Pharmacokinetics of sulfamethoxazole and trimethoprim in Pacific white shrimp, Litopenaeus vannamei, after oral administration of single-dose and multiple-dose

The tissue distribution and depletion of sulfamethoxazole (SMZ) and trimethoprim (TMP) were studied in Pacific white shrimp, Litopenaeus vannamei, after single-dose and multiple-dose oral administration of SMZ-TMP (5:1) via medicated feed. In single-dose oral administration, shrimps were fed once at a dose of 100 mg/kg (drug weight/body weight). In multiple-dose oral administration, shrimps were fed three times a day for three consecutive days at a dose of 100mg/kg. The results showed the kinetic characteristic of SMZ was different from TMP in Pacific white shrimp. In the single-dose administration, the SMZ was widely distributed in the tissues, while TMP was highly concentrated in the hepatopancreas. The t_1/2z values of SMZ were larger and persist longer than TMP in Pacific white shrimp. In the multiple-dose administration, SMZ accumulated well in the tissues, and reached steady state level after successive administrations, while TMP did not. TMP concentration even appeared the downward trend with the increase of drug times. Compared with the single dose, the t_1/2z values of SMZ in hepatopancreas (8.22-11.33h) and muscle (6.53-10.92h) of Pacific white shrimps rose, but the haemolymph dropped (13.76-11.03) in the multiple-dose oral administration. Meanwhile, the corresponding values of TMP also rose in hepatopancreas (4.53-9.65h) and muscle (2.12-2.71h), and declined in haemolymph (7.38-5.25h) following single-dose and multiple-dose oral administration in Pacific white shrimps. In addition, it is worth mentioning that the ratios of SMZ and TMP were unusually larger than the general aim ratio.

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.).

Hepatic disposition of trimethoprim and sulfamethoxazole

Hepatic disposition of trimethoprim (TMP) and sulfamethoxazole (SMX) and the liver distributional volumes were investigated in the in situ perfused rat liver preparation. Perfusion experiments were conducted using Krebs-bicarbonate buffer delivered via the portal vein (15 ml/min) in a single-pass mode. Erythrocytes (intravascular marker) and Evans blue (extracellular marker) were used for the estimation of liver distributional volumes, and desiccation and freeze-drying methods were used for the estimation of liver water content. TMP and SMX were administered together as a bolus in the presence (1%) and absence of protein. Although SMX profiles displayed a characteristic sharp peak followed by a slower eluting tail in all cases, TMP profiles were dependent on protein; in the absence of protein, the early sharp peak was replaced by a flatter profile with a later peak. Fractional effluent recovery (F; 0.77 vs. 0.82) and hepatic clearance (CL(H); 3.44 vs. 2.70 ml/min) for TMP were not influenced by albumin; with SMX, F increased (0.32 vs. 0.60) and CL(H) decreased (10.2 vs. 6.0 ml/min) with an increase in the perfusate protein concentration. Hepatic extraction of TMP was low (<0.30), whereas it was intermediate (<0.70) for SMX. In addition, distributional volumes and total water content of the liver were successfully determined.

A Novel In Vivo Rabbit Model that Mimics Human Dosing to Determine the Distribution of Antibiotics in Ocular Tissues

PURPOSE

The aim of this study was to establish a novel method to predict the human ocular penetration and distribution of topical antibiotics by using a controlled rabbit model that mimics the human eye with manual blinking and tear flow.

METHODS

After anesthetizing the rabbits, a single dose of commercial antibiotic formulations was given with precision directly onto the cornea. This was followed by a 30-min controlled period applying manual blinking (4 blinks/min) and a supplementary tear flow (2 microL/min) that mimics the human eye. Tear samples were collected every 5 min and after euthanasia, conjunctival, aqueous humor, iris-ciliary body, and scleral samples were collected. The corneas were mounted in perfusion chambers to determine the level and continuing rate of release of the antibiotics, the levels of which were all determined using high-performance liquid chromatography analysis.

RESULTS

U.S. formulations achieved conjunctival and corneal levels (μg/g) as follows: moxifloxacin, 6.6 +/- 0.3 and 50 +/- 5; tobramycin, 3.1 +/- 1.4 and 20 +/- 5; gentamicin, <2 and <2; levofloxacin, 1.5 +/- 0.3 and 19 +/- 2; gatifloxacin, 0.9 +/- 0.1 and 11 +/- 1; and trimethoprim, <0.1 and 2 +/- 1. Japan formulations achieved conjunctival and corneal levels as follows: levofloxacin 2.1 +/- 0.8 and 12 +/- 2; gatifloxacin, 2.2 +/- 0.9 and 7 +/- 1; ofloxacin, 1.6 +/- 0.5 and 7 +/- 1; and tosufloxacin, 0.7 +/- 0.1 and 1.5 +/- 0.3 (mean +/- standard error, n = 4).

CONCLUSIONS

Moxifloxacin achieved the highest levels of antibiotic in ocular tissues. In the conjunctiva and cornea, the moxifloxacin level was 3-30 times the level of other fluoroquinolones, at least twice the level of the aminoglycosides, and 25 times the level of the antibacterial trimethoprim.

Pharmacokinetics of piperaquine after repeated oral administration of the antimalarial combination CV8 in 12 healthy male subjects

OBJECTIVE

To investigate the pharmacokinetic properties of piperaquine after repeated oral administration of the antimalarial combination CV8 in healthy subjects.

METHODS

Twelve healthy fasted Vietnamese males were administered four tablets CV8 (320 mg piperaquine phosphate, 32 mg dihydroartemisinin, 5 mg primaquine phosphate, 90 mg trimethoprim) on day 1, followed by two tablets every 24th hour, for a total of 3 days. Blood samples were frequently drawn on days 1 and 3 and sparsely drawn until day 29. Samples were analyzed for piperaquine using solid phase extraction followed by high-performance liquid chromatography. Population pharmacokinetic parameter estimates were obtained by nonlinear mixed effects modeling of the observed data using NONMEM.

RESULTS

A two-compartment disposition model with an absorption lag time described the observed piperaquine concentrations. Absorption profiles were found to be irregular with double or multiple peaks. A dual pathway first-order absorption model improved the goodness of fit. Piperaquine pharmacokinetics were characterized by a large volume of distribution and a terminal half-life of several days. Estimates [95% confidence interval (CI)] of CL/F, V(ss)/F and t(1/2)(z) were found to be 56.4 (29-84) l/h, 6,000 (3,500-8,500) l and 11.7 (8.3-15.7) days, respectively.

CONCLUSION

Piperaquine pharmacokinetics after repeated oral doses were characterized by multiple concentration peaks and multiphasic disposition, resulting in a long terminal half-life. Sustained exposure to the drug after treatment should be taken into account when designing future clinical studies, e.g. duration of follow-up, and may also drive resistance development in areas of high malaria transmission.

Liquid chromatographic method for the simultaneous determination of cefalexin and trimethoprim in dog plasma and application to the pharmacokinetic studies of a coformulated preparation

A liquid chromatographic method is described for the simultaneous determination of cefalexin and trimethoprim in dog plasma. A simple protein precipitation procedure was adopted for the sample preparation with satisfactory extraction recoveries for both analytes. Chromatographic separation of the analytes was achieved on a C(18) column using a mixture of 2 mol/l formate buffer (pH 3.5), methanol and acetonitrile (22:7:7, v/v/v) containing a 0.002 mol/l sodium dodecyl sulfate as mobile phase and detection was performed at 240 nm. The linearity was obtained over the concentration ranges of 1.0-100.0 microg/ml for cefalexin and 0.5-50.0 microg/ml for trimethoprim. For each level of QC samples including the lower limit of quantification, both inter- and intra-day precisions (R.S.D.) were < or =14.0% for cefalexin and < or =11.4% for trimethoprim, and accuracy (RE) was -1.4% for cefalexin and -3.0% for trimethoprim. The present LC method was successfully applied to the pharmacokinetic studies of coformulated cefalexin dispersible tablets after oral administration to beagle dogs.

