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Description  |
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BACKGROUND OF THE INVENTION
The invention relates to the preparation of infection-resistant materials
for use within the interior of a human or animal body, and more
particularly, to the provision of certain antimicrobial agents into or
onto polymeric materials, natural or synthetic, such as Dacron polyester,
polytetrafluoroethylene, or silicone, which are usable as prostheses,
grafts, implants, sutures, etc.
Infection is one of the most common complications occurring from any injury
or surgical procedure. As a specific example, reconstructive surgery for
patients suffering from isthemic vascular disease is now standard
practice; however, vascular grafts employed in such surgery frequently
develop infections, leading to serious, and often catastrophic,
complications. Even with the use of perioperative antibiotics, the
incidence of infection remains at about 1% to 5%. This low figure is
misleading, however, for while the rate of infection is low, the morbidity
and mortality associated with such infection is quite high. The mortality
rate of infected aortic implant has been reported to be as high as 100
percent. Excision of an infected prosthesis is the typical treatment. In
the case of infected distal grafts, the result is frequently limb loss.
The problems, and known solutions, associated with vascular prosthetic
infection are set forth in detail in Infections in Surgery, pp. 45-55,
September 1982.
When infection is present prior to the operation, direct placement of a
synthetic implant is often contraindicated. This could result in the need
for an extra-anatomic bypass procedure, or the sacrifice of a limb. Such
catastrophic complications have stimulated the search for an
infection-resistant vascular prosthesis which is also compatible with
biological vascular tissue.
It is known that, while vascular grafts remain susceptible to bacterial
infection until the complete pseudointima has formed, graft contamination
usually occurs at the time of implantation. It is difficult, if not
impossible, to totally eliminate bacteria during surgical proceedings. At
best, the surgeon attempts to provide a bacteriostatic environment for the
graft, i.e., an environment in which the concentration of bacteria is kept
at a low level by creating an environment which is hostile to bacterial
growth. The attempts to limit such contamination have included application
of systemic antibiotics and local irrigation with antibiotic solutions.
Furthermore, the grafts are typically soaked in a solution of penicillin
and heparin at the operating table immediately prior to insertion in the
patient. Such attempts, however, have proven not to be completely
effective, probably because of the brief residence of antibacterial agents
at the implantation site. Greater success could be achieved, though, if
the implantation site were kept bacteriostatic for a longer period of
time.
Silver and silver compounds are recognized by those involved in fields
where the prevention of infection is important, as powerful and effective
bactericidal and bacteriostatic agents. Silver sulfadiazine, in
particular, is known to be an excellent material for combating bacterial
infection. Generally, however, the treatment of infection with silver
sulfadiazine and related compounds has been approached from the standpoint
of topically applying bactericidal or bacteriostatic agents in an ointment
to the surface of a wound. For example, U.S. Pat. Nos. 3,761,590 and
3,792,161, the disclosures of which are herein incorporated by reference
and made part of this disclosure, describe the use of silver sulfadiazine
(AgSD) ointment for surface wound burn therapy.
U.S. Pat. Nos. 4,049,802 and 4,292,324, discloses zinc compounds such as
zinc sulfadiazine (ZnSD), again for use in surface wound therapy.
Additionally, several organic acids and their metallic salts, including
silver salts, have been found to be useful in ointments for surface wound
therapy. See, for example, U.S. Pat. No. 4,404,197 and U.S. patent
application Ser. No. 479,029, filed Mar. 25, 1983 in the names of two of
the inventors hereof, the disclosures of which are also incorporated
herein by reference and made part of this disclosure. Other references
also provide information on covering materials which are useful in surface
wound therapy. See, e.g., U.S. Pat. No. 4,287,177 disclosing a synthetic
composition suitable for use as wound coverings.
