Pharmacokinetics of sulfamethoxazole plus trimethoprim in man and their distribution in the rat

Sulfamethoxazole-induced crystal nephropathy: characterization and prognosis in a case series

Cotrimoxazole (Trimethoprim/Sulfamethoxazole-SMX) is frequently used in critically ill and immunocompromised patients. SMX is converted to N-acetyl-sulfamethoxazole (NASM) and excreted by the kidneys. NASM may form crystals in urine, especially in acid urine, that may induce a crystalline nephropathy. However, the imputability of crystals in acute kidney injury (AKI) has not been proven. We aimed to assess whether NASM crystals may promote AKI and to investigate risk factors associated with NASM crystalline nephropathy. Patients from Ile-de-France, France who developed AKI under SMX treatment introduced during hospitalization and had a crystalluria positive for NASM crystals were selected. Patients with excessive preanalytical delay for crystalluria or missing data regarding SMX treatment were excluded. We used the Naranjo score to assess the causal relationship between SMX and the development of AKI in patients with positive NASM crystalluria. Fourteen patients were included. SMX was the probable cause of AKI for 11 patients and a possible cause for 3 patients according to Naranjo score. Patients were exposed to high doses of SMX (but within recommended ranges), and most of them had a preexisting chronic kidney disease and were hypoalbuminemic. Urine pH was mildly acid (median 5.9). AKI occured more rapidly than expected after introduction of SMX (median 4 days) and recovered rapidly after drug discontinuation in most, but not all, cases. SMX is a probable cause of crystalline nephropathy. Monitoring of crystalluria in patients exposed to SMX may be of interest to prevent the development of crystalline nephropathy. Approval number of the study: BPD-2018-DIAG-008.

Human Apparent Volume of Distribution Predicts Bioaccumulation of Ionizable Organic Chemicals in Zebrafish Embryos

Chemicals with elevated bioaccumulation profiles present potential hazards to public health and the environment. Ionizable organic compounds (IOCs) increasingly represent a large proportion of commercial chemicals; however, historical approaches for bioaccumulation determinations are mainly developed for neutral chemicals, which were not appropriate for IOCs. Herein, we employed the zebrafish embryo, a common vertebrate model in environmental and biomedical studies, to elucidate toxicokinetics and bioconcentration of eight IOCs with diverse physicochemical properties and pharmacokinetic parameters. At an environmentally relevant pH (7.5), most IOCs exhibited rapid uptake and depuration in zebrafish, suggesting the ionized forms of IOCs are readily bioavailable. Bioconcentration factors (BCF) of these IOCs ranged from 0.0530 to 250 L·kg^-1 wet weight. The human pharmacokinetic proportionality factor, apparent volume of distribution (V_D), better predicted the BCF of selected IOCs than more commonly used hydrophobicity-based parameters (e.g., pH-dependent octanol-water distribution ratio, D_ow). Predictive bioaccumulation models for IOCs were constructed and validated using V_D alone or with D_ow. Significant relationships between fish BCF and human V_D, which is readily available for pharmaceuticals, highlighted the utility of biologically based "read-across" approaches for predicting bioaccumulative potential of IOCs. Our novel findings thus provided an understanding of the partitioning behavior and improved predictive bioconcentration modeling for IOCs.

Uropathogenic Escherichia coli Shows Antibiotic Tolerance and Growth Heterogeneity in an In Vitro Model of Intracellular Infection

Uropathogenic Escherichia coli (UPEC), the major causative agent of urinary tract infections, can invade different types of host cells. To compare the pharmacodynamic properties of antibiotics against intra- and extracellular UPEC, an in vitro model of intracellular infection was established in J774 mouse macrophages infected by the UPEC strain CFT073. We tested antibiotics commonly prescribed against urinary tract infections (gentamicin, ampicillin, nitrofurantoin, trimethoprim, sulfamethoxazole, and ciprofloxacin) and the investigational fluoroquinolone finafloxacin. The metabolic activity of individual bacteria was assessed by expressing the fluorescent reporter protein TIMERbac within CFT073. Concentration-response experiments revealed that all tested antibiotics were much less effective against intracellular bacteria than extracellular ones. Most antibiotics, except fluoroquinolones, were unable to reach a bactericidal effect intracellularly at clinically achievable concentrations. Ciprofloxacin and finafloxacin killed 99.9% of extracellular bacteria at concentrations around the MIC, while for intracellular bacteria, concentrations more than 100× over the MIC were required to achieve a bactericidal effect. Time-kill curves showed that finafloxacin was more rapidly bactericidal in acidic medium than at neutral pH, while the reverse observation was made for ciprofloxacin. Intracellularly, kill curves showed biphasic kinetics for both fluoroquinolones, suggesting the presence of drug-tolerant subpopulations. Flow cytometry analysis of TIMERbac fluorescence revealed a marked heterogeneity in intracellular growth of individual bacteria, suggesting that the presence of subpopulations reaching a state of metabolic dormancy was the main reason for increased antibiotic tolerance of intracellular UPEC.

Adsorption and Release of Sulfamethizole from Mesoporous Silica Nanoparticles Functionalised with Triethylenetetramine

Mesoporous silica nanoparticles (MSN) were synthesised and functionalised with triethylenetetramine (MSN-TETA). The samples were fully characterised (transmission electron microscopy, small angle X-ray scattering, Fourier transform infrared spectroscopy, thermogravimetric analysis, zeta potential and nitrogen adsorption/desorption isotherms) and used as carriers for the adsorption of the antimicrobial drug sulphamethizole (SMZ). SMZ loading, quantified by UV-Vis spectroscopy, was higher on MSN-TETA (345.8 mg g-1) compared with bare MSN (215.4 mg g-1) even in the presence of a lower surface area (671 vs. 942 m2 g-1). The kinetics of SMZ adsorption on MSN and MSN-TETA followed a pseudo-second-order model. The adsorption isotherm is described better by a Langmuir model rather than a Temkin or Freundlich model. Release kinetics showed a burst release of SMZ from bare MSN samples (k1 = 136 h-1) in contrast to a slower release found with MSN-TETA (k1 = 3.04 h-1), suggesting attractive intermolecular interactions slow down SMZ release from MSN-TETA. In summary, the MSN surface area did not influence SMZ adsorption and release. On the contrary, the design of an effective drug delivery system must consider the intermolecular interactions between the adsorbent and the adsorbate.

