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The Effectiveness, Safety, and use of Carbenicillin in Ophthalmology
T H E EFFECTIVENESS, SAFETY, AND USE O F CARBENICILLIN IN OPHTHALMOLOGY ALAN M. R I C H , M.D., WELDON A. DUNLAP, M.D., AND J O H N R. PARTRIDGE, M.D.
Chapel Hill, North Carolina Carbenicillin is a semi-synthetic penicillin that has proved valuable to combat Gramnegative pathogens such as Pseudomonas and Proteus. Septicemia, burns, pneumonia, severe urinary tract disease, and meningitis caused by these organisms have often been dramatically cleared with carbenicillin.1"6 Its potential value in eye infections, however, is still being explored. Such potential is partic ularly relevant for Pseudomonas ocular in fections which are quite often disastrous and for which no current antibiotic regimen is fully adequate.7"10 It is the purpose of this study to determine the therapeutic efficacy of subconjunctival carbenicillin and any signifi cant ocular irritation or toxic effects result ing from its use. Carbenicillin is bactericidal and has the characteristic low toxicity of the penicillins. Because it is unstable in acid solution, it must be given parenterally. The intravenous route is usually employed because high doses of up to 20 to 40 g a day are often required. While the major use of carbenicillin has been for Pseudomonas and indole-positrve Proteus infections, it is also effective against most Escherichia coli, many enterobacter and a few salmonella strains. Most Grampositive cocci and pathogenic Neisseria are susceptible. Penicillinase-producing staphylococci are resistant, however, as are Klebsiella strains and most Serratia. 3-4
were used in these experiments. All had neg ative tuberculin and hepatitis tests, and all were acclimated to the laboratory environ ment for two weeks before treatment. The monkeys were paired and housed in primate cages, provided drinking water at all times, and fed an adequate quantity of primate chow supplemented with daily fresh vegeta bles. In addition, 72 adult New Zealand al bino rabbits weighing 2-3 kg were accli mated to the laboratory environment for seven days before treatment. Rabbits were individually housed, provided fresh drinking water at all times, and fed an adequate quan tity of rabbit chow daily. Prior to beginning the study, both eyes of all animals were care fully examined by direct illumination, slit lamp, and ophthalmoscopy and only animals with normal eyes were used in the study. Clinical evaluation of ocular irritation and toxicity—The right eyes of all animals were given subconjunctival injections of carbeni cillin in the following regimen : Group I: Six monkeys received 50 mg 0.25 ml daily for 10 days. Group I I : Six monkeys received 25 mg 0.25 ml daily for 10 days. Group III : Six rabbits received 50 mg 0.25 ml daily for 10 days. Group I V : Six rabbits received 25 mg 0.25 ml daily for 10 days. Group V: Six rabbits received 50 mg 0.25 ml daily for 10 days. Group VI : Six rabbits received 25 mg 0.25 ml daily for 10 days.
METHODS AND MATERIALS
Animals—Twelve healthy adult owl mon keys (Aotus trivirgatus) weighing 1-2 kg From the Department of Ophthalmology, Uni versity of North Carolina School of Medicine, Chapel Hill, and McPherson Hospital, Durham, North Carolina. Reprint requests to Alan M. Rich, M.D., Depart ment of Ophthalmology, North Carolina School of Medicine, Chapel Hill, North Carolina 27S14.
in in in in in in
Untreated left eyes served as controls. Group V and VI animals were inoculated with Pseudomonas as described below. All eyes were examined daily for 10 days and then every other day until 21 days. Eyes were scored according to the Draize method11 for corneal, iridial, and conjunctival changes.
