Validating an empiric sulfadiazine-trimethoprim dosage regimen for treatment of Escherichia coli and Staphylococcus delphini infections in mink (Neovison vison).

Antimicrobial agents are used extensively off-label in mink, as almost no agents are registered for this animal species. Pharmacokinetic (PK) and pharmacodynamic (PD) data are required to determine antimicrobial dosages specifically targeting mink bacterial pathogens. The aims of this study were to assess, in a PKPD framework, the empirical dosage regimen for a combination of trimethoprim (TMP) and sulfadiazine (SDZ) in mink, and secondarily to produce data for future setting of clinical breakpoints. TMP and SDZ PK parameters were obtained experimentally in 22 minks following IV or oral administration of TMP/SDZ (30 mg/kg, i.e. 5 mg/kg TMP and 25 mg/kg SDZ). fAUC/MIC with a target value of 24 hr was selected as the PKPD index predictive of TMP/SDZ efficacy. Using a modeling approach, PKPD cutoffs for TMP and SDZ were determined as 0.062 and 16 mg/L, respectively. By incorporating an anticipated potentiation effect of SDZ on TMP against Escherichia coli and Staphylococcus delphini, the PKPD cutoff of TMP was revised to 0.312 mg/L, which is above the tentative epidemiological cutoffs (TECOFF) for these species. The current empirical TMP/SDZ dosage regimen (30 mg/kg, PO, once daily) therefore appears adequate for treatment of wild-type E. coli and S. delphini infections in mink.

Identification of the In Vivo Pharmacokinetics and Pharmacodynamic Driver of Iclaprim.

The neutropenic murine thigh infection model was used to define the pharmacokinetic/pharmacodynamic index linked to efficacy of iclaprim against Staphylococcus aureus ATCC 29213 and Staphylococcus pneumoniae ATCC 10813. The 24-h area under the curve (AUC)/MIC index was most closely linked to efficacy for S. aureus (R2, 0.65), while both the 24-h AUC/MIC and the percentage of time that drug concentrations remain above the MIC (%T>MIC) were strongly associated with effect (R2, 0.86 for both parameters) for S. pneumoniae.

Bioactivation of Trimethoprim to Protein-Reactive Metabolites in Human Liver Microsomes.

The formation of drug-protein adducts via metabolic activation and covalent binding may stimulate an immune response or may result in direct cell toxicity. Protein covalent binding is a potentially pivotal step in the development of idiosyncratic adverse drug reactions (IADRs). Trimethoprim (TMP)-sulfamethoxazole (SMX) is a combination antibiotic that commonly causes IADRs. Recent data suggest that the contribution of the TMP component of TMP-SMX to IADRs may be underappreciated. We previously demonstrated that TMP is bioactivated to chemically reactive intermediates that can be trapped in vitro by N-acetyl cysteine (NAC), and we have detected TMP-NAC adducts (i.e., mercapturic acids) in the urine of patients taking TMP-SMX. However, the occurrence and extent of TMP covalent binding to proteins was unknown. To determine the ability of TMP to form protein adducts, we incubated [(14)C]TMP with human liver microsomes in the presence and absence of NADPH. We observed protein covalent binding that was NADPH dependent and increased with incubation time and concentration of both protein and TMP. The estimated covalent binding was 0.8 nmol Eq TMP/mg protein, which is comparable to the level of covalent binding for several other drugs that have been associated with covalent binding-induced toxicity and/or IADRs. NAC and selective inhibitors of CYP2B6 and CYP3A4 significantly reduced TMP covalent binding. These results demonstrate for the first time that TMP bioactivation can lead directly to protein adduct formation, suggesting that TMP has been overlooked as a potential contributor of TMP-SMX IADRs.

Determination of sulfadiazine, trimethoprim, and N(4) -acetyl-sulfadiazine in fish muscle plus skin by Liquid Chromatography-Mass Spectrometry. Withdrawal-time calculation after in-feed administration in gilthead sea bream (Sparus aurata L.) fed two different diets.

