Stereoselective Renal Tubular Secretion of Carbenicillin

Transcription

1 ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Nov. 1993, p /93/ $2./ Copyright 1993, Americn Society for Microbiology Vol. 37, No. 11 Stereoselective Renl Tubulr Secretion of Crbenicillin TOMOO ITOH,1* MARIKO ISHIDA,1 YOUICHI ONUKI,1 YASUYUKI TSUDA,1 HIDEYO SHIMADA,2 AND HIDEO YAMADA' Deprtment of Phnncokinetics nd Biophrnceutics' nd Deprtment of Clinicl Phrmcology, 2 School ofphrmceuticl Sciences, Kitsto University, Shirokne, Minto-ku, Tokyo 18, Jpn Received 16 Februry 1993/Returned for modifiction 2 My 1993/Accepted 21 August 1993 The stereoselective disposition of crbenicillin epimers ws studied in helthy humn volunteers. There ws difference between the two epimers in the extent of plsm protein binding in vitro, with the unbound frction of the R epimer being greter thn tht of the S epimer. Renl clernce (CLR) of ech epimer ws greter thn the glomerulr filtrtion rte, suggesting renl tubulr secretion of both epimers. Although the CLR ws greter for the R epimer, renl tubulr secretion ws greter for the S epimer. When probenecid ws codministered, the CLR of ech epimer ws significntly reduced nd ws pproximtely equl to the glomerulr filtrtion rte. The difference in CLR between the two epimers ws simply due to differences in plsm protein binding. The observtions in the present study suggest tht both crbenicillin epimers re secreted by n orgnic nion trnsport system in the renl proximl tubule in humns nd tht the two epimers my be distinguished in the secretion process, resulting in the differences in the secretion rtes. Crbenicillin (CBPC) hs been used cliniclly since the lte 196s, nd its phrmcokinetics hve been extensively studied both in humns (8, 12, 13, 17, 19, 2) nd in nimls (1, 9, 16, 21). However, it hs been used s mixture of two epimers (R-CBPC nd S-CBPC) becuse of the chirlity of (crboxyphenylcetyl)mino group ttched to the 6 position of penicillnic cid. The phrmcokinetics of ech CBPC epimer hve yet to be clrified, since lmost ll the previous studies used microbiologic ssy method becuse of the lck of relible nd convenient stereospecific nlyticl method. However, it is importnt to understnd the phrmcokinetic behvior of ech epimer becuse ntimicrobil ctivity is different mong the epimers of,-lctm ntibiotics (4, 14). For exmple, the R epimer of sulbenicillin hs been reported to be bout 4 times s potent s the S epimer (14). However, the difference in ctivity between CBPC epimers is not fully understood becuse of epimeriztion in the ntimicrobil ssy procedures, which usully uses incubtion times of severl hours to severl dys (4). A stereospecific high-performnce liquid chromtogrphic (HPLC) method hs been developed in our lbortory for the nlysis of CBPC epimers in biologicl fluids (11); this HPLC method enbled us to conduct the present study. In the present study, the stereoselectivities of CBPC epimers in plsm protein binding nd renl tubulr secretion were studied in helthy humn volunteers, since renl excretion is the mjor elimintion route for CBPC (8, 17). MATERIALS AND METHODS Volunteer study. Four mle volunteers between 23 nd 26 yers of ge prticipted in the present study. The study ws pproved by the Ethicl Review Bord of the School of Phrmceuticl Sciences, Kitsto University, nd ll the volunteers gve written informed consent. The weight nd surfce re of the volunteers were 59.7 ± 3.8 kg nd m2 (men + stndrd devition [SD]), respectively. They hd no evidence of disese, s determined by physicl