U.S. patent application number 10/780907 was filed with the patent office on 2005-02-03 for anaesthetic bone cement.
This patent application is currently assigned to Queen's University at Kingston. Invention is credited to Adams, Michael A., Bond, David M., Rudan, John F..
Application Number | 20050027034 10/780907 |
Document ID | / |
Family ID | 27408689 |
Filed Date | 2005-02-03 |
United States Patent
Application |
20050027034 |
Kind Code |
A1 |
Bond, David M. ; et
al. |
February 3, 2005 |
Anaesthetic bone cement
Abstract
The invention relates to surgical bone cement compositions and
more particularly to bone cement compositions having anaesthetic
properties, and to methods for producing analgesia.
Inventors: |
Bond, David M.; (Glenburne,
CA) ; Rudan, John F.; (Kingston, CA) ; Adams,
Michael A.; (Kingston, CA) |
Correspondence
Address: |
LAHIVE & COCKFIELD, LLP.
28 STATE STREET
BOSTON
MA
02109
US
|
Assignee: |
Queen's University at
Kingston
Kingston
CA
|
Family ID: |
27408689 |
Appl. No.: |
10/780907 |
Filed: |
February 17, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10780907 |
Feb 17, 2004 |
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10003769 |
Nov 15, 2001 |
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6713527 |
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10003769 |
Nov 15, 2001 |
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09365175 |
Aug 2, 1999 |
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09365175 |
Aug 2, 1999 |
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PCT/CA98/00060 |
Feb 2, 1998 |
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PCT/CA98/00060 |
Feb 2, 1998 |
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08799007 |
Feb 7, 1997 |
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PCT/CA98/00060 |
Feb 2, 1998 |
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08825943 |
Apr 1, 1997 |
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6355705 |
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Current U.S.
Class: |
523/118 |
Current CPC
Class: |
A61L 2300/402 20130101;
Y10S 514/817 20130101; A61L 24/0015 20130101; A61L 2430/02
20130101; Y10S 514/816 20130101; Y10S 514/818 20130101 |
Class at
Publication: |
523/118 |
International
Class: |
C08K 003/00 |
Claims
1. An anaesthetic bone cement composition comprising a bone cement
including an effective amount up to about 5% by weight of a local
anaesthetic.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/003,769, filed Nov. 15, 2001, allowed,
which is a continuation of 09/365,175 filed on Aug. 2, 1999,
abandoned, which is a continuation of PCT/CA98/00060 filed Feb. 2,
1998, which is a continuation-in-part of U.S. patent application
Ser. No. 08/799,007, filed Feb. 7, 1997, abandoned, and is a
continuation-in-part of U.S. patent application Ser. No.
08/825,943, filed Apr. 1, 1997, issued as U.S. Pat. No. 6,355,705,
the specifications of which are incorporated herein in their
entirety by reference.
FIELD OF THE INVENTION
[0002] This invention relates to surgical bone cement compositions
and more particularly to bone cement compositions having
anaesthetic properties, and to methods for producing analgesia.
BACKGROUND OF THE INVENTION
[0003] Polymer based surgical bone cements have been used for many
years to fill voids in bones and to improve fixation of implanted
orthopaedic prosthetic devices. Typically such cements contain
polymers or copolymers of alkyl methacrylate and/or copolymers of
methyl methacrylate with methyl acrylate or styrene. The liquid
compound consisting of esters of acrylic or methacrylic add
(typically methyl methacrylate) is packaged in an ampoule, possibly
with additives such as premature polymerization preventers such as
hydroquinone, and curing promoters such as
N,N-dimethyl-p-toluidine. A polymerization initiator, typically an
organic peroxy compound such as powdered benzoyl peroxide, is
combined with the polymeric component and a radiopacifier (such as
barium sulphate or zirconium dioxide) for rendering the bone cement
opaque to X-rays. The polymeric materials are generally sterilized
by either irradiation or gas sterilization. In use, typically a
bone is cut and prepared to receive a surgical implant and then the
liquid and dry components of the cement, contained in the ampoule
and powder bag are mixed together to form a paste which can then be
applied by the surgeon to the cut bone. The implant can then be set
in the paste which, when fully polymerized, forms a continuous
solid interface between the implant and the bone.
