Carbenicillin: Activity In Vitro and Absorption

Transcription

1 APPLIED MICROBIOLOGY, Nov. 1968, p Copyright 1968 Americn Society for Microbiology Vol. 16, No. II Printed in U.S.A. Crbenicillin: Activity In Vitro nd Absorption nd Excretion in Norml Young Men CHARLES B. SMITH' AND MAXWELL FINLAND Thorndike Memoril Lbortory, Second nd Fourth (Hrvrd) Medicl Services, Boston City Hospitl, nd Deprtment of Medicine, Hrvrd Medicl School, Boston, Msschusetts Received for publiction 11 September 1968 Crbenicillin is new semisynthetic penicillin which differs from other penicillins in showing moderte ntibcteril ctivity ginst Pseudomons. Its ctivity in vitro is enhnced t low ph. Serum binding is of low order nd does not pprecibly lter ctivity. Strins of Pseudomons exposed to subinhibitory concentrtions of crbenicillin rpidly develop resistnce by mechnism tht does not depend upon destruction of the drug. In norml subjects, high levels of nti-pseudomons ctivity re redily obtined in the urine fter intrmusculr injection. Levels of crbenicillin dequte to inhibit mny strins of Pseudomons cn be chieved in serum only with n intrvenous dministrtion of lrge dose. Crbenicillin ppers to exhibit the sme low degree of toxicity s do other penicillins. Infections with grm-negtive bcilli hve become incresingly common nd serious for the hospitlized ptient since the introduction nd widespred use of ntibiotics (5, 9). Some of the most severe nd intrctble mong those infections re cused by strins of Pseudomons. These re encountered in ptients with prolonged debilitting illnesses nd in others whose host defenses hve been compromised by other severe infections, hemtologicl disorders, or the use of immunosuppressive nd ntibiotic therpy (7). Although most strins of Pseudomons re modertely susceptible to the vilble polymyxins nd gentmicin in vitro, clinicl response to therpy with these gents hs often been unstisfctory nd there is need for more effective nd less toxic ntibiotics in their tretment (6, 13). Acred et l. (2) reported tht new semisynthetic penicillin, disodium crboxybenzyl penicillin (crbenicillin), showed moderte in vitro ctivity ginst clinicl isoltes of Pseudomons, nd preliminry clinicl reports suggested tht this semisynthetic penicillin might be useful for treting Pseudomons infections (4, 8, 16). This report presents observtions on the ctivity of crbenicillin in vitro, nd on its bsorption nd excretion following dministrtion of single intrvenous nd intrmusculr doses to helthy young men. IReserch Fellow of the Helen Hy Whitney Foundtion. MATERLALS AND METHODS Crbenicillin (disodium slt) ws supplied by Beechm Phrmceuticls s the dry powder nd ws stored in dessictor t 4 C. Fresh solutions were prepred ech dy in ph 7.35 buffered phosphte solution. For prenterl use, it ws furnished in sterile vils contining 1.0 g ech. The test strin of P. pyocyne (Ellsworth, NCTC 10490) ws received from Beechm Phrmceuticls. In repeted tests over n 8-month period in our lbortory, the minimum inhibiting concentrtion (MIC) of crbenicillin for this orgnism ws 0.25 to 0.5,ug/ml when 10- dilution of n overnight culture ws used for the inoculum. The bcteri tested were (except for few lbortory strins) recently isolted s the only or predominnt pthogen from hospitlized ptients in the Bcteriology Lbortory of the Boston City Hospitl. Susceptibility of bcteri to crbenicillin ws tested by the inocul-replicting method of Steers, Foltz, nd Grves (14). Antibcteril ctivity of serum, urine, nd culture filtrtes ws ssyed in twofold dilutions of broth utilizing the Microtiter system (pprtus mnufctured by Cooke Engineering Co., Alexndri, V.) s employed by Abrmowicz et l. (1); n dpttion of this method ws lso used to test the susceptibility of some strins of Pseudomons. When 49 ser contining vrious concentrtions of crbenicillin were ssyed for nti-pseudomons ctivity in prllel by the stndrd tube dilution technique used in this lbortory (10) nd by the Microtiter method, the results with individul ser were the sme or vried by no more thn single twofold dilution. Beef-hert infusion broth (Difco) nd Hert Infusion Agr (Difco) were used in these studies. Assys for crbenicillin ctivity were lso crried out by Chrles 1753

