PHARMACOKINETICS OF SULFAMETHOXAZOLE AND TRIMETHOPRIM IN MEXICANS: BIOEQUIVALENCE OF TWO ORAL FORMULATIONS (URO-TS AND BACTRIM

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1 IOPHRMCEUTICS & DRUG DISPOSITION, VOL. 11, (199) PHRMCOKINETICS OF SULFMETHOXZOLE ND TRIMETHOPRIM IN MEXICNS: IOEQUIVLENCE OF TWO ORL FORMULTIONS (URO-TS ND CTRIM F. J. FLORES-MUFUUET*$, G. CST~ED-HERN~NDEZ*, J.. MENENDEZ*, F. CHkVEZt, J. E. HERRER*t ND E. HONG* *Seidn de Terapdutia Experimental, Departumento de Farmaologia y Toxiologia, Centro de Investigaidn y de Estudios vanzados del I. P. N., partado Postal 2226, 14 Mdxio, D.F. Mexio, and TDepartamento de Investigaidn Clinia y iomddia, Hospital General 'Dr Miguel Silva', Moreliu, Mih.. Mexio STRCT Two oral pharmaeutial formulations (URO-TS D" and atrim F") ontaining 8 mg of sulfamethoxazole (SMZ) and 16 mg of trimethoprim (TMP) were given to 1 Mexian healthy volunteers, following a randomized ross-over design. lood and urine samples were obtained, onentrations of TMP, SMZ, and its metabolite N4-aetyl SMZ were measured by HPLC and pharmaokineti analyses were performed. The observed C, tmax, half-life, UC, and umulative urinary exretion values for the three ompounds studied were within the ranges that have been previously reported for European and North merian subjets. Therefore, it appears that pharmaokinetis of SMZ and TMP in Mexians are similar to those observed in Cauasian populations. When the two studied formulations were ompared, no statistially signifiant differenes were deteted in any pharmaokineti parameter. Therefore, it is onluded that both brands tested are bioequivalent. Moreover, these two formulations manufatured in Mexio yield SMZ and TMP plasma and urine levels similar to those obtained with equivalent formulations of European or North merian origin. KEY WORDS Sulfamethoxazole Trimethoprim Pharmaokinetis Mexian subjets ioequivalene INTRODUCTION Trimethoprim (TMP) and sulfamethoxazole (SMZ) are ompounds that interfere with the baterial synthesis of tetrahydrofolate at different levels. TMP inhibits the redution of dihydrofolate to tetrahydrofolate, while SMZ bloks the de novo synthesis of dihydrofolate.1,2 When ombined, both ompounds mutually potentiate their antibaterial ativity resulting in a more rapid bateriidal ation, a broader antimirobial spetrum, and a lower potentiality to $ ddressee for orrespondene /9/9765-O8$ by John Wiley & Sons, Ltd. Reeived 2 Otober 1989 Revised 26 January 199

2 766 F. J. FLORES-MURRIET ET L. indue baterial re~istane.~,~ The assoiation of TMP and SMZ has proven to be highly effetive for the treatment of a wide variety of infetious diseases and is one of the most useful tools for antimirobial therapeuti^.^ In vitro studies have demonstrated that the optimal bateriidal ativity is observed when SMZ onentrations are 1 to 4 times higher than those of TMP.6 To obtain these onditions in vivo, oral formulations of SMZ-TMP frequently ontain the ompounds in a 5: 1 ratio. Shwartz and Rieder, studying subjets from a Swiss population who reeived an oral formulation ontaining 8 mg of SMZ and 16 mg of TMP, showed that after the absorption phase the unhanged SMZ/TMP ratio ranges between 2 and 5 and is maintained during the 1 h following administration. The ratios of the ative frations of SMZ and TMP (non-metabolized, non-protein-bound) in plasma, whih are omparable with those obtained in extraellular fluid, were similar to those of the total plasma levels of the unhanged drugs.7 It then appears that an adequate treatment with SMZ-TMP depends on the bioavailabilities of both ompounds in the pharmaeutial formulation and on individual pharmaokinetis. SMZ is metabolized by the N4-aetyl transferase* and it is known that the ativity of this enzyme varies among different population^.^ Moreover, we have reently reported that the disposition kinetis of some drugs, like nifedipine, in subjets from a Mexian population are different from the one observed in Europeans.*oJ1 In this work we studied the pharmaokinetis of SMZ and TMP in Mexian subjets. dditionally, we ompared the bioavailabilities of the ative priniples after administration of two of the most used formulations manufatured in Mexio. Subjets METHODS Ten male adult healthy volunteers were inluded in the study. No abnormalities were deteted on routine linial and laboratory (biohemial and haematologial) tests. Demographi data appear in Table 1. None of the subjets was an alohol or drug abuser or was taking any onomitant mediation at the time of the study. ll subjets read the protool approved by the Hospital Ethial Committee and gave written informed onsent for partiipation before entering the study. Study plan This study was arried out aording to the reommendations of the Delaration of Helsinki. ll subjets reeived two pharmaeutial formulations ontaining 8 mg of SMZ and 16 mg of TMP in two separate trial sessions, aording to a randomized ross-over design. I-week wash-out period was allowed between sessions.

