) were
observed along with minoxidil micro crystals. Most of the liposomes were
closely associated with each other forming unusual conglomerates of the
lipid vesicles interspaced with the hydrocolloid (methylcellulose)
bridges.
EXAMPLE 3
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Formula
______________________________________
(i) DL alpha dipalmitoyl 400 mg
phosphatidylcholine (DPPC)
Cholesterol 100 mg
Minoxidil 100 mg
(ii) Minoxidil 20 mg
Sodium Carboxymethylcellulose
10 mg
Ethanol (95%) 1 ml
Propylene glycol 0.7 ml
(iii) Calcium chloride (8 mM)
8.3 ml
solution
______________________________________
(i) Components of (i) DPPC, cholesterol and minoxidil were codissolved in
100 ml of chloroform-methanol solvent (2:1) in a 500 ml pear-shaped flask.
The solvent was evaporated under vacuum in a rotary evaporator; the lipid
and minoxidil residue formed a thin film on the wall of the pear-shaped
flask. (ii) Separately 20 mg minoxidil was dissolved in 0.7 ml propylene
glycol and 1 ml ethanol. This solution is gradually added to 10 mg sodium
carboxymethylcellulose to prewet the hydrocolloid. CaCl.sub.2 solution
(8.3 ml) is heated up to 55.degree.-60.degree. C. and added to the flask
containing the lipid-minoxidil film. Within 1-2 seconds the sodium
carboxymethylcellulose suspension was added to the same flask which was
immersed in a water bath set to 60.degree. C. Then the flask was shaken
with the aid of a wrist shaker for 30 minutes immersed in a water bath set
to 60.degree. C. The resultant liposomal suspension was allowed to stand
for one hour at room temperature.
One droplet of this preparation was examined microscopically under
polarized light with 640.times.magnification. Spherical and tubular shaped
liposomes of various sizes (between 1.mu. to 15.mu. diameters) were
observed along with a few micro crystals. Most of the liposomes were
closely associated with each other forming unusual conglomerates of the
lipid vesicles interspaced with the hydrocolloid (sodium carboxy
methylcellulose) bridges.
EXAMPLE 4
In a manner similar to the preceding examples several other compositions
were prepared and tested, including
(a) varying the concentrations of methylcellulose (0.1%-1%), and minoxidil
(3%);
(b) using purified soybean or egg lecithin in place of the DPPC;
(c) using other hydrocolloids (e.g, Veegum, colloidal silica, xanthan,
tragacanth);
(d) including preservative or antioxidant agents (e.g., benzoic acid,
methyl and propyl paraben, BHA, tocopherol, benzyl alcohol);
(e) varying the proportion of DPPC, or other type of lecithins, and
cholesterol; and
(f) using other slightly soluble compounds in place of the minoxidil, e.g.,
econazole base, econazole nitrate, progesterone, .beta.-estradiol,
testosterone and the others described above.
Glass beads (40-60 beads with 5 mm diameter) usually were placed in the
pear-shaped flask before the evaporation of the organic solvent. The
products prepared in the presence of glass beads always had a better
quality in comparison to those prepared without glass beads; i.e., they
contained a higher number of liposomes and a smaller number of minoxidil
crystals. Another advantage of using the glass beads is that the minoxidil
crystal size was greatly reduced and the intermingling of the
hydrocolloids and lipid vesicles was more noticeable. The major advantage
of using the glass beads or any solid contact masses is of course the
possibility of large, industrial scale production.
EXAMPLE 5
In this example minoxidii as a model for a slightly soluble biologically
active material is incorporated in the multicomponent (heterogeneous)
liposomal system of Examples 1 and 2. This compound was selected, because
of its physicochemical properties, because of its solubility properties
(very slightly soluble in aqueous or in lipid media), it is not a good
candidate for liposomal encapsulation. This compound is an oral
antihypertensive agent (the active ingredient of LONITEN Tablets), and is
useful topically to grow hair (See U.S. Pat. No. 4,139,619). The known
methods to encapsulate minoxidil in uni- and multilamellar liposomes
resulted in liposomal preparations containing no more than 0.2-0.4%
minoxidil (see Table I). The liposomal encapsulation of the bioactive
ingredient is always limited by its solubility, i.e., one cannot make the
liposomal preparation more concentrated, than the solubility of the
bioactive ingredient in the liposomal media. Minoxidil solubility in
deionized water is 2.4 mg/ml (0.24%), and in organic solvents (e.g.,
chloroform, acetone, ethyl acetate, benzene, diethyl ether, 2-propanol,
etc.) minoxidil solubility is less than 1 mg/ml (0.1%).
According to the present invention multicomponent liposomal systems that
contain 1.2%, 2%, and 3% minoxidil were prepared. It is possible to
increase the minoxidil concentration even higher. The total amount of
minoxidil was not present within the lipid vesicles; some portion of the
minoxidil was outside the lipid vesicle in solution and in solid form, but
as a drug delivery system this is advantageous for topical application,
for localizing the bioactive ingredient (i.e., minoxidil) at or within the
organ to which the composition is applied. Results of animal experiments
for drug disposition studies confirm this. The test preparations contained
1.2%, 2%, and 3% minoxidil in the multicomponent liposomal drug delivery
system. Two control preparations were used, containing corresponding
concentrations of minoxidil (i.e., 1.2%, 2%, and 3%) in a solution form. A
2% minoxidil suspension, containing the identical lipid components in a
nonliposomal form, was also prepared for control purposes.
The hair of the dorsal area of albino guinea pigs (300-500 g) was clipped
off and an area of 3.times.3 cm was marked. Five groups of guinea pigs
were used; the first group was treated with multiphase liposomal minoxidil
1.2%, the second group with 1.2% minoxidil solution, the third with 1.2%
minoxidil in a multiphase liposome containing 0.1% methyl cellulose, the
fourth group with 3% minoxidil solution, and the fifth group with 3%
monoxidil in a multiphase liposome containing 0.1% methylcellulose. A 0.1
ml dose was applied in a twice a day dosage schedule. A does of 0.05 ml
twice a day was used for the 2% minoxidil preparations.
The guinea pigs were treated at t=0, 8, 24, 32, 48, 56, and 72 hours, for a
total of seven doses. The drug disposition was determined four hours after
the last dose was applied.
The results are presented in Tables II and III.
The multicomponent liposomal dosage form produced higher concentration of
minoxidil in all skin tissues compared to the conventional solution form.
There was no significant difference between the drug concentrations
measured in the internal organs of guinea pigs treated with minoxidil in
liposomal or in solution form.
EXAMPLE 6
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(i) L .alpha. dipalmitoyl phosphatidylcholine
400 mg
Cholesterol 100 mg
Econazole base 100 mg
(ii) Benzoic acid 20 mg
Butylated hydroxyanisole
0.5 mg
Ethanol 1 ml
CaCl.sub.2 solution, 8 mM
9 ml
(iii) Methylcellulose 1500 10 mg
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In this example the fine powder form of the lipid components and of the
econazole base was placed in a 500 ml pear-shaped flask alon | | |