This study presents a depletion study for sulfadiazine and trimethoprim in muscle plus skin of gilthead sea bream (Sparus aurata L.). N(4) -acetyl-sulfadiazine, the main metabolite of sulfadiazine (SDZ), was also examined. The fish were held in seawater at a temperature of 24-26 °C. SDZ and trimethoprim (TMP) were administered orally with medicated feed for five consecutive days at daily doses of 25 mg SDZ and 5 mg TMP per kg of fish body weight per day. Two different diets, fish oil- and plant oil-based diets, were investigated. Ten fish were sampled at each of the days 1, 3, 5, 6, 8, 9, 10, and 12 after the start of veterinary medicine administration. However for the calculation of the withdrawal periods, sampling day 1 was set as 24 h after the last dose of the treatment. Fish samples were analyzed for SDZ, TMP, and acetyl-sulfadiazine (AcSDZ) residues by liquid chromatography-mass spectrometry. SDZ and TMP concentrations declined rapidly from muscle plus skin. Considering a maximum residue limit of 100 µg/kg for the total of sulfonamides and 50 µg/kg for TMP residues in fish muscle plus skin, the withdrawal periods of the premix trimethoprim-sulfadiazine 50% were calculated as 5 and 6 days, at 24-26 °C, in fish oil (FO) and plant oil (PO) groups, respectively. The investigation of this work is important to protect consumers by controlling the undesirable residues in fish.

A pharmacokinetic and residual study of sulfadiazine/trimethoprim in mandarin fish (Siniperca chuatsi) with single- and multiple-dose oral administrations.

A pharmacokinetic and tissue residue study of sulfadiazine combined with trimethoprim (SDZ/TMP = 5/1) was conducted in Siniperca chuatsi after single- (120 mg/kg) or multiple-dose (an initial dose of 120 mg/kg followed by a 5-day consecutive dose of 60 mg/kg) oral administrations at 28 °C. The absorption half-life (t1/2α ), elimination half-life (t1/2ß ), volume of distribution (Vd /F), and the total body clearance (ClB /F) for SDZ and TMP were 4.3 ± 1.7 to 6.3 ± 1.8 h and 2.4 ± 1.0 to 3.9 ± 0.9 h, 25.9 ± 4.5 to 53.0 ± 5.6 h and 11.8 ± 3.5 to 17.1 ± 3.4 h, 2.34 ± 0.78 to 3.67 ± 0.99 L/kg and 0.39 ± 0.01 to 1.33 ± 0.57 L/kg, and 0.03 ± 0.01 to 0.06 ± 0.01 L/kg·h and 0.02 ± 0.01 to 0.05 ± 0.01 L/kg·h, respectively, after the single dose. The elimination half-life (t1/2ß ) and mean residue time (MRT) for SDZ and TMP were 68.8 ± 7.8 to 139.8 ± 12.3 h and 34.0 ± 5.5 to 56.1 ± 6.8 h, and 99.3 ± 6.1 to 201.7 ± 11.5 h and 49.1 ± 3.5 to 81.0 ± 5.1 h, respectively, after the multiple-dose administration. The daily oral SDZ/TMP administration might cause a high tissue concentration and long t1/2ß , thereby affecting antibacterial activity. The withdrawal time for this oral SDZ/TMP formulation (according to the accepted guidelines in Europe for maximum residue limits, <0.1 mg/kg of tissues for sulfonamides, and <0.05 mg/kg for TMP) should not be <36 days for fish.

In Vitro Hepatic Oxidative Biotransformation of Trimethoprim.