2 1754 SMITH AND FINLAND APPL. MICROBIOL. West of Beechm Phrmceuticls by the cup-plte, gr diffusion method nd the sme test orgnism. Sensitivity tests on Pseudomons strins were lso crried out with 6-mm pper discs impregnted with 100 ug of crbenicillin (supplied by Bltimore Biologicl Lbortory). A sterile cotton swb ws immersed in 1:10 dilution of n ovemight culture of the orgnism to be tested, excess fluid ws squeezed out on the side of the dilution tube, nd the swb ws thoroughly rubbed over the surfce of gr in 60-mm petri plte. The crbenicillin disc ws plced in the center of the plte, the plte ws incubted for 18 hr t 37 C, nd the dimeter of the cler zone ws then recorded. Growth curves were obtined by growing cultures in 50-mi volumes in 250-ml Erlenmeyer flsks which hd tubulr side rms mtched for opticl density. Turbidity ws ssyed by tipping the contents of the flsk into the side rm nd reding the opticl density in Colemn (model 6A) spectrophotometer. A crossover study of bsorption nd excretion of crbenicillin ws performed in eight norml men, 25 to 33 yers old, who weighed 80 to 94 (verge, 86) kg. Ech subject received 1 g of crbenicillin intrmusculrly (im) in the glutel region fter n ovemight fst on two seprte occsions, one of the doses given following the orl dministrtion of probenecid (0.5 g 14 nd 8 hr before injection, nd 1.0 g 1 hr before injection); the other dose ws given without probenecid. The two injections were dministered 3 dys prt, hlf of the men receiving probenecid ech time. Venous blood for serum ws collected before, nd 0.5, 1, 2, 4, nd 6 hr fter injection. In ddition, three of the volunteers lso received 1 g of crbenicillin in 10 ml of 0.85% sline intrvenously (iv) in 5 min, blood smples being drwn t the sme intervls nd lso t 15 nd 45 min fter the iv dose. The bldder ws emptied just before ech injection, nd smple of the voided urine ws obtined s control; ll urine ws then collected for 0 to 4 nd 4 to 8 hr, the volumes were mesured, nd smples were stored t -20 C until thetime of ssy. Ser were seprted within 6 hr nd stored t -20 C. All smples from the eight-mn crossover study were ssyed simultneously by the Microtiter method. Becuse specimens of ser nd urines from the initil eight-mn crossover study were mishndled in trnsit to the Beechm Lbortories for ssy of ctivity by the cup-plte gr diffusion method, those results were discrded. However, third 1-g im dose ws dministered to three of the originl subjects. Serum nd urine specimens were shipped nd mintined in frozen stte nd the ssys were performed within 2 weeks. RESULTS Stbility of crbenicillin. No deteriortion in crbenicillin ctivity ws demonstrble when the drug ws incubted for 24 hr t 37 C in humn serum, or in urine t ph 4, 5, 6, 7, or 8, or in ph 7.35 phosphte buffer. The ntibcteril ctivity of 37 ser contining crbenicillin ws retested fter storge t -20 C for 24 hr nd 14 dys; no pprecible differences in ctivity were found. However, ntibcteril ctivity of these ser declined more thn 50% fter storge for 12 weeks t -20 C (P < 0.05, t test). Effect of ph. The ctivity of crbenicillin ginst the test strin of P. eruginos (NCIC 10490) incresed 12-fold when tested in broth t ph 5.5 (Tble 1). Growth of the test orgnism ws reduced nerly one-hlf when it ws incubted in the bsence of the drug in medi t ph 5.5, s compred with tht found t ph 7.4, indicting tht the greter ctivity of crbenicillin t the lower ph ws not due to inhibition of growth of the test orgnism. Serum binding. No significnt difference in MIC of crbenicillin ws observed when six strins of Pseudomons were tested in broth contining 50% humn serum s compred with prllel tests in broth without serum (Tble 2). Susceptibility of pthogenic bcteri to crbenicillin in vitro. The "ntibcteril spectrum" of crbenicillin for recent clinicl isoltes of severl bcteril species is depicted in Fig. 1. TABLE 1. Effect of ph of medium on nti-pseudomons ctivity of crbenicillin ph MIC Colony-forming units/mi fter 24 hr t 37 C1, pg/mi X X X X 108 Geometric men of six seprte tests with twofold dilutions of ntibiotic in brin-hert infusion broth. Pp. eruginos 10490, growth t indicted ph without ntibiotic. TABLE 2. Effect of humn serum on nti-pseudomons ctivity of crbenicillin Strin Broth MIC (j,g/ml) 50% Serum in broth Menb Twofold dilution, Microtiter method. b P = 0.20, t test.