490
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CARBENICILLIN IN OPHTHALMOLOGY
Histologie evaluation—On day 21, all treated eyes and two control eyes from each group were enucleated. Serial histologie sec tions were made and stained with hemotoxylin and eosin and specific stains when deemed appropriate. All sections were exam ined for any histopathologic change. Aqueous penetration studies—Forty-eight rabbits underwent subconjunctival injections of either 50 or 25 mg of carbenicillin and primary aqueous withdrawal at either 30, 60, 90, or 180 minutes thereafter. Antibiotic levels were determined by a microtiter serial dilution technique, modified from a method reported for the detection of penicillin levels in serum.12 Aqueous samples were placed in the first well of a row of 12 wells in a plastic dilution plate. Twofold serial dilutions of aqueous samples in trypticase soy broth were carried out with wire loop microdilutors. All wells were inoculated with 0.025 ml of a 10"4 dilution of an overnight trypticase broth mixture of Ps. aeruginosa (ATCC 25619). The carbenicillin level in each sam ple was determined by multiplying the MIC of the assay organism by the reciprocal of the lowest dilution of aqueous humor in which no growth appeared. Treatment of Pseudomonas keratitis— Group V and VI animals were infected with Pseudomonas strain ATCC 23389 prepared according to the method of Hessburg. 13 A curved Grieshaber corneal needle was threaded with 3.5 inches of 6-0 black silk which had been placed in a Petri dish con taining a few ml of washed diluted organ isms. Corneas were inoculated by drawing a freshly soaked suture through a 2 to 3 mm needle tract deep within the corneal stroma with care being exercised to prevent penetra tion of the anterior chamber. Both eyes of all animals were infected. The right eyes of all animals then received subconjunctival car benicillin injections for 10 days and the un treated left eyes served as controls. The eyes were examined daily with scoring by the Draize fnethod and by the Wiggins method for grading corneal ulcers as well as severity
491
of keratitis, epithelial destruction and stromal involvement. Eyes were photographed when deemed ap propriate for comparative evaluation. Following the 10-day treatment, all eyes were observed every other clay until day 21 when the animals were sacrificed for histo logie studies. RESULTS
Clinical evaluation of ocular irritation and toxicity—Carbenicillin was well tolerated by all monkeys and rabbits during the 10 days of successive subconjunctival injections. Little pain was apparent upon injection. Evaluation of eye irritation by the Draize method showed that the corneas of all mon keys and rabbits remained clear and without reaction. Iris reaction was found to be zero for all monkeys tested. One rabbit exhibited a transient anterior chamber flare and iris congestion. However, this was felt to be re lated to a previous paracentesis for aqueous humor bioassay. Conjunctival reaction was quite similar in rabbits and monkeys during the 10-day course of drug administration. Conjunctival injection, chemosis, and dis charge were minimal throughout with mean scores of rabbits and monkeys closely paral lel (Fig. 1). All rabbits showed a prompt re turn of conjunctiva to normal following dis continuance of the drug with the majority of rabbits displaying entirely quiet anterior seg ments after four days. Conjunctiva in the owl monkeys, however, showed a more grad ual return to normality, requiring about ten days to become completely quiet. Conjuncti val irritation in rabbits appeared essentially the same for 50 or 25 mg injections while the 50 mg dose in monkeys produced slightly more reaction. Histologie evaluation—Extensive review of all eyes in Groups I through IV that had undergone 10 days of subconjunctival car benicillin supported the clinical impression of minimal tissue irritation or toxicity. No inflammatory changes or abnormalities were found in any posterior segments or in any
492
AMERICAN JOURNAL OF OPHTHALMOLOGY
MARCH, 1973
EYE IRRITATION SCORES (DRAIZE) MONKEYS Ul
g 50
— GROUP 1 - 5 0 mgqd for 10 days - GROUP l l - 2 5 m g q d for 10 days
CORNEA MEAN ERAGE SCORE
o (Λ 40
UJ
<3 30 < cc UJ 2 0
< 10z <
UJ
10 DAY
§
20
CONJUNCTIVA
IRIS
10 DAY
20
10
20 DAY
RABBITS ui 50
o
O 40 UJ 3 0 o UJ 20
3 UJ
10
GROUP l l l - 5 0 m g q d for 10 days GROUP IV - 2 5 mg qd for
CORNEA UJ θ3Γ < UJ
oUJ <
CONJUNCTIVA
10 days
IRIS λ
11
10 10 20 20 DAY DAY Fig. 1 (Rich, Dunlap, and Partridge). Ocular irritation effects of subconjunctival carbenicillin injected for 10 successive days.