Trimethoprim (TMP) has been widely used since the 1960s, both alone and in combination with sulfamethoxazole. Unfortunately, information regarding the role that cytochrome P450 enzymes (P450s) play in the formation of TMP primary metabolites is scarce. Hence, we undertook in vitro studies to identify and more fully characterize the P450s that catalyze formation of six TMP primary metabolites: TMP 1-N-oxide (1-NO-TMP) and 3-N-oxide (3-NO-TMP), 3'- and 4'-desmethyl-TMP, a benzylic alcohol (Cα-OH-TMP), and an N-acetyl cysteine (NAC) adduct of TMP (Cα-NAC-TMP). Formation kinetics for each TMP metabolite in human liver microsomes (HLMs) were consistent with single-enzyme Michaelis-Menten kinetics, and Km values were markedly above (≥10-fold) the therapeutic concentrations of TMP (50 µM). The combined results from correlation studies between rates of metabolite formation and marker P450 activities in a panel of HLMs along with inhibition studies utilizing selective P450 inhibitors incubated with pooled HLMs suggested that 1-NO-TMP, Cα-NAC-TMP, and Cα-OH-TMP were predominantly formed by CYP3A4. In contrast, 3-NO-TMP was formed predominantly by CYP1A2 in HLMs and inhibited by α-naphthoflavone. 4'-Desmethyl-TMP, which is believed to be a reactive TMP metabolite precursor, was formed by several P450s, including CYP3A4, correlated with multiple P450 activities, but was inhibited primarily by ketoconazole (up to 50%), suggesting that CYP3A4 makes a major contribution to TMP 4'-demethylation. TMP 3'-demethylation was catalyzed by multiple P450s, including CYP2C9, correlated with CYP2C9 activity, and was inhibited by sulfaphenazole (up to 40%). Overall, CYP2C9 and CYP3A4 appear to be the most significant contributors to TMP primary metabolism.

N(1)-methylnicotinamide as an endogenous probe for drug interactions by renal cation transporters: studies on the metformin-trimethoprim interaction.

PURPOSE: N(1)-methylnicotinamide (NMN) was proposed as an in vivo probe for drug interactions involving renal cation transporters, which, for example, transport the oral antidiabetic drug metformin, based on a study with the inhibitor pyrimethamine. The role of NMN for predicting other interactions with involvement of renal cation transporters (organic cation transporter 2, OCT2; multidrug and toxin extrusion proteins 1 and 2-K, MATE1 and MATE2-K) is unclear. METHODS: We determined inhibition of metformin or NMN transport by trimethoprim using cell lines expressing OCT2, MATE1, or MATE2-K. Moreover, a randomized, open-label, two-phase crossover study was performed in 12 healthy volunteers. In each phase, 850 mg metformin hydrochloride was administered p.o. in the evening of day 4 and in the morning of day 5. In phase B, 200 mg trimethoprim was administered additionally p.o. twice daily for 5 days. Metformin pharmacokinetics and effects (measured by OGTT) and NMN pharmacokinetics were determined. RESULTS: Trimethoprim inhibited metformin transport with K i values of 27.2, 6.3, and 28.9 µM and NMN transport with IC50 values of 133.9, 29.1, and 0.61 µM for OCT2, MATE1, and MATE2-K, respectively. In the clinical study, trimethoprim increased metformin area under the plasma concentration-time curve (AUC) by 29.5 % and decreased metformin and NMN renal clearances by 26.4 and 19.9 %, respectively (p ≤ 0.01). Moreover, decreases of NMN and metformin renal clearances due to trimethoprim correlated significantly (r S=0.727, p=0.010). CONCLUSIONS: These data on the metformin-trimethoprim interaction support the potential utility of N(1)-methylnicotinamide as an endogenous probe for renal drug-drug interactions with involvement of renal cation transporters.

Urinary concentrations and antibacterial activities of nitroxoline at 250 milligrams versus trimethoprim at 200 milligrams against uropathogens in healthy volunteers.