[0004] It is also known to incorporate therapeutic or diagnostic
substances into the bone cement for various purposes. For example,
U.S. Pat. No. 4,900,546, issued 13 Feb. 1990, to Posayn Dowty et
al, teaches the incorporation of antibiotics such as gentamycin,
penicillin and tetracycline; anti-cancer drugs; anti-inflammatory
drugs; immuno-stimulants; immuno-suppressants; osteogenic promoters
and diagnostic substances such as radioactive tracers. While some
anti-inflammatory drugs may have analgesic properties, such
compounds are not anaesthetics.
[0005] Although local anaesthetics, such as lidocaine and
prilocaine are known to have potent anti-microbial activity
(anti-bacterial and anti-fungal), when used in relatively high
dosages (0.5-2% solution) (J. Infect. Diseases, 121:597-607, 1970),
heretofore such anaesthetic compounds have not been incorporated
into bone cements for the promotion of anaesthesia. It has now been
found that substantial pain relief can be achieved by incorporating
into a known bone cement composition a local anaesthetic at a
dosage level several orders of magnitude lower than would be
required to achieve an anti-microbial effect with such
anaesthetic.
OBJECT OF THE INVENTION
[0006] An object of the present invention is to provide novel bone
cement compositions which incorporate an anaesthetic, and have
analgesic properties. Another object of this invention is to
provide a method for producing analgesia in the vicinity of a bone
surgery site.
SUMMARY OF THE INVENTION
[0007] By a broad aspect of this invention, there is provided an
anaesthetic bone cement comprising a bone cement composition
including an effective amount up to about 5% by weight of an
anaesthetic, preferably a local anaesthetic.
[0008] By a preferred aspect of this invention, there is provided
an anaesthetic bone cement composition comprising: (a) a liquid
monomeric (meth)acrylate composition; (b) a powder comprising at
least one of a homopolymer and a copolymer of methyl methacrylate
containing an effective amount of a polymerization initiator and a
radiopacifier; and (c) an effective amount up to about 5% by weight
of said bone cement composition of a local anaesthetic.
[0009] An anaesthetic bone cement composition in accordance with
the invention includes a local anaesthetic in a physical form such
as, for example, liquids and solids, and a chemical form such as,
for example, acids and bases. A local anaesthetic is released from
the bone cement in a preselected characteristic release profile
that is determined by at least one of chemical form and physical
form of the anaesthetic. An anaesthetic bone cement composition
according to the invention comprises an anaesthetic in an amount
between about 0.007% and about 5% by weight of said cement
composition. An anaesthetic bone cement composition according to
the invention can comprise a local anaesthetic provided in at least
two different forms, the forms being, for example, acids, bases,
solids, and liquids. Also in accordance with the invention, an
anaesthetic bone cement composition can comprises a combination of
at least two anaesthetics selected from the group consisting of
lidocaine, bupivacaine, prilocaine and tetracaine. When a
combination of two or more different anaesthetics are included in
the bone cement composition of the invention, they can be in two
different forms, the forms being selected from the group consisting
of acids, bases, solids, and liquids, or they can be of the same
form.
[0010] By another aspect of this invention, there is provided a
process for producing an anaesthetic bone cement comprising
combining: (a) a liquid monomeric (meth)acrylate; (b) a powdered
component comprising at least one of a homopolymer and a copolymer
of methyl methacrylate, an effective amount of a polymerization
initiator and a radiopacifier; and (c) an effective amount up to
about 5% by weight of a local anaesthetic.
[0011] By yet another aspect of this invention there is provided a
method for producing analgesia at an orthopaedic implant site in a
patient, comprising cutting and preparing a bone at said site to
receive said implant and applying to said prepared bone a bone
cement composition comprising: (a) a liquid monomeric
(meth)acrylate composition; (b) a powder comprising at least one of
a homopolymer and a copolymer of methyl methacrylate containing an
effective amount of a polymerization initiator and a radiopacifier;
and (c) an effective amount up to about 5% by weight of said bone
cement composition of a local anaesthetic.
[0012] According to the method of the invention, a local
anaesthetic included in a bone cement composition can be in a
physical form such as, for example, liquids and solids, and a
chemical form such as, for example, acids and bases. A local
anaesthetic is released from the bone cement in a preselected
characteristic release profile that is determined by at least one
of chemical form and physical form of the anaesthetic. An
anaesthetic bone cement composition according to the method of the
invention comprises an anaesthetic in an amount between about
0.007% and about 5% by weight of said cement composition. An
anaesthetic bone cement composition according to the method of the
invention can comprise a local anaesthetic provided in at least two
different forms, the forms being, for example, acids, bases,
solids, and liquids. Also in accordance with the method of the
invention, an anaesthetic bone cement composition can comprises a
combination of at least two anaesthetics selected from the group
consisting of lidocaine, bupivacaine, prilocaine and tetracaine.