3
anterior segment tissues except conjunctiva. Surrounding the injection sites beneath con junctiva there were often focal areas of in flammation, generally accumulations of neutrophils and a few lymphocytes. Plasma cells were seen infrequently. An occasional find ing was neutrophil invasion of adjacent mus cle producing a focal myositis. All of these findings were fairly mild and localized and unaccompanied by tissue necrosis. Sciera un derlying areas of injection showed minimal inflammatory reaction. Little difference in inflammatory reaction was noted between monkey and rabbit eyes or between the 50 or 25 mg injection. Aqueous penetration—Bioassays of pri
mary aqueous humor from 94 rabbit eyes showed quite variable levels of carbenicillin for any given time period. Higher drug lev els were found following the 50 mg injection at all time periods evaluated. Average car benicillin levels peaked at 90 minutes with a concentration of 56.8 μg/ml following in jection of the 50 mg dose (Fig. 2 ) . The range of aqueous levels at this time varied from 3.9 to 190 μg/ml. Following injection of 25 mg subconjunctivally, an average peak dose of 20.3 μg/ml at 60 minutes was ob tained with a range of levels from 3.9 to 95 μg/ml. Carbenicillin treatment in expérimental Pseudomonas keratitis—All 24 eyes inocu-
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CARBENICILLIN IN OPHTHALMOLOGY
lated with Pseudomonas developed a prompt keratitis. Untreated control eyes in most cases developed progressive severe inflam mation that often resulted in perforation. No treated eyes perforated. Only one treated eye (on 50 mg dose regimen) failed to respond satisfactorily to carbenicillin and maintained a persistent low grade infection with moder ate corneal scarring. All other eyes given subconjunctival injections responded favor ably and promptly (Fig. 3). Infection in these eyes was controlled in five to seven days. After completion of the 10 day course of antibiotics, conjunctival inflammation in treated eyes returned to normal in one week.
493
Iritis was slower to subside. The corneas of several treated eyes exhibited minimal but permanent scarring where inoculated. DISCUSSION
Following subconjunctival carbenicillin in the rabbit and owl monkey, ocular irritation was noted to be transient and toxicity nil. In a previous study in a small number of hu man subjects, carbenicillin was found to be safe for subconjunctival injection.14 Lack of untoward ocular effects is in agreement with this drug's remarkably low toxicity when given systemically, even in massive doses.1·3'4 Penetration into aqueous humor after sub-
AVERAGE CARBENICILLIN LEVELS IN AQUEOUS HUMOR 60r
25 mg dose 50 mg dose
/ /
50
N \ \
E o E
w
j _i
30
\
Ö
V
sv
w 20 \
GO <
10
30
60
90 120 MINUTES
150
180
210
Fig. 2 (Rich, Dunlap, and Partridge). Aqueous penetration of carbenicillin in the rabbit following sub conjunctival injection of 50 or 25 mg. Each point represents average of 12 determinations.
494
AMERICAN JOURNAL OF OPHTHALMOLOGY
MARCH, 1973
SUBCONJUNCTIVAL CARBENICILLIN IN THE TREATMENT OF PSEUDOMONAS KERATITIS UNTREATED EYES 50mgqdxlOd 25mgq4xlOd
CORNEA
CONJUNCTIVA
DAY Fig. 3 (Rich, Dunlap, and Partridge). Clinical comparison of untreated and carbenicillin-treated rabbit eyes with Pseudomonas keratitis.