Sulfamethoxazole/Trimethoprim ratio as a new marker in raw wastewaters: A critical review

Global Trimethoprim (TMP) and Sulfamethoxazole (SMX) occurrences in raw wastewaters were systematically collected from the literature (n = 140 articles) in order to assess the relevance of using the SMX/TMP ratio as a marker of the main origin of wastewaters. These two antibiotics were selected due to their frequent use in association (i.e. co-trimoxazole) in a 5:1 ratio (SMX:TMP) for medication purposes, generating a unique opportunity to globally evaluate the validity of this ratio based on concentration values. Several parameters (e.g. sorption, biodegradation) may affect the theoretical SMX/TMP ratio. However, the collected data highlighted the good agreement between the theoretical ratio and the experimental one, especially in wastewater treatment plant influents and hospital effluents. Only livestock effluents displayed a very high SMX/TMP ratio, indicative of the very significant use of sulfonamide alone in this industry. Conversely, several countries displayed low SMX/TMP ratio values, highlighting local features in the human pharmacopoeia. This review provides new insights in order to develop an easy to handle and sound marker of wastewater origins (i.e. human/livestock), beyond atypical local customs.

The Antimicrobial Implications of the Pharmacokinetics of Cotrimoxazole in CAPO Patients

Cotrimoxazole (TMP/SMX) has been used to treat continuous ambulatory peritoneal dialysis (CAPD) associated peritonitis. It is considered bactericidal for some species. The most common single organism responsible for this type of peritonitis is Staph. epidermidis (SE). When the drug is given orally, the typical ratio of TMP to SMX achieved in the peritoneal fluid is 1:5, which is different from the optimal combination for antimicrobial synergy of 1:19. This study investigated the antimicrobial activity of TMP alone and TMP/SMX by agar dilution at ratios of 1:19, 1:10 and 1:5 against 99 strains of Staphylococcus epidermis (SE). The majority of strains were susceptible to TMP and to all ratios of TMP/SMX by the routine agar dilution methods. We studied the bactericidal activity of TMP/SMX against one strain each of SE and of Staph. aureus (SA) in pooled uninfected spent dialysate by killing curve experiments. TMP at concentrations of 0.5 to 2.0 μg/ml was bacteriostatic. TMP/SMX became slowly bactericidal when 5 % lysed horse blood, a source of thymidine phosphorylase, was added to the dialysate.

It is concluded that susceptibility tests of inhibition do not predict bactericidal activity of TMP/SMX in recovered dialysate. Inhibition of TMP/ SMX is most likely due to thymidine present in dialysate. TMP alone was as effective against SE as TMP/ SMX. Until it is shown that bactericidal activity is not required for cure of CAPD-related peritonitis, cotrimoxazole should not be used routinely for its treatment.

Factors Influencing Renal Distribution of Antibiotics a Key to Therapy of Pyelonephritis

Pyelonephritis is often considered a benign disease, yet in some studies as high as 35 percent of the cases progressed to severe renal disease. Treatment failures occur because of relapse of infection, emergence of secondary infecting organisms, re-infection and the development of antibiotic resistance. In addition, inadequate renal tissue concentrations of antibiotics account for a majority of treatment failures. The factors which influence diffusion of antibiotics into renal tissues are discussed. The importance of renal medullary tissue levels of antibiotics is emphasized, as well as the influence that protein binding, non-ionic diffusion and the state of hydration have on these levels. Distribution kinetics of sulfisoxazole, ampicillin, tetracyclines, cephalosporins, nalidixic acid, nitrofurantoin, gentamicin, carbenicillin indanyl sodium, sulfamethoxazole and trimethoprim as they relate to the treatment of pyelonephritis are also presented.

Pharmacokinetics and pharmacodynamics of sulfamethoxazole and trimethoprim in swimming crabs (Portunus trituberculatus) and in vitro antibacterial activity against Vibrio: PK/PD of SMZ-TMP in crabs and antibacterial activity against Vibrio

Serious bacterial pathogens have recently become a major cause of massive mortality in swimming crabs (Portunus trituberculatus). In this study, the antibacterial activity against Vibrio and the pharmacokinetics (PK) of sulfamethoxazole (SMZ)-trimethoprim (TMP) in crabs were estimated to explore the pharmacokinetics/pharmacodynamics (PK/PD) properties of the SMZ-TMP combination. The in vitro bacteriostatic activity and the anti-Vibrio infection activity of the SMZ-TMP combination at various ratios in crabs were studied. A degree of synergism was observed in the SMZ-TMP combination at ratios ranging from 50:1 to 1:5. The results showed that the MIC50 and MIC90 values for different SMZ-TMP combinations were in the ranges of 0.62-5 and 0.62-10μg/mL, respectively. The distribution of the MIC values of the SMZ-TMP combination at ratios of 1:1 and 5:1 were 0.31-5 and 0.31-10μg/mL, respectively. Crabs were then fed the SMZ-TMP combination (at ratios of 5:1 and 1:1) six successive times and then challenged with Vibrio parahaemolyticus at 1×10(5), 1×10(6), and 5×10(6) colony forming units (cfu) per crab. The results showed that the number of surviving crabs administered SMZ-TMP at a ratio of 1:1 was greater than that of the crabs given SMZ-TMP at a ratio of 5:1. In addition, the tissue distribution and absorption of SMZ-TMP (ratios of 5:1 and 1:1) in crabs were studied through high-performance liquid chromatography (HPLC). In the crabs fed SMZ-TMP at a ratio of 5:1, the CmaxSMZ/TMP values in the hemolymph, hepatopancreas, muscle and gill were 104:1. 0.57:1, 19:1 and 6:1, respectively. In contrast, the corresponding CmaxSMZ/TMP values in these tissues in the crabs fed SMZ-TMP at a ratio of 1:1 were 34:1, 0.14:1, 4:1 and 3:1, respectively. The results showed that TMP was better absorbed and eliminated in the crabs fed SMZ-TMP at a ratio of 1:1 than in the crabs fed this combination at a ratio of 5:1. In addition, TMP was absorbed and eliminated more rapidly in the hepatopancreas than in the gill, muscle and hemolymph. The distribution volume of TMP in the hepatopancreas exceeded that of SMZ observed in the experiments. The results indicated that the PK/PD effect of the SMZ-TMP at a ratio of 1:1 was greater than that of the combination at a ratio of 5:1. Our study suggests that a SMZ-TMP ratio of 1:1 may be used to control bacterial disease in aquatic animals.