3 SULFMETHOXZOLE TRIMETHOPRIM IOVILILITY 767 t eah session, volunteers, who had abstained from alohol for at least 24 h, ame to the hospital at 8:OO pm. fter an overnight fast (1 h) they reeived a tablet of either URO-TS D@ (treatment ) or atrim F@ (treatment ) as stated in Table 1, with 2 ml of water. n indwelling annula with a heparin lok was inserted in a suitable forearm vein and blood samples were drawn at.5, 1, 2, 3, 4, 6, 8, 12, 16, 24, 36, and 48 h after mediation. Urine samples were obtained orresponding to the periods between -1, 1-2, 2-4, 4-6, 6-8, 8-12, 12-24, 24-36, and 3U8 h after SMZ-TMP administration; subjets were asked to empty their bladder at the end of eah olletion period. They remained fasting for 4 h after mediation. Table 1. Demographi data and drug administration shedule ge Weight Height Drug administration session Subjet (Years) (kg) (m) I I1 I Determination of SMZ and TMP SMZ, N4-aetyl SMZ, and TMP were onurrently determined in plasma and in urine samples by HPLC proedures developed in our laboratory, based on the data reported by Van der Steuijt and Sonneveld.12 Plasma samples (1 ml) were spiked with.1 mg of sulfapyridine (internal standard) and.2 ml of a 1 M sodium dihydrogenphosphate-disodium hydrogenphosphate buffer solution (ph 6.8) were added. Samples were extrated with 6 ml of ethyl aetate and the solvent was evaporated at 5" under a nitrogen stream. The dry residue was redissolved in.16 ml of mobile phase (vide infra) and -4 ml of onentrated perhlori aid were added. liquots (.1 ml) were injeted into a HPLC system onsisting of a 25 X 4 mm (2-18 olumn of 5vm partile size (ioanalytial Systems, West Lafayette, IN, US) kept at a onstant temperature of 45". The mobile phase onsisted of a mixture of diammonium hydrogenphosphate.15 M, ph 4.4, with aetonitrile

4 768 F. J. FLORES-MURRIET ET L. (88.5:11*5). Flow rate was kept onstant at 2mlmin-. The absorbane of the olumn effluent was monitorized using a model 49 programmable multiwavelength detetor (Waters sso., Milford, M, US). Letures were initially arried out at 254 nm (from to 12 rnin after sample injetion) for determination of sulfapyridine, whih eluted at 6.3 min. Then wavelength was hanged to 23 nm from 12 to 17 rnin for TMP, whih eluted at 13.7 min. Finally, wavelength was returned to 254 for SMZ and N4-aetyl SMZ, that exhibited retention times of 19.2 and 3.2 min, respetively. Urine samples (.2 ml) were spiked with.2 mg of sulfapyridine (internal standard) and.1 ml of the 1 M sodium phosphate buffer (ph 6.8) were added. Samples were extrated with 1 ml of ethyl aetate and the solvent was evaporated. The dry residue was redissolved in.1 ml of mobile phase (vide infra) and.25 ml aliquots were injeted to a Varian 5 liquid hromatograph equipped with a programmable multiwavelength detetor and a 4 x 3mm MCH-1 olumn (Varian Instruments, Palo lto, C, US). The mobile phase was a mixture of ammonium dihydrogenphosphate.2 M, ph 5, with aetonitrile and methanol (71524). Flow rate was kept onstant at 2 ml min-i. bsorbane was monitorized at 254 nm for 1-5 rnin and then hanged to 23 nm. Retention times were 3.7 rnin for sulfapyridine, 6.2 rnin for SMZ, 8.3 rnin for N4-aetyl SMZ, and 12.7 rnin for TMP. Drugs and reagents URO-TS D@ tablets and pure SMZ and TMP standards were provided by Laboratorios ristol de MCxio S.. (Mexio City). Commerially available atrim F@ tablets were manufatured by Produtos Rohe S.. (Mexio City). Pure N4-aetyl SMZ standard was a gift from Hoffmann-La Rohe (asle, Switzerland). Methanol and aetonitrile hromatographi grade were purhased from E. Merk (Darmstadt, FRG). Deionized water was prepared using a Milli-Q reagent water system (Continental Water Systems, El Paso, TX, US) and was used for all solutions. ll other reagents were of analytial grade. Pharmaokineti analysis and statistis Individual plasma level versus time urves were onstruted using semilog oordinates. Peak plasma onentration (C,,,) and time to reah the peak onentration (&,) were diretly determined from these urves. Half-life (t%) was alulated by least squares linear regression of the terminal onentration deay phase. rea under the urve (UC) was determined by the trapezoidal rule. The area from the last point to infinity was determined by dividing the last detetable plasma onentration by the terminal slope. Data are presented as mean fsem. Pharmaokineti parameters observed with the two assayed formulations were ompared by the Student s t-test for paired data.