Because of the increasing bacterial resistance of uropathogens against standard antibiotics, such as trimethoprim (TMP), older antimicrobial drugs, such as nitroxoline (NTX), should be reevaluated. This randomized crossover study investigated the urinary concentrations of parent drugs and their metabolites and their antibacterial activities (urinary inhibitory titers [UITs] and urinary bactericidal titers [UBTs]) against uropathogens at three different urinary pH values within 24 h in six healthy volunteers after a single oral dose of NTX at 250 mg versus TMP at 200 mg. In three additional volunteers, urinary bactericidal kinetics (UBK) were studied after oral administration of NTX at 250 mg three times a day. The mean urinary concentrations of NTX and NTX sulfate in 24 h were 0.012 to 0.507 mg/liter and 0.28 to 27.83 mg/liter, respectively. The mean urinary concentrations of TMP were 18.79 to 41.59 mg/liter. The antibacterial activity of NTX was higher in acidic urine than in alkaline urine, and that of TMP was higher in alkaline urine than in acidic urine. The UITs and UBTs of NTX were generally lower than those of TMP except for a TMP-resistant Escherichia coli strain, for which NTX showed higher UITs/UBTs than did TMP. UBK showed mainly bacteriostatic activity of NTX in urine. NTX exhibits mainly bacteriostatic activity and TMP also shows bactericidal activity in urine against susceptible strains. NTX is a more active antibacterial in acidic urine, and TMP is more active in alkaline urine. The cumulative effects of multiple doses or inhibition of bacterial adherence could not be evaluated. (This study has been registered at EudraCT under registration no. 2009-015631-32.).

Urinary biomarkers of trimethoprim bioactivation in vivo following therapeutic dosing in children.

The antimicrobial trimethoprim-sulfamethoxazole (TMP-SMX) is widely used for the treatment of skin and soft-tissue infections in the outpatient setting. Despite its therapeutic benefits, TMP-SMX has been associated with a number of adverse drug reactions, which have been primarily attributed to the formation of reactive metabolites from SMX. Recently, in vitro experiments have demonstrated that TMP may form reactive intermediates as well. However, evidence of TMP bioactivation in patients has not yet been demonstrated. In this study, we performed in vitro trapping experiments with N-acetyl-l-cysteine (NAC) to determine stable markers of reactive TMP intermediates, focusing on eight potential markers (NAC-TMP adducts), some of which were previously identified in vitro. We developed a specific and sensitive assay involving liquid chromatography followed by tandem mass spectrometry for measurement of these adducts in human liver microsomal samples and expanded the methodology toward the detection of these analytes in human urine. Urine samples from four patients receiving TMP-SMX treatment were analyzed, and all samples demonstrated the presence of six NAC-TMP adducts, which were also detected in vitro. These adducts are consistent with the formation of imino-quinone-methide and para-quinone-methide reactive intermediates in vivo. As a result, the TMP component of TMP-SMX should be considered as well when evaluating adverse drug reactions to TMP-SMX.

Pharmacokinetic interaction of enrofloxacin/trimethoprim combination following single-dose intraperitoneal and oral administration in rats.

The pharmacokinetic interaction of enrofloxacin and trimethoprim was evaluated after single-dose intraperitoneal or oral co-administration in rats. Plasma concentrations of the two drugs were determined by high-performance liquid chromatography. Following intraperitoneal combination, a significant (P < 0.05) increase in mean values of plasma half-life (t 1/2) and maximum plasma concentration (C max) was observed for enrofloxacin and trimethoprim, respectively. There was a significant (P < 0.05) increase in mean values of area under the plasma drug concentration versus time from time zero to infinity (AUC0-∞) and C max between combined oral doses (10, 30 and 100 mg/kg) of both antibacterial drugs. Also, after oral conjugation a significant difference in mean values of MRT0-∞ was observed between lower (10 mg/kg) and higher (100 mg/kg) doses of both drugs. A significant increase in pharmacokinetic parameters of both drugs in combined intraperitoneal and oral doses indicated pharmacokinetic interaction of enrofloxacin and trimethoprim. Further study is recommended in other species of animals.

Pharmacokinetic modeling of sulfamethoxazole-trimethoprim and sulfadiazine-trimethoprim combinations in broilers.