3 VOL. 16, 1968 CARBENICILLIN 1755 w r I o z z K I- I~z Z w hi 0 0 Jw-, 011- T I i - - i~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > 400 MINIMUM INHIBITING CONCENTRATION OF CARBENICILLIN, MICROGRAMS PER ML. * REPLICA-INOCULATING METHOD, UNDILUTED INOCULUM; KLERSIELLA, 30 STRAINS - M.I.C. OF 97% - >200 FIG. 1. Susceptibility of recently isolted bcteri to crbenicillin. Meningococci, gonococci, pneumococci, group A bet-hemolytic streptococci, nd Viridns (lph or gmm) streptococci were ll inhibited by crbenicillin in low concentrtions. Susceptibility of stphylococci to crbenicillin prlleled their sensitivity to penicillin G. (Five strins which were sensitive to penicillin G were inhibited by 1.6 or 3.1,ug of crbenicillin per ml; the others were resistnt to penicillin G nd required higher concentrtions of crbenicillin.) All 35 strins of enterococci required 50 or 100,gg/ml for inhibition. The medin MIC for ll of the grm-negtive bcilli tested ws greter thn 100 Ag/ml when undiluted overnight cultures were used in the inocul-replicting test (Fig. 1); for the strins of Pseudomons nd Proteus, the medin MIC ws more thn 400,g/ml. Effect of inoculum size. When 104 dilution of n overnight culture ws used s the inoculum, no reduction in the medin MIC ws generlly noted for strins of Klebsiell nd Serrti. In contrst, considerble reductions in the medin MIC with the lower inoculum were noted for strins of Proteus, Pseudomons, Escherichi coli, nd Enterobcter. The medin MIC for the strins of Pseudomons ws 31 Ag/ml when the smll inoculum ws used in the inoculreplicting method; it ws 50,g/ml when the sme inoculum ws used in tests done by the seril twofold dilution technique in micropltes (Fig. 2d). Most strins of P. mirbilis were less sensitive thn the indole-positive ones when the full inoculum ws used, but some of the former were more sensitive when tested with the dilute inoculum. Disc sensitivity. Pper discs contining 100 jig of crbenicillin were used in tests for inhibiting effects on 70 strins of Pseudomons. Zones of inhibition rnged from 12 to 24 mm in dimeter, but there ws poor correltion between the dimeters of the cler zones observed round these discs nd the MIC determined by the replic-inoculting or Microtiter method. Development ofresistnce in vitro. Three recent clinicl isoltes of P. eruginos were pssed serilly on gr contining twofold dilutions of crbenicillin. Individul colonies were picked from the gr contining the highest concentrtion of drug tht supported growth nd inoculted into ntibiotic-free broth, which ws incubted overnight; loopfuls of the growth were then streked on gr pltes contining seril dilutions of crbenicillin. Rpid development of resistnce ws observed, one of the strins growing uninhibited on 2,000 Ag of crbenicillin per ml on the fifth, nd nother on the sixth, pssge (Fig. 3). Prllel subcultures of one of the prent strins (no ) on ntibiotic-free gr did not result in ny chnge in MIC. The resistnt orgnisms tht emerged differed from the prent cultures by growing s smller

4 1756 I- 100 metriclly) nerly prlleled tht of the culture grown without the ntibiotic, indicting tht resistnce to crbenicillin hd developed during the first exposure. When tested by the twofold dilution method, with 104 inoculum, the MIC for both orgnisms ws found to hve incresed so- 60- X 40- z z _. 0- o REPLICA - INOCULATING METHOD l'- UNDILUTED INOCULUM _ INOCULUM SMITH AND FINLAND 100 jj% b ', /,,I I, P MIRASILIS-36,- r _.-_-_0-0 I I,r \ II/, 1~ I, PROTEUS, INDOLE POSITIVE -31) il I;,,x1, ''400' 0' >400 07; IC 2- DILUTION IN BROTH / 6 so o MI1ROPLATE METHOD / APPL. MICROBIOL. W/ r INOCULUM J6.~ ~~ 70 14,.