When the method of the invention involves use of a combination of
two or more different anaesthetics, they can be in two different
forms, the forms being selected from the group consisting of acids,
bases, solids, and liquids, or they can be of the same form.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a graph showing release of lidocaine from
Howmedica bone cement;
[0014] FIG. 2 is a graph showing release of lidocaine from Zimmer
bone cement;
[0015] FIG. 3 is a graph showing release of lidocaine from DePuy
CMW3 bone cement;
[0016] FIG. 4 is a graph showing release profiles of crystalline
and liquid lidocaine and prilocaine base from DePuy CMW3 bone
cement;
[0017] FIG. 5 is a graph showing release profiles of crystalline
and liquid lidocaine HCl from DePuy CMW3 bone cement; and
[0018] FIG. 6 is a graph showing release profiles of crystalline
lidocaine base and crystalline lidocaine HCl from DePuy CMW3 bone
cement.
DETAILED DESCRIPTION OF THE INVENTION
[0019] By one aspect, this invention pertains to compositions
comprising bone cement and an anaesthetic, preferably a local
anaesthetic. The compositions of the invention provide a means by
which the anaesthetic can be delivered precisely to the site where
it is required, for reduction or elimination of pain,
simultaneously with the application of bone cement. Compositions of
the invention are useful in, but not limited to, surgical
procedures involving, for example, manipulation, repair, and
replacement of bone and of joints between bones. A typical example
of a procedure in which compositions of the invention may be
employed is hip replacement surgery. Compositions according to the
invention are therefore also useful in procedures in which
prosthetic devices or orthopaedic implants are attached to bone. In
general, therefore, the compositions of the invention may be
employed in any surgical procedure in which bone cement is employed
and analgesia is desired.
[0020] One advantage of the compositions according to the invention
is that the combination of bone cement and an anaesthetic does not
result in any reduction in efficacy of the anaesthetic or of the
bone cement. Moreover, the combination of bone cement and
anaesthetic according to the invention provides a sustained release
of the anaesthetic over a prolonged period such as, for example,
several days, eliminating the need for repeated administration of
anaesthetic. A further advantage of the compositions of the
invention is that delivery of the anaesthetic precisely to the
source of pain permits smaller doses of anaesthetic to be used,
relative to conventional modes of administration such as
intramuscular injection. Further, local delivery of the anaesthetic
to the site where it is required may provide enhanced efficacy.
[0021] Bone cements suitable for use in the compositions of the
invention include any commercially available bone cements generally
comprising a liquid monomeric (meth)acrylate composition and a
powder comprising at least one of a homopolymer and a copolymer of
methyl methacrylate containing an effective amount of a
polymerization initiator and a radiopacifier. Suitable bone cements
are, for example, Howmedica Simplex.RTM. (Limerick, Ireland),
Zimmer Osteobond.TM. (Warsaw, Ind.), and DePuy.RTM. CMW3.TM. and
CMW Endurance.TM. (Warsaw, Ind.). DePuy CMW3 is a preferred bone
cement. However, the invention is not limited to these bone cements
and others may be equally suitable.
[0022] Anaesthetics suitable for use in the compositions of the
invention are, for example, lidocaine, bupivacaine, prilocaine
(amide family), and tetracaine (ester family). However, the
invention is not limited to these anaesthetics and others may be
equally suitable. A preferred anaesthetic is Xylocaine.RTM. (Astra
Pharmaceuticals, Sodertalje, Sweden) brand of lidocaine. The
compositions of the invention contain an effective amount of the
anaesthetic, which amount is up to about 5% by weight of the bone
cement composition. In some cases, the anaesthetic incorporated in
the bone cement composition may be provided in a precursor (or
"prodrug") form which is converted in vivo to an anaesthetic that
produces analgesia according to the invention. (See R. B.
Silverman, The Organic Chemistry of Drug Design and Drug Action,
Academic Press, Chapter 8, 1992.) Prodrugs (for example, an ester
which is hydrolyzed in vivo) are employed in the art to alter
biodistribution of an active compound or to modify metabolic or
kinetic properties thereof.