Assessing the concentrations and risks of toxicity from the antibiotics ciprofloxacin, sulfamethoxazole, trimethoprim and erythromycin in European rivers

This study evaluated the potential concentrations of four antibiotics: ciprofloxacin (CIP), sulfamethoxazole (SUF), trimethoprim (TRI) and erythromycin (ERY) throughout the rivers of Europe. This involved reviewing national consumption rates together with assessing excretion and sewage treatment removal rates. From this information, it was possible to construct best, expected and worst case scenarios for the discharge of these antibiotics into rivers. Consumption data showed surprising variations, up to 200-fold in the popularity of different antibiotics across different European nations. Using the water resources model GWAVA which has a spatial resolution of approximately 6×9 km, river water concentrations throughout Europe were predicted based on 31-year climate data. The modelled antibiotic concentrations were within the range of measurements reported previously in European effluents and rivers. With the expected scenario, the predicted annual-average antibiotic concentrations ranged between 0 and 10 ng/L for 90% by length of surface waters. In the worst case scenario concentrations could reach between 0.1 and 1 μg/L at the most exposed locations. As both predicted and observed sewage effluent concentrations were below reported effect levels for the most sensitive aquatic wildlife, no direct toxicity in rivers is expected. Predicted river concentrations for CIP and ERY were closest to effect levels in wildlife, followed by SUF which was 2-3 orders of magnitude lower. TRI appeared to be of the least concern with around 6 orders of magnitude difference between predicted and effect levels. However, mixture toxicity may elevate this risk and antibiotic levels of 0.1-1 μg/L in hotspots may contribute to local environmental antibiotic resistance in microorganisms.

Dosing regimens of cotrimoxazole (trimethoprim-sulfamethoxazole) for melioidosis

Melioidosis is an infectious disease with a propensity for relapse, despite prolonged antibiotic eradication therapy for 12 to 20 weeks. A pharmacokinetic (PK) simulation study was performed to determine the optimal dosing of cotrimoxazole (trimethoprim-sulfamethoxazole [TMP-SMX]) used in current eradication regimens in Thailand and Australia. Data for bioavailability, protein binding, and coefficients of absorption and elimination were taken from published literature. Apparent volumes of distribution were correlated with body mass and were estimated separately for Thai and Australian populations. In vitro experiments demonstrated concentration-dependent killing. In Australia, the currently used eradication regimen (320 [TMP]/1,600 [SMX] mg every 12 h [q12h]) was predicted to achieve the PK-pharmacodynamic (PD) target (an area under the concentration-time curve from 0 to 24 h/MIC ratio of >25 for both TMP and SMX) for strains with the MIC90 of Australian strains (< or = 1/19 mg/liter). In Thailand, the former regimen of 160/800 mg q12h would not be expected to attain the target for strains with an MIC of > or = 1/19 mg/liter, but the recently implemented weight-based regimen (<40 kg [body weight], 160/800 mg q12h; 40 to 60 kg, 240/1,200 mg q12h; >60 kg, 320/1,600 mg q12h) would be expected to achieve adequate concentrations for strains with an MIC of < or = 1/19 mg/liter. The results were sensitive to the variance of the PK parameters. Prospective PK-PD studies of Asian populations are needed to optimize TMP-SMX dosing in melioidosis.

Occurrence and sorption behavior of sulfonamides, macrolides, and trimethoprim in activated sludge treatment

The occurrence of sulfonamide and macrolide antimicrobials, as well as trimethoprim, was investigated in conventional activated sludge treatment. Average daily loads in untreated wastewater correlated well with those estimated from annual consumption data and pharmacokinetic behavior. Considerable variations were found during a day, and seasonal differences seem to occur for the macrolides, probably caused by a higher consumption of these substances in winter. The most predominant macrolide and sulfonamide antimicrobials were clarithromycin and sulfamethoxazole, respectively. In the case of sulfamethoxazole, the main human metabolite, N4-acetylsulfamethoxazole, was included as an analyte, accounting for up to 86% of the total load in untreated wastewater. The results obtained illustrate the importance of considering retransformable substances, for example human metabolites, when investigating the behavior and fate of pharmaceuticals. Average concentrations of sulfapyridine, sulfamethoxazole, trimethoprim, azithromycin, and clarithromycin in activated sludge ranged between 28 and 68 microg/kg of dry weight. Overall the sorption to activated sludge was shown to be low for the investigated antimicrobials, with estimated sorption constants for activated sludge below 500 L/kg. Elimination in activated sludge treatment was found to be incomplete for all investigated compounds. In final effluents, the median concentrations for sulfamethoxazole and clarithromycin were 290 and 240 ng/L, respectively.