conjunctival injection was moderate in the non-inflamed eye and drug levels were found to be in the general range reported elsewhere.14·15 The major ophthalmic potential for car benicillin lies in the treatment of Pseudomo nas eye infections. Certainly a satisfactory response was noted in this study of animals infected with a sensitive strain of Ps. aeruginosa (MIC reported as 1.0 pg/ml). Mini mum inhibitory concentrations for most Pseudomonas strains are exceptionally higher, however, with 50% of strains having MICs greater than 50 μg/ml.4-6 Average drug levels at the peak of concentration were found to be 56.8 μg/ml in this study. In the inflamed eye, higher drug leevels might be expected.15 In one reported study of Pseudo monas keratitis in rabbits, subconjunctival carbenicillin was found to be effective against
Pseudomonas strains with MICs of 125-250 μ^/πιΐ.10 It is uncertain, however, if bacteri cidal levels for the large majority of Pseudo monas strains could be obtained following subconjunctival carbenicillin. A dosage con centration between 25 and 57 mg/0.25 ml has been shown to be optimal in three differ ent laboratories,8·14'15 and increasing the dos age to 100 mg/0.25 ml or greater has not in creased aqueous penetration in the rabbit or human. Some conflicting data, however, has been recently reported in 20 clinical patients by Boyle, Gwon, Zinn and Leopold.17 High aqueous levels of carbenicillin were incon stantly found following subconjunctival in jections of 500 mg in 1.0 ml, 250 mg in 0.5 ml, and 100 mg in 0.2 ml. Following a 50 mg dose in 0.1 ml, carbenicillin was detected within two hours in one of three aqueous samples. Curiously, iris samples bathed in
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CARBENICILLIN IN OPHTHALMOLOGY
high drug concentrations in aqueous did not show any antibiotic activity. Lack of any aqueous penetration at times when fully ex pected was not explained. Because of the small number of patients in that study with little data for the same time intervals, hard conclusions might be misleading. Of consid erable credibility, however, were the adverse local reactions that were reported to follow subconjunctival injections of such high drug concentrations. Intraocular drug levels following com bined subconjunctival and systemic adminis tration have not been evaluated but might be expected to effect greater Pseudomonacidal action. Also more effective ocular therapy might be expected when carbenicillin is used synergistically with gentamycin although some reports of synergy are conflicting.18·19 Limited data is available to evaluate such synergism in eye infections.8 SUMMARY
Twelve owl monkeys and 12 rabbits were given subconjunctival carbenicillin for 10 successive days and evaluated for untoward effects. Clinically, only conjunctival chemosis and injection of slight to moderate degree were noted. Histologie findings were limited to a mild localized conjunctivitis and, infre quently, a focal myositis. Aqueous levels of carbenicillin were deter mined in 94 rabbit eyes following subcon junctival injection. The average peak con centration was 56.8 μg/ml at 90 minutes af ter injection of 50 mg. The MICs for a ma jority of Pseudomonas strains exceed this value and therapeutic success of carbenicillin against eye infections with these strains is indeterminate. Subconjunctival carbenicillin cleared 11 of 12 rabbit eyes with Pseudomonas keratitis induced with a sensitive strain while most untreated eyes perforated or developed se vere permanent scarring. ACKNOWLEDGMENT
Carbenicillin and technical assistance in this study
495
were kindly provided by Beecham-Massengill Phar maceuticals, Clifton, New Jersey.
REFERENCES
1. Symposium on carbenicillin : A clinical profile. Rockefeller University, Januar}', 1970. J. Infect. Dis. 122 (Suppl.):543, 1970. 2. Smith, C. B., Wilfert, T. N., and Dans, P. E. : In vitro activity of carbenicillin and results of treatment compared with other penicillins. J. Infect. Dis. 122 (Suppl.) :S14, 1970. 3. Rolinson, G. N., and Sutherland, R. : Human pharmacology of carbenicillin. Antimicrob. Chemother. 7:614, 1967. 4. Michaeli, D., and Weinster, L. : Clinical and microbiologie studies of carbenicillin. J. Infect. Dis. 122 (Suppl) :S90, 1970. 5. Lyons, R. W., Thorton, G. F., and Andriale, V. T. : Carbenicillin-Clinical and laboratory studies. J. Infect. Dis. 122 (Suppl.) :S104, 1970. 