[0023] As used herein, the term "effective amount" means an amount
of anaesthetic required to achieve the desired result of reduction
or elimination of pain.
[0024] As used herein, the term "anaesthetic" refers to a compound
that reversibly depresses neuronal function, producing loss of
ability to perceive pain or other sensations.
[0025] As used herein, the term "local anaesthetic" refers to a
compound that reversibly depresses neuronal function, producing
loss of ability to perceive pain or other sensations, the local
anaesthetic acting locally, i.e., at the site or vicinity of its
application, to prevent perception of pain.
[0026] Anaesthetics are generally amides or ester compounds which
depress neuronal function and thus deaden or block pain by
inhibiting the neural transmission of pain signals. Anaesthetics
are therefore different from NSAID analgesic compounds such as
aspirin or acetaminophen which act in an entirely different manner
to provide analgesia but not anaesthesia.
[0027] As used herein, the term "analgesia" refers to a
neurological or pharmacological state characterized by an absence
of normal sensibility to pain, without an effect on consciousness.
Accordingly, painful stimuli are either not perceived at all, or
they are moderated such that, even though they may still be
perceived, they are no longer painful.
[0028] The present invention is concerned with the use of local
anaesthetics, such as lidocaine, bupivacaine, prilocaine (amide
family), and tetracaine (ester family) to provide analgesia in body
tissues surrounding a surgical site in which a bone cement has been
employed.
[0029] By another aspect, this invention pertains to a process for
producing an anaesthetic bone cement composition comprising
combining a commercially available bone cement such as, but not
limited to, Howmedica Simplex, Zimmer Osteobond, and DePuy CMW3 and
CMW Endurance, with an effective amount up to about 5% by weight of
a local anaesthetic. Bone cements suitable for use in the process
of the invention generally comprise a liquid monomeric
(meth)acrylate composition and a powder comprising at least one of
a homopolymer and a copolymer of methyl methacrylate containing an
effective amount of a polymerization initiator and a radiopacifier.
Examples of anaesthetics suitable for use in the process of the
invention are lidocaine, bupivacaine, prilocaine (amide family),
and tetracaine (ester family), and others may be equally
suitable.
[0030] By yet another aspect, this invention pertains to a method
for producing analgesia in a patient at the site of a surgical
procedure involving manipulating, repairing, and/or replacing bone
and joints between bones, and including, for example, implanting
prosthetic or orthopaedic devices. The method of the invention
comprises preparing bones at the site and applying to the prepared
bones a bone cement composition comprising a liquid monomeric
(meth)acrylate composition, a powder comprising at least one of a
homopolymer and a copolymer of methyl methacrylate containing an
effective amount of a polymerization initiator and a radiopacifier,
and an effective amount up to about 5% by weight of the bone cement
composition of an anaesthetic. Bone cements suitable for use in the
method of the invention include, but are not limited to,
commercially available bone cements such as Howmedica Simplex,
Zimmer Osteobond, and DePuy CMW3 and CMW Endurance. Anaesthetics
suitable for use in the method of the invention include lidocaine,
bupivacaine, prilocaine (amide family), and tetracaine (ester
family), and others may be equally suitable.
[0031] To determine whether local anaesthetics elute from a bone
cement containing from about 2.0% to about 5.0% by weight of the
anaesthetic, a series of elution studies were performed in which
lidocaine (Xylocaine, Astra Pharmaceuticals) was combined with
Howmedica, Zimmer, and DePuy bone cement (see Example 1). The
elution profiles shown in FIGS. 1, 2, and 3 indicate that this form
of lidocaine is released from the bone cement mixture in an amount
proportional to the amount of lidocaine in the mixture. The elution
profiles further Indicate that adequate amounts of lidocaine are
released from bone cement to provide the desired efficacy and hence
that concentrations of the anaesthetic less than 2% by weight of
the bone cement also would provide the desired efficacy.
[0032] Anaesthetics suitable for use according to the invention are
available as liquids and solids, wherein the solid form is a
crystalline powder. In addition, anaesthetics such as lidocaine are
also available in base or acid (HCl) forms. Lidocaine used in the
studies of Example 1 was crystalline lidocaine base, whereas the
studies described in Example 2 concern the release characteristics
of alternate forms of anaesthetics when combined with bone
cement.