exmintion, urinlysis, nd blood chem- * Corresponding uthor icl tests. Control nd probenecid studies were conducted with crossover study design with 2-week wshout period. For the control study, 2 g of CBPC (2.71 g s CBPC disodium slt; R-CBPC:S-CBPC, 1.24:1; Geopen, Pfizer Phrmceuticl Co., Tokyo, Jpn) ws dissolved in 15 ml of sline nd ws injected into forerm vein over n pproximtely 4-min injection time. Blood smples were collected in heprinized disposble syringes from the vein of the contrlterl forerm before CBPC injection nd t.25,.5,.75, 1, 1.5, 2.5, 3.5, nd 5 h following injection of CBPC s bolus. Plsm ws immeditely obtined by centrifugtion nd ws stored t -7 C until it ws nlyzed. Urine ws collected before CBPC injection s well s t the following time intervls fter the injection: to.5,.5 to 1, 1 to 2, 2 to 3, 3 to 4, 4 to 6, 6 to 12, nd 12 to 24 h. Immeditely fter ech collection, the urine volume ws recorded nd the urine ws diluted 5-fold with deionized wter, nd the diluted urine smple ws stored t -7 C until it ws nlyzed. The urine volume in hlf-hour intervl ws ml (men + SD; n = 8). For the probenecid study, 1 g of probenecid (Probenemid tblets; Bnyu Phrmceuticl Co., Tokyo, Jpn) ws orlly dministered t 12 nd 1 h before CBPC injection. CBPC ws dministered in the sme mnner s in the control study. Blood smples were collected before CBPC injection nd t.25,.5,.75, 1, 1.5, 2.5, 3.5, 5, nd 9 h fter the injection. Urine smples were collected t the sme time intervls s for the control study. The urine volume in hlf-hour intervl ws ml (men + SD; n = 8). Urine nd plsm smples were stored in the sme mnner s for the control study. Probenecid concentrtions in plsm were determined for ech volunteer t 15 min before CBPC injection nd t 2.5 nd 9 h fter the injection. Smple preprtion for HPLC nlysis. A solid-phse extrction column (SAX-Bond Elut; Anlytichem Interntionl, Hrbor City, Clif.) ws preconditioned with 2 ml of methnol nd then 2 ml of distilled wter. Plsm smples were filtered through Cosmonice filter (pore size,.45,um; type W; Nihon Millipore Kogyo, Kyoto, Jpn), nd n liquot (.5 ml) ws mixed with 5 ml of.5 M mmonium cette (AcONH4). The mixture ws loded onto preconditioned SAX column nd ws drwn through the column Downloded from on November 18, 218 by guest

2 2328 ITOH ET AL. under vcuum. The column ws flushed with 3 ml of mixture consisting of.5 M AcOH-CH3CN (1:1 [vouvol]) nd then with 2 ml of mixture of.1 M AcONH4-CH3H (1:1 [vol/vol]), which were discrded. This procedure ws necessry to eliminte interfering substnces on the chromtogrph used for HPLC. The smple ws then eluted with.5 ml of mixture of 1% LiCl-CH3H (3:2), nd 2-,ul portion of the finl eluent ws injected into the chromtogrph.for HPLC. Five hundred microliters of diluted urine smple ws mixed with 5 ml of.5 M AcONH4, nd the smple ws prepred for HPLC nlysis by the sme procedure used for the plsm smples. The detection limit ws bout 5,ug/ml for ech epimer, nd the dy-to-dy vribility ws low, with coefficient of vrition of less thn 1% (11). No epimeriztion ws observed in the procedures described bove. HPLC conditions for CBPC determintion. A high-performnce liquid chromtogrph ws used to determine R-CBPC nd S-CBPC concentrtions in plsm nd urine. The HPLC system consisted of dul-piston pump (model LC-9A), UV detector (model SPD-6A), nd n integrtor (model C-R4A), ll from Shimdzu Co., Kyoto, Jpn. A Cosmosil nlyticl column ws used (4.6 mm [inner dimeter] by 25 mm; 5C18-AR; Ncli Tesque Co., Kyoto, Jpn) with gurd column (Cosmosil; 4.6 