-79,'IilI- 20/- IPSEUDOMONAS ~~~~~AERUGINOSA WI 40,- du > S >1000 MINIMUM INHISITING CONCENTRATION OF CARSENICILLIN, MICROGRAMS PER MILLILITER FIG. 2. Effect of inoculum size on susceptibility of selected grm-negtive bcilli to crbenicillin. Orgnisms were grown t 37 Cfor 18 hr nd used undiluted or in JO-4 dilution in the replic-inoculting method (14), except tht strins of P. eruginos were lso tested with O-4 inoculum in twofold broth dilution of the ntibiotic with the Microtiter method (I) s shown in Fig. 2d. MAXIMUM CONCENTRATION /50- OF CARBENICILLIN SUPPORTING t/s- GROWTH. / 3 RECENT CLINICAL ISOLATES MICROM/L/M/ Of PSEUSOMONAS AERUGINOSA 31v * * 10 NUMBER OF SUBCULTURES ON CARBENICILLIN IN AGAR FIG. 3. Increse in resistnce of Pseudomons to crbenicillin. nd smoother colonies, nd two of the three strins lost the bility to produce green pigment. The three strins, however, ll retined the chrcteristic odor nd surfce growth in broth. The resistnt vrint of strin ws subcultured nine times on ntibiotic-free gr, without demonstrble chnge in the growth chrcteristics or MIC for crbenicillin. Turbidimnetric growth curves (Fig. 4) were developed for two of the prent strins (67971 nd 83753) in broth t 37 C without nd with crbenicillin (100,ug/ml). No increse in turbidity developed in the ntibiotic-contining cultures of either orgnism during the first 12 hr. At 24 hr, there ws still no chnge in strin exposed to ntibiotic, but moderte turbidity ws noted in the flsk contining strin with ntibiotic (equivlent to the 8-hr growth of the culture without ntibiotic). By 48 hr, both strins hd grown to lmost the mximum turbidity observed in control cultures. To test whether resistnce hd developed in the presence of crbenicillin, portion of ech culture ws tken t 24 hr, diluted 1:100 in ntibiotic-free broth, nd incubted overnight in fresh broth without ntibiotic. The remining cultures were then grown in broth with crbenicillin (100,ug/ml). In ech instnce, growth in the presence of crbenicillin (determined turbidi-

5 VOL. 16X1968 CARBENICILLIN 1757 from 62.5 to 250,ug/ml fter the first 24 hr of exposure to crbenicillin in broth. The possibility tht the lte growth of orgnisms in the originl cultures contining crbenicillin might hve been due to bcteril enzymtic destruction of the drug ws investigted HOURS OF INCUBATION AT 37' C FIG. 4. Development of resistnce to crbenicillin by two strins of P. eruginos. The prent cultures (I) were grown t 37 C with (@-@) nd without (- -0) crbenicillin (100,g/ml). A portion of the ltter culture ws withdrwn t 24 hr, diluted I :100, grown overnight in ntibiotic-free broth, nd then used s n inoculum for culture II for growth in broth with (X-X) nd without (X- -X) crbenicillin (100,ug/ml). Smples of these crbenicillin-contining culture fluids obtined 24 nd 48 hr fter incubtion were pssed through 0.3-,um Millipore filter nd the filtrte ws ssyed for inhibition of the ssy strin (NCTC 10490). No significnt difference in ntibcteril ctivity ws noted in these filtrtes s compred to control broths contining 100,ug/ml tht hd been incubted for comprble periods t 37 C. Two other recently isolted strins of Pseudomons (MIC, 250,ug/ml) lso filed to inctivte crbenicillin when tested in the sme mnner. Absorption fter im nd iv doses. The ntibcteril ctivity of ser obtined from men fter im nd iv doses of crbenicillin, expressed s the men number of twofold inhibiting dilutions, is given in Tble 3. In Fig. 5, ntibcteril ctivity is expressed s the reciprocl of the mximum inhibiting dilution of serum. The levels of crbenicillin in the three men who received 1 g of crbenicillin im without probenecid were ssyed by both the cup-plte method (Beechm) nd by the twofold dilution technique in broth (Tble 4). Antibcteril ctivity in titer of 1:2 to 1:4 ws detectble in nerly ll control specimens of serum when tested in