[0033] The studies of Example 2 employed crystalline lidocaine base
from three manufacturers (Sigma, St. Louis, Mo.; Spectrum, Gardena,
Calif.; and Wyckoff, South Haven, Mich.) and Depuy CMW3 and CMW
Endurance bone cement. Studies examined the effects of manufacturer
of anaesthetic, type of anaesthetic (i.e., lidocaine vs.
prilocaine), physical form (i.e., crystalline vs. liquid), particle
size of crystalline anaesthetic, type of bone cement (CMW3 vs. CMW
Endurance), concentration of anaesthetic (about 0.008% to about
3.5% by weight of bone cement), and chemical form (base vs. HCl),
on release profiles (i.e., the amount of anaesthetic released after
a given period and the change in rate of elution of anaesthetic
over time).
[0034] The studies of Example 2 demonstrate that lidocaine
currently available from three different manufacturers has the same
release characteristics when combined with bone cement according to
the invention. In addition, although crystalline forms of
anaesthetic from different manufacturers may vary with respect to
the proportions of different-sized particles present, particle size
does not affect the overall release of anaesthetic after a period
of 72 hours. However, as smaller particles of anaesthetic elute
faster than larger particles, particularly in the case of lidocaine
HCl, particle size should be considered in preparing compositions
of the invention when specific elution profiles are desired. For
example, by incorporating primarily smaller partides (e.g., 75 to
150 um, see Example 2), a bone cement composition having faster
initial release of anaesthetic, and a relatively shorter overall
period of release, can be prepared. Conversely, by incorporating
primarily larger particles (e.g., >250 um), a bone cement
composition having slower initial release of anaesthetic, and a
relatively longer overall period of release, can be prepared. Thus
it can be seen how anaesthetic bone cement compositions according
to the invention may be prepared in various ways to suit specific
applications.
[0035] The Example 2 studies demonstrate yet another way in which
anaesthetic bone cement compositions according to the invention may
be prepared to suit specific applications. Specifically, the type
of bone cement employed can be used to control the characteristics
of the release of anaesthetic. For example, the studies show that,
when employing DePuy CMW3, crystalline lidocaine base, crystalline
lidocaine HCl, and liquid prilocaine base, are eluted in greater
quantities both initially and after 72 hours, than when employing
Depuy CMW Endurance bone cement. Therefore, as discussed above with
respect to the effect of particle size on anaesthetic release
profiles, the use of a specific brand of bone cement in combination
with a specific anaesthetic can provide an anaesthetic bone cement
with a desired release profile. The profile can be optimized, for
example, for fast or slow initial release, as required for a
specific therapeutic application. Suitable combinations of bone
cement and anaesthetic would be determined through routine
experimentation using techniques described in the below examples.
Although studies involving bone cement from other manufacturers are
not described in Example 2, it is expected that other combinations
of bone cement and forms of anaesthetic would similarly provide
different release profiles suitable for a range of
applications.
[0036] The studies of Example 2 further indicate that the choice of
acid or base form of an anaesthetic can substantially affect how
much of the anaesthetic is released from the bone cement. For
example, when crystalline lidocaine is combined with DePuy CMW3
bone cement, there is substantially more total release of the
anaesthetic after 72 hours if lidocaine HCl is used. Similarly, the
physical form of anaesthetic is a variable that significantly
affects the release of anaesthetic when combined with, for example,
DePuy CMW3 bone cement. For example, as shown in FIG. 5, there is
substantial release of crystalline lidocaine HCl, and only a small
release of liquid lidocaine HCl. It is apparent from these studies
that the opposite applies for prilocaine base, wherein release of
the liquid form was superior to that of the crystalline form. It is
again evident that a desired release profile of an anaesthetic bone
cement according to the invention can be designed by selecting, for
example, a base or HCl, or a liquid or crystalline, form of an
anaesthetic in combination with a suitable bone cement. The
invention also contemplates the incorporation of a combination of
anaesthetics with different properties into bone cement. Such a
combination would comprise, for example, two or more different
anaesthetics (e.g., lidocaine and prilocaine), or two or more
different forms of an anaesthetic (e.g. HCl and base, or
crystalline and liquid). Provision of such a combination of
anaesthetics into bone cement would allow the release profile of
anaesthetics, and hence profile of the analgesia produced thereby,
to be further customized for particular therapeutic applications.