Effect of severe protein-calorie malnutrition on the penetration kinetics of trimethoprim and sulfamethoxazole to the deep tissues of Wistar rats

This study shows the effect that severe malnourishment has on the kinetics of antibiotic penetration in tissues. A total of 104 male Wistar rats, 21 days old, were randomly divided into eight groups. Five groups of experimental rats were severely malnourished (SM) and three further groups were considered well-nourished control groups (WN). A single dose of trimethoprim-sulfamethoxazole (TMP-SMX) was administered intraperitoneally. Blood samples were taken by heart puncture and five organs were extracted 0-24 h after the administration of the drug. HPLC was used to assess the amount of trimethoprim and sulfamethoxazole in fluids. The elimination half-life for trimethoprim from plasma was longer in SM rats with a median of 3.15 h; in WN rats, it was 0.390 h. Clearance was slower in SM rats: 646.72 mL microg(-1) h(-1) vs 3036.38 mL microg(-1) h(-1) in WN rats (P < 0.05). Tissue penetration was much higher for trimethoprim, with penetration indexes of 0.80-5.66 in WN rats, compared with 0.35-2.14 in SM rats. In the case of sulfamethoxazole, penetration indexes were 0.029-1.13 for WN and 0.075-0.657 for SM rats. Similarly, the penetration ratio to muscle and heart tissue was lower in SM rats. However, penetration to kidney, lung, liver and spleen was greater in SM rats. It is evident that severe SM decreases the capacity of trimethoprim more importantly than sulfamethoxazole biotransformation.

Efficacy of trimethoprim in murine experimental infection with a thymidine kinase-deficient mutant of Escherichia coli

The antimicrobial activity of trimethoprim is antagonized by thymidine in in vitro susceptibility tests. The purpose of this investigation was to determine whether this antagonism also occurred during experimental infection in mice, which have high serum thymidine concentrations. We derived a mutant strain of Escherichia coli, TT-48, incapable of utilizing exogenous thymidine from parent strain E. coli KC-14 and then investigated the in vitro and in vivo antimicrobial activities of trimethoprim, sulfamethoxazole, cefdinir, and ofloxacin against these strains. E. coli TT-48 lacked the activity of thymidine kinase, which catalyzes the conversion of thymidine to thymidylate, but its growth curve remained close to that of the parent strain. The MICs of all of the antimicrobial agents tested, except cefdinir, for the mutant strain were slightly inferior to those for the parent strain. The bactericidal effect of trimethoprim against the parent strain was antagonized by thymidine at concentrations of more than 1 microg/ml, while that against the mutant strain was not affected by thymidine even at the highest concentration (10 microg/ml). The therapeutic efficacy of trimethoprim in experimental murine infections was significantly higher when the mutant rather than the parent strain was used, whereas the therapeutic efficacy of cefdinir or ofloxacin, whose antimicrobial action is independent of folic acid synthesis, was the same with both strains. Unexpectedly, sulfamethoxazole also had similar efficacy against both strains. Thus, high thymidine concentrations antagonized the antimicrobial activity of trimethoprim in vitro and in vivo.

6,7-disubstituted 2,4-diaminopteridines: novel inhibitors of Pneumocystis carinii and Toxoplasma gondii dihydrofolate reductase

Four novel, disubstituted diaminopteridines have been identified which antagonize the uptake of a folate precursor (para-aminobenzoic acid) by rat-derived Pneumocystis carinii maintained in short-term axenic culture at concentrations ranging from 4.5 to 26 microM. The compounds were at least 10 to 100 times more active than trimethoprim in this assay. None of these entities exhibited toxicity to mammalian cell lines at < 100 microM. The same structures also caused significant inhibition of Toxoplasma gondii tachyzoite replication within Madin-Darby bovine kidney cells at concentrations ranging from 0.1 to 10 microM. Three of the structures (GR92754, AH10639, and AH2504) were at least an order of magnitude more potent than the standard anti-T. gondii agent, pyrimethamine. All three entities were also significantly more potent and selective than pyrimethamine as inhibitors of T. gondii dihydrofolate reductase (DHFR), with 50% inhibitory concentrations within the range of 0.018 to 0.033 microM. One of these compounds, 6,7-dibutyl-2,4-diaminopteridine (GR92754), was also a potent and selective inhibitor of P. carinii DHFR (50% inhibitory concentration, 0.082 microM). GR92754 is the first DHFR inhibitor described that exhibits greater potency, selectivity, and intracellular activity against both organisms than any of the DHFR agents used clinically, namely, trimethoprim, pyrimethamine, and trimetrexate. This information could provide the starting point for examination of the pharmacokinetic and therapeutic potential of GR92754 and related chemical entities with animal models.

Studies on the mechanism of trimethoprim-induced hyperkalemia

We examined the effects of trimethoprim (TMP) on metabolic parameters and renal ATPases in rats after a 90 minute infusion (9.6 mg/hr/kg body wt, i.v.) and after 14 days (20 mg/kg body wt/day, i.p.). After one dose of TMP, plasma electrolytes, arterial pH and aldosterone levels were normal, but a natriuresis, bicarbonaturia, and decreased urinary potassium excretion occurred. Na-K-ATPase activity in microdissected segments from these animals was decreased by 36 +/- 0.9% in proximal convoluted tubule (PCT) (P < 0.005); decreases of 50 +/- 2.1% and 40 +/- 1.1% were seen in cortical and medullary collecting tubules (CCT and MCT), respectively (P < 0.005). Na-K-ATPase activity was unaffected in medullary thick ascending limb (MTAL). H-ATPase (in PCT and collecting duct) and H-K-ATPase (in CCT and MCT)-activities were not changed. Following chronic TMP administration, plasma potassium increased as compared to control (5.16 +/- 0.05 mEq/liter vs. 3.97 +/- 0.05 mEq/liter, P < 0.05), however, acid-base status and plasma aldosterone levels were normal. Na-K-ATPase activity was decreased by 45 +/- 2.6% in PCT (P < 0.005), 73 +/- 2.0% in CCT (P < 0.001), and 53 +/- 2.5% in MCT (P < 0.005). Na-K-ATPase, activity in MTAL and H-K-ATPase activity in CCT and MCT were unchanged. H-ATPase activity in PCT and MTAL was normal, but in the collecting tubule (CCT and MCT) it was decreased by approximately 25% (P < 0.05). TMP inhibited Na-K-ATPase activity in a dose-dependent fashion in PCT, CCT, and MCT when tubules from normal animals were incubated in vitro with the drug; TMP in vitro did not affect H-ATPase or H-K-ATPase activity. These results suggest that TMP-induced hyperkalemia may result from decreased urinary potassium excretion caused by inhibition of distal Na-K-ATPase, in the face of intact H-K-ATPase activity.