The prior art references described above all pertain to surface wound
therapy. Topical application of a bactericide is not practical for an
in-dwelling or surgically implanted device intended to remain in the body
for a significant period of time, such as a vascular graft. Parenteral
administration of antibiotics is usually unsuccessful in controlling
bacterial activity at a graft or implant site because the artificial graft
or implant does not have a blood supply therein. Thus, the body's natural
resistance to infection is low in the graft, making it prone to infection.
This problem is compounded because the circulatory system cannot transport
antibiotic to the site where it is most needed. Direct incorporation of an
antibiotic in the graft, however, obviates the need to rely on the
circulatory system for transference of the drug. Moreover, direct
incorporation places a hundred fold or greater concentration of drug at
the graft site than does parenteral administration.
Application of antimicrobials at the time of insertion of the device does
not solve the problem since most antimicrobial agents are rapidly absorbed
into the system. However, the silver salts of certain antimicrobial agents
are high molecular weight polymers (See, Inorg. Chem., Vol. 15, pp.
1807-1809 (1976)) which complex with polymeric materials such as collagen,
or Dacron polyester, and release silver slowly to provide antimicrobial
activity for a long time. In contrast, silver applied to Dacron polyester
by evaporative techniques is not inhibitory of microbial activity.
It is, therefore, an object of the invention to provide biological or
synthetic materials which are compatible with body tissues, and which also
prevent bacterial and microbial infection over a significant period of
time.
It is further an object of the invention to provide vascular grafts,
prostheses, or implants with incorporated antibacterial or antimicrobial
agents, such as metal salts of sulfonamides.
It is yet a further object of the invention to provide materials for
grafts, prostheses, or implants with an incorporated antibacterial or
antimicrobial agent which will remain in the mateial for long-term
bacteriostatic effect.
It is still a further object of the invention to provide methods of
preparing synthetic vascular grafts, prostheses, or implants with
incorporated antibacterial or antimicrobial agents, wherein the material
comprises, inter alia, polymeric materials such as polyester,
polytetrafluoroethylene, or silk.
It is yet a still further object of the invention to provide a method of
treatment designed to prevent or to alleviate infections resulting from
vascular surgery or implantation, comprising the employment of the
polymeric materials, herein named, with antibacterial or antimicrobial
agents incorporated therewith.
SUMMARY OF THE INVENTION
The foregoing and other objects are achieved by this invention wherein
infection-resistant materials are provided for use within the interior of
a human or animal body which comprise a polymeric substrate with a
therapeutically effective amount of antibacterial or antimicrobial agents
such as metal salts of sulfonamides. In a particularly advantageous
embodiment, the antimicrobial agent is silver sulfadiazine. The polymeric
substrate may be either natural or synthetic, examples of which are Dacron
polyester, polytetrafluoroethylene, polyurethane, polyamide (Nylon),
silastic or silicone, silk, umbilical cord, etc.
When the resulting product is used, for example, as graft material in
vascular surgery, the treated graft materials prevent or alleviate
infections. Additionally, the graft material is compatible with arterial
and venous tissue, need not be examined frequently, and does not require
periodic changing. Moreover, the release of drug products from the graft
material proceeds at a pace conducive to long-term prevention of infection
by bacterial and microbial agents.
The antibacterial or antimicrobial agents may be applied to the substrate
or base material by direct incorporation from a solution or a suspension.
In specific illustrative embodiments, Dacron polyester is suspended in an
ammoniacal solution of 4% by weight of the agent or drug, such as silver
sulfadiazine or an aqueous suspension of silver sulfadiazine to cause
incorporation of the antimicrobial agent.
In an alternative embodiment, the silver salt of the organic compound,
e.g., of the sulfonamide can be formed in situ on the polymeric substrate.
More specifically, the substrate material is sequentially exposed to an
aqueous solution of a soluble salt of the organic compound, such as a
sodium salt, and to an aqueous solution of a silver salt, such as silver
nitrate.
In yet another embodiment, an additional antibacterial agent,
illustratively sodium piperacillin, is used in combination with the
sulfonamide.