All such combinations are considered to be within the scope of the
present invention.
[0037] Thus, the studies of Example 2 dearly demonstrate that
particular combinations of bone cement and anaesthetic may
advantageously be chosen to achieve a desired result. The primary
advantage of choosing a combination with superior release of
anaesthetic is that less anaesthetic need be used. This is
exemplified by the comparison below of 2.0 g lidocaine base with
0.05 g lidocaine HCl, from which it can be seen that 40 times less
lidocaine HCl is required to achieve the same result as that
achieved with lidocaine base (FIG. 6). Indeed, as shown in Example
2, efficacious amounts of crystalline lidocaine HCl are released
from bone cement when 0.005 g of lidocaine are combined with 57.9 g
wet bone cement (i.e., 0.0086% by weight of bone cement). The
invention thus encompasses the use of potent, i.e., highly
releasable, forms of anaesthetics in combination with bone cement.
Further, the invention contemplates the use of compounds for
increasing the potency or releasability of anaesthetics from bone
cement.
[0038] A further advantage of choosing a particular combination as
taught by the invention is that, in combinations where release of
anaesthetic is greater initially, the desired efficacy (i.e. pain
reduction or elimination) is achieved within a shorter period
following application of the bone cement and anaesthetic
combination. For example, elution of liquid prilocaine base from
CMW3 bone cement is initially greater than that of its crystalline
counterpart as well as either form of lidocaine base (see FIG. 4).
On the other hand, where a slower initial release of anaesthetic is
desired, use of crystalline prilocaine base, for example, in CMW3
bone cement would be suitable.
[0039] That the compositions, process, and method of the invention
are efficacious in clinical applications can be seen from the
results of a knee replacement surgery described in Example 3. From
this example, it is apparent that lidocaine is eluted from
Howmedica bone cement and within 6 hours of the application of the
bone cement, sufficient lidocaine has eluted to provide an
analgesic effect which persists for at least 24 hours and probably
at least several days before the anaesthetic is metabolized in the
body.
[0040] An additional study was undertaken to address the question
of whether the incorporation of an anaesthetic into bone cement
according to the invention produces any undesirable effects on the
mechanical properties of bone cement (see Example 4). Lidocaine
(Xylocaine, Astra Pharmaceuticals) was combined with DePuy CMW3
bone cement as described in Example 1, and mechanical properties
including dough time, setting time, exotherm, compressive strength,
flexural strength, flexural modulus, and impact strength were
analyzed.
[0041] As can be seen from Table 1, the incorporation of lidocaine
into bone cement had no negative effects on the mechanical
properties of the bone cement. In fact, there was a small increase
in impact strength and an increase in dough time and setting time,
which increases may be considered advantageous under certain
circumstances.
[0042] It will, of course, be appreciated that other proprietary
bone cements can equally well be employed, such as, for example,
Palacos.RTM.R which is distributed by Schering Plough in Europe and
by Richards in North America. The invention also contemplates
incorporation of local anaesthetics into proprietary bone wax
compositions, such as Ethicon.RTM. Bone Wax, which is a sterile
mixture of beeswax and isopropyl palmitate, a wax softening used to
control bleeding from bone surfaces. The invention further
contemplates incorporation of local anaesthetics into injectable
bone substitutes, or bone paste, such as Norian Skeletal Repair
System (Norican SRS.TM.) developed by Norian Corporation of
Cupertino, Calif., which is a calcium phosphate based cement which,
when injected, forms carbonated apatite.
EXAMPLE 1
[0043] Method
[0044] Forty grams of bone cement powder from each of three
manufacturers: Howmedica (Simplex), Zimmer (Osteobond) and DePuy
(CMW3), were mixed with 0.5, 1.0 and 2.0 g of gas-sterilized
crystalline lidocaine base (Xylocaine, Astra Pharmaceuticals). The
polymerization initiated mixtures were formed into discs 50
mm.times.1 mm and allowed to harden. The hardened discs were then
placed in a stirred solution (100 ml) containing 0.2% saline at
37.degree. C. 100 .mu.l aliquots were taken at 1, 2, 3, 4, 6, 24,
48 and 72 hours and subjected to HPLC with electrochemical
detection analysis to determine the lidocaine level in each
sample.