broth. In subsequent studies, this nti-pseudomons ctivity ws completely eliminted in most instnces by heting the ser for 30 min t 56 C. Anti-Pseudomons ctivity in control ser ws not detected by the cup-plte ssy. Pek levels in the serum were reched 0.5 to 2 hr fter the im dose, nd vried from 14 to 20,ug/ml (Tble 4). In those subjects who did not receive probenecid, significnt ntibcteril ctivity ws not detectble 6 hr fter the dose (Fig. 5, Tble 4). Premediction with orl probenecid TABLE 3. Anti-Pseudomons ctivity of serum of norml dult mles fter single doses of 1.0 g of crbenicillin Hours fter injection of crbenicillin Cycle subjects Route Probenecid No. of twofold inhibiting dilutions of serumb A 8 im No 1.5 ± ± ± ± B 8 im Yesc ±4 0.5 C 3 ivd No 1.3 ± ±0 5.7 ± ± ±0.6 Significnce of differences (P vlues) A vs. B A vs. C <0.02 < Twofold dilution, Microtiter method, in broth. b Men i SD. c Doses of 0.5 g given orlly 14 nd 8 hr before injection nd 1 g orlly 1 hr before injection. d Men vlues t 15 nd 45 min were nd 6.0 ± 0, respectively.

6 1758 SMITH AND FINLAND APPL. MICROBIOL O 256 : IL 128- In 64- U. 0 z 32- I 6- I-e x ASSAY ORGANISM P. AERUGINOSA, NCTC 10490; M.I.C. :0.25 MICROGM./ML. NO. DOSE: 1.0 GM. VOLUNT I.M.; NO PROBENECID --- I.M.; PROBENECID P.O. *K I.V.; NO PROBENECID 3 O HOURS AFTER INJECTION OF CARBENICILLIN FiG. 5. Men levels ofnti-pseudomons ctivity of serum fter single 1.0-g dose of crbenicillin given intrmusculrly with nd without premediction with orl probenecid, nd fter 1.0 g intrvenously. resulted in significntly higher levels of ntibcteril ctivity in the serum 2, 4, nd 6 hr fter the im doses (Tble 3). Pek levels of ntibcteril ctivity fter iv doses were fourfold higher thn those tht followed the im doses (Fig. 5). The levels declined more rpidly fter iv dministrtion nd were less thn those following the im doses within 2 hr. Urinry excretion. Concentrtions nd mounts of crbenicillin excreted in the urine by the three men who received 1 g im were determined by the cup-plte method (Tble 4). Concentrtions between 1,870 nd 3,090,ug/ml were found in the 0 to 4 hr collections, nd 790 to 3,020,ug/ml in the 4 to 8 hr urines. From bout 80% to nerly 100% of the dministered drug ws ccounted for in the urine excreted in the first 8 hr, twothirds or more of the totl being recovered in the first 4 hr. Untowrd effects. All subjects who received the intrmusculr injections complined of modertely severe pin t the injection site, similr to tht experienced following injections of queous penicillin G. No other untowrd rections were observed. DiscussIoN Initil studies of the phrmcology of crbenicillin indicted tht it is similr in mny respects to other penicillin nlogues (2, 4). It 1 6 TABLE 4. Levels in serum nd urinry excretion of crbenicillin in three norml young men fter single im dose of 1.O Determintin eerm; ion Time injection fter Subject A Sub'ect ii Subject hr Crbenicillin in serum (ig/ml)b Inhibiting dilu- 0 <4 8 8 tion of serumc Crbenicillin in Control urine (ug/ml) 0-4 2,760 3,090 1, , Amount (mg) Percent of d ministered dose recovered in urine in 8 hr Serum nd urine were ssyed by both methods fter 2 weeks of storge, with P. eruginos NCTC s the test strin; MIC = 0.25 g/ml by the Microtiter method. b Agr diffusion method; 0 = <2 jig/ml; ssy orgnism: NCTC Microtiter method; dilutions in broth. is redily soluble in wter nd stble in the physiologicl rnges of ph for resonble periods of time. However, s shown in the present study, prolonged storge my result in loss of ctivity, pprently becuse of degrdtion of the compound to benzylpenicillin nd crbon dioxide (2). Our observtions gree with the erly report (2) tht binding to humn serum protein is only moderte. Toxicity studies in nimls nd mn indicted tht lrge doses were well tolerted, nd tht crbenicillin hs the sme low degree of toxicity chrcteristic of other penicillins (2). Our results re in greement with previous reports tht crbenicillin is effective in low concentrtions ginst most of the nonpenicillinseproducing grm-positive orgnisms nd Neisseri (2, 4); however, penicillin G is significntly more effective ginst these orgnisms (11). Among