mm [inner dimeter] by 1 mm). The mobile phse ws mixture consisting of.5 M AcONH4-CH3H (9:1 [vol/vol]) with flow rte of 1.2 ml/min. Both R-CBPC nd S-CBPC were detected t 254 nm Ṗlsm protein binding study. For both the control nd the probenecid studies, plsm ws obtined from ech volunteer 15 min before the CBPC injection nd ws used for in vitro binding studies. Binding of CBPC in humn plsm in vitro ws mesured by n ultrfiltrtion method. Amicon Centrifree ws used s n ultrfiltrtion device with type YMT membrne (Amicon Division, W. R. Grce & Co., Beverly, Mss.). Plsm (2.5 ml) ws mixed with 125,ul of vrious concentrtions of CBPC queous solution, nd n liquot (.3 ml) ws prepred for HPLC s described previously to determine the totl (bound plus unbound) concentrtion of ech epimer. The reminder of the smple (c. 2.2 ml) ws centrifuged t 1, x g for 7 min t 37 C, nd 3-pl liquot of the filtrte ws prepred for HPLC nlysis in the sme mnner s described bove for the plsm smple in order to determine the unbound concentrtion of ech epimer. A customized Himc 15D centrifuge (Hitchi, Tokyo, Jpn) ws used to control the temperture during ultrfiltrtion. The concentrtion of ech epimer rnged from 2 to 2,ug/ml; the CBPC used for the binding study ws purchsed from Sigm Chemicl Co. (St. Louis, Mo.); it hd n R-CBPC to S-CBPC rtio of 1.1. HPLC methods for probenecid determintions. One milliliter of.2 M phosphte buffer (ph 2.) ws dded to.1-ml plsm smple together with 1,ul of 1 mg fenbufen per ml in methnol (s n internl stndrd). The mixture ws extrcted twice with 5 ml of ether, nd the combined ether lyer ws wshed with 2 ml of.1 M phosphte buffer (ph 6.). The ether lyer ws then evported to dryness under vcuum t 3 C with rotry evportor, nd the residue ws dissolved with.3 ml of mobile phse. The smple ws filtered through Cosmonice filter nd ws injected into chromtogrph for HPLC. A Nucleosil nlyticl column (5C18; 4 mm [inner dimeter] by 25 mm; Sumik Anlyticl Service, Osk, Jpn) ws used, with the mobile phse consisting of.1 M phosphte buffer (ph 7.)-cetonitrile (8:2). The flow rte ws.9 ml/min, nd probenecid ws ANTIMICROB. AGENTS CHEMOTHER. detected t 254 nm. All other equipment ws the sme s tht for CBPC determintions. Cretinine determintion. Cretinine concentrtions in plsm nd urine were determined with Cretinine-Test Wko kit (Wko Pure Chemicls, Osk, Jpn). Phrmcokinetic nlysis. Plsm protein binding dt were nlyzed by the Sctchrd eqution with single binding site. The unbound (free) frction of ech epimer in plsm ws clculted on the bsis of the prmeter vlues obtined in in vitro binding studies. Prmeters were estimted seprtely for the plsm obtined in the control nd probenecid studies. The following eqution ws used to clculte the unbound frction (f.) t ech concentrtion: fu = - [(1 + nkpt) - (CtK)] + V/ LC where A is (1 + nkp, - CK)2 + 4C,K, n is the number of binding sites, K is the binding constnt, P, is the lbumin concentrtion in plsm (ssumed to be.6 mm), nd C, is the totl concentrtion (bound plus unbound) of ech epimer in plsm. CBPC concentrtion-in-plsm-versus-time curves were nlyzed by nonliner lest squres method (MULTI) (23) with weight of 1/C2 for ech dtum point, where C is the concentrtion of ech epimer in plsm. In the control study, profiles of drug concentrtion in plsm were nlyzed with one-comprtment open model which showed better fit compred with tht obtined with two-comprtment open model. In the probenecid study, however, profiles of drug concentrtions in plsm were nlyzed with two-comprtment open