Assessment of arylamine N-acetyltransferase (NAT1) activity in mononuclear leukocytes of cystic fibrosis patients

The clearance of sulphamethoxazole (SMX), a compound metabolised primarily by the N-acetyltransferase NAT1, is increased in cystic fibrosis (CF) patients. We assessed the activity and kinetic properties of NAT1 in lysates of peripheral blood mononuclear leukocytes (MNL) from CF (n = 17) and control (n = 22) subjects using SMX and p-aminobenzoic acid (PABA) as test substrates. The Km and Vmax values of both substrates in MNL from CF patients and control subjects were not significantly different. The acetylation of PABA (100 microM) by intact MNL from CF patients (n = 4) was not different from the observed in intact MNL from controls (n = 9) (25 +/- 3 pmol h-1 per 10(6) MNL vs 27 +/- 4 pmol h-1 per 10(6) MNL). These results suggest that there are not systemic changes in this enzyme in CF. The increased metabolic clearance of SMX may therefore be related to factors other than alterations in the level of activity of the N-acetyltransferase NAT1.

Limitations of and indications for the use of co-trimoxazole

Co-trimoxazole is still widely used for indications where trimethoprim alone is equally effective. Microbiological and pharmacokinetic considerations reveal that trimethoprim alone provides adequate anti-microbial activity for treatment of conditions for which co-trimoxazole is often given. Synergy may be shown in vitro, but in clinical practice is an unusual occurrence. There is no evidence from clinical studies that the sulphonamide moiety fo co-trimoxazole prevents the development of resistance to trimethoprim. The adverse event profile of co-trimoxazole is a summation of that of sulphonamide and of trimethoprim. Thus, using trimethoprim alone should reduce both the incidence and potential severity of adverse events seen when co-trimoxazole is used. Clinical trials have shown trimethoprim to be as effective as co-trimoxazole in many of the common bacterial infections of the urinary and respiratory tracts. However, there are a few specific varieties of infection for which co-trimoxazole can be shown to be superior to trimethoprim: these include toxoplasmosis, brucellosis, nocardiosis, chancroid and pneumonia caused by Pneumocystis carinii. For many common infections, scientific, rational, economic and clinical reasons dictate that trimethoprim is preferable to co-trimoxazole.

Pharmacokinetics of sulfamethoxazole and trimethoprim in Mexicans: bioequivalence of two oral formulations (URO-TS D and Bactrim F)

Two oral pharmaceutical formulations (URO-TS D and Bactrim F) containing 800 mg of sulfamethoxazole (SMZ) and 160 mg of trimethoprim (TMP) were given to 10 Mexican healthy volunteers, following a randomized cross-over design. Blood and urine samples were obtained, concentrations of TMP, SMZ, and its metabolite N4-acetyl SMZ were measured by HPLC and pharmacokinetic analyses were performed. The observed Cmax, tmax, half-life, AUC, and cumulative urinary excretion values for the three compounds studied were within the ranges that have been previously reported for European and North American subjects. Therefore, it appears that pharmacokinetics of SMZ and TMP in Mexicans are similar to those observed in Caucasian populations. When the two studied formulations were compared, no statistically significant differences were detected in any pharmacokinetic parameter. Therefore, it is concluded that both brands tested are bioequivalent. Moreover, these two formulations manufactured in Mexico yield SMZ and TMP plasma and urine levels similar to those obtained with equivalent formulations of European or North American origin.

Pharmacokinetics of trimethoprim in the rat

The pharmacokinetics of trimethoprim was studied in male Sprague-Dawley rats following the intravenous administration of trimethoprim at a dose of 25 mg/kg. Plasma and tissue levels of trimethoprim, as a function of time, were determined by reversed-phase high-performance liquid chromatography. The disposition of trimethoprim was described by both a two-compartment open model with elimination from a central compartment and a noncompartmental method. For the compartmental analysis, the terminal elimination rate constant, elimination half-life, apparent volume of distribution in the central compartment, apparent volume of distribution in the central compartment based on the area under the plasma concentration-time curve, and volume of distribution at steady state, were determined to be 0.007 min-1, 99 min, 2059 mL/kg, 5729 mL/kg, and 2473 mL/kg, respectively. Noncompartmental pharmacokinetic parameters were obtained by the statistical moment theory. The estimates for mean residence time, clearance, and volume of distribution at steady state of trimethoprim were calculated to be 52 min, 40 mL.min-1kg-1, and 2097 mL, respectively. Tissue distribution of trimethoprim followed a biphasic phenomenon with a maximum concentration at 30 min for heart, lung, spleen, liver, kidney, seminal vesicles, and muscle, and at 45 min for testicles, 20 min for prostate gland, and less than 10 min for brain. The data show that compared with the plasma concentration, higher levels of trimethoprim were found in heart, lung, spleen, liver, kidney, prostate gland, and seminal vesicles; a similar concentration was found for muscle, but lower levels of trimethoprim were found for brain and testicles.