7 VOL. 16, 1968 CARBENICILLIN 1759 the grm-negtive bcilli, Hemophilus influenze nd E. coli strins were the most sensitive to crbenicillin. Previous studies of mpicillin in this lbortory, however, suggest tht the ltter is likely to be more effective ginst these orgnisms (10). No significnt ctivity ws observed ginst Klebsiellee (Kiebsiell-Enterobcter-Serrti). Becuse the MIC of crbenicillin for Pseudomons vries considerbly, depending on the size of the inoculum (2, 4), it is importnt to tke this into considertion when compring results from different lbortories. In the present study, 94% of 70 strins of Pseudomons were inhibited by 62.5 jig/ml when 10-4 dilutions of overnight cultures were used in the inoculreplicting ssy. Acred et l. (2) reported similr results, 68 of their 74 strins being inhibited by 50,ig/ml or less when 10-2 dilution of n overnight culture ws used s the inoculum on gr. Using n inoculum of 104 orgnisms, Brumfitt et l. (4) found tht 81% of 99 strins tested were inhibited by concentrtions of 100,ug/ml or less in the tube dilution test. On the other hnd, Bodey nd Terrell (3) found tht only 8% of 143 strins of Pseudomons were inhibited by 100,ug/ml or less when 10-3 dilution of n overnight culture ws used s the inoculum in the tube dilution test. Since their results with other grm-negtive bcteri were in greement with those in other reports, it is possible tht the strins of Pseudomons in their hospitl were unusully resistnt to crbenicillin. Strins of Pseudomons grown in the presence of crbenicillin hve been shown to develop resistnce to the drug rpidly both in vitro (4, 8) nd in vivo (16). Although the resistnt strins were stble on subculture in the bsence of crbenicillin, they were shown to be less virulent for burned mice (8). In contrst to the findings of Acred et l. (2), we found tht the growth of Pseudomons orgnisms which ppered fter 24 hr in broth cultures contining crbenicillin ws due to the selection of resistnt orgnisms. Our observtions re in greement with reports tht both lbortory-induced nd initil isoltes of resistnt strins pprently do not inctivte crbenicillin (2, 4, 8). There is generl greement tht most strins of Proteus re susceptible to crbenicillin t concentrtion of 6 j,g/ml or less when smll inocul re used (2, 4). Acred et l. (2) suggested tht crbenicillin might be of prticulr usefulness ginst those penicillinse-producing indolepositive Proteus strins which re sensitive to crbenicillin nd resistnt to mpicillin. In previous studies of mpicillin in this lbortory (15), strins of P. mirbilis were inhibited by 3.1,ug/ml, wheres the MIC for indole-positive strins ws 50,ug/ml when 10-s culture dilution ws used s inoculum. Using 10-i dilution for the inoculum, we found tht crbenicillin hd ctivity similr to mpicillin ginst P. mirbilis nd significntly greter ctivity (MIC, 1.6 j,g/ml) ginst the indole-positive strins. The gretest potentil usefulness of crbenicillin is in the tretment of Pseudomons infections, prticulrly those of the urinry trct. Although the MIC for most strins is reltively high by usul stndrds, the low degree of toxicity of crbenicillin permits the use of doses lrge enough to chieve inhibitory levels for most Pseudomons strins, even in serum or tissues. Studies of the bsorption nd excretion of crbenicillin indicte tht, fter n im dose of 1 g, pek serum levels