Bioavailability and Pharmacokinetics of Sulphadiazine, N4-acetylsulphadiazine and Trimethoprim following Intravenous and Intramuscular Administration of a Sulphadiazine/Trimethoprim Combination in Sheep

The combination of sulphadiazine and trimethoprim is extensively used in farm animal species; however, there are no data concerning its pharmacokinetics after intramuscular administration in sheep. Twelve rams of the Chios breed were used to study the disposition of sulphadiazine, its metabolite N4-acetylsulphadiazine and trimethoprim after intravenous (i.v.) and intramuscular (i.m.) administration of a sulphadiazine/trimethoprim (5:1) combination in sheep. Sulphadiazine bioavailability (+/-SD) was 69.00%+/-10.51%. The half-life of the terminal phase (4.10+/-0.58 h after i. v., and 4.03+/-0.31 h after i.m. administration) was significantly higher than the respective value for trimethoprim (0.59+/-0.19 h) after i.v. administration. The maintenance of a constant plasma concentration ratio after i.v. administration was therefore impossible. The acetylation capacity in sheep, determined by the AUC ratio between N4-acetylsulphadiazine and the parent compound, sulphadiazine, was very low (less than 4%). The most remarkable finding of this study was that trimethoprim was not detected in sheep plasma after i.m. injection. In conclusion, according to the findings of the present study, following i.v. administration of the sulphadiazine/trimethoprim combination, trimethoprim can be considered as the limiting factor for any possible synergistic effect, and the i.m. route cannot be recommended in sheep.

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.

Clinical efficacy of prophylactic administration of trimethoprim/sulfadiazine in a Streptococcus equi subsp. zooepidemicus infection model in ponies

Tissue chambers, implanted subcutaneously in the neck in six ponies, were inoculated with Streptococcus equi subsp. zooepidemicus in order to determine the clinical efficacy of prophylactic administration of trimethoprim/sulfadiazine (TMP/SDZ) against this infection. The TMP/SDZ treatment consisted of one intravenous (i.v.) injection of 5 mg/kg TMP and 25 mg/kg SDZ and the same dose of TMP/SDZ per os (p.o.), both given 3 h before inoculation. The oral dose was then repeated every 12 h for 5 days. TMP/SDZ concentrations in tissue chamber fluid (TCF) were above 10 times MIC at the moment of inoculation, and they were maintained at this level or higher throughout the duration of treatment. Trimethoprim/sulfadiazine treatment resulted in a marked reduction of viable bacteria in the tissue chamber but did not eliminate the infection, resulting in abscessation from day 19 onwards in all six ponies. This shows that, even when TCF is not yet purulent, TMP/SDZ is unable to eliminate the streptococci. Therefore, TMP/SDZ should not be the antimicrobial treatment of choice in infections in secluded sites in horses.

Determination of trimethoprim in low-volume human plasma by liquid chromatography

Trimethoprim is an anti-infective agent used in the treatment of urinary and respiratory tract infections and mild to moderate pneumocystis carinii pneumonia. Trimethoprim is also a selective in vitro inhibitor of cytochrome P450 2C8 and may have utility as an in vivo inhibitor of this enzyme. A simplified high performance liquid chromatography (HPLC) method was developed to determine trimethoprim in human plasma. Samples are processed by protein precipitation with perchloric acid and chromatographic separation is achieved on a Synergi Polar-RP column (4 micron, 150 mm x 4.6 mm) using a mobile phase consisting of 50 mM ammonium formate-acetonitrile-methanol (pH=3.0; 90:6:4 (v/v/v)). Detection is monitored at 280 nm. Intra- and inter-day precision ranged from 1.1 to 1.9 and 0.9 to 4.1%, respectively. The assay is simple, economical, precise, and is directly applicable to human studies involving steady state trimethoprim pharmacokinetics.

Serum activity/concentration profiles of a sustained-released formulation of sulphathiazole-trimethoprim (2.5:1) in calves

Thirty-six two-week-old healthy Holstein-Friesian calves weighing between 52 and 58 kg were divided at random into three groups of 12; group A calves were given a single oral bolus containing 2.5 g sulphathiazole and 1 g trimethoprim in a sustained-release formulation; group B received the same doses of the drugs but the trimethoprim was not in a sustained-release formulation; group C received a bolus containing 2.5 g sulphathiazole and 0.5 g conventional trimethoprim. Blood samples were collected at intervals for two days, the serum was separated and the composite antibacterial activity profiles of the mixture were analysed by an agar-diffusion microbiological method. The mean maximum activities in the serum of the three groups were 23.4 microg/ml in group A, 9.25 microg/ml in group B and 8.01 microg/ml in group C. The mean areas under the curves of the serum activity time curves were 838 microg/ml/hour in group A, 216 microg/ml/hour in group B and 182 microg/ml/hour in group C.

Effects of trimethoprim and rifampin on the pharmacokinetics of the cytochrome P450 2C8 substrate rosiglitazone

BACKGROUND

Trimethoprim is a relatively selective inhibitor of the cytochrome P450 (CYP) 2C8 enzyme in vitro. Rifampin (INN, rifampicin) is a potent inducer of several CYP enzymes, and in vitro studies have suggested that it also induces CYP2C8.

OBJECTIVE

Our aims were to investigate possible effects of trimethoprim and rifampin on CYP2C8 activity by use of rosiglitazone, a thiazolidinedione antidiabetic drug metabolized primarily by CYP2C8, as an in vivo probe.

METHODS

Two separate randomized crossover studies with 2 phases were conducted. In study 1, 10 healthy volunteers took 160 mg trimethoprim or placebo orally twice daily for 4 days. On day 3, they ingested a single 4-mg dose of rosiglitazone. In study 2, 10 healthy volunteers took 600 mg rifampin or placebo orally once daily for 5 days. On day 6, they ingested a single 4-mg dose of rosiglitazone. In both studies, plasma rosiglitazone and N -desmethylrosiglitazone concentrations were measured for up to 48 hours. Results In study 1, trimethoprim raised the area under the plasma rosiglitazone concentration-time curve [AUC(0- infinity )] by 37% (range, 16% to 51%; P <.0001) and the peak plasma rosiglitazone concentration (C max ) by 14% (range, -3% to 38%; P =.0014). The elimination half-life (t 1/2 ) of rosiglitazone was prolonged from 3.8 to 4.8 hours ( P =.0013). Trimethoprim reduced the formation of N -desmethylrosiglitazone. In study 2, rifampin reduced the AUC(0- infinity ) and C max of rosiglitazone by 54% (range, 46% to 63%; P <.0001) and 28% (range, 2% to 56%; P =.0003), respectively. The t 1/2 of rosiglitazone was shortened from 3.8 to 1.9 hours ( P <.0001). Rifampin increased the formation of N -desmethylrosiglitazone.

CONCLUSIONS

Trimethoprim raises and rifampin reduces the plasma concentrations of rosiglitazone by inhibiting and inducing, respectively, the CYP2C8-catalyzed biotransformation of rosiglitazone.

Physiologically based pharmacokinetic (PBPK) modeling of disposition of epiroprim in humans

The objective of this study was to use in synergy physiologically based and empirical approaches to estimate the drug-specific input parameters of PBPK models of disposition to simulate the plasma concentration-time profile of epiroprim in human. The estimated input parameters were the tissue:plasma partition coefficients (Pt:p) for distribution and the blood clearance (CL) for the in vivo conditions. Epiroprim represents a challenge for such methods, because it shows large interspecies differences in its pharmacokinetic properties. Two approaches were used to predict the human Pt:p values: the tissue composition model (TCM) and the "Arundel approach" based on the volume of distribution at steady state (Vdss) determined in vivo in the rat. CL in human was predicted by (1) conventional allometric scaling of in vivo animal clearances (CAS), (2) physiologically based direct scaling up of in vitro hepatocyte data (DSU), and (3) allometric scaling of animal intrinsic in vivo blood CL normalized by the ratios of animal:human intrinsic clearances determined in vitro with hepatocytes (NAS). The performance of prediction was assessed by comparing separately the above pharmacokinetic parameters (Vdss estimated from the Pt:p values and blood CL) with the corresponding in vivo data obtained from the plasma kinetic profiles. These input parameters were used in PBPK models, and the resulting plasma concentration-time profiles of epiroprim were compared with those observed in rat and human. Previously to the construction of the human PBPK model, a model for the rat was also developed to gain more confidence on the model structure and assumptions. Overall, using the TCM and the NAS for the parameterization of the distribution and clearance, respectively, the PBPK model gave the more accurate predictions of epiroprim's disposition in human. This study represents therefore an attractive approach, which may potentially help the clinical candidate selection.