Pharmacokinetics of the trimethoprim-sulphamethoxazole combination in the elderly

The pharmacokinetics of a co-trimoxazole preparation (Bactrim Forte) containing trimethoprim (TMP) 160 mg and sulphamethoxazole (SMZ) 800 mg were determined in six young adults (29.3 +/- 4.4 s.d. years) and six elderly people (78.6 +/- 6.6 s.d. years). Following oral administration of a single dose, the pharmacokinetic parameters of SMZ and its N4-acetylated metabolite (N4SMZ) were similar in both groups. However Cmax of TMP was greater (2.06 +/- 0.29 s.d. vs 1.57 +/- 0.32 s.d. mg l-1; P less than 0.01) and its area under the curve was larger (34.30 +/- 6.98 s.d. vs 23.87 +/- 3.82 s.d. mg l-1 h; P less than 0.001) in elderly people than in younger subjects. Total clearance (CL/F) of TMP normalized to body weight was not significantly different in the two groups. There was no significant difference in serum protein binding of TMP and SMZ between the two groups. Urinary excretion of TMP, SMZ and N4SMZ was reduced by about 50% in the elderly compared to the young subjects. Renal clearance of TMP was significantly lower in the elderly group (19 +/- 10 s.d. vs 55 +/- 14 s.d. ml h-1 kg-1; P less than 0.001). Renal clearance of SMZ was not significantly different in the two groups. A study of plasma concentrations of TMP, SMZ and N4SMZ during continuous dosing in seven elderly patients treated for urinary or respiratory infections showed that steady state was reached after 3 days of treatment and that plasma drug concentrations were about two to three times higher than those observed after a single dose.

Comparative in vitro activity of five quinoline derivatives and five other antimicrobial agents used in oral therapy

The antibacterial activity of ciprofloxacin was compared to those of norfloxacin, pefloxacin, pipemidic acid, nalidixic acid, nitrofurantoin, sulfamethoxazole, trimethoprim, cephradine and amoxycillin. Agar dilution tests were performed with 631 clinical isolates from urinary and respiratory tract infections. Ciprofloxacin was found to be the most active drug tested against all gram-negative organisms and streptococci, with the exception of Streptococcus faecalis and Streptococcus pneumoniae. MIC 90 values of ciprofloxacin were as follows: for Enterobacteriaceae, 0.03-0.23 mg/l, Pseudomonas aeruginosa, 0.37 mg/l, Haemophilus influenzae, less than 0.015 mg/l, Staphylococcus aureus, 0.75 mg/l, Streptococcus pneumoniae, 1.89 mg/l, and Streptococcus faecalis, 0.95 mg/l. The inhibitory quotients for urine, serum and bronchial secretion showed that ciprofloxacin had the broadest spectrum of all agents tested and covered and clinically significant bacteria.

Dosing implications of rapid elimination of trimethoprim-sulfamethoxazole in patients with cystic fibrosis

The first-dose and steady-state pharmacokinetics of trimethoprim and sulfamethoxazole were determined in 14 patients with cystic fibrosis. When pharmacokinetic data from the first dose were compared with those at steady state, both TMP and SMZ showed expected accumulations in serum concentrations and decreases in total body clearance. The area under the SMZ serum concentration-time curve was significantly greater at steady state, suggesting drug accumulation during long-term therapy. When pharmacokinetic characteristics for TMP and SMZ obtained in patients with cystic fibrosis were compared with those reported for normal adults, the patients were found to have shorter elimination half-lives and greater plasma clearances. In addition, the apparent volume of distribution for TMP was smaller for patients with cystic fibrosis than for normal adults, consistent with their reduced mass of adipose tissue. Our data support the need for increased dosing or decreased dosing intervals when administering TMP-SMZ to patients with cystic fibrosis.

Co-trimoxazole and trimethoprim in complicated urinary tract infection

Previous work has suggested that co-trimoxazole may be superior to trimethoprim in the treatment of complicated urinary tract infection. A prospective study has been done to assess the relative value of the drugs in this situation using trimethoprim at higher than normal dosage. Fifty three patients (33 women and 20 men) were randomly allocated to either a fourteen-day course of co-trimoxazole tabs, 2 twice a day (27 patients) or trimethoprim 250 mg twice a day (26 patients). After patient withdrawals from the study, 17 (77%) of the co-trimoxazole group achieved a sterile urine three weeks after starting treatment compared with 15 (65%) in the trimethoprim group (X2 = 0.80). When those patients with sterile urine at three weeks who could be reassessed four weeks later were analyzed, 8 (89%) of the co-trimoxazole patients maintained a sterile urine against 7 (58%) in the trimethoprim group (X2 = 1.09). Although statistical significance was not attained, the results suggest that even at increased dosage, trimethoprim would not appear to be as efficient as co-trimoxazole in complicated urinary tract infection.

Determination of trimethoprim, sulphamethoxazole and its N4-acetyl metabolite in biological fluids by high-performance liquid chromatography

A normal-phase high-performance liquid chromatographic method was developed to determine therapeutic concentrations of trimethoprim, sulphamethoxazole, and its N4-acetyl derivative in biological fluids. The compounds are extracted at pH 6.2 using ethyl acetate--chloroform in a single extraction. The detection limit is 15 ng/ml for trimethoprim, 20 ng/ml for sulphamethoxazole, and 10 ng/ml for its N4-acetyl metabolite. The method is rapid, sensitive, precise, and well suited to clinical pharmacokinetic investigations.