DETAILED DESCRIPTION OF THE INVENTION
Preparation of Infection-Resistant Materials
Infection-resistant materials can be prepared by novel techniques which
complex an antibacterial or antimicrobial agent with a substrate material.
The word "complex" is used herein to indicate some form of binding wherein
the active agent is incorporated on, or with, the substrate material in
such a manner to provide slow release of the active agent. The
infection-resistant material is ideally suited for body-invasive uses such
as for vascular grafts, heart valves, in-dwelling catheters and numerous
other prosthetic or implanted devices such as intrauterine devices,
sutures, etc. wherein long-term invasive contact with the body, and hence
long-term prevention of infection is required.
Given below are several specific illustrative embodiments of methods of
producing infection-resistant materials wherein antimicrobial or
antibacterial agents are incorporated on a substrate material which may be
a synthetic organic polymer such as polyester, polytetrafluoroethylene,
polyurethane, nylon or silastic or other silicone-based material or a
biological polymer such as collagen or silk. Although the examples given
are primarily directed to the preparation of infection-resistant Dacron
polyester vascular grafts prostheses, the techniques described herein are
applicable to the creation of devices or implants comprising materials.
The word material is used herein in its broadest sense, and can encompass,
inter alia, knit or woven fabrics, single or plural filaments, extruded or
molded items, etc.
The antimicrobial agents employed, are preferably, and advantageously,
silver salts of sulfonamides. Sulfonamides have the general form:
##STR1##
wherein R is, typically a heterocyclic organic group. A particularly
advantageous, and efficacious, antimicrobial agent is
2-sulfanilamidopyrimidine silver, commonly known as silver sulfadiazine.
Silver sulfadiazine, and its characteristics, are described more
completely in Surgery, Vol. 157, pp. 82-88, July 1983, for example. Silver
Sulfadiazine (AgSD), as used in the following experiments, was prepared in
the inventors' laboratories, following the procedures set forth in Arch.
Surg. 96:184 (1968).
Other antibacterial or antimicrobial agents, or a combination of agents,
particularly those selected from the group of heavy metal salts (e.g.,
zinc salts) of sulfonamides, are within the contemplation of this
invention. In particular, it was discovered that the addition of an
antibacterial agent, such as sodium piperacillin, creates a synergistic
effect on efficacy, particularly when combined with silver sulfadiazine.
EXAMPLE 1
Treating Grafts With A Solution Of Silver Salts
Commerically procurable Dacron polyester prosthetic vascular grafts are
typically woven, knit, or velour. Samples used in experiments described
herein were obtained from C. R. Bard, Inc., Implants Division, Billercia,
Mass. These vascular graft samples have a diameter ranging from 6 mm for
the woven variety to 8 mm for the velour.
Water-insoluble silver salts were dissolved in an ammoniacal solution. A 5
cm long piece of a Dacron polyester vascular graft was suspended in an
ammoniacal solution of 4% by weight AgSD for one hour and dried in a
vacuum dessicator for four hours. Then the graft was washed once with
water and dried again in the vacuum dessicator. The dried graft may be
stored in a refrigerator until ready for use. Just prior to use, it may be
sterilized with ethylene oxide in a manner which is well known to those of
skill in the art.
Moreover, it should be noted that the 4% drug concentration is given for
purposes of illustration, and can be varied by those of skill in the art
because it is greatly in excess of the therapeutically effective amount.
Of course, other concentrations of ammonia may be either preferable or
desirable. However, the ability to incorporate such high concentrations in
the graft, thereby placing a high concentration of drug at the potential
site of infection is a significant advantage of this invention over the
prior art.