model. When probenecid ws codministered, smll distribution phse ws observed nd the two-comprtment model gve smller vlues for AIC (Akike's informtion criterion [23]). Totl body clernce (CL) ws clculted s the dose divided by the re under the curve in both the control nd probenecid studies. The mount of ech CBPC epimer excreted in urine during ech collection intervl ws determined s the concentrtion of ech isomer in the urine multiplied by the urine volume. Renl clernce (CLR) ws clculted s the renl excretion rte divided by the concentrtion in plsm t the midpoint of ech urine collection intervl (7, 18). On the other hnd, CLR cn generlly be expressed by eqution 2: CLR = (fu * GFR + CLsec) (1- Rbs) (eqution 2), where CLR is the renl clernce, GFR is the glomerulr filtrtion rte, f. is the unbound frction in plsm, CLsec is the clernce by renl secretion, nd R5b5 is the extent of rebsorption (7, 18). However, RbS cn be neglected for CBPC, since it hs been reported tht CBPC is not rebsorbed in the renl tubule (19). This ssumption ws lso supported by the results of the present study, becuse the CLR vlue ws lmost equl to f* GFR when renl secretion ws blocked with probenecid. Therefore, intrinsic clernce by renl tubulr secretion (CLint,sec) ws clculted by using equtions 3 nd 4: CLSec = CLR -f. * GFR (eqution 3) nd CLint,sec = (Q * CLc)/[f. * (Q - CL.,,)] (eqution 4), where Q is the renl plsm flow rte (7, 18). Sttisticl nlysis. Sttisticl nlyses were conducted with pired or n unpired t test. RESULTS R-CBPC nd S-CBPC concentrtion profiles in plsm following CBPC injection with nd without probenecid cod- (1) Downloded from on November 18, 218 by guest

3 VOL. 37, A E E o co E Ė 1 co E CL o 1 I I I l Q 9.t 1 2 Time (h) Time (h) FIG. 1. Men concentrtions of R-CBPC () nd S-CBPC () in plsm following intrvenous injection of 2 g of CBPC (R:S = 1.24:1) to helthy volunteers with (B) nd without (A) probenecid codministrtion. The verticl brs represent the stndrd error (n = 4).. ls C) c. - C._ if c C STEREOSELECTIVE CBPC RENAL SECRETION ministrtion re shown in Fig. 1A nd B. In the control study, R-CBPC concentrtions in plsm were slightly greter thn S-CBPC concentrtions in plsm until pproximtely 1 h fter CBPC injection, which ws prtly becuse the R-CBPC content ws greter in the preprtion tht we dministered. When the content of ech epimer in the preprtion ws mesured by HPLC, the R epimer to S epimer rtio ws However, R-CBPC nd S-CBPC concentrtions in plsm becme similr s time progressed. This ws reflected in the CL, which ws slightly but significntly greter for the R epimer (P <.1). CL vlues were nd ml/min (men -+ SD; n = 4) for R-CBPC nd S-CBPC, respectively. The volume of distribution ws lso slightly greter for the R epimer ( nd liters for R-CBPC nd S-CBPC, respectively (men + SD; n = 4), which ws probbly due to the difference in plsm binding, s will be discussed below. In the probenecid study, the profiles of drug concentrtion in plsm were nlyzed with two-comprtment open model nd CL vlues were nd (men SD; n = 4) for R-CBPC nd S-CBPC, respectively. The CL vlues for both epimers were significntly lower (P <.1) thn those in the control study, suggesting tht elimintion of both CBPC epimers from the body is inhibited by probenecid. 