Pharmacokinetics and oral bioavailability of sulfadiazine and trimethoprim in broiler chickens

Sulfonamides and trimethoprim are chemotherapeutics that are extensively used in various animal species. Little information about the pharmacokinetics of these compounds in chickens exists in the literature. In this study, a new commercial formulation of sulfadiazine in combination with trimethoprim was administered both intravenously and orally, according to a crossover design, to healthy, 7-week-old broilers. The plasma concentrations of the drugs were determined by validated high-performance liquid chromatographic methods, and pharmacokinetic parameters were calculated. After intravenous or oral administration of trimethoprim (6.67 mg/kg body weight) and sulfadiazine (33.34 mg/kg body weight), both active substances were rapidly eliminated from the plasma. There was a mean half-life of 1.61 h for trimethoprim and 3.2 h for sulfadiazine. The apparent volumes of distribution (2.2 and 0.43 L/kg, respectively, indicated that the tissue distribution of trimethoprim was more extensive than that of sulfadiazine. The oral bioavailability was approximately 80% for both components.

Efficacy of trimethoprim-sulfadoxine against Escherichia coli in a tissue cage model in calves

Tissue cages implanted subcutaneously in calves were infected with Escherichia coli. Twenty-four hours later, the calves were treated either with single doses of 2.5 + 12.5 or 5 + 25 mg/kg trimethoprim (TMP) + sulfadoxine (SDX) or with five doses of 7.5 + 37.5 mg/kg TMP + SDX at 12-h intervals. In addition, one cage in each of three calves in the highest dose group was infected 3 h after initiation of treatment. Untreated calves were kept as controls. Concentrations of TMP and SDX in plasma and tissue cage fluid (TCF) and counts of viable bacteria in TCF were determined. In the highest dose group, concentrations of TMP in TCF remained above the minimum inhibitory concentration of the test strain for 94-101 h and peak to minimum inhibitory concentration (MIC) ratio was close to 10. In spite of this, an effect of treatment was noted only in cages infected after initiation of treatment. In vitro studies and analysis of thymidine content in serum and TCF from calves suggest that levels of thymidine in TCF are high enough to antagonize the antibacterial effect of TMP. The results indicate that soft tissue infections in secluded infection sites of calves are refractory to treatment with TMP + SDX.

Penetration of topically administered ofloxacin and trimethoprim into aqueous humor

Ocular penetration of two topical antibiotics used to treat bacterial conjunctivitis was assessed in adult volunteers scheduled for cataract surgery. In this randomized, parallel-group study, patients instilled trimethoprim sulfate 0.1%/polymyxin B (n = 23) or ofloxacin 0.3% (n = 25) QID for 3 days, plus 4 instillations in the hour before surgery. Analysis of aqueous humor samples obtained during surgery showed a 2.4-fold greater concentration of ofloxacin over trimethoprim (1.135 micro g/ml vs 0.470 micro g/ml; P <.0001). The greater concentration of ofloxacin in ocular tissue coupled with its superior antibacterial activity profile supports its use as an alternative to trimethoprim/polymyxin B for treatment of bacterial conjunctivitis.

Distribution of orally administered trimethoprim and sulfadiazine into noninfected subcutaneous tissue chambers in adult ponies

The distribution of trimethoprim (TMP) and sulfadiazine (SDZ) into subcutaneously implanted noninfected tissue chambers was studied in healthy adult ponies. Six ponies were given an oral TMP/SDZ paste formulation at a dose of 5 mg/kg TMP and 25 mg/kg SDZ at 12 h intervals for 2 days in order to reach steady-state concentrations. Plasma concentrations and tissue chamber fluid (TCF) concentrations of both drugs were measured at regular intervals during a period commencing 24 h after the last oral administration. The peak concentration of TMP (mean +/- SD) was 2.92 +/- 0.86 microg/mL for plasma and 1.09 +/- 0.25 microg/mL for TCF. For SDZ, the mean peak concentration was 40.20 +/- 14.74 microg/mL for plasma and 23.48 +/- 5.84 microg/mL for TCF. TMP peak concentrations in plasma were reached at 3.17 +/- 03.48 h and those in TCF at 7.33 +/- 03.72 h. SDZ peak concentrations in plasma were reached at 1.83 +/- 02.04 h and those in TCF at 8.00 +/- 03.10 h. Concentrations of TMP and SDZ in TCF remained above the generally accepted breakpoint for susceptibility (0.5/9.5 for the TMP/SDZ combination) for 12 h. Therefore, in ponies oral administration of TMP/SDZ at a dose rate of 30 mg/kg given twice daily in the form of a paste should be appropriate for effective treatment of infections caused by susceptible bacteria.

New simple liquid chromatographic method for the determination of trimethoprim, sulfadiazine and N4-acetylsulfadiazine in plasma of broilers

A new method for simultaneous quantification of trimethoprim, sulfadiazine and N4-acetylsulfadiazine in plasma of broilers at levels down to 13-16 ng/ml has been developed. Samples were deproteinized with acetonitrile, defatted with hexane, and extracted with dichloromethane. Chromatographic analysis was carried out on a C18 column in the presence of tetrabutylammonium hydrogen sulfate, a competing base, while detection was performed at 240 nm for trimethoprim, and 270 nm for both sulfadiazine and N4-acetylsulfadiazine. Accuracy and precision data showed recoveries and relative standard deviation values better than 87.3% and 3.1%, respectively, for all three analytes. The good analytical characteristics of the method could allow limits of detection in the low ng/ml range to be realised. The method was successfully applied to determine drug concentrations in plasma samples from broilers administered a combination of sulfadiazine and trimethoprim.

[Skin penetration of sulfamethoxazole and trimethoprim after oral administration]

The aim of this study was to determine the penetration of trimethoprim, sulphamethoxazole and its main metabolite--N4-acetylsulphamethoxazole into cantharidin-induced skin blister fluid following administration of a single oral combination dose of 320 mg trimethoprim and 1600 mg sulphamethoxazole. Moreover, penetration of the two drugs into skin blister fluid was compared with penetration into the theoretical peripheral compartment calculated on the basis of plasma levels found. The material consisted of 12 male patients with bacterial skin diseases, treated at the Department of Dermatology and Venerology, Pomeranian Academy of Medicine in Szczecin. The age of the patients was 19-64 years (mean 42 +/- 14), weight 61-112 kg (mean 77 +/- 15), height 166-196 cm (mean 175 +/- 8). Prior to enrollment, normal function of gastrointestinal tract, liver and kidneys, and absence of allergy to the drugs studied was ascertained. The susceptibility of pathogens of cotrimoxazole (trimethoprim + sulphamethoxazole) was confirmed with bacteriological tests. Skin blisters were induced by applying 0.25% cantharidin ointment. Drug concentrations in plasma and skin blister fluid were measured with high-performance liquid chromatography. Peak concentrations of trimethoprim in plasma and skin blister fluid were 8.5 +/- 1.1 mumol/L after 3 +/- 1 h and 5.6 +/- 0.8 mumol/L after 7 +/- 2 h, respectively. The differences between both compartments as to parameters measured were statistically significant. In the theoretical peripheral compartment, peak concentration was 5.8 +/- 2.2 mumol/L after 9 +/- 6 h. Half-times of trimethoprim in plasma and skin blister fluid were 11.1 +/- 4.5 h and 12.3 +/- 4.9 h, respectively, and did not differ significantly. The degree of drug penetration into blister fluid defined as the ratio of area under concentration-time curves for blister fluid and plasma was 0.94 +/- 0.23. The differences between pharmacokinetic parameters of trimethoprim in skin blister fluid and theoretical peripheral compartment were not significant. Peak concentrations of sulphamethoxazole in plasma and skin blister fluid were 295 +/- 47 mumol/L after 3 +/- 1 h and 182 +/- 46 mumol/L after 8 +/- 2 h, respectively. The differences between both compartments as to parameters measured were statistically significant. In the theoretical peripheral compartment, peak concentration was 239 +/- 58 mumol/L after 7 +/- 4 h. Half-times of sulphamethoxazole in skin blister fluid and plasma were 9.7 +/- 3.3 h and 10.0 +/- 1.1 h, respectively and did not differ significantly. The drug penetrated into blister fluid to a high extent, although less than trimethoprim, the degree of penetration being 0.82 +/- 0.21. The majority of pharmacokinetic parameters in blister fluid and theoretical peripheral compartment did not differ significantly except for time to peak concentration. Peak concentration of N4-acetylsulphamethoxazole, the main metabolite of sulphamethoxazole, was significantly lower in blister fluid than plasma and took longer to achieve. The half-time of the metabolite was significantly longer in blister fluid than in plasma, whereas the ratio of area under concentration-time curves in these two biological fluids of 0.86 +/- 0.18 was similar to that of the parent drug. The results show that both trimethoprim and sulphamethoxazole administered together penetrate from plasma into skin blister fluid to a great extent and achieve concentrations exceeding the MIC for susceptible pathogens. This finding confirms the usefulness of this treatment in bacterial skin diseases. The cantharidin-induced skin blister is a useful technique to determine the penetration into skin of a drug and its metabolite and to evaluate pharmacokinetic parameters. In some cases, this test cannot be replaced with theoretical calculations based on drug concentrations in blood.