Sulfonamides (S) are old bacteriostatic antibiotics which are widely prescribed in combination with trimethoprim (TMP) for the treatment of various diseases in food-producing animals such as poultry. Nowadays, the 1:5 dose ratio of TMP/S used in broilers is a direct transposition of the ratio determined in Human decades ago for TMP/sulfamethoxazole (SMX), aiming to obtain a supposed synergistic plasma concentration ratio of 1:19. However, major pharmacokinetics (PK) differences exist according to the sulfonamide used in the combination. Here, we generated new PK data in broilers after a cross-over design with IV and the oral administration of 2 major sulfonamides, sulfadiazine (SDZ) and SMX, in combination with TMP, and analyzed the data via a population pharmacokinetic (popPK) modeling approach. Results showed that TMP has a greater plasma to tissue distribution than both sulfonamides with a higher volume of distribution (0.51 L/kg for SDZ, 0.62 L/kg for SMX and 3.14 L/kg for TMP). SMX has the highest elimination half-life (2.83 h) followed by SDZ and TMP (2.01 h and 1.49 h, respectively). The oral bioavailability of the 3 molecules was approximately 100%. Bodyweight could explain some of the inter-individual variability in the volume of distribution of SDZ and SMX and the clearance of SDZ and TMP, as heavier broilers have higher typical values. Monte Carlo simulations of a large virtual broiler population (n = 1,000) showed that the targeted plasma ratio of TMP:S of 1:19 was rarely or never reached at the individual level for both combinations at the marketed doses and greatly varies over time and between individuals, questioning the relevance of the 1:5 dose ratio for current formulations of TMP/S.

Application of in vitro-in vivo extrapolation (IVIVE) and physiologically based pharmacokinetic (PBPK) modelling to investigate the impact of the CYP2C8 polymorphism on rosiglitazone exposure.

PURPOSE: To predict the impact of the CYP2C8 3 genotype on rosiglitazone exposure in the absence and presence of trimethoprim. METHODS: Prior in vitro and in vivo information for rosiglitazone and trimethoprim were collated from the literature. Specifically, data on the frequency of the different allelic forms of CYP2C8 and their metabolic activity for rosiglitazone were incorporated into a physiologically-based pharmacokinetic (PBPK) model within the Simcyp Simulator (V11.1) to predict differences in the relative exposure of rosiglitazone according to CYP2C8 3 genotype in a virtual population. RESULTS: Following multiple doses of 8 mg rosiglitazone, the predicted mean AUC(0-24) was 37 % lower in CYP2C8 3 homozygotes compared with wildtype homozygotes (p < 0.001), which was consistent with the 36 % lower value observed in vivo (p < 0.001) Kirchheiner et al. (Clin Pharmacol Ther 80:657-667, 2006). Predicted median AUC ratios of rosiglitazone in the presence and absence of trimethoprim ranged from 1.35 to 1.66 for ten virtual trials of subjects with the CYP2C8 1/1 genotype, which included the observed value of 1.42. In subjects with the CYP2C8 1/3 genotype, the predicted AUC ratios for all trials were higher than the observed value of 1.18 Kirchheiner et al. (Clin Pharmacol Ther 80:657-667, 2006). CONCLUSIONS: Investigating the drug interactions in individuals with rare allelic forms of drug metabolising enzymes is fraught with many practical problems. Current study demonstrates the utility of prior in vitro metabolism data from such allelic forms to predict the relative exposure of a drug as a function of genotype. However, in vitro inhibition data obtained in one allelic variant (e.g. CYP2C8 1) may not be adequate to predict the in vivo interactions in another allele (e.g. CYP2C8 3), since the inhibitory characteristics of perpetrator might be different in each allelic variant in the same way as that of metabolism of the victim drug by such variants of the enzyme.

Characterization of in vitro metabolites of trimethoprim and diaveridine in pig liver microsomes by liquid chromatography combined with hybrid ion trap/time-of-flight mass spectrometry.

Trimethoprim (TMP) and diaveridine (DVD) are used in combination with sulfonamides and sulfaquinoxlaine as an effective antibacterial agent and antiprotozoal agent, respectively, in humans and animals. To gain a better understanding of the metabolism of TMP and DVD in the food-producing animals, the metabolites incubated with liver microsomes of pigs were analyzed for the first time with high-performance liquid chromatography combined with hybrid ion trap/time-of-flight mass spectrometry. Seven TMP-related and six DVD-related metabolites were characterized based on the accurate MS² spectra and known structure of the parent drug, respectively. The metabolites of TMP were identified as two O-demethylation metabolites, a di-O-demethylation metabolite, two N-oxides metabolites, a hydroxylated metabolite on the methylene carbon and a hydroxylated metabolite on the methyl group. DVD was also biotransformed to two O-demethylation metabolites, a di-O-demethylation metabolite, an N-oxide metabolite, a hydroxylation metabolite on the methylene carbon and a hydroxylation metabolite followed by O-demethylation. The results indicate that the two compounds have similar biotransformation pathways in pigs. O-Demethylation was the major metabolic route of TMP and DVD in the pig liver microsomes. The proposed metabolic pathways of TMP and DVD in liver microsomes will provide a basis for further studies of the in vivo metabolism of the two drugs in food-producing animals.

Antimicrobial disposition in pulmonary epithelial lining fluid of horses. Part I. Sulfadiazine and trimethoprim.

Sulfadiazine (SDZ) and trimethoprim (TMP) concentrations were examined in plasma and pulmonary epithelial lining fluid (PELF), following intravenous and oral administration and compared to minimum inhibitory concentrations (MICs) of common bacterial isolates from equine lower airway infections. SDZ/TMP (25/5 mg/kg) was administered intravenously, intragastric or per os to fed horses, and blood samples were collected before and 11 times, over 24 h, after administration. PELF samples were collected via a tampon device four times after drug administration and analysed for drug concentrations. Additionally, MICs of SDZ and TMP alone and in combination were determined in a selection of clinical respiratory isolates. Bioavailability was 74% for SDZ and 46% for TMP after paste administration in fed horses. The degree of penetration of SDZ and TMP into PELF, as described by AUC(PELF) /AUC(plasma) ratios, was 0.68 and 0.72, respectively, after intravenous administration. After oral administration, the degree of penetration for SDZ and TMP was 0.92 and 0.46, respectively. MIC measurements using SDZ/TMP ratios of 5:1 and 10:1 did not affect the interpretation of the results. The results indicate that clinically relevant drug concentrations of mainly TMP are difficult to maintain in PELF, especially after oral administration of SDZ/TMP.

Development of antibacterial compounds that constrain evolutionary pathways to resistance.

Antibiotic resistance is a worldwide challenge. A potential approach to block resistance is to simultaneously inhibit WT and known escape variants of the target bacterial protein. Here, we applied an integrated computational and experimental approach to discover compounds that inhibit both WT and trimethoprim (TMP) resistant mutants of E. coli dihydrofolate reductase (DHFR). We identified a novel compound (CD15-3) that inhibits WT DHFR and its TMP resistant variants L28R, P21L and A26T with IC50 50-75 µM against WT and TMP-resistant strains. Resistance to CD15-3 was dramatically delayed compared to TMP in in vitro evolution. Whole genome sequencing of CD15-3-resistant strains showed no mutations in the target folA locus. Rather, gene duplication of several efflux pumps gave rise to weak (about twofold increase in IC50) resistance against CD15-3. Altogether, our results demonstrate the promise of strategy to develop evolution drugs - compounds which constrain evolutionary escape routes in pathogens.

Physiologically-Based Pharmacokinetic Modelling of Creatinine-Drug Interactions in the Chronic Kidney Disease Population.