6. Brunfitt, W., Percivol, A., and Leigh, D. A. : Clinical and laboratory studies with carbenicillin. Lancet 1:1289, 1967. 7. Moorman, L., and Harbert, F. : Treatment of Pseudomonas corneal ulcers. Arch. Ophth. 53:345, 1955. 8. Bohigian G., Okumoto, M., and Valenton, M. : Experimental Pseudomonas keratitis. Arch. Ophth. 86:432, 1971. 9. Burns, R. P. : Pseudomonas aeruginosa kerati tis. Am. J. Ophth. 67:257, 1969. 10. Hessburg, P. C. : Treatment of Pseudomonas keratitis in humans. Am. J. Ophth. 61:896, 1966. 11. Appraisal of the Safety of Chemicals in Food, Drugs, and Cosmetics, Baltimore, Associa tion of Food and Drug Officials, 1959, p. 49. 12. Abramowicz, M., Klein, J. O., Ingall, D., and Finland, M. : Levels of penicillin in serum of new born infants. Am. J. Dis. Child. 111:267, 1966. 13. Hessburg, P. C, Truant, J. P., and Penn, W. P. : Corneal infections in experimental animals. Am. J. Ophth. 53:359, 1962. 14. Rich, A. M., and Crawford, J. R. : Intraocu lar penetration of subconjunctival carbenicillin. In vest. Ophth. 11:68, 1972. 15. Rich, A. M., and Crawford, J. R. : Subcon junctival carbenicillin. Proc. Ann. Staff Meet. UNC School Med. 9:25, 1971. 16. Cashwell, F., and Rich, A. M. : Gentamycin and carbenicillin in the treatment of Pseudomonas keratitis. Proc. Ann. Staff Meet. UNC School Med. In press. 17. Boyle, G. L., Gwon, A. E., Zinn, K. M., and Leopold, I. H. : Intraocular penetration of carbeni cillin. Am. J. Ophth. 73:754, 1972. 18. Smith, C. B., Dans, P. E., Wilfert, N., and Finland, M. : Use of gentamycin in combination with other antibiotics. J. Infect. Dis. 119:370, 1969. 19. Eickhoff, T. C. : In vitro effects of carbenicil lin combined with gentamycin or polymyxin B against Pseudomonas. Appl. Microbiol. 18:469, 1969.
Chapel Hill, North Carolina Carbenicillin is a semi-synthetic penicillin that has proved valuable to combat Gramnegative pathogens such as Pseudomonas and Proteus. Septicemia, burns, pneumonia, severe urinary tract disease, and meningitis caused by these organisms have often been dramatically cleared with carbenicillin.1"6 Its potential value in eye infections, however, is still being explored. Such potential is partic ularly relevant for Pseudomonas ocular in fections which are quite often disastrous and for which no current antibiotic regimen is fully adequate.7"10 It is the purpose of this study to determine the therapeutic efficacy of subconjunctival carbenicillin and any signifi cant ocular irritation or toxic effects result ing from its use. Carbenicillin is bactericidal and has the characteristic low toxicity of the penicillins. Because it is unstable in acid solution, it must be given parenterally. The intravenous route is usually employed because high doses of up to 20 to 40 g a day are often required. While the major use of carbenicillin has been for Pseudomonas and indole-positrve Proteus infections, it is also effective against most Escherichia coli, many enterobacter and a few salmonella strains. Most Grampositive cocci and pathogenic Neisseria are susceptible. Penicillinase-producing staphylococci are resistant, however, as are Klebsiella strains and most Serratia. 3-4
were used in these experiments. All had neg ative tuberculin and hepatitis tests, and all were acclimated to the laboratory environ ment for two weeks before treatment. The monkeys were paired and housed in primate cages, provided drinking water at all times, and fed an adequate quantity of primate chow supplemented with daily fresh vegeta bles. In addition, 72 adult New Zealand al bino rabbits weighing 2-3 kg were accli mated to the laboratory environment for seven days before treatment. Rabbits were individually housed, provided fresh drinking water at all times, and fed an adequate quan tity of rabbit chow daily. Prior to beginning the study, both eyes of all animals were care fully examined by direct illumination, slit lamp, and ophthalmoscopy and only animals with normal eyes were used in the study. Clinical evaluation of ocular irritation and toxicity—The right eyes of all animals were given subconjunctival injections of carbeni cillin in the following regimen : Group I: Six monkeys received 50 mg 0.25 ml daily for 10 days. Group I I : Six monkeys received 25 mg 0.25 ml daily for 10 days. Group III : Six rabbits received 50 mg 0.25 ml daily for 10 days. Group I V : Six rabbits received 25 mg 0.25 ml daily for 10 days. Group V: Six rabbits received 50 mg 0.25 ml daily for 10 days. Group VI : Six rabbits received 25 mg 0.25 ml daily for 10 days.