Plasma protein binding of sulphadiazine, sulphamethoxazole and trimethoprim determined by ultrafiltration

The plasma protein binding of trimethoprim, sulphadiazine and sulphamethoxazole was studied at 37 degrees C by ultrafiltration. Plasma samples contained steady state levels of the drugs from ten volunteers from a cross-over comparative pharmacokinetic study on co-trimazine and co-trimoxazole. The three compounds were determined in plasma and ultrafiltrate by HPLC, the recoveries being close to 100% in each case. Freezing of spiked samples had no influence on the binding. Trimethoprim was 48.5-52.2% bound (mean 50.0%); sulphadiazine was 50.9-60.6% bound (mean 56.2%); and sulphamethoxazole was 74.3-80.8% bound (mean 76.9%). The significantly lower protein binding of sulphadiazine compared to sulphamethoxazole means that equivalent non-protein bound plasma levels of the two sulphonamides are achieved from smaller doses of co-trimazine than co-trimoxazole. Use of co-trimazine may thus minimize the risk of adverse reactions.

Some pharmacokinetic and biochemical aspects of sulphadiazine and sulphadimidine in ewes

Eight experiments were carried out on eight clinically healthy non-pregnant ewes. Each animal was injected intravenously with either sulphadiazine or sulphadimidine at a dose rate of 100 mg/kg body weight. A two-compartment pharmacokinetic model was developed to describe the disposition of these drugs. The elimination half-lives were 7.15 +/- 0.58 h and 9.51 +/- 0.59 h and the distribution half-lives were 0.56 +/- 0.07 h and 0.42 +/- 0.05 h for sulphadiazine and sulphadimidine, respectively. The apparent specific volumes of distribution were less than 1 litre/kg (0.410 and 0.501 litres/kg for sulphadiazine and sulphadimidine, respectively) which indicates a relatively lower distribution of these drugs to tissues than in plasma in sheep. The degree of plasma protein binding was similar for both drugs (19.15 +/- 0.55% and 23.12 +/- 0.32%) for sulphadiazine and sulphadimidine, respectively). Serum concentrations of ketone bodies, total lipids and calcium were significantly reduced, and blood glucose concentration significantly increased following administration of both of these sulphonamides, whilst serum total protein concentration was unaltered. The serum cholesterol concentration was significantly reduced following sulphadiazine administration, but not after sulphadimidine.

Pharmacokinetics of co-trimoxazole and co-tetroxazine in geriatric patients

Following a single dose of co-trimoxazole or co-tetroxazine, the plasma and urine levels of intact trimethoprim (TMP) and sulphamethoxazole (SMZ) and of tetroxoprim and sulphadiazine (SDZ) were determined in six geriatric patients in a cross-over design by high pressure liquid chromatography. The pharmacokinetic analysis showed a plasma elimination half-life in the terminal phase of 10.39 h for TMP, 11.79 h for SMZ, 6.55 h for TXP and 10.46 h for SDZ. The resulting distribution volumes Vd beta and total plasma clearance values corresponded with the data obtained in young patients or volunteers. Recovery in urine, measured for up to 96 h, was 49.2% (TMP), 19.8% (SMZ), 57.03% (TXP) and 61.1% (SDZ). In contrast to young volunteers, geriatric patients experienced a slight prolongation of renal excretion for both sulphonamides. In this group of patients the renal clearance was 2.42 ml/min for SMZ and 10.7 ml/min for SDZ.

Trimethoprim: clinical use and pharmacokinetics

The recent marketing of trimethoprim (TMP) as a single drug has resulted in interest in the use of this drug to treat common infections. The history and antibacterial properties of TMP are reviewed. Indications for the clinical use of TMP are presented, and possible new uses for the drug are considered. The significance of adverse effects is discussed. The pharmacokinetic properties of TMP are reviewed with particular emphasis on the renal handling of the drug and its advantages over TMP/sulfonamide combinations in relation to renal function and toxicity.

Intrarenal distribution of trimethoprim and sulfamethoxazole

In the present study, rats were given trimethoprim (TMP, 10 mg/kg), sulfamethoxazole (SMZ, 50 mg/kg), or a combination of the respective doses of TMP and SMZ. Thirty-six rats received each of the drugs studied. Six recipients of a compound (or mixture) were evaluated hourly, from 1 to 6 h after intraperitoneal injection of the agent. At each timed interval, serum, urine, cortex, medulla, and papilla were analyzed for drug content. Peak serum values of 1.1 microgram of TMP and 131.1 microgram of active SMZ (nonacetylated sulfonamide) per ml were observed after injection of the combination TMP-SMZ. Although the cortical, medullary, and papillary TMP concentrations were severalfold higher than the respective serum values (P < 0.01), microbiologically active SMZ did not concentrate in the renal parenchyma and was found in lower concentration there than in the serum (P < 0.01). The levels of SMZ in all parts of the kidney of animals which received the mixture SMZ-TMP were lower than those detected in the animals which were given SMZ alone. The average ratio of active SMZ to TMP within the medulla and the papilla was less than 20 to 1 in the first 2 h. The intrarenal distribution of these drugs may have therapeutic implications.

Trimethoprim enhances the antibacterial activity of nalidixic and oxolinic acids and delays the emergence of resistance

Trimethoprim enhances the in vitro activity of nalidixic and oxolinic acids against some representative pathogenic microorganisms, including those which are most frequently responsible for urinary tract infections, and delays the emergence of resistance in many of them.

The metabolic N-oxidation of 3-substituted pyridines in various animal species in vivo

The intraperitoneal administration of pyridine, 3-methylpyridine and 3-chloropyridine to mice, hamsters, rats, guinea-pigs, rabbits and ferrets, resulted in the urinary excretion of their N-oxides. Pyridine-N-oxide was found to be a quantitatively important metabolite of pyridine in all the species studied; the percentage of the dose excreted in the urine as pyridine-N-oxide ranged from 10% in rats to about 40% in mice and guinea-pigs. 3-Chloropyridine-N-oxide and 3-methylpyridine-N-oxide accounted for less than 7% of the administered dose of the parent base. The urinary excretion of pyridine-N-oxide was considerably greater in mice pretreated with phenobarbitone, compared to control mice, whereas 3-methylchloranthrene pretreatment had no appreciable effect on the excretion of pyridine-N-oxide.