Depletion study of trimethoprim and sulphadiazine in milk and its relationship with mastitis pathogenic bacteria strains minimum inhibitory concentrations (MICs) in dairy cows

Time-related concentrations in milk of a combination of trimethoprim-sulphadiazine (TMP-SDZ) intramammary formulated infusion and its relationship with pathogenic bacteria strains minimum inhibitory concentrations (MICs) isolated from clinical mastitis cows were analysed. The MICs study was performed for Escherichia coli, Staphylococcus aureus and Streptococcus sp. strains. The SDZ concentrations in milk were analysed using high-performance liquid chromatography (HPLC) and TMP using a microbiological assay. Ten lactating cows milked three times daily were used in the time-concentration studies of TMP-SDZ. Milk samples (approximately 20 mL) from the treated mammary quarters were taken at 6, 12, 24, 30 and 36 h after first administration. In order to define the withdrawal time, milk samples from the treated mammary quarters were taken at 24, 36, 48, 72, 84 and 96 h, after finishing the therapy. The MICs fluctuated between 1 and 8 microg/mL. Effective therapeutic concentrations lasted for 36 h when intramammary infusion was repeated three times every 12 h. No TMP was detected in milk for 24 h after finishing therapy. Milk SDZ concentrations were below 0.1 microg/mL in all treated cows after 84 h finishing therapy. At 96 h after finishing therapy, no SDZ milk concentrations were found in six animals, although four animals of the experimental group still had concentrations of 0.07 microg/mL.

Pharmacokinetics of sulphadoxine and trimethoprim and tissue irritation caused by two sulphadoxine-trimethoprim containing products after subcutaneous administration in pre-ruminant calves

The pharmacokinetics of sulphadoxine-trimethoprim was studied in 6 pre-ruminant calves using two different products. Product A, which contained 200 mg sulphadoxine and 40 mg trimethoprim per mL, was administered intravenously or subcutaneously at a dosage of 25 mg sulphadoxine and 5 mg trimethoprim.kg-1 bodyweight. Product B, containing 62.5 mg sulphadoxine and 12.5 mg trimethoprim per mL plus lidocaine (1 mg.mL-1), was given subcutaneously at the same dosage. After intravenous administration of product A the mean time of half-life of elimination phase (t1/2) for sulphadoxine was 12.9 h, steady-state volume of distribution (Vd(ss)) was 0.44 L.kg-1 and clearance was 0.024 L.kg-1.h-1. Respective values for trimethoprim were 1.9 h, 2.0 L.kg-1 and 0.9 L.kg-1.h-1. After subcutaneous administration, the bioavailability of sulphadoxine was 96% and 98% and the time to reach a maximum concentration was 6.3 and 8.0 h for products A and B, respectively. The Cmax for trimethoprim was higher for product A (0.49 microgram.mL-1) than for product B (0.32 microgram.mL-1) (p = 0.014). Slow absorption from the injection site appeared to delay the elimination of trimethoprim after subcutaneous administration when compared to that after intravenous administration: apparent elimination t1/2 for trimethoprim after intravenous administration of product A was 1.9 h compared to 3.9 h and 3.6 h after subcutaneous administration of products A and B, respectively. The difference between intravenous and subcutaneous administrations was statistically significant (p < 0.05). Also the mean residence time was significantly shorter (p < 0.05) after intravenous administration (2.4 h) than that after subcutaneous administration of product A (6.9 h) and B (7.1 h). The bioavailability of trimethoprim was lower than that of sulphadoxine: 76% and 74% for products A and B, respectively. All 6 calves showed pain after subcutaneous administration of product A and the injection sites were warm and showed soft oedematous reactions 5-8 cm in diameter. Three of the calves also showed some pain after subcutaneous administration of product B; the local reactions were less severe. A marked increase was seen in creatine kinase activity after subcutaneous administration of both products. Product A caused a more pronounced increase but the difference was not statistically significant. We suggest 30 mg.kg-1 at 24-h intervals or alternatively 15 mg.kg-1 at 12-h intervals as the minimum dosage of sulphadoxine-trimethoprim combination for pre-ruminant calves. Extravascular routes of administration should be avoided due to marked tissue irritation at the injection site.

Patient recruitment--European perspective

A considerable number of patients have to be recruited in a clinical trial to obtain solid results. In pediatric studies, patient recruitment is frequently problematic. In the simple common childhood illnesses, the number of recruitable patients is certainly large, but they may be hard to reach, and the imbalance between potential benefit and inconvenience of participation may reduce motivation to enroll. In severe diseases, the balance may be right, but the available number of patients may be small. Good communication with the child and family, as well as the motivation of colleagues to admit, is another key element in success. Proper study design, including realistically identified sources of patients, reasonable inclusion, and exclusion criteria, also are required.

The pharmacokinetics and safety profile of oral ganciclovir in combination with trimethoprim in HIV- and CMV-seropositive patients

AIMS

We investigated the pharmacokinetics and safety profile of oral ganciclovir coadministered with trimethoprim in HIV-and CMV-seropositive patients.

METHODS

In an open-label, randomized, 3-way crossover study, 12 adult males received oral ganciclovir 1000 mg every 8h, oral trimethoprim 200 mg once daily, or both drugs concomitantly in a sequence of three 7-day treatment periods. Pharmacokinetic parameters were determined and adverse events recorded for each treatment.

RESULTS

The presence of trimethoprim significantly decreased CLr (12.9%, P=0.0068) and increased t1/2 (18.1%, P=0.0378) of ganciclovir. However, these changes are unlikely to be clinically meaningful. There were no statistically significant changes in trimethoprim pharmacokinetic parameters in the presence of ganciclovir, with the exception of a 12.7% increase in Cmin. Ganciclovir was well tolerated when administered alone or in combination with trimethoprin.

CONCLUSIONS

There was no clinically significant pharmacokinetic interaction between oral ganciclovir and trimethoprim when coadministered.

Influence of crystal habit on trimethoprim suspension formulation

PURPOSE

The role of crystal habit in influencing the physical stability and pharmacokinetics of trimethoprim suspensions was examined.

METHODS

Different habits for trimethoprim (TMP) were obtained by recrystallizing the commercial sample (PD) utilizing solvent-change precipitation method. Four distinct habits (microscopic observation) belonging to the same polymorphic state (DSC studies) were selected for studies. Preformulation and formulation studies were carried out on suspension dosage forms containing these crystals. The freshly prepared suspensions were also evaluated for their pharmacokinetic behaviour on healthy human volunteers using a cross over study.