5 SULFMETHOXZOLE TRIMETHOPFUM IOVILILITY L C Q) Figure 1. Mean (ksem) plasma levels of sulfamethoxazole (, O), N4-aetyl sulfamethoxazole (, ), and trimethoprim (, W) observed in 1 Mexian healthy volunteers after ingestion of two oral formulations: treatment (white symbols) and treatment (dark symbols) RESULTS Figure 1 depits the mean (rtsem) plasma onentration of SMZ, TMP, and N4-aetyl SMZ observed in the 1 subjets studied after the administration of two oral pharmaeutial formulations: treatments and. Pharmaokineti parameters alulated from individual plasma level-time urves are shown in Table 2. No statistially signifiant differene was observed in plasma levels, and hene in pharmaokineti parameters, when treatments and were ompared. Table 2. Pharmaokineti parameters of sulfamethoxazole (SMZ), trimethoprim (TMP), and N4-aetyl sulfamethoxazole (N4- SMZ) observed after administration of two oral formulations ontaining 8 mg of SMZ and 16 mg of TMP in 1 Mexian healthy volunteers (mean f SEM) ISMZ * f f f 67.6 ISMZ f f f f.24.9 RMP 1.76 f f f f 4.23 /TMP 1.75 f f f f 5.8 /N- SMZ 7.49 f f f f 17.9 /N- SMZ 9.12 f f f

6 77 F. J. FLOES-MURRIET ETL. I- W a X W 1 2 v U Q) CI W 2 t- a -J I - 6 Y N I a Q) z 41 2 I Time (hours) r Figure 2. Cumulative urinary exretion of sulfamethoxazole (, O), trimethoprim (, m), and N4-aetyl sulfamethoxazole (, ) in 1 Mexian healthy volunteers after ingestion of two oral formulations: treatment (white symbols) and treatment (dark symbols) The ratios of unhanged SMZ/TMP plasma onentrations in all but one subjets ranged between 7.4 and 75.5 during the 12 h following administration; this was observed with both, treatment and treatment. One volunteer, subjet 4, exhibited low (less than.3pgml-') TMP plasma levels, whereas SMZ onentrations were similar to those observed with the other subjets. Hene, SMZ/TMP ratios obtained with either treatment or in this partiular individual were onsiderably higher, being above 3 during the 12 h following administration.