1- A e g%too R- or S-CBPC Concentrtion in Humn Plsm (gg/mi) B O~~~~~~~~~~~~ c9 6 -~. :11&.U 2-4- f.. I R- or S-CBPC Concentrtion in Humn Plsm (g / ml) FIG. 2. f, of R-CBPC () nd S-CBPC (-) in the plsm of control (A) nd probenecid-treted (B) subjects. Probenecid concentrtions in the plsm of ech volunteer were , , nd 97 18,ug/ml (men + SD; n = 4) t.25 h before nd t 2.5 nd 9 h fter CBPC injection, respectively. Since probenecid concentrtions in plsm exceeded 9,g/ml over the 9-h period, the probenecid concentrtions obtined in the present study ppered to be high enough to inhibit the renl tubulr secretion of penicillins (1), which resulted in the slower elimintion of CBPC. Thejf, mesured in plsm in vitro ws plotted ginst the concentrtion of ech epimer (Fig. 2A nd B), nd the binding prmeters clculted re listed in Tble 1. There ws difference in the extent of plsm protein binding between the two epimers; tht is,f ws significntly greter (P <.1) for R-CBPC thn for S-CBPC in the plsm of TABLE 1. Binding prmeters of R-CBPC nd S-CBPC in the plsm of control nd probenecid-treted subjects obtined from Sctchrd plots Study group Epimer n K (M-1, 13) Without probenecid R-CBPC S-CBPC With probenecid R-CBPC S-CBPC n is the number of binding sites. Downloded from on November 18, 218 by guest

4 233 ITOH ET AL. TABLE 2. Urinry excretion rtes of R-CBPC nd S-CBPC following intrvenous injection of 2 g of CBPC to helthy volunteers with nd without probenecid codministrtion Urinry excretion rte Study group Time (mg/min) period (h) R-CBPC S-CBPC Without probenecid ± ± ± ± ± ± ± ±.14 With probenecid ± ± ± ± ± ± ± ±.8 Vlues re mens + SDs for four subjects in ech group. both control nd probenecid-treted volunteers. In the plsm of control subjects, the rtio off, for the R epimer to tht for the S epimer [ft(r)if.(s)] ws pproximtely 1.4. The greterf, for the R epimer my t lest prtly contribute to the greter volume of distribution mentioned bove. The f. of ech epimer in the plsm of control nd probenecid-treted subjects ws lso different, with the f of ech epimer in the plsm of subjects treted with probenecid being slightly greter thn tht in the plsm of control subjects. This ws reflected in the binding constnts (K) in Tble 1, where the K vlues of both epimers were greter in the plsm of control subjects thn in the plsm of those treted with probenecid. Urinry excretion rtes of CBPC for ech time intervl re summrized in Tble 2 for ech epimer with nd without probenecid codministrtion. Approximtely 84% of the dose ws excreted in urine within 12 h fter CBPC injection in the control study, while the urinry excretion of CBPC ws bout 74% in 12 h with probenecid codministrtion. These results suggest tht urinry excretion is the mjor elimintion pthwy for CBPC. As shown in Tble 2, urinry excretion rtes of both R nd S epimers were significntly reduced when probenecid ws codministered. The urinry excretion rte ws divided by the concentrtion of ech epimer in plsm t the midpoint of ech urine collection intervl, nd the vlues obtined re listed in Tble 3 s CLR. In the control study, CLR for the R epimer TABLE 3. CLR of R-CBPC nd S-CBPC following intrvenous injection of 2 g of CBPC to helthy volunteers with nd without probenecid codministrtion Time CLR(R) CLR(S) CL()L() Study group period (ml/mm) (mviin) LR(R)CLR(S) (h) Without probenecid ± ± ±.2& ± ± ±.4" ± ± ±.2" ± ±.4" With probenecid ± 2.8c 49.5 ± 2.8c 1.32 ±.4b ± 7.8c 41.2 ± 6.2" 1.37 ± O.& ± 5.c 4.5 ± 3.8c 1.41 ±.12" ± 7.8c 41.6 ± 5A ±.14b Vlues re mens + SDs for four subjects in ech group. "Significntly different from unity (P <.1). c Significntly different from the control (P <.1). ANTIMICROB. AGENTS CHEMOTHER. TABLE 4. CLint,sec of R-CBPC nd S-CBPC following intrvenous injection of 2 g of CBPC to helthy volunteers without probenecid codministrtion Time period (h) CLint,S.C(R) CLInt,.,6(S) CLint,..