re usully in the rnge of 20 to 25,ug/ml, nd ctive secretion of the drug into the urine usully produces levels greter thn 1,000,ug/ml (2, 4). Becuse the MIC for most strins of Pseudomons is 30 to 60,ug/ml, it is unlikely tht im dministrtion of this drug will provide levels in blood or tissue tht re dequte for the tretment of Pseudomons infections outside of the urinry trct. Knudsen et l. (12) showed tht serum levels in excess of 100,ug/ml my be chieved-fter iv injection of 1 g of crbenicillin nd recommended doses of 1 g hourly by the iv route in ssocition with orl probenecid s therpy for serious Pseudomons infections. Initil clinicl trils of crbenicillin reveled poor responses of non-urinry trct Pseudomons infections to im tretment with crbenicillin (4). More recent studies, utilizing lrge frequent or continuous iv doses of crbenicillin, were ssocited with higher rte of success in Pseudomons infections, suggesting tht further clinicl trils of crbenicillin in such infections re wrrnted (16). ACKNOWLEDGMENTS We re indebted to Clre Wilcox nd Wendy Wollish for technicl ssistnce, to Beechm Phrmceuticls, Clifton, N.J., for providing the crbenicillin (Pyopen) nd for performing some of the ssys, nd to A. Kthleen Dly nd Alice McDonld for furnishing nd identifying the freshly isolted strins used in this study. This investigtion ws supported by Public Helth Service grnts AI-23 nd 5TI-AI-86 from the Ntionl Institute of Allergy nd Infectious Diseses. LITERATURE CITED 1. Abrmowicz, M., J. 0. Klein, D. Ingll, nd M..Finlnd Levels of penicillin in serum of

8 1760 SMITH AND FINLAND APPL. MICROBIOL. newborn infnts. Am. J. Diseses Children 111: Acred, P., D. M. Brown, E. T. Knudsen, G. N. Rolinson, nd R. Sutherlnd New semisynthetic penicillin ctive ginst Pseudomons pyocyne. Nture 215 : Bodey, G. P., nd L. M. Terrell In vitro ctivity of crbenicillin ginst grm-negtive bcilli. J. Bcteriol. 95: Brumfitt, W., A. Percivl, nd D. A. Leigh Clinicl nd lbortory studies with crbenicillin. Lncet 1: Finlnd, M., W. F. Jones, nd M. W. Brnes Occurrence of bcteril infections since introduction of ntibcteril gents. J. Am. Med. Assoc. 170: Finlnd, M., W. M. M. Kirby, Y. A. Chbbert, E. B. Chin, H. F. Dowling, L. P. Grrod, C. W. Petting, nd A. C. Todd Round tble: Are new ntibiotics needed? Antimicrobil Agents nd Chemotherpy-1965, p Hersh, E. M., G. P. Bodey, B. A. Nies, nd E. J. Freireich Cuses of deth in cute leukemi: ten-yer study of 414 ptients from J. Am. Med. Assoc. 193: Jones, R. J., nd E. J. L. Lowbury Prophylxis nd therpy for Pseudomons eruginos infection with crbenicillin nd gentmicin. Brit. Med. J. 2: Kessner, D. M., nd M. H. Lepper Epidemiologic studies of grm-negtive bcilli in the hospitl nd community. Am. J. Epidemiol. 85: Klein, J. O., nd M. Finlnd Ampicillin: ctivity in vitro nd bsorption nd excretion in norml young men. Am. J. Med. Sci. 245: Klein, J. O., nd M. Finlnd The new penicillins. New Engl. J. Med. 269: ; ; Knudsen, E. T., G. N. Rolinson, nd R. Sutherlnd Crbenicillin: new semisynthetic penicillin ctive ginst Pseudomons pyocyne. Brit. Med. J. 2: Pines, A., H. Rft, nd K. Plucinski Gentmicin nd colistin in chronic purulent bronchil infections. Brit. Med. J. 2: Steers, E., E. L. Foltz, nd B. S. Grves Inocul replicting pprtus for routine testing of bcteril susceptibility to ntibiotics. Antibiot. Chemotherpy 9: Steigbigel, N. H., C. E. McCll, C. W. Reed, nd M. Finlnd Antibcteril ction of "brod spectrum" penicillins, cephlosporins, nd other ntibiotics ginst grm-negtive bcilli isolted from bcteremi ptients. Ann. N.Y. Acd. Sci. 145: vn Rooyen, C. E., J. F. Ross, G. W. Bethune, nd A. C. McDonld Bcteriologicl observtions on crbenicillin in the control of Pseudomons eruginos infection in burns. Cn. Med. Assoc. J. 97: