Safety and pharmacokinetics of dicloxacillin in healthy Chinese volunteers following single and multiple oral doses.

BACKGROUND: Dicloxacillin, a semisynthetic isoxazolyl penicillin antibiotic, has antimicrobial activity against a wide variety of gram-positive bacteria including Staphylococcus aureus, Streptococcus pyogenes, Streptococcus pneumonia, Streptococcus epidermidis, Streptococcus viridans, Streptococcus agalactiae, and Neisseria meningitidis. The objective of this study was to evaluate the safety and pharmacokinetic profile of dicloxacillin after single and multiple oral dose in healthy Chinese volunteers. METHODS: A single-center, open-label, randomized, two-phase study was conducted in 16 subjects. In the single-dose phase, subjects were randomly assigned to receive single doses of 0.25, 0.5, 1.0, and 2.0 g of dicloxacillin sodium capsule in a 4-way crossover design with a 5-day washout period between administrations. In the multiple-dose phase, subjects were assigned to receive 0.25 or 0.5 g every 6 hours for 3 days in a 2-way crossover design. Plasma and urine pharmacokinetic samples were assayed by a validated high-performance liquid chromatography-tandem mass spectrometry method. Pharmacokinetic parameters were calculated and analyzed statistically. Safety assessments were conducted throughout the study. RESULTS: Following a single oral dose of 0.25-2.0 g dicloxacillin sodium, the maximum plasma drug concentration (Cmax) and the corresponding values for the area under the concentration- time curve from 0 to 10 hours (AUC0-10 h) increased in a dose-proportional manner. The mean elimination half-life (t1/2) was in the range of 1.38-1.71 hours. Dicloxacillin was excreted in its unchanged form via the kidney, with no tendency of accumulation, and varied from 38.65% to 50.10%. No appreciable accumulation of drug occurred with multiple oral doses of dicloxacillin. No serious adverse events were reported. Adverse events were generally mild. CONCLUSION: Dicloxacillin was safe and well tolerated in the volunteers and displayed linear increases in the Cmax and AUC0-10 h values.

Bioanalytical method development and validation for simultaneous estimation of cefixime and dicloxacillin by RP-HPLC in human plasma.

An accurate, rapid and simple reversed-phase high performance liquid chromatography (RP-HPLC) bioanalytical method was developed and validated for simultaneous estimation of cefixime, dicloxacillin in human plasma using ezetimibe as an internal standard. The cefixime, dicloxacillin and internal standard were extracted by liquid-liquid extraction technique. Chromatographic separation is accomplished using CAPCELL PAK C18 (4.6 mm × 250 mm, 5 m) analytical column. The mobile phase consisted of phosphate buffer, acetonitrile and methanol in 42:55:03 proportions. Detection and quantification were performed by UV/Vis detection at 225 nm. The lower limit of quantification was 0.5 µg mL(-1) for both cefixime and dicloxacillin in human plasma. The calibration curves were linear over the concentration range 0.5 to 40 µg mL(-1) for both drugs in human plasma. The method was quantitatively evaluated in terms of linearity, precision, accuracy, recovery, selectivity, and stability. The method was found to be simple, convenient and suitable for the analysis of cefixime and dicloxacillin from biological fluids.

Intra- and extracellular activities of dicloxacillin against Staphylococcus aureus in vivo and in vitro.

Antibiotic treatment of Staphylococcus aureus infections is often problematic due to the slow response and recurrences. The intracellular persistence of the staphylococci offers a plausible explanation for the treatment difficulties because of the impaired intracellular efficacies of the antibiotics. The intra- and extracellular time- and concentration-kill relationships were examined in vitro with THP-1 cells and in vivo by use of a mouse peritonitis model. The in vivo model was further used to estimate the most predictive pharmacokinetic/pharmacodynamic (PK/PD) indices (the ratio of the maximum concentration of drug in plasma/MIC, the ratio of the area under the concentration-time curve/MIC, or the cumulative percentage of a 24-h period that the free [f] drug concentration exceeded the MIC under steady-state pharmacokinetic conditions [fT(MIC)]) for dicloxacillin (DCX) intra- and extracellularly. In general, DCX was found to have similar intracellular activities, regardless of the model used. Both models showed (i) the relative maximal efficacy (1-log-unit reduction in the numbers of CFU) of DCX intracellularly and (ii) the equal relative potency of DCX intra- and extracellularly, with the MIC being a good indicator of the overall response in both situations. Discordant results, based on data obtained different times after dosing, were obtained from the two models when the extracellular activity of DCX was measured, in which the in vitro model showed a considerable reduction in the number of CFU from that in the original inoculum (3-log-unit decrease in the number of CFU after 24 h), whereas the extracellular CFU reduction achieved in vivo after 4 h did not exceed 1 log unit. Multiple dosing of DCX in vivo revealed increased extra- and intracellular efficacies (2.5 log and 2 log units of reduction in the numbers of CFU after 24 h, respectively), confirming that DCX is a highly active antistaphylococcal antibiotic. PK/PD analysis revealed that fT(MIC) is the index that is the most predictive of the outcome of infection both intra- and extracellularly.

Lack of effect of P-glycoprotein inhibition on renal clearance of dicloxacillin in patients with cystic fibrosis.