EXAMPLE 2
Treating Grafts In Aqueous Suspension Of Silver Salts
The relatively insoluble silver salts can be utilized from an aqueous
suspension. In an illustrative embodiment, silver sulfadiazine containing
Dacron polyester vascular grafts were prepared by cutting samples of 8 mm
diameter to 5 cm in length. The pieces of Dacron were placed in an aqueous
suspension containing 20 micromole AgSD per ml sterile water in an opaque
tube. The tube containing the Dacron and AgSD was shaken for 24 hours. The
Dacron grafts were then washed several times, covered with sterile gauze,
and dried in dessicators. Prior to actual in vivo use as grafts, the
Dacron polyester samples should be sterilized with ethylene oxide.
The properties of the infection-resistant Dacron polyester graft materials,
prepared in the foregoing examples, are set forth below.
EXPERIMENTAL RESULTS
The concentration of silver salts incorporated on the graft materials are
determined by employing radioactive samples of AgSD in the incorporation
process described above. The radioactivity of these grafts was measured in
a manner well known in the art to determine drug concentration. It was
found that 20-30 micromoles of drug was incorporated in a 1 cm long sample
of Dacron graft material.
The zone of inhibition of silver and several silver salts directly
incorporated into Dacron polyester grafts was determined. Grafts were cut
into 1 cm long pieces and soaked for 24 hours in suspensions of 10
micromole/ml of the silver salts AgSD and silver nitrate (AgNO.sub.3). For
comparative purposes, Dacron grafts of the same length were coated on both
sides with silver. All grafts were rinsed twice with sterile water and
then placed on blood agar plate cultures containing samples of Pseudomonas
aeruginosa (Boston), as described in Arch. Surgery 101:508 (1970), or
Staphylococcus aureus, at concentration levels of 10.sup.4, 10.sup.3, and
10.sup.2 organisms. The diameter of the zone of inhibition for each case
is given in mm, in Table I.
TABLE I
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Incorporation Using Aqueous Suspension Of Drug
Zone Of Inhibition Of Drug-
Concentration
Treated Graft, mm
Bacteria Of Bacteria AgSD AgNO.sub.3
Silver
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Pseudomonas
10.sup.4 18 8 0
Aeruginosa
10.sup.3 19 14 0
(Boston) 10.sup.2 28 20 0
Staphylococcus
10.sup.4 19 8 0
aureus 10.sup.3 18 14 0
10.sup.2 18 15 0
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The diffusion of incorporated drugs was tested on blood agar plates,
nutrient broth culture, and in whole blood. The method used was identical
to that used in the zone of inhibition study described above in connection
with Table I. After testing for the amount of drug remaining in the
treated graft on the first day, a fresh culture plate or tube was used
each day for ten days. The zone of inhibition and bacterial turbidity was
measured. The results of this investigation are set forth in Table II.
Table II shows the release of drug from AgSD-containing Dacron in the
presence of various culture media and blood by the concentration of drug
remaining in the graft after exposure to the medium. A (0) indicates no
turbidity, and hence, no growth. A (+) indicates bacterial growth.
TABLE II
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Concentration Of Drug Anti-
Remaining in Graft bacterial
Activity
(micromole/2 mm) Zone In Turbidity
Days Of Blood Agar
Nutrient Plate In
Incubation
Plate Broth Blood (mm) Broth
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0 4.0 4.0 4.0 25 0
1 3.2 3.1 2.7 22 0
3 2.8 2.7 2.5 22 0
4 2.7 2.5 1.8 22 0
5 2.3 2.3 0.9 0
6 2.2 2.2 0.8 0
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The inhibitory effect of Dacron polyester grafts including different
antibacterial agents was tested. Graft materials were prepared as
indicated in the examples above, and were then soaked in 5 ml of nutrient
broth containing the bacteria Pseudomonas aeruginosa (Boston), or
Staphylococcus aureus, at various concentration levels. These samples were
then incubated for 24 to 48 hours, and observed for growth of bacteria.
For purposes of comparison, elemental silver (Ag) was coated on Dacron
graft material. The results are given in Table III, wherein a (+)
indicates growth of bacteria, where a (-) indicates absence of growth.