RESULTS

Variation of crystallization conditions produces different habits of TMP. Among the different crystal habits exhibiting same polymorphic state, the most anisometric crystal showed best physical stability in terms of sedimentation volume and redispersibility. However, habit did not significantly affect the extent of TMP excreted in urine.

CONCLUSIONS

Modification of surface morphology without significantly altering the polymorphic state can be utilized for improving physical stability of TMP suspensions. However, the pharmacokinetic profile remains unaltered.

Repeated administration of trimethoprim/sulfadiazine in the horse--pharmacokinetics, plasma protein binding and influence on the intestinal microflora

Six healthy adult horses were given repeated administrations of trimethoprim/ sulfadiazine (TMP/SDZ) intravenously (i.v.) (2.5 mg/kg TMP and 12.5 mg/kg SDZ) and orally (p.o.) as a paste (5 mg/kg TMP and 25 mg/kg SDZ). Both formulations were given twice daily for 5 days, with a 3-week interval between i.v. and oral administration. The influence of the drug combination on the intestinal microflora was examined and the plasma concentrations, pharmacokinetic parameters and plasma protein binding were determined. There were no major changes in the bacterial intestinal flora and no clinical evidence of gastrointestinal disturbances following the i.v. and oral TMP/SDZ administration. An initial reduction in the number of coliform bacteria during the treatment was notable, though with no evident difference between i.v. and oral treatment. The minimum concentration during a dose interval at steady state (Cminss), the elimination half-life (t1/2beta) and the mean residence time (MRT) were significantly greater after oral administration compared to i.v. for both TMP and SDZ. The plasma protein binding was measured to be 20% for SDZ and 35% for TMP. Oral administration of TMP/SDZ in a dose of 30 mg/kg given twice daily in the form of paste appeared as a satisfactory method for obtaining plasma levels above MIC (minimum inhibitory concentration in vitro) values during the interdosing interval.

Polyphosphazene membranes and microspheres in periodontal diseases and implant surgery

Membranes or microcapsules made from polyphosphazenes bearing amino acid side groups are proposed for the treatment of periodontal diseases. Polyphosphazene membranes, prepared with alanine ethyl ester and imidazole in the molar ratio of 80:20 as phosphorus substituents, gave a degradation rate that corresponded to the healing of the bone defect. These membranes were much more successful in promoting healing of rabbit tibia defects than polytetrafluoroethylene membranes. Antibacterial or anti-inflammatory drugs, useful in periodontal tissue regeneration, could be entrapped in the polyphosphazene membranes and released both in vitro and in vivo at a rate that ensured therapeutic concentrations in the surrounding tissue. Polyphosphazene microspheres, prepared with phenylalanine ethyl ester as a phosphorus substituent and loaded with succinylsulphathiazole or naproxen, were also obtained. The kinetics of release from these matrices were very convenient in yielding local concentrations of the two drugs that are useful per se or when mixed with hydroxyapatite for better bone formation.

Pharmacokinetics of sulphadiazine-trimethoprim in lactating dairy cows

Five Finnish Ayrshire cows in mid or end-lactation were treated with 40 mg sulphadiazine/kg and 8 mg trimethoprim/kg using intravenous (i.v.), intramuscular (i.m.) and subcutaneous (s.c.) routes. Elimination of sulphadiazine was not affected by the route of administration (median t1/2 4.4-5.0 h) while elimination of trimethoprim was strongly limited by slow absorption from the injection site after s.c. and i.m. administration (median for apparent t1/2 21-25 h) compared to that after i.v. administration (median t1/2 1.2 h; p < 0.05). The median bioavailability of trimethoprim was also decreased, being 37% and 55% after s.c. and i.m. administration, respectively. When i.v. administration was used, trimethoprim concentration exceeded 0.1 mg/l in milk between 0.15-8 h while sulphadiazine concentrations above 2 mg/l were maintained from 0.5-2 h to 8 h. After s.c. and i.m. administration sulphadiazine in milk behaved similar to that after i.v. administration, while trimethoprim time-concentration curves were flat and trimethoprim concentrations were around 0.1 mg/l for an extended period of time (8-12 h). Median Cmax values in milk were only 0.07 mg/l and 0.10 mg/l for s.c. and i.m. administrations, respectively. After s.c. administration, 4 out of 5 cows showed signs of pain. After i.m. administration, 2 of the cows showed clear signs of pain and one had some local tenderness at the site of injection.

[Experiences with the rectal use of a chemotherapeutic agent. 1. In vitro biopharmaceutical examinations; selection of the optimal vehicle]

The factors influencing in vitro liberation (Part 1) and in vivo absorption (Part 2) from trimethoprim-containing rectal suppositories and the authors' results related to them are reported in this two-part publication. Special emphasis was laid on selecting the optimal suppository base which is harmless physiologically yet not indifferent pharmacologically. From among the 24 compositions studied, a lipophilic mixture containing a surface active additive (Witepsol W 35) and a hydrophilic (Macrogolum) mixture were found to be the best in all respects. Liberation from the trimethoprim-containing rectal suppositories was measured with in vitro dynamic diffusion and spectrophotometrically. A power relation was found to exist between the quantity of the released pharmacon and the diffusion time, and a significant negative exponential relation was observed between the doses and their respective in vitro availability values.

[Experiences with the rectal use of chemotherapeutic agents. 2. Pharmacokinetic examinations with animals]

The aim of the investigations was to optimise vehicle for trimethoprim (TMP) suppositories ready for clinical trials. The rectal absorption of TMP was studied in anaesthetized rats. The drug liberation properties of the five mixed vehicles with promising in vitro results (Part 1.) were studied. The course of the blood level curves was monitored with serial sampling. The TMP concentration of blood was determined by bioassay. Individual bases were compared with the use of the pharmacokinetic parameters derived from the analysis of the obtained blood level curves, with special respect to biological availability (BA). The extent of bioavailability is influenced considerably by the hydro-, lipo- or lipohydrophilic property of the vehicle. TMP, if incorporated in the proper vehicle, is absorbed well. With three vehicles the extent of absorption exceeded the absorption seen with oral administration on the same model (BA = 38.8%). The best results were achieved with the lipophilic base Witepsol W 35 containing 10% of Polysorbate 20 and 10% of Polysorbate 61 (BA = 63.8%) and with Witepsol W 35 containing 10% of Polysorbate 60 (BA = 64.9%). The hydrophilic Macrogol 1540 vehicle containing 5% of Macrogol 400 had only slightly worse results (BA = 52.9%). In the case of the lipohydrophilic Witepsol W 35 vehicle with 10% of Polysorbate 20 and 10% of Polysorbate 61 content a significant negative exponential relation was found between the administered doses and their respective bioavailability values, this tendency had been observed during the in vitro examinations, too. No such relation was found in the case of the lipophilic Witepsol W 35 vehicle containing 10% of Miglyol 812.

Pharmacokinetics of sulfonamides and trimethoprim in the donkey (Equus asinus)

The body disposition of sulfadimidine (SDM), sulfadiazine (SDZ), sulfamethoxypyridazine (SMPZ) and a trimethoprim-sulfadimethoxine combination (TMP-SDMX) was investigated in the donkey. The four sulfonamides and TMP were injected intravenously at doses of 20 mg/kg (SDM, SDZ, SMPZ), 12.5 mg/kg (SDMX) and 2.5 mg/kg (TMP). The body clearance (ClB) of SDZ (1.70 +/- 0.14 ml/min/kg) was significantly higher than those of SDM (1.13 +/- 0.18 ml/min/kg), SMPZ (1.10 +/- 0.09 ml/min/kg) and SDMX (0.75 +/- 0.04 ml/min/kg). In contrast, the volume of distribution at steady state (Vss) was similar for the four sulfonamides (0.68 +/- 0.08 L/kg, 0.63 +/- 0.07 L/kg, 0.47 +/- 0.06 L/kg, and 0.46 +/- 0.05 L/kg for SDM, SDZ, SMPZ and SDMX, respectively). Both ClB and Vss were significantly higher for TMP (4.36 +/- 0.60 ml/min/kg and 2.71 +/- 0.86 L/kg) than for sulfonamides. Antipyrine ClB (3.49 +/- 0.35 ml/min/kg) and Vss (0.66 +/- 0.16 L/kg), determined in order to assess hepatic oxidative function and total body water volume, respectively, were either different from (ClB), or similar to (Vss), values calculated for sulfonamides. The results obtained were compared to those reported in horses.