(R) (mi/min) (mi/mmn) CLint,sec(S) ± ± ±.55b ± ± 4.77 ±.4b ± ± ±.2b ± ± ±.49b Vlues re mens t SDs for four subjects. b Significntly different from unity (P <.1). ws greter thn tht for the S epimer, nd the rtio of CLR for the R epimer to tht for the S epimer [CLR(R)/CLR(S)] ws pproximtely 1.2. This ws consistent with the previous results with CL, in which the CL for the R epimer ws greter thn tht for the S epimer. Also in the control study, CLR for ech epimer tended to increse with decrese in the concentrtion of drug in plsm s time progressed, suggesting tht sturble mechnism is involved in the renl excretion process. When probenecid ws codministered, CLR ws significntly reduced compred with tht in control subjects, indicting tht both epimers re normlly secreted vi n orgnic nion trnsporter in the renl tubules. Although CLR for the R epimer ws greter thn tht for the S epimer, when CLR ws divided by ft. the vlues (CLR/If) were lmost identicl between the epimers ( nd 17 ± 14 ml/min [men ± SD; n = 16] for R-CBPC nd S-CBPC, respectively) nd were pproximtely equl to the GFR (5). When cretinine clernce (CLCR) ws mesured in ech subject, the CLCR vlues were 11 ± 11 nd 11 ± 7 (men ± SD; n = 4) in the control nd probenecid studies, respectively. Also, in the probenecid study, the CLR for ech epimer ppered to be consistent throughout the study, regrdless of the plsm CBPC concentrtion. These results suggest tht renl tubulr secretion is lmost completely inhibited by probenecid nd tht both epimers re excreted only by glomerulr filtrtion. Therefore, the difference in CLR ws simply due to the difference in plsm protein binding. Indeed, the clernce rtio of the two epimers [CLR(R)/ CLR(S) = 1.4] in the probenecid study ws equl to the ft (R)Ift (S) rtio. CLmnt,sec ws clculted for ech time intervl ccording to equtions 3 nd 4. For the clcultion of CLint,sc CLCR in the control study (1.84 ml/min/kg) ws used s the GFR nd Q ws ssumed to be 1 ml/min/kg (3). The CLint,sec vlues thus clculted re listed in Tble 4. As shown in Tble 4, CLmt,sec for the S epimer ws greter thn tht for the R epimer, suggesting tht the S epimer is secreted fster in the renl proximl tubules. The rtio of CLint,sec for the R epimer to tht for the S epimer ws pproximtely.78, which ws significntly different from unity. Moreover, the CLi.,Se, vlues for both epimers incresed with decrese in the concentrtion of drug in plsm s time progressed, indicting concentrtion dependency of CBPC secretion. It should be noted tht in the control study, CLR ws greter for the R epimer (Tble 3), wheres CLint,sec ws greter for the S epimer. These results suggest differences in the stereoselectivity t different steps in the whole renl excretion processes. Downloded from on November 18, 218 by guest

5 VOL. 37, 1993 DISCUSSION The extent of CBPC binding in plsm ws different between the two epimers, s hs been reported for n oxcephem ntibiotic, moxlctm (22). When the binding prmeters were compred, binding ffinity (K) ws greter for S-CBPC thn for R-CBPC. On the other hnd, the extent of binding in rt plsm ws pproximtely equl between the two CBPC epimers, wheres the unbound frction ws greter for the S epimer in rbbit plsm (dt not shown). Therefore, there ppers to be significnt species differences in the stereoselectivity of CBPC binding in plsm, which mkes it difficult to predict the stereoselectivity of CBPC in humns from niml dt. In the control study, the CLR of the R epimer ws