TABLE III
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Antibacterial Agents
Bacteria Concentration
AgSD AgNO.sub.3
Ag
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Pseudomonas
10.sup.6 + + +
aeruginosa 10.sup.4 - + +
10.sup.3 - - +
Staphylococcus
10.sup.6 - - +
aureus 10.sup.4 - - +
10.sup.3 - - +
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In a particularly advantageous embodiment of the invention, the metal salt
of the organic compound can be formed in situ on the substrate material.
The following Examples 3, 4, and 9 illustrate this technique.
EXAMPLE 3
In Situ Formation Of Silver Salts
This procedure can be utilized with any of the aforementioned materials,
irrespective of whether the material is synthetic or natural. For the
purpose of illustration, Dacron polyester, PTFE, and rubber or
silicone-containing Foley catheter materials were treated to render them
infection-resistant.
Samples of these materials were placed in an aqueous solution of a soluble
sulfonamide salt, illustratively a 30 micromole solution of sodium
sulfadiazine, for a period of about an hour. The samples were removed from
the solution and blotted dry. Then, the samples were placed in aqueous
solution of a soluble silver salt such as silver nitrate for a period of
time sufficient to allow reaction between the sulfadiazine salt and the
metal salt so as to produce the metal salt of sulfadiazine in, or on, the
sample. In the actual tests performed, a period of about five to ten
minutes was found to be sufficient.
The thus-treated samples were washed vigorously in water, dried for about
an hour, and then stored in a dark place until ready for use. The samples
can be sterilized by means, well known in the art, prior to use in vivo.
The in situ technique for incorporating a metal salt of a sulfonamide has
several advantages. It is believed that the freshly precipitated metal
salt intercalates the substrate better and yet releases more gradually. We
have also found that the therapeutically effective concentration of the
antimicrobial agent is less for the in situ technique. Moreover, since the
salts are water soluble, delicate biological tissue, such as porcine heart
valves, can be safely treated by the method of Example 3.
It should be noted, however, that the solvent for the organic and metal
salts does not have to be water. The choice of another solvent is well
within the skill of one of ordinary skill in the art. It should further be
noted that while silver is particularly effective, other metals, such as
zinc, can be used to create the antimicrobial agents. A specific example
of a known non-silver complexed antimicrobial agent is zinc sulfadiazine.
EXPERIMENTAL RESULTS
The concentration of silver salts incorporated on the sample materials by
the in situ technique of Example 3 was determined by employing radioactive
samples of silver nitrate in the in situ reaction. The radioactivity of
the samples was measured in a manner well known in the art. The results
are set forth in Table IV wherein the concentration of silver subsequent
to preparation of the sample is shown in column (A).
1 cm long samples of Dacron polyester vascular graft material were
suspended in tubes containing 5 ml of a culture medium comprising nutrient
broth in a known concentration of bacteria. The tubes containing the
samples were incubated for 24 hours. The results of this experiment for
concentrations of Staphylococcus aureus on the order of 10.sup.5,
10.sup.6, and 10.sup.7 organisms are given in Table IV. A sample of the
broth from each tube was cultured on a blood agar plate and incubated in
order to defect bacterial growth. The results are indicated on Table IV as
a plus (+) for growth and a minus (-) for no growth.
The in vitro activity of the samples was further tested by measuring the
zone of inhibition, in mm, by standard disc inhibition studies on a blood
agar plate according to techniques described above. The concentration of
silver was again measured after the disc inhibition studies and is given
in column (B) of Table IV.
TABLE IV
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DRUG CONTENT AND IN VITRO ACTIVITY OF GRAFTS
(A) (B)
Silver Silver Antibacterial Activity
(micro-
(micro- Concentration
Growth Zone In
mole) mole) Of Bacteria In Tube Plate (mm)
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AgSD
10-12 5-8 10.sup.5 - 15-18
10-12 5-8 10.sup.6 - 15-18
10-12 5-8 10.sup.7 + 15-18
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EXAMPLE 4
In a specific advantageous embodiment of the in situ technique for
producing infection-resistant materials, vaginal sponges were treated to
incorporate silver sulfadiazine.