[0045] Results
[0046] Typical elution profiles are shown in FIGS. 1 (Howmedica), 2
(Zimmer) and 3 (DePuy). These profiles demonstrate that lidocaine
elutes from the bone cement mixture in an amount proportional to
the amount of lidocaine in the mixture. The rate of elution is at a
maximum during the first 24 hours and then tapers off. The curves
also indicate that there is a peak dose at about the 6 hour point.
The peak dose then provides sustained release over a 72-hour test
period. It also appears that elution occurs mainly from the surface
of the disc and is related to the porosity and other surface
properties of the disc.
EXAMPLE 2
[0047] Method
[0048] Crystalline lidocaine base from three manufacturers (Sigma,
Spectrum, and Wyckoff) was used in these studies. It was observed
that the relative proportions of crystals of different size varied
substantially among the three brands. Thus, an initial study
compared the effect of crystal size on elution and release
characteristics using Spectrum lidocaine base. Crystals were sorted
using a series of molecular sieves into three groups (small, 75 to
150 um; medium, 150 to 250 um; and large, >250 um) and 2.0 g
samples from each group were incorporated into bone cement and
tested, as indicated below.
[0049] All studies adhered to the following procedure: Forty grams
of bone cement (DePuy CMW3 unless otherwise specified) were mixed
with 2.0, 0.5, 0.05, or 0.005 g of liquid or crystalline
anaesthetic (lidocaine: Sigma, Spectrum, Wyckoff; prilocaine:
Colour Your Enzyme, Queen's University, Kingston, Ontario, Canada).
The polymerization initiated mixtures were formed into discs 50
mm.times.1 mm and allowed to cure. The cured discs were then placed
in a solution (100 ml) containing 0.2% saline, and kept at
37.degree. C. in a shaking water bath. 1 ml aliquots were taken at
0, 1, 2, 3, 4, 6, 24, 48 and 72 hours and to each was added 1
.mu.g/ml bupivacaine as an internal standard. 50 .mu.l aliquots
were subjected to HPLC using a Beckman reverse phase column having
a mobile phase of 40 mM ammonium phosphate:acetonitrile (60:40) and
a flow rate of 1 ml/min, followed by electrochemical detection, to
determine the amount of anaesthetic in each sample.
[0050] The percentage of anaesthetic released was calculated from
the mass of the bone cement/anaesthetic mixture: anaesthetic (e.g.,
0.05 g)+bone cement powder (40 g)+bone cement liquid (17.9 g)=57.95
g. The mean mass of bone cement discs in an individual experiment
was, for example, 3.75 g, which corresponds to 15.45 discs per
mixture. For elution of, for example, 1000 ug after 72 hours, 1000
ug.times.15.45 discs=0.015 g anaesthetic released. Since 0.05 g
anaesthetic was used, 30.9% was released.
[0051] Studies examined the effects of manufacturer of anaesthetic,
type of anaesthetic (i.e., lidocaine vs. prilocaine), physical form
(i.e., crystalline vs. liquid), partide size, type of bone cement,
concentration of anaesthetic, and chemical form (i.e., base vs.
HCl) on release profiles (i.e., the amount of anaesthetic released
after a given period and the change in rate of elution of
anaesthetic over time).
[0052] Results
[0053] Manufacturer of Lidocaine Base
[0054] Crystalline lidocaine base produced by the three
manufacturers had similar elution profiles. In each case, about 1%
of the 2.0 g of lidocaine was released over 72 hours.
[0055] Prilocaine Base vs. Lidocaine Base:
[0056] As shown in FIG. 4, elution and release of crystalline forms
of both anaesthetics were the same, with about 0.4% and 1% of the
2.0 g of each of prilocaine and lidocaine, respectively, being
released. Initial release of anaesthetic was greatest for liquid
prilocaine base. Further, about 2% of liquid prilocaine base was
released, while only 1% of liquid lidocaine base was released.
[0057] Crystalline vs. Liquid Anaesthetic:
[0058] Lidocaine base: Elution characteristics of crystalline and
liquid lidocaine base were the same. In both cases, about 1% of the
2 g of lidocaine was released over 72 hours.
[0059] Lidocaine HCl: As shown in FIG. 5, about 25% of the 0.05 g
of crystalline lidocaine HCl was released from CMW3 bone cement. In
contrast, only 0.3% of the 0.05 g sample of liquid lidocaine HCl
was released.