Concentrations of sulfadoxine and trimethoprim in plasma, lymph fluids and some tissues 24 h after intramuscular administration to Angora goats

This study was carried out to determine the concentrations of sulfadoxine and trimethoprim in plasma, lymph, and some tissues in goats after administration of a single recommended therapeutic dose. Five healthy, adult Angora goats were used. The drug combination, containing 200 mg sulfadoxine and 40 mg trimethoprim per millilitre, was given as a single IM injection at the recommended dose level, 15 mg/kg body weight for sulfadoxine and 3 mg/kg body weight for trimethoprim. The goats were slaughtered 24 hours after drug administration and samples were taken from liver, bone marrow, pelvic limb muscles, hepatic, thoracic duct, and the pelvic limb lymph fluids for analysis of drug concentrations by HPLC. The concentrations of trimethoprim in bone marrow, liver, pelvic limb muscles, hepatic lymph, the pelvic limb lymph, and thoracic duct lymph were found to be 6, 5, 4, 2, 5 and 15 times higher than those of plasma, respectively. Although the sulfadoxine concentrations in bone marrow, pelvic limb muscles, and liver were 2, 3 and 2 times higher than the plasma concentrations, respectively, the sulfadoxine concentrations in hepatic lymph, the pelvic limb lymph, and thoracic duct lymph were lower than those of plasma. The results show that the trimethoprim concentrations in lymph fluids were quite similar to those in tissues. However, the sulfadoxine concentrations in lymph fluids were different in each tissue.

A silicone ventricular catheter coated with a combination of rifampin and trimethoprim for the prevention of catheter-related infections

So-called antiinfective catheters which are generated by incorporation of antimicrobial substances into polymers appear to be effectful devices in the prevention of catheter related infections. Such devices mainly act by prevention of bacterial colonization of the catheter surface rather than by inhibition of adherence. In a preceding study, we developed a rifampin-containing silicone catheter for the prevention of ventricular shunt infection. In the present study, this work was continued with a combination of antimicrobials incorporated in silicone ventricular catheters to reduce the risk of rifampin resistance and to expand the antimicrobial spectrum. We found that the drug release kinetics could be greatly influenced by the incorporation conditions. It was possible to incorporate an optimal antibiotic combination of rifampin and trimethoprim into the polymer resulting in defined release rates and a defined total release. A catheter loaded with this combination showed an excellent reduction of the colonization with Staphylococcus aureus (99.97% reduction within 3 hours) under in-vitro conditions.

A population pharmacokinetic model of trimethoprim in patients with pneumocystis pneumonia, made with parametric and nonparametric methods

A population pharmacokinetic model of intravenously and orally administered trimethoprim in patients with acquired immunodeficiency syndrome and Pneumocystis carinii pneumonia has been made using a parametric iterative two-stage Bayesian and a nonparametric expectation maximization computer program. When good information was present in the serum level data, both methods obtained similar results. With the nonparametric expectation maximization program, the median apparent rate constant for absorption (Ka) was 1.602 hr-1, median slope (Ks) of the relationship between creatinine clearance and elimination was 0.001168 hr-1, median apparent volume of distribution (Vs) was 1.058 l/kg, and median fraction of oral dose absorbed (Fa) was 0.955. These results permit dosage individualization adjusted to body weight and renal function to achieve chosen serum level peak and trough goals. Peak goals of 9 ug/ml and trough goals of 5 ug/ml appear reasonable for most patients in this population, and should permit most to complete an effective course of therapy with a reduced risk for treatment-terminating hematologic toxicity. However, therapeutic goals should always be selected based on each patient's apparent need for the drug and the risk of toxicity that is justifiably acceptable to obtain the expected benefits of the drug.

Experiences with the rectal use of trimethoprim

The possibility of rectal use of trimethoprim was studied. The in-vitro liberation of the drug from 24 different suppository bases was examined and the results used to select bases for in-vivo examination. The in-vitro liberation from the suppositories containing 50-200 mg trimethoprim was studied by the method of dynamic diffusion, and the released drug content was measured spectrophotometrically. The in-vivo examinations were performed in anaesthetized rats. The concentration of trimethoprim in blood was determined by bioassay. The absorption of the drug in the form of oral suspension, rectal solution and suppository was also studied. The pharmacokinetic parameters obtained after blood-level curve fitting were compared by use of the MedUSA 1.6 program. The best in-vivo results were achieved with the lipohydrophilic Witepsol W 35 vehicle containing 10% polysorbate 20 and 10% polysorbate 61 (bioavailability = 63.8%) and with Witepsol W 35 containing 10% polysorbate 60 (bioavailability = 63.8%). The results for hydrophilic Macrogol 1540 vehicle containing 5% of Macrogol 400 were only slightly worse (bioavailability = 52.9%). In the case of the lipohydrophilic Witepsol W 35 vehicle with 10% polysorbate 20 and 10% polysorbate 61 content a significant negative exponential relationship was found between the administered doses and their respective bioavailability values; this tendency was also observed during in-vitro examinations. When incorporated in the appropriate vehicle trimethoprim was absorbed well. With three vehicles the extent of absorption exceeded that for oral administration on the same model (bioavailability = 38.8%). Trimethoprim rectal suppositories, which are formulated with the vehicles having the best in-vitro and in-vivo results, are suitable for clinical pharmacological investigation.

Interspecies comparisons of plasma half-life of trimethoprim in relation to body mass

The relationship between body mass and plasma half-life of trimethoprim was studied in 10 different species of animals and man using published data. Log half-life was positively and significantly correlated to log body mass based on individual measurements in herbivorous animals (n = 23, P < 0.01), in herbivorous animals+pigs (n = 29, P < 0.01), in ungulates (n = 27, P < 0.01), in ruminants (n = 16, P < 0.01) and in non-herbivorous mammals, except pigs (n = 6, P < 0.05). The correlation was described by the allometric equations: t 1/2 beta = 27 W0.26 in herbivorous animals and t 1/2 beta = 125 W0.32 in non-herbivorous animals except pigs.

A study of the pharmacokinetics and tissue residues of an oral trimethoprim/sulphadiazine formulation in healthy pigs

Twenty-six healthy female pigs weighing 19.5-33 kg were used in three separate experiments. The animals were fed individually twice a day. Trimethoprim/sulphadiazine (TMP/SDZ) formulation was added to feed in the amount of 6 mg/kg bw (TMP) and 30 mg/kg bw (SDZ). TMP and SDZ concentrations in blood plasma, muscles, liver and kidneys were measured. Pharmacokinetic parameters show that the absorption of TMP from the alimentary tract in pigs is faster than the absorption of SDZ, and the elimination of TMP is slower than that of SDZ. The absorption half-lives were 0.96 (TMP) and 2.24 h (SDZ), whereas elimination half-lives were 5.49 (TMP) and 4.19 h (SDZ). The observed TMP:SDZ ratios in blood plasma after multiple dose administration ranged from 1:11.4 to 1:23.2. One day after administration of the last dose of TMP/SDZ the plasma concentration ratio was 1:15.5, but in muscles, liver and kidneys it was much lower: 1:0.79, 1:0.14 and 1:1.53 respectively. The absolute TMP and SDZ tissue concentrations 1 day after the last multiple dose administration were very low (maximum TMP: 0.29 micrograms/g in liver; maximum SDZ: 0.23 micrograms/g in kidneys). Neither drug was detected in any tissue 8 days after the last administration of TMP/SDZ. Based on our results, it was concluded that there is no support for the TMP:SDZ pharmaceutical ratio 1:5 in oral formulations of these compounds for pigs. The administration oral TMP/SDZ formulations once a day may result in the absolute tissue concentrations of these drugs being too low for antibacterial activity. The withdrawal period for such an oral TMP/SDZ formulation for pigs (according to accepted guidelines in Europe for MRL of TMP < 0.05 mg/kg of tissue) should not be less than 5 days.