Double blind comparison of short and medium term sulfonamides, sulfamethizole and sulfamethoxazole, in uncomplicated acute urinary tract infections

Sulfamethizole and sulfamethoxazole were compared in a prospective, randomized, double blind study on uncomplicated, acute urinary tract infections. 59 patients were evaluable for therapeutic effect of sulfamethizole and 53 for sulfamethoxazole. The cure rates were 91.5 and 92.5% respectively for sulfamethizole and sulfamethoxazole. The rates of side effects were the same in the two groups, 5.4% and 4.2%. Also instances where the infecting bacteria were sulfonamide-resistant were cured.

Development of sulphonamide-trimethoprim combinations for urinary tract infections. Part 3: Pharmacokinetic characterization of sulphadiazine and sulphamethoxazole given with trimethoprim

Plasma levels and renal excretion of sulphonamide and trimethoprim following oral administration of co-trimazine (140 mg sulphadiazine + 90 mg trimethoprim) and co-trimoxazole (800 mg sulphamethoxazole + 180 mg trimethoprim) were monitored in healthy volunteers after a single dose and in the steady state after 12-hourly dosage. The plasma levels of free, non-protein bound components after co-trimazine were approximately half those after co-trimoxazole and thus correlated with the doses given. Urine recovery of trimethoprim was better after co-trimazine (70%) than after co-trimoxazole (58%). Sixty-six percent of the sulphadiazine was recovered as unchanged, active sulphonamide in the urine compared with only 13% of the sulphamethoxazole. Consequently, the sulphonamide levels of sulphadiazine were 2.5 times those of sulphamethoxazole. With respect to plasma half-life after the first dose, sulphadiazine with 8.0 hours was closer to trimethoprim with a half-life of 8.8 hours after cotrimazine and 9.6 hours after co-trimoxazole than to the half-life of sulphamethoxazole which was 7.7 hours. The distribution volume of sulphadiazine was closer to that of trimethoprim than was that of sulphamethoxazole. On the basis of these characteristics, it has been concluded that sulphadiazine is more suitable for a fixed combination tablet with trimethoprim than sulphamethoxazole, particularly for the treatment of urinary tract infections. Some renal tubular reabsorption occurs with both unchanged sulphonamides but is more pronounced with sulphamethoxazole. The solubilities of the sulphonamides and their acetylated metabolites at acid urinary pH indicate that therapy with co-trimazine is at least as safe as with co-trimoxazole. With the former drug, the result of scrutiny for crystals after dosage until the steady state was negative, whereas crystals of acetylated sulphamethoxazole were detected and verified chemically in two of eight subjects.

Development of sulphonamide-trimethoprim combinations for urinary tract infections. Part 2: Comparative pharmacokinetics of five sulphonamides

The pharmacokinetics and renal excretion of the sulphonamides sulphachloropyridazine, sulphadiazine, sulphaisodimidine, sulphamerazine, and sulphamethoxazole were investigated in a cross-over study with doses of 800 mg each. The serum half-life, urine levels, distribution volume, protein binding and potential antibacterial activity in the urine renders sulphadiazine the preferred component in a combination tablet together with trimethoprim for the treatment of urinary tract infections.

The pharmacokinetics of trimethoprim and trimethoprim/sulphonamide combinations, including penetration into body tissues

In this review the pharmacokinetic properties of trimethoprim (TMP) and TMP/sulphonamide combinations are discussed. The concentration of both substances in the various body fluids and tissues differ considerably from the concentrations in blood due to the different distribution of TMP and sulphonamides in the body. As a rule the ratio of the concentration of TMP to sulphonamide is higher in most body fluids and secretions than in blood. If inflammation is present, the concentrations vary considerably. The pharmacokinetic data must be taken into account when making in vitro tests. At the site of inflammation a TMP/sulphonamide concentration factor of 1:0.5 to 1:4 can be expected in urine and of 1:2 to 1:5 in tissue.

Pharmacokinetics of sulfadiazine and trimethoprim in man

Sulfadiazine (SDZ) 800 mg and trimethoprim (TMP) 160 mg were given orally to 10 normal subjects and the concentration of SDZ and TMP in serum and urine was followed for 24 h. Both drugs showed a significant negative correlation between individual "peak" concentrations in serum and the body weight of the subject. Twelve hours after dosing the serum concentration was 12 to 25 microgram/ml for SDZ and 0.3 to 1.1 microgram/ml for TMP. Individual concentration ratios between SDZ and TMP in serum were 4.8 (1 h)--145 (24 h), and in the urine the ratio was close to 6 throughout the 24 h collection period. The range of urinary concentrations was from 65 to 400 microgram/ml for SDZ and from 13.8 to 93.4 microgram/ml for TMP. The fraction (formula: see text) was 21% during the 0--8 h period, 33% during the 8--15 h period and 41% during the 15--24 period. The average "t1/2" was 15.2 +/- 7.4 h for SDZ and 7.4 +/- 1.9 h for TMP. Individual subjects showed a significant correlation between the serum clearance of TMP and SDZ (p less than 0.01) and also between the renal clearance of the two drugs (p less than 0.05). The serum clearance was significantly correlated with the renal clearance for TMP but not for SDZ. For SDZ Vd was significantly negatively correlated with the elimination constant; for TMP no such correlation was found. The serum clearance of SDZ was significantly correlated with the percentage of SDZ which was excreted as the (presumably) acetylated compound. The renal clearance of SDZ was independent of the serum concentration of SDZ. There was a highly significant negative correlation between the renal clearance and serum concentration of TMP, as well as for "acetylated SDZ". The renal clearance of "acetylated SDZ" averaged more than six times that of unconjugated SDZ. With increased urine flow the renal clearances of TMP and SDZ were significantly increased.