7 SULFMETHOXZOLE TRIMETHOPRIM IOVILILITY 77 1 Cumulative urinary exretion of SMZ, N4-aetyl SMZ, and TMP is shown in Figure 2. Exretion of unhanged SMZ in 48 h amounted to 1-5 f 1.6 per ent and to 9.7 f.8 per ent of the dose for treatments and, respetively; whereas exretion of N4-aetyl SMZ was equivalent to 65.5 f 5. per ent and to 71.7 f 4.5 per ent of the SMZ dose, in mole-to-mole basis. Exretion of unhanged TMP in 48 h amounted to 67.8 f 3.3 per ent of the dose with treatment and to 71.3 f 4.2 per ent with treatment. s observed with the plasma determinations, there were no statistially signifiant differenes between treatments in the urinary exretion of these ompounds. DISCUSSION In this work we report the pharmaokinetis of SMZ, N4-aetyl SMZ and TMP in Mexian healthy volunteers after administration of two oral pharmaeutial formulations ontaining 8 mg of SMZ and 16 mg of TMP. Plasma levels and urinary exretion of SMZ and of TMP, hene their pharmaokineti parameters, were very similar to those previously reported in healthy volunteers from Duth,13 Frenh,14 and North merian15 populations after oral administration of equivalent doses. However, Shwartz and Rieder7 observed lower C,, values, being about 2 pgml-' for SMZ and of less than 1 pgml-l for TMP, in Swiss subjets; although t, tm, and urinary exretion were within the same range as in our study. It is noteworthy that the Swiss investigators used fluorimetri proedures, instead of HPLC, for the determination of the ompounds. Our data onerning N4-aetyl SMZ were also similar to those reported for E~ropeans.'~J~ Therefore, results show that pharmaokinetis of SMZ and TMP in Mexians do not differ from those observed in subjets from Cauasian populations. In nine of the studied volunteers, the ratio of unhanged SMZ/TMP plasma onentrations ranged between 7 and 76. Sine it has been shown that the ratios of total unhanged plasma levels are similar to those of the ative frations of these ompound^,^ it an be expeted that in most individuals the administration of 8 mg of SMZ with 16 mg of TMP would result in an adequate bateriidal ativity. However, in one subjet the ratio of SMZiTMP plasma levels was kept above 3 during the whole observation period, due to poor TMP absorption. This type of interindividual differene in drug disposition ould explain some ases in whih treatment with SMZ-TMP is not suessful. There were no statistially signifiant differenes between the two oral pharmaeutial formulations examined in UC values or in any of the other determined pharmaokineti parameters. Hene, it is onluded that both URO-TS D@ and atrim F@ are bioequivalent. Moreover, results show that these formulations manufatured in Mexio yield plasma and urine levels similar to those obtained with equivalent formulations of European or North merian origin.

8 772 F. J. FLORES-MURRIEP ET L. CKNOWLEDGEMENTS The authors wish to thank Dr C. Hoyo-Vadillo and Dr J. Carranza for their partiipation in the study, Ms H. Garduiio for tehnial assistane, and Mr. Frano for graphi work. This work was supported by COSNET-SEP, grant PEP 4.88, and by Laboratorios ristol de MCxio S.. J. C. MenCndez is a CONCYT fellow. REFERENCES 1. G. H. Hithings, nn. N. Y. ad. Si., 186: 444 (1971). 2. G. H. Hithings, J. Znfe. Dis., 128: S433 (1973). 3. E. ohni, Chemotherapy, 14 (suppl.): 1 (1969). 4. S. R. ushby and G. H. Hithings, rit. J. Pharmaol., 33: 72 (1968). 5. G. L. Mandell and M.. Sande, in The Pharmaologial asis of Therapeutis, 7th edn,. Goodman Gilman, L. S. Goodman, T. W. Rall and F. Murad (Eds), MaMillan, New York, 1985, p W. rudtt. J. M. T. Hamilton-Miller and J. Kosmidis. J. Znfe. Dis.., 128,. S778 (1973).., 7. D. E. Shwa'rtz and J. Rieder, Chemotherapy, 15,337 (197)." 8. J. Rieder, J. Znfe. Dis., 128, S:567 (1973). 9.. K. M. Karim, M. S. Elfellah and D.. P. Evans, J. Med. Genet., 18, 325 (1981). 1. C. Hoyo-Vadillo, G. Castaiieda-Hernandez, J. E. Herrera, J. Vidal-Garate,. Moreno-Ramos, F. Chavez, I. Tena and E. Hong, J. Clin. Pharmaol., 29,251 (1989). 11. C. Hoyo-Vadillo, G. Castaiieda-Hernandez, J. E. Herrera, J. Vidal-Garate,. Moreno-Ramos, F. Chivez and E. Hong, J. Clin. Pharmaol., 29,816 (1989). 12. K. Van Der Steuijt and P. Sonneveld, J. Chromatogr., 422,328 (1987). 13. T.. Vree, Y.. Hekster,. M. aars, J. E. Damsma and E. Van Der Kleijn, J. Chromatogr., 146,13 (1978) Spreux-Varoquaux, J. P. Chapalain, P. Cordonnier, C. dvenier, M. Pays and L. Lamine, J. Chomatogr., 274, 187 (1983). 15. M. C. ah,. Gold and M. Finland, J. Znfe. Dis., 128, S584 (1973).