greter thn tht of the S epimer by fctor of bout 1.2, becuse the difference in plsm protein binding plys dominnt role in the glomerulr filtrtion process, which, in turn, overrides the difference in the secretion process. When CLR ws divided by ft. the CLR/If vlues were greter thn the GFR for ech epimer, suggesting the renl secretion of both epimers. CBPC my be ctively secreted by n orgnic nion trnsporter in the renl proximl tubule, since codministered probenecid hs been shown to increse CBPC concentrtions in humn plsm (12, 19). Indeed, CBPC hs been shown to be ctively secreted but not rebsorbed in the renl proximl tubule in rts (2). The results of the present study with probenecid codministrtion re consistent with those previous observtions. When CLint,sec ws clculted, the CLint,sec vlues were greter for the S epimer thn for the R epimer by fctor of bout 1.3, suggesting tht the S epimer my be secreted more rpidly thn the R epimer. However, CLint,sec vlues depend on Q, s shown in eqution 4, nd the Q vlues my differ from one subject to nother. Since the Q vlues hve been reported to vry with coefficient of vrition of bout 15% in helthy subjects (6), CLint,sec vlues were clculted with 3% smller or greter Q vlue (7 or 13 ml/min/kg). The CLint,sec vlues thus clculted were different from the corresponding vlues in Tble 4 by less thn 1%. Moreover, the CLint,sec(R)/CLint,sec(S) rtios were lmost equl to those listed in Tble 4, with differences of less thn 2%. These observtions suggest tht CLint,sec nd CLint,sec(R)/ CLint,sec(S) vlues re reltively insensitive to chnges in Q nd tht the results in Tble 4 my hold true even if the Q vlue differs mong subjects. Although it hs been reported tht quinidine is secreted fster thn one of its distereomers (quninine) vi n orgnic ction trnsporter in the humn kidney (15), the present study is the first to revel differences in the renl secretion rtes of orgnic nion stereoisomers in humns. From these observtions, both nion nd ction trnsporters in the humn renl proximl tubule my be stereoselective in the secretion process. However, the differences in the renl secretion rtes between CBPC epimers pper to be much smller thn those between quinidine nd quinine, in which the CLR of quinidine ws bout six times s gret s tht of quinine. The present study showed difference in the extent of plsm protein binding between CBPC epimers. There ws lso difference in the secretion rte between CBPC epimers in the humn renl proximl tubule, suggesting tht the orgnic nion trnsport system my distinguish CBPC epimers in the secretion process. In the whole renl excretion process, the fster glomerulr filtrtion of the R epimer STEREOSELECTIVE CBPC RENAL SECRETION 2331 (becuse of its greter ft in plsm) overrides the fster tubulr secretion of the S epimer, resulting in greter CLR for the R epimer. Since stereophrmcokinetics hs become n importnt issue in recent yers in order to fully understnd the phrmcokinetics nd phrmcodynmics of chirl drugs, the results obtined in the present study will contribute to better understnding of the stereoselectivity in the renl excretion process. Studies re under wy to exmine the stereoselectivity of CBPC in plsm protein binding nd in the renl excretion process in other niml species. REFERENCES 1. Benoni, G., M. E. Bertzonni, nd F. G. Cntelli Comprtive investigtion of phrmcokinetic properties of sulbenicillin nd crbenicillin in rt. Drugs Exp. Clin. Res. 8: Bergeron, M. G., F. J. Gennri, M. Brz, L. Weinstein, nd S. Cortell Renl tubulr trnsport of penicillin G nd crbenicillin in the rt. J. Infect. Dis. 132: Bischoff, K. B., R. L. Dedrick, D. S. Zhrko, nd J. A. Longstreth Methotrexte phrmcokinetics. J. Phrm. Sci. 6: Butler, K., A. R. English, V. A. Ry, nd A. E. Timreck Crbenicillin: chemistry nd mode of ction. J. Infect. Dis. 122(Suppl):S1-S8. 