The disposition of five therapeutically important antimicrobial agents in llamas

The disposition of five therapeutic antimicrobial agents was studied in llamas (Lama glama) following intravenous bolus administration. Six llamas were each given ampicillin, tobramycin, trimethoprim, sulfamethoxazole, enrofloxacin and ceftiofur at a dose of 12 mg/kg, 1 mg/kg, 3 mg/kg, 15 mg/kg, 5 mg/kg, and 2.2 mg/kg of body weight, respectively, with a wash out period of at least 3 days between treatments. Plasma concentrations of these antimicrobial agents over 12 h following i.v. bolus dosing were determined by reverse phase HPLC. Disposition of the five antimicrobial agents was described by a two compartment open model with elimination from the central compartment, and also by non-compartmental methods. From compartmental analysis, the elimination rate constant, half-life, and apparent volume of distribution in the central compartment were determined. Statistical moment theory was used to determine noncompartmental pharmacokinetic parameters of mean residence time, clearance, and volume of distribution at steady state. Based on the disposition parameters determined, and stated assumptions of likely effective minimum inhibitory concentrations (MIC) a dose and dosing interval for each of five antimicrobial agents were suggested as 6 mg/kg every 12 h for ampicillin; 4 mg/kg once a day or 0.75 mg/kg every 8 h for tobramycin; 3.0 mg/kg/15 mg/kg every 12 h for trimethoprim/sulfamethoxazole; 5 mg/kg every 12 h for enrofloxacin; and 2.2 mg/kg every 12 h for ceftiofur sodium for llamas. Steady-state peak and trough plasma concentrations were also predicted for the drugs in this study for llamas.

In vitro and in vivo binding of trimethoprim and sulphachlorpyridazine to equine food and digesta and their stability in caecal contents

Binding of antibiotics to food has received little attention in equine medicine, although such binding could potentially reduce the bioavailability and clinical efficacy. In the present study, binding of trimethoprim (TMP) and sulphachlorpyridazine (SCP) to hay, grass silage and concentrate was investigated in vitro in buffer at pH 6.8 at different concentrations. The binding of TMP and SCP to caecal contents was also studied. In addition, the degradation of TMP and SCP by the caecal microflora was investigated by incubating sterilized and non-sterilized caecal contents for 3 h at 37 degrees C under anaerobic conditions and comparing the TMP and SCP contents. Further, a TMP/SCP powder formulation was adminstered orally with concentrate at a dose rate of 5 mg/kg TMP and 25 mg/kg SCP to three ponies with a caecum fistula; the animals were deprived of food for 8 h before administration. Blood samples, caecal contents samples and faecal samples were collected and analysed for TMP and SCP concentrations by means of high performance liquid chromatography (HPLC). Three non-fistulated ponies, acting as control animals, were fed the same dose of TMP/SCP with concentrate after 8 h of food deprivation and blood samples were taken. The percentage of in vitro binding of TMP as well as SCP to hay, grass silage and concentrate at concentrations of 4 micrograms/mL to 10 micrograms/mL was high (60-90%). TMP and SCP were also extensively bound to caecal contents (50-70%). At spiking concentrations above 10 micrograms/mL the percentage of binding decreased. There was no evidence of biodegradation of TMP or SCP in caecal contents. In vivo, both drugs could be detected in the caecal contents and in the faeces of three fistulated ponies. However, the fistulated ponies differed from the control ponies in that their TMP and SCP plasma concentrations were higher, and two fistulated ponies did not show double peaks in their plasma concentration-time curves. Therefore, the fistulated ponies did not provide an optimal model for in vivo binding studies. Despite this limitation, it can be concluded that binding of TMP and SCP to food is a major cause of the limited bioavailability of these drugs in the horse. It is hypothesized that the binding is reversible, and that a second absorption phase occurs in the large intestine, but part of the administered dose remains bound as both drugs were found in the faeces.

Accumulation of trimethoprim, sulfamethoxazole, and N-acetylsulfamethoxazole in fish and shrimp fed medicated Artemia franciscana

In a previous paper (H.J. Nelis, P. Léger, P. Sorgeloos, and A. P. De Leenheer, Antimicrob. Agents Chemother. 35:2486-2489, 1991) it was reported that two selected antibacterial agents, i.e., trimethoprim and sulfamethoxazole, can be efficiently bioencapsulated in nauplii of the brine shrimp Artemia franciscana for administration to fish. This follow-up study showed that larvae of the sea bass and the turbot as well as postlarvae of the white shrimp accumulate the therapeutic agents in high quantities when fed medicated A. franciscana. To monitor their levels as a function of time, the liquid chromatographic method originally developed for the analysis of A. franciscana was modified with respect to chromatography, internal standardization, and sample pretreatment. The levels of trimethoprim ranged from 1 to 7 micrograms/g (sea bass), 1 to 13 micrograms/g (turbot), and 4 to 38 micrograms/g (white shrimp). The corresponding values for sulfamethoxazole were 0.3 to 4 micrograms/g (sea bass), 1 to 42 micrograms/g (turbot), and 4 to 35 micrograms/g (white shrimp). Only the two fish species, unlike the shrimp, metabolized the latter to N-acetylsulfamethoxazole (concentration range, 1 to 10 micrograms/g). These data suggest the potential of the bioencapsulation of therapeutic agents in live food as a tool to control infectious diseases in aquaculture. A preliminary challenge test also confirmed the in vivo efficacy of this approach.

[Demonstration of activity of two potentiated sulfonamides in feces of horses after oral or intravenous administration]

Both, the oral and intravenous application of two trimethoprim-potentiated sulfonamides induced measurable antibacterial activities in the feces of horses. With regard to the risk of antibiotic-induced alterations of the gastrointestinal flora, the route of application of potentiated sulfonamides seems to be of minor importance. The antibiotics used were Sulfadimethoxine/Trimethoprim (Trafigal 30% ad us. vet.) for oral and Sulfadoxine/Trimethoprim (Borgal 24% ad us. vet., both Hoechst AG, Frankfurt) for intravenous application. As recommended, both drugs were given in a dose of 20 mg per kg bodyweight. The detection method is based on a procedure layed down in German laws for sulfonamide residues in meat-samples and has undergone some modifications for the examination of feces.

Contribution of alpha 1-acid glycoprotein to plasma protein binding of some basic antimicrobials in pigs

Protein binding kinetics of basic antimicrobials including trimethoprim (TMP), erythromycin (EM), lincomycin (LM) and clindamycin (CM) were studied using porcine plasma, albumin and alpha 1-acid glycoprotein (AGP). Rosenthal plots of these basic drugs in porcine plasma suggest saturable and non-saturable binding. Dissociation constants (kd) and binding capacity (Bmax) for saturable binding were as follows: TMP, kd = 8.58 mumol/L, Bmax = 5.26 mumol/L; EM, kd = 2.72 mumol/L, Bmax = 3.06 mumol/L, LM, kd = 3.96 mumol/L, Bmax = 6.58 mumol/L and CM, kd = 4.43 mumol/L, Bmax = 21.7 mumol/L. The proportionality constants (Bmax2/kd2) for non-saturable binding were 0.29 in TMP, 0.52 in EM, 0.17 in LM and 3.2 in CM. The kds of the drugs in porcine AGP solution were determined by a fluorescence quenching method, using 1-anilino-8-naphthalene sulphonate (ANS) as a fluorescent probe: 9.51 mumol/L in TMP, 1.89 mumol/L in EM, 4.48 mumol/L in LM and 9.69 mumol/L, in CM. Comparable kd values between porcine plasma and AGP solution indicated that AGP is a major saturable binder in porcine plasma. Binding property to porcine albumin presented linearity, showing the following proportionality constants: 0.23 in TMP, 0.38 in EM, 0.01 in LM and 0.76 in CM. The comparable proportionality constants of TMP and EM between porcine plasma and albumin solution indicate that albumin is a major non-saturable binder, whereas proportionality constants of LM and CM in albumin solution compared to those in porcine plasma were low, implying another non-saturable binder, i.e. lipoprotein. Simulation curve of drug-binding percentage vs. AGP concentrations showed that in pigs under a pathologic state, or during early growth stage with high AGP levels, AGP could be a main contributor to drug-plasma protein binding for all drugs examined. The increase of AGP from normal to pathological concentrations induced a decrease in the unbound fraction: LM > CM > EM > TMP in order of AGP contribution to drug binding. Therefore, the disposition and efficacy of basic antimicrobials which bind to AGP with high affinity could be markedly influenced by altered AGP levels, implying AGP contribution to pharmacokinetics and pharmacodynamics.