Vaginal sponges are being widely accepted as a means of contraception or as
a means of administering medications to the female vaginal cavity and
cervix due to the ability of the sponge to provide long-term retention and
slow release of medicaments. Typically, vaginal sponges comprise an
expandible polymer, such as polyurethane. If used as a means of
contraception, a well known spermicide, such as Nonoxynol-9 is included in
the polymeric sponge. U.S. Pat. No. 4,393,871 provides a detailed
description of a vaginal sponge device wherein the sponge is formed by
mixing a polyurethane prepolymer with an aqueous solution of Nonoxynol-9
which acts as a surfactant, or foaming agent, during formation of the
polymeric sponge, and as a spermicide in the final device. In addition to
the spermicide Nonoxynol-9, U.S. Pat. No. 4,393,871 also suggests that
other drugs, or medicaments, can be added to the polyurethane prepolymer.
We have discovered that Nonoxynol-9 exhibits very little infection
resistance. Silver Sulfadiazine, on the other hand, is extremely effective
at killing a wide spectrum of microorganisms. In particular, silver
sulfadiazine is lethal to venereal disease producing organisms such as
Treponea pallida, Gonococcus, Staphalococcus aureus-coagulate positive,
Candida albicans and Herpes hominus. Moreover, the addition of silver
sulfadiazine may prevent toxic shock syndrome. While not as effective as
Nonoxynol-9, silver sulfadiazine also exhibits some spermicidal activity.
Thus, incorporation of silver sulfadiazine in a vaginal sponge would have
many beneficial effects.
Pieces of commercially procured vaginal sponges weighing 600 mg were placed
in an aqueous 120 millimole solution of sodium sulfadiazine for about an
hour. The pieces were blotted to remove excess fluid and then suspended in
an aqueous 100 millimole solution of silver nitrate for about five
minutes. Again, the excess fluid was blotted off and the sponge pieces
were dried in a vacuum dessicator for about an hour. The sponge pieces
were washed with sterile water and then dried again.
Pieces of vaginal sponge weighing 20 mg apiece and containing about 3
micromole of silver sulfadiazine, were placed in nutrient broth containing
various concentrations of bacteria and then a sample of the broth was
tested for bacterial growth. The results are given in TABLE V as a plus
(+) for growth and a minus (-) for no growth. Sponge samples were also
placed in Sabouraud broth to test anti-fungal properties against various
concentrations of Candida albicans. None of the cultures containing
treated sponges exhibited bacterial, or fungal, growth. On the other hand,
all of the cultures from control samples of untreated vaginal sponges,
containing only Nonoxynol-9, exhibited heavy bacterial growth.
TABLE V
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Antibacterial Effect of AgSD Impregnated Sponge
STERILITY OF CULTURES
(concentration of bacterial)
ORGANISM 10.sup.7
10.sup.6 10.sup.5
10.sup.4
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Pseudomonas aeruginosa
-- -- -- --
Staph. aureus (FID)
-- -- -- --
Staph. aureus (Harlem)
-- -- -- --
Staph. epidermidis
-- -- -- --
Eschechia coli -- -- -- --
Klebsiella pneumonia
-- -- -- --
Candida albicans
-- -- -- --
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Several miscellaneous examples of specific devices, rendered
infection-resistant by application of the techniques set forth herein, are
given below in Example 5-8.
EXAMPLE 5
It has been discovered that the strings on intrauterine devices permit
bacteria to travel into the uterus and Fallopian tubes. These strings can
be provided with an antimicrobial agent by treating a polymeric filament,
such as nylon, or a plurality of such filaments comprising the string, in
accordance with the methods of Examples 1-3. Vaginal sponges are typically
provided with a ribbon loop to aid in their removal, these too, can be
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