METHODS AND MATERIALS
Animals—Twelve healthy adult owl mon keys (Aotus trivirgatus) weighing 1-2 kg From the Department of Ophthalmology, Uni versity of North Carolina School of Medicine, Chapel Hill, and McPherson Hospital, Durham, North Carolina. Reprint requests to Alan M. Rich, M.D., Depart ment of Ophthalmology, North Carolina School of Medicine, Chapel Hill, North Carolina 27S14.
in in in in in in
Untreated left eyes served as controls. Group V and VI animals were inoculated with Pseudomonas as described below. All eyes were examined daily for 10 days and then every other day until 21 days. Eyes were scored according to the Draize method11 for corneal, iridial, and conjunctival changes.
490
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CARBENICILLIN IN OPHTHALMOLOGY
Histologie evaluation—On day 21, all treated eyes and two control eyes from each group were enucleated. Serial histologie sec tions were made and stained with hemotoxylin and eosin and specific stains when deemed appropriate. All sections were exam ined for any histopathologic change. Aqueous penetration studies—Forty-eight rabbits underwent subconjunctival injections of either 50 or 25 mg of carbenicillin and primary aqueous withdrawal at either 30, 60, 90, or 180 minutes thereafter. Antibiotic levels were determined by a microtiter serial dilution technique, modified from a method reported for the detection of penicillin levels in serum.12 Aqueous samples were placed in the first well of a row of 12 wells in a plastic dilution plate. Twofold serial dilutions of aqueous samples in trypticase soy broth were carried out with wire loop microdilutors. All wells were inoculated with 0.025 ml of a 10"4 dilution of an overnight trypticase broth mixture of Ps. aeruginosa (ATCC 25619). The carbenicillin level in each sam ple was determined by multiplying the MIC of the assay organism by the reciprocal of the lowest dilution of aqueous humor in which no growth appeared. Treatment of Pseudomonas keratitis— Group V and VI animals were infected with Pseudomonas strain ATCC 23389 prepared according to the method of Hessburg. 13 A curved Grieshaber corneal needle was threaded with 3.5 inches of 6-0 black silk which had been placed in a Petri dish con taining a few ml of washed diluted organ isms. Corneas were inoculated by drawing a freshly soaked suture through a 2 to 3 mm needle tract deep within the corneal stroma with care being exercised to prevent penetra tion of the anterior chamber. Both eyes of all animals were infected. The right eyes of all animals then received subconjunctival car benicillin injections for 10 days and the un treated left eyes served as controls. The eyes were examined daily with scoring by the Draize fnethod and by the Wiggins method for grading corneal ulcers as well as severity
491
of keratitis, epithelial destruction and stromal involvement. Eyes were photographed when deemed ap propriate for comparative evaluation. Following the 10-day treatment, all eyes were observed every other clay until day 21 when the animals were sacrificed for histo logie studies. RESULTS
Clinical evaluation of ocular irritation and toxicity—Carbenicillin was well tolerated by all monkeys and rabbits during the 10 days of successive subconjunctival injections. Little pain was apparent upon injection. Evaluation of eye irritation by the Draize method showed that the corneas of all mon keys and rabbits remained clear and without reaction. Iris reaction was found to be zero for all monkeys tested. One rabbit exhibited a transient anterior chamber flare and iris congestion. However, this was felt to be re lated to a previous paracentesis for aqueous humor bioassay. Conjunctival reaction was quite similar in rabbits and monkeys during the 10-day course of drug administration. Conjunctival injection, chemosis, and dis charge were minimal throughout with mean scores of rabbits and monkeys closely paral lel (Fig. 1). All rabbits showed a prompt re turn of conjunctiva to normal following dis continuance of the drug with the majority of rabbits displaying entirely quiet anterior seg ments after four days. Conjunctiva in the owl monkeys, however, showed a more grad ual return to normality, requiring about ten days to become completely quiet. Conjuncti val irritation in rabbits appeared essentially the same for 50 or 25 mg injections while the 50 mg dose in monkeys produced slightly more reaction. Histologie evaluation—Extensive review of all eyes in Groups I through IV that had undergone 10 days of subconjunctival car benicillin supported the clinical impression of minimal tissue irritation or toxicity. No inflammatory changes or abnormalities were found in any posterior segments or in any
492
AMERICAN JOURNAL OF OPHTHALMOLOGY
MARCH, 1973
EYE IRRITATION SCORES (DRAIZE) MONKEYS Ul
g 50
— GROUP 1 - 5 0 mgqd for 10 days - GROUP l l - 2 5 m g q d for 10 days
CORNEA MEAN ERAGE SCORE
o (Λ 40
UJ
<3 30 < cc UJ 2 0
< 10z <
UJ
10 DAY
§
20
CONJUNCTIVA
IRIS
10 DAY
20
10
20 DAY
RABBITS ui 50
o
O 40 UJ 3 0 o UJ 20
3 UJ
10
GROUP l l l - 5 0 m g q d for 10 days GROUP IV - 2 5 mg qd for
CORNEA UJ θ3Γ < UJ
oUJ <
CONJUNCTIVA
10 days
IRIS λ
11
10 10 20 20 DAY DAY Fig. 1 (Rich, Dunlap, and Partridge). Ocular irritation effects of subconjunctival carbenicillin injected for 10 successive days.
3
anterior segment tissues except conjunctiva. Surrounding the injection sites beneath con junctiva there were often focal areas of in flammation, generally accumulations of neutrophils and a few lymphocytes. Plasma cells were seen infrequently. An occasional find ing was neutrophil invasion of adjacent mus cle producing a focal myositis. All of these findings were fairly mild and localized and unaccompanied by tissue necrosis. Sciera un derlying areas of injection showed minimal inflammatory reaction. Little difference in inflammatory reaction was noted between monkey and rabbit eyes or between the 50 or 25 mg injection. Aqueous penetration—Bioassays of pri
mary aqueous humor from 94 rabbit eyes showed quite variable levels of carbenicillin for any given time period. Higher drug lev els were found following the 50 mg injection at all time periods evaluated. Average car benicillin levels peaked at 90 minutes with a concentration of 56.8 μg/ml following in jection of the 50 mg dose (Fig. 2 ) . The range of aqueous levels at this time varied from 3.9 to 190 μg/ml. Following injection of 25 mg subconjunctivally, an average peak dose of 20.3 μg/ml at 60 minutes was ob tained with a range of levels from 3.9 to 95 μg/ml. Carbenicillin treatment in expérimental Pseudomonas keratitis—All 24 eyes inocu-
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CARBENICILLIN IN OPHTHALMOLOGY
lated with Pseudomonas developed a prompt keratitis. Untreated control eyes in most cases developed progressive severe inflam mation that often resulted in perforation. No treated eyes perforated. Only one treated eye (on 50 mg dose regimen) failed to respond satisfactorily to carbenicillin and maintained a persistent low grade infection with moder ate corneal scarring. All other eyes given subconjunctival injections responded favor ably and promptly (Fig. 3). Infection in these eyes was controlled in five to seven days. After completion of the 10 day course of antibiotics, conjunctival inflammation in treated eyes returned to normal in one week.
493
Iritis was slower to subside. The corneas of several treated eyes exhibited minimal but permanent scarring where inoculated. DISCUSSION
Following subconjunctival carbenicillin in the rabbit and owl monkey, ocular irritation was noted to be transient and toxicity nil. In a previous study in a small number of hu man subjects, carbenicillin was found to be safe for subconjunctival injection.14 Lack of untoward ocular effects is in agreement with this drug's remarkably low toxicity when given systemically, even in massive doses.1·3'4 Penetration into aqueous humor after sub-
AVERAGE CARBENICILLIN LEVELS IN AQUEOUS HUMOR 60r
25 mg dose 50 mg dose
/ /
50
N \ \
E o E
w
j _i
30
\
Ö
V
sv
w 20 \
GO <
10
30
60
90 120 MINUTES
150
180
210
Fig. 2 (Rich, Dunlap, and Partridge). Aqueous penetration of carbenicillin in the rabbit following sub conjunctival injection of 50 or 25 mg. Each point represents average of 12 determinations.