Zidovudine, trimethoprim, and dapsone pharmacokinetic interactions in patients with human immunodeficiency virus infection

Zidovudine is widely prescribed for the treatment of human immunodeficiency virus (HIV) infection. Trimethoprim and dapsone are commonly used in the management of Pneumocystis carinii pneumonia in HIV-infected patients. To examine the pharmacokinetic interactions among these drugs, eight HIV-infected patients (26 to 43 years old) with a mean CD4 count of 524.4 +/- 405.7 cells per mm3 received zidovudine (200 mg), trimethoprim (200 mg), and dapsone (100 mg) as single agents and in two- and three-drug combinations. Blood and urine samples were collected at a specified time and analyzed for zidovudine, zidovudine-glucuronide, trimethoprim, dapsone, and monoacetyl-dapsone concentrations under single-dose and steady-state conditions. Zidovudine did not influence the pharmacokinetic disposition of dapsone or trimethoprim. Dapsone had no effect on the pharmacokinetic disposition of zidovudine. Trimethoprim significantly decreased the renal clearance of zidovudine by 58% (5.0 +/- 1.8 versus 2.1 +/- 0.5 ml/min/kg of body weight [P < 0.05]). There was a concurrent 54% decrease in the mean urinary recovery of zidovudine (11.7 +/- 3.5 versus 5.4 +/- 3.0 [P < 0.05]), and the metabolic ratio was decreased by 78% (0.32 +/- 0.4 versus 0.07 +/- 0.05 [P < 0.05]). The mean area under the concentration-time curve from 0 to 6 h of the zidovudine-glucuronide/ zidovudine ratio was unchanged. We conclude that zidovudine, trimethoprim, and dapsone can be coadministered to patients with AIDS without significant pharmacokinetic interaction. However, in AIDS patients with liver impairment and impaired glucuronidation, doses of zidovudine may need to be decreased.

Efficacy of epiroprim (Ro11-8958), a new dihydrofolate reductase inhibitor, in the treatment of acute Toxoplasma infection in mice

Toxoplasma gondii is a major cause of focal encephalitis in patients with acquired immunodeficiency syndrome. Epiroprim, an inhibitor of dihydrofolate reductase, was evaluated in vitro and in a mouse model of acute infection for activity against T. gondii. The 50% inhibitory concentration (IC50) of epiroprim for T. gondii dihydrofolate reductase was 0.9 micromole, similar to that of pyrimethamine, but epiroprim was 650-fold more selective than pyrimethamine for T. gondii compared with human dihydrofolate reductase. While intraperitoneally administered epiroprim (300 mg/kg/day for 14 days) alone was ineffective in mice acutely infected with the RH strain of T. gondii, 100% survival was seen when it was combined with orally administered sulfadiazine (375 mg/kg/day), which alone was also ineffective. Increases in survival were seen in combination with doses of sulfadiazine as low as 0.375 mg/kg/day. Orally administered epiroprim combined with dapsone also prolonged survival. Thus epiroprim is an active and potentially less toxic alternative pyrimethamine for the treatment of toxoplasmosis.

Pharmacokinetics and therapeutic potential for repeated oral doses of trimethoprim/sulphachlorpyridazine in horses

The pharmacokinetic parameters of a powder formulation of trimethoprim/sulphachlorpyridazine were studied in eight healthy horses which received 5 mg/kg trimethoprim and 25 mg/kg sulphachlorpyridazine 12-hourly with concentrate for five days. The intake of the medicated concentrate by the horses was variable during the first two days, but after they became accustomed to the taste the intake by all the horses during the last three days was good. Faecal samples taken before and on the last day of the drug administrations were negative when cultured for salmonella. Compared with the results of a previous single-dose experiment, higher plasma concentrations and a higher area under the curve for both the drugs were observed. The repeated doses provided plasma concentrations above the minimal inhibitory concentration for Streptococcus zooepidemicus, S equi, Actinobacillus equuli and Rhodococcus equi isolated from the respiratory tract of horses. Synergism between the two drugs occurred at different drug concentration ratios with different bacterial species.

Pharmacokinetics of sulfadimethoxine and sulfamethoxazole in combination with trimethoprim after intravenous administration to healthy and pneumonic pigs

The pharmacokinetics of two sulfonamide/trimethoprim combinations were investigated after intravenous administration to clinically healthy pigs and to the same pigs following a challenge with Actinobacillus pleuropneumoniae toxins. Endobronchial challenge with A. pleuropneumoniae toxins resulted in fever, increased white blood cell counts and decreased water and feed consumption. Healthy, as well as febrile, pigs were given sulfadimethoxine (SDM) or sulfamethoxazole (SMX) intravenously at a dose of 25 mg/kg b.w. in combination with 5 mg trimethoprim (TMP) per kg body weight. The pharmacokinetic parameters of the sulfonamides as well as their main metabolites (acetyl sulfonamides) were not significantly different in healthy and febrile pigs. In healthy and pneumonic pigs, the mean elimination half-lives of SDM were 12.9 h and 13.4 h, respectively, those of SMX 2.5 h and 2.7 h, respectively, and those of TMP 2.8 h and 2.6 h, respectively. Distribution volumes in healthy and febrile pigs of SDM and SMX varied between 0.2 and 0.4 L/kg, and those of TMP between 1.1 and 1.6 L/kg. The mean AUC of TMP was decreased and the volume of distribution and total body clearance of TMP were increased in febrile pigs. Protein binding of the drugs and metabolites studied were not significantly changed after toxin-induced fever. The extent of protein binding of SDM, SMX and TMP was in the range 94-99%, 45-56% and 40-50%, respectively. Based on knowledge of in vitro antimicrobial activity of the drug combinations against A. pleuropneumoniae it was concluded that after intravenous administration of the dose administered (30 mg/kg of the combination preparations) to healthy and pneumonic pigs, plasma concentrations of SMX and TMP were above the concentration required for growth inhibition of 50% of A., pleuropneumoniae strains for approximately 16 h, whereas bacteriostatic plasma concentrations of SDM were still present after TMP had been eliminated from plasma. Because of similar elimination half-lives of SMX and TMP in pigs this combination is preferred to the combination of SDM with TMP.

Disposition kinetics of trimethoprim in rainbow trout (Oncorhynchus mykiss)

1. The pharmacokinetics of trimethoprim (TMP) following intra-aortic administration were investigated in rainbow trout. 2. The disposition kinetics for TMP were best described by a three-compartment open model. The disappearance of TMP from fish blood was characterized by rapid and pronounced distribution phases and a slow terminal elimination phase. 3. In contrast with pharmacokinetic data of TMP in mammals, the present study documented a long terminal elimination t1/2(36.1 h), large Vdss(5980 ml/kg) and small Clb(2.4 ml/min/kg) for TMP in rainbow trout, thus illustrating the slow biotransformation and elimination capacity, particularly the strong 'holding' capacity (storage) for the drug in trout. 4. The pharmacokinetic profiles in the present study indicated no dose dependency of TMP following three different bolus doses (5, 10 and 50 mg/kg). Hence, the first-order kinetic assumption was verified. 5. Urinary excretion of TMP was a minor elimination route in trout (14.4% dose).