STUDY OBJECTIVE: To determine whether upregulation of P-glycoprotein is responsible for the enhanced renal clearance of dicloxacillin in patients with cystic fibrosis. DESIGN: Single-center, prospective, open-label, randomized, three-part crossover pharmacokinetic study. SETTING: General clinical research center. SUBJECTS: Eleven patients with cystic fibrosis and 11 age-matched healthy volunteers. INTERVENTION: All subjects received a single oral dose of dicloxacillin 500 mg alone, dicloxacillin 500 mg plus probenecid (an organic anion transport inhibitor) 1 g, and dicloxacillin 500 mg plus cyclosporine (a P-glycoprotein inhibitor) 5 mg/kg; each treatment was separated by a washout period of 48 hours. A bolus dose of iothalamate meglumine 456 mg was administered on each study day as a marker of glomerular filtration. MEASUREMENTS AND MAIN RESULTS: Blood and urine samples were taken serially up to 6 hours after each dose. Pharmacokinetics of dicloxacillin and iothalamate were determined by using compartmental and noncompartmental methods. Quantitative polymerase chain reaction was performed on peripheral blood mononuclear cells to measure expression of multidrug resistance 1 (MDR1) messenger RNA (mRNA). Genotyping for ABCB1 was performed to determine the presence of single nucleotide polymorphisms (exons 21 and 26). In both healthy subjects and patients with cystic fibrosis, compared with dicloxacillin alone, coadministration with probenecid produced a significantly lower renal clearance of dicloxacillin, whereas coadministration with cyclosporine resulted in no significant change; renal clearance was not significantly different between the two study groups. No correlation was found between MDR1 mRNA expression and renal clearance of dicloxacillin. The renal excretion of dicloxacillin was significantly greater in subjects with the ABCB1 exon 26 TT polymorphism when compared with subjects with the CT genotype. CONCLUSION: We found no significant difference in the pharmacokinetics of dicloxacillin between patients with cystic fibrosis and healthy volunteers. Renal clearance of dicloxacillin was significantly reduced in the presence of probenecid but not with cyclosporine, suggesting that the rate-limiting step in tubular secretion of dicloxacillin is uptake mediated by the organic anion transporter, and not P-glycoprotein inhibition.

Liquid chromatographic assay for dicloxacillin in plasma.

A simple high-performance liquid chromatographic method for the determination of dicloxacillin in plasma has been developed. The method only requires 0.5 ml of plasma, phosphate buffer solution (pH = 4.7), acidification with 0.5N hydrochloride acid and liquid extraction with dichloromethane. Posterior evaporation of organic under nitrogen steam and redissolution in mobile phase is carried out. The analysis was performed on a Spherisorb C18 (5 microm) column, using methanol -0.05 M phosphate buffer, pH = 4.7 (75:25; v/v) as mobile phase, with ultraviolet detection at 220 nm. Results showed that the assay is sensitive: 0.5 microg/ml. The response is linear in the range of 0.5 - 10 microg/ml. Maximum inter-day coefficient of variation was 12.4%. Mean extraction recovery obtained was 96.95%. Stability studies showed that the loss was not higher than 10%, samples are stable at room temperature for 6 h, at -20 Celsius for 2 months, processed samples were stable at least for 24 h and also after two freeze-thaw cycles. The method has been used to perform pharmacokinetic and bioequivalence studies in humans.

Antibiotic concentrations in serum and wound fluid after local gentamicin or intravenous dicloxacillin prophylaxis in cardiac surgery.

One important aim of antibiotic prophylaxis in cardiac surgery is preventing mediastinitis and thus it would appear to be relevant to study the antibiotic concentrations in pericardial/mediastinal fluid. Local administration of gentamicin in the wound before sternal closure is a novel way of antibiotic prophylaxis and could be effective against bacteria resistant to intravenous antibiotics. This study measured dicloxacillin concentrations in 101 patients in serum and wound fluid following intravenous administration of dicloxacillin. Similarly, concentrations of gentamicin in serum and wound fluid were determined in 30 patients after administration of 260 mg gentamicin in the wound at sternal closure. Median dicloxacillin concentrations in serum and wound fluid at sternal closure were 59.4 and 55.35 mg/l, respectively. Gentamicin levels in the wound were very high (median 304 mg/l), whereas serum concentrations were low (peak median 2.05 mg/l). Dicloxacillin, 1 g given intravenously, according to the clinical protocol, resulted in levels in serum and wound fluid at sternal closure likely to prevent Staphylococcus aureus infections. Locally administered gentamicin resulted in high local concentrations, potentially effective against agents normally considered resistant.

PKQuest: capillary permeability limitation and plasma protein binding - application to human inulin, dicloxacillin and ceftriaxone pharmacokinetics.

BACKGROUND: It is generally assumed that the tissue exchange of antibiotics is flow limited (complete equilibration between the capillary and the tissue water). This assumption may not be valid if there is a large amount of plasma protein binding because the effective capillary permeability depends on the product of the intrinsic capillary permeability (PS) and the fraction of solute that is free in the blood (fwB). PKQuest, a new generic physiologically based pharmacokinetic software routine (PBPK), provides a novel approach to modeling capillary permeability in which the only adjustable parameter is the PS of muscle. METHODS: All the results were obtained by applying PKQuest to previously published human pharmacokinetic data. RESULTS: The PKQuest analysis suggests that the highly protein bound antibiotics dicloxacillin and ceftriaxone have a significant capillary permeability limitation. The human muscle capillary PS of inulin, dicloxacillin and ceftriaxone was 0.6, 13 and 6 ml/min/100 gm, respectively. The ceftriaxone protein binding is non-linear, saturating at high plasma concentrations. The experimental ceftriaxone data over a wide range of intravenous inputs (0.15 to 3 gms) was well described by PKQuest. PKQuest is the first PBPK that includes both permeability limitation and non-linear binding. CONCLUSIONS: Because of their high degree of plasma protein binding, dicloxacillin and ceftriaxone appear to have a diffusion limited exchange rate between the blood and tissue and are not flow limited as had been previously assumed. PKQuest and all the examples are freely available at http:\\www.pkquest.com