494
AMERICAN JOURNAL OF OPHTHALMOLOGY
MARCH, 1973
SUBCONJUNCTIVAL CARBENICILLIN IN THE TREATMENT OF PSEUDOMONAS KERATITIS UNTREATED EYES 50mgqdxlOd 25mgq4xlOd
CORNEA
CONJUNCTIVA
DAY Fig. 3 (Rich, Dunlap, and Partridge). Clinical comparison of untreated and carbenicillin-treated rabbit eyes with Pseudomonas keratitis.
conjunctival injection was moderate in the non-inflamed eye and drug levels were found to be in the general range reported elsewhere.14·15 The major ophthalmic potential for car benicillin lies in the treatment of Pseudomo nas eye infections. Certainly a satisfactory response was noted in this study of animals infected with a sensitive strain of Ps. aeruginosa (MIC reported as 1.0 pg/ml). Mini mum inhibitory concentrations for most Pseudomonas strains are exceptionally higher, however, with 50% of strains having MICs greater than 50 μg/ml.4-6 Average drug levels at the peak of concentration were found to be 56.8 μg/ml in this study. In the inflamed eye, higher drug leevels might be expected.15 In one reported study of Pseudo monas keratitis in rabbits, subconjunctival carbenicillin was found to be effective against
Pseudomonas strains with MICs of 125-250 μ^/πιΐ.10 It is uncertain, however, if bacteri cidal levels for the large majority of Pseudo monas strains could be obtained following subconjunctival carbenicillin. A dosage con centration between 25 and 57 mg/0.25 ml has been shown to be optimal in three differ ent laboratories,8·14'15 and increasing the dos age to 100 mg/0.25 ml or greater has not in creased aqueous penetration in the rabbit or human. Some conflicting data, however, has been recently reported in 20 clinical patients by Boyle, Gwon, Zinn and Leopold.17 High aqueous levels of carbenicillin were incon stantly found following subconjunctival in jections of 500 mg in 1.0 ml, 250 mg in 0.5 ml, and 100 mg in 0.2 ml. Following a 50 mg dose in 0.1 ml, carbenicillin was detected within two hours in one of three aqueous samples. Curiously, iris samples bathed in
VOL. 75, NO. 3
CARBENICILLIN IN OPHTHALMOLOGY
high drug concentrations in aqueous did not show any antibiotic activity. Lack of any aqueous penetration at times when fully ex pected was not explained. Because of the small number of patients in that study with little data for the same time intervals, hard conclusions might be misleading. Of consid erable credibility, however, were the adverse local reactions that were reported to follow subconjunctival injections of such high drug concentrations. Intraocular drug levels following com bined subconjunctival and systemic adminis tration have not been evaluated but might be expected to effect greater Pseudomonacidal action. Also more effective ocular therapy might be expected when carbenicillin is used synergistically with gentamycin although some reports of synergy are conflicting.18·19 Limited data is available to evaluate such synergism in eye infections.8 SUMMARY
Twelve owl monkeys and 12 rabbits were given subconjunctival carbenicillin for 10 successive days and evaluated for untoward effects. Clinically, only conjunctival chemosis and injection of slight to moderate degree were noted. Histologie findings were limited to a mild localized conjunctivitis and, infre quently, a focal myositis. Aqueous levels of carbenicillin were deter mined in 94 rabbit eyes following subcon junctival injection. The average peak con centration was 56.8 μg/ml at 90 minutes af ter injection of 50 mg. The MICs for a ma jority of Pseudomonas strains exceed this value and therapeutic success of carbenicillin against eye infections with these strains is indeterminate. Subconjunctival carbenicillin cleared 11 of 12 rabbit eyes with Pseudomonas keratitis induced with a sensitive strain while most untreated eyes perforated or developed se vere permanent scarring. ACKNOWLEDGMENT
Carbenicillin and technical assistance in this study
495
were kindly provided by Beecham-Massengill Phar maceuticals, Clifton, New Jersey.
REFERENCES
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