[0060] Prilocaine base: There was a difference between crystalline
and liquid prilocaine, wherein 0.4% of the 2.0 g of crystals, and
2% of the 2.0 g of liquid was released.
[0061] Particle Size
[0062] Lidocaine base: There was no effect of particle size on the
release profile or overall release of lidocaine base. In all size
groups (75 to 150 um, 150 to 250 um, and >250 um), about 1% of
the 2.0 g of lidocaine used was released over the 72 hour
period.
[0063] Lidocaine HCl: Smaller particles eluted faster, such that
elution during the latter portion of the 72 hour period was
predominantly from larger particles. Overall, 30 to 34% of the
lidocaine of the 0.05 g samples was released for all three ranges
of particle size. Similar results were obtained with 0.005 g
samples, with 17 to 26% overall release.
[0064] DePuy CMW3 Bone Cement vs. DePuy CMW Endurance Bone
Cement:
[0065] Lidocaine base: Release of crystalline lidocaine base from
CMW3 bone cement was about 1% after 72 h in CMW3, and only about
0.3% after 72 h in CMW Endurance.
[0066] Lidocaine HCl: A similar effect of type of bone cement was
obtained when 0.5 g samples of crystalline lidocaine HCl were used,
wherein about 33% was released from CMW3, and 23% from CMW
Endurance.
[0067] Prilocaine base: Release of crystalline prilocaine base from
both types of bone cement was similar, and about 0.4% of the 2.0 g
of prilocaine was released. However, substantially more liquid
prilocaine base was released from CMW3 than from CMW Endurance (2%
vs about 0.3%).
[0068] Concentration of Crystalline Lidocaine HCl:
[0069] There was no apparent substantive difference in elution
profile of three concentrations of lidocaine HCl (0.5, 0.05, and
0.005 g per 40 g bone cement). At 0.5 g, release was about 33%; at
0.05 g, about 25%; and at 0.005 g, 17 to 26%.
[0070] Lidocaine Base vs. Lidocaine HCl:
[0071] Comparison of 2.0 g lidocaine base with 0.05 g lidocaine HCl
indicated that the two forms of lidocaine had similar release
profiles (see FIG. 6). However, because of the differences in
release, approximately 40 times less anaesthetic is needed to
achieve the same effect if lidocaine HCl is used, rather than
lidocaine base.
EXAMPLE 3
[0072] A female patient, 68 years old, having a previous total knee
replacement and a below-the-knee amputation, presented with latent
infection in the knee. A revision to remove the knee prosthesis was
performed and the cut ends of the bone were treated with an
anti-bacterial bone cement to keep the bones spaced. Three weeks
later, the bone cement was removed and tissue samples were taken
for laboratory analysis for signs of infection. Bone cement was
temporarily applied to keep the bones spaced and aligned, but this
time the cement was Howmedica bone cement containing 2 g of
lidocaine (Xylocaine) per 40 g package of cement. The
lidocaine-containing bone cement was gas sterilized but not
irradiated. After recovery from anaesthesia the patient reported
severe pain in the knee for a period of approximately 6 hours and
thereafter no pain at all. 24 hours post surgery, the patient was
sleeping without the aid of pain killers and was also able to
receive physiotherapy without feeling undue discomfort.
EXAMPLE 4
[0073] The effects of lidocaine (Xylocaine) on the mechanical
properties of Depuy CMW3 bone cement were evaluated and are
summarized in Table 1 below.
1 TABLE 1 Cement Property CMW3 CMW3 + Lidocaine Dough time
(min:sec) 2:50 7:05 Setting time (min:sec) 10:06 14:20 Exotherm
(.degree. C.) 70.8 69.1 Compressive strength (Mpa) 112.0 113.3
Flexural strength (Mpa) 65.0 66.3 Flexural modulus (Mpa) 2785 2753
Impact strength (J/m) 3.03 3.61
[0074] From Table 1 it can be seen that addition of lidocaine to
CMW3 improves impact strength by about 10%, but has little effect
on compressive strength, flexural strength or flexural modulus. It
is particularly noted that lidocaine additions increase the cement
setting time by about 40% and the "doughing time," i.e., the time
needed to reach a working mix that can be readily handled, by a
factor of 3.
[0075] Those skilled in the art will recognize, or be able to
ascertain through routine experimentation, equivalents to the
specific embodiments described herein. Such equivalents are
considered to be within the scope of this invention and are covered
by the appended claims.
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