Elevated serum creatinine (SCr ) caused by the inhibition of renal transporter(s) may be misinterpreted as kidney injury. The interpretation is more complicated in patients with chronic kidney disease (CKD) due to altered disposition of creatinine and renal transporter inhibitors. A clinical study was conducted in 17 patients with CKD (estimated glomerular filtration rate 15-59 mL/min/1.73 m2 ); changes in SCr were monitored during trimethoprim treatment (100-200 mg/day), administered to prevent recurrent urinary infection, relative to the baseline level. Additional SCr -interaction data with trimethoprim, cimetidine, and famotidine in patients with CKD were collated from the literature. Our published physiologically-based creatinine model was extended to predict the effect of the CKD on SCr and creatinine-drug interaction. The creatinine-CKD model incorporated age/sex-related differences in creatinine synthesis, CKD-related glomerular filtration deterioration; change in transporter activity either proportional or disproportional to glomerular filtration rate (GFR) decline were explored. Optimized models successfully recovered baseline SCr from 64 patients with CKD (geometric mean fold-error of 1.1). Combined with pharmacokinetic models of inhibitors, the creatinine model was used to simulate transporter-mediated creatinine-drug interactions. Use of inhibitor unbound plasma concentrations resulted in 66% of simulated SCr interaction data within the prediction limits, with cimetidine interaction significantly underestimated. Assuming that transporter activity deteriorates disproportional to GFR decline resulted in higher predicted sensitivity to transporter inhibition in patients with CKD relative to healthy patients, consistent with sparse clinical data. For the first time, this novel modelling approach enables quantitative prediction of SCr in CKD and delineation of the effect of disease and renal transporter inhibition in this patient population.

Pharmacokinetics of Sulfamethoxazole and Trimethoprim During Venovenous Extracorporeal Membrane Oxygenation: A Case Report.

Extracorporeal membrane oxygenation (ECMO) therapy could affect drug concentrations via adsorption onto the oxygenator and/or associated circuit. We describe a case of a 33-year-old man with severe respiratory failure due to Pneumocystis jirovecii infection on a background of recently diagnosed human immunodeficiency virus infection. He required venovenous ECMO therapy for refractory respiratory failure. Intravenous sulfamethoxazole-trimethoprim (100 and 20 mg/kg/day) was administered in a dosing regimen every 6 hours. Pre-oxygenator, post-oxygenator, and arterial blood samples were collected after antibiotic administration and were analyzed for total sulfamethoxazole and trimethoprim concentrations. The peak sulfamethoxazole and trimethoprim concentrations were 122 mg/L and 5.3 mg/L, respectively. The volume of distribution for sulfamethoxazole was 0.37 and 2.30 L/kg for trimethoprim. The clearance for sulfamethoxazole was 0.35 ml/minute/kg and for trimethoprim was 1.64 ml/minute/kg. The pharmacokinetics of sulfamethoxazole and trimethoprim appear not to be affected by ECMO therapy, and dosing adjustment may not be required.

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.

In vitro and in vivo properties of dihydrophthalazine antifolates, a novel family of antibacterial drugs.

Racemic 2,4-diaminopyrimidine dihydrophthalazine derivatives BAL0030543, BAL0030544, and BAL0030545 exhibited low in vitro MICs toward small, selected panels of Enterococcus faecalis, Enterococcus faecium, Streptococcus pneumoniae, Moraxella catarrhalis, and Mycobacterium avium, though the compounds were less active against Haemophilus influenzae. The constellation of dihydrofolate reductases (DHFRs) present in 20 enterococci and 40 staphylococci was analyzed and correlated with the antibacterial activities of the dihydrophthalazines and trimethoprim. DHFRs encoded by dfrB, dfrA (S1 isozyme), dfrE, and folA were susceptible to the dihydrophthalazines, whereas DHFRs encoded by dfrG (S3 isozyme) and dfrF were not. Studies with the separated enantiomers of BAL0030543, BAL0030544, and BAL0030545 revealed preferential inhibition of susceptible DHFRs by the (R)-enantiomers. BAL0030543, BAL0030544, and BAL0030545 were well tolerated by mice during 5- and 10-day oral toxicity studies at doses of up to 400 mg/kg of body weight. Using a nonoptimized formulation, the dihydrophthalazines displayed acceptable oral bioavailabilities in mice, and efficacy studies with a septicemia model of mice infected with trimethoprim-resistant, methicillin-resistant Staphylococcus aureus gave 50% effective dose values in the range of 1.6 to 6.25 mg/kg.