5. Di Mrio, U., S. Bssi, S. Morno, G. Pugliese, P. Pietrvlle, D. Andreni, S. Morbito, B. Simonetti, nd A. Pierucci Selective decrement of nionic immunoglobulin clernce fter induced renl hemodynmic chnges in dibetic ptients. Am. J. Physiol. 262:F381-F Fuvel, J. P., A. Hdj-Aiss, M. Lville, S. Doud, M. Lbeeuw, N. Pozet, nd P. Zech Stress-induced renl functionl ltertions in normotensives. Am. J. Hypertension 4: Gibldi, M., nd D. Perrier Clernce concepts, p In Phrmcokinetics, 2nd ed. Mrcel Dekker, Inc., New York. 8. Hnsen, I., E. Jcobson, nd J. Weis Phrmcokinetics of sulbenicillin, new brod spectrum semisynthetic penicillin. Clin. Phrmcol. Ther. 17: Htl, M., J. Morvek, nd. SchucL Crbenicillin phrmcokinetics in rts with reduced renl prenchym (with specil reference to combined use of gentmicin nd crbenicillin). Int. J. Clin. Phrmcol. 1: Inotsume, N., M. Nishimur, M. Nkno, S. Fujiym, nd T. Sto The inhibitory effect of probenecid on renl excretion of fmotidine in young, helthy volunteers. J. Clin. Phrmcol. 3: Ishid, M., Y. Tsud, Y. Onuki, T. Itoh, H. Shimd, nd H. Ymd. Submitted for publiction. 12. Lees, L. J., nd R. Horton Serum concentrtion nd urinry excretion in mn fter intrvenous dministrtion of ticrcillin nd crbenicillin, p In G. K. Dikos (ed.), Progress in chemotherpy. Proceedings of the 8th Interntionl Congress of Chemotherpy. Hellenic Society for Chemotherpy, Athens, Greece. 13. Meyers, B. R., S. Z. Hirschmn, L. Strougo, nd E. Srulevitch Comprtive study of pipercillin, ticrcillin nd crbenicillin phrmcokinetics. Antimicrob. Agents Chemother. 17: Nomur, H., K. Kwmur, M. Shinohr, Y. Msud, Y. Okd, nd S. Fujii Studies on distereomer of sulbenicillin by nucler mgnetic resonnce. J. Tked Res. Lb. 31: Nottermn, D. A., D. E. Dryer, L. Metkis, nd M. M. Reidenberg Stereoselective renl tubulr secretion of quinidine nd quinine. Clin. Phrmcol. Ther. 4: Nouws, J. F. M., G. Zir, C. A. M. Vn Ginneken, nd T. B. Vree Clinicl phrmcokinetics of crbenicillin, crfecillin, ticrcillin nd BL-P1654 in diry cows. J. Vet. Phrmcol. Ther. 7: Pncost, S. J., nd H. C. Neu Kinetics of mezlocillin nd crbenicillin. Clin. Phrmcol. Ther. 24: Downloded from on November 18, 218 by guest

6 2332 ITOH ET AL. ANTIMICROB. AGENTS CHEMOTHER. 18. Rowlnd, M., nd T. N. Tozer Clernce nd renl excretion, p In Clinicl phrmcokinetics-concepts nd pplictions. Le & Febiger, Phildelphi. 19. Stndiford, H. C., M. C. Jordn, nd W. M. M. Kirby Clinicl phrmcology of crbenicillin compred with other penicillins. J. Infect. Dis. 122:S9-S Tn, J. S., nd S. J. Sistrom Levels of crbenicillin, ticrcillin, cephlothin, cefzolin, cefmndole, gentmicin, tobrmycin, nd mikcin in humn serum nd interstitil fluid. Antimicrob. Agents Chemother. 11: Tsuchiy, K., T. Ymzki, A. Kuchimur, nd T. Fugono Absorption, excretion nd tissue distribution of sulfocillin dministered prenterlly in mice, rts, rbbits nd dogs. J. Antibiot. 25: Ymd, H., T. Ichihshi, K. Hirno, nd H. Kinoshit Plsm protein binding nd urinry excretion of R- nd S-epimers of n rylmlonylmino I-oxcephem. I. In humns. J. Phrm. Sci. 7: Ymok, K., T. Tnigwr, T. Nkgw, nd T. Uno A phrmcokinetic nlysis progrm (MULTI) for microcomputer. J. Phrmcobio.-Dyn. 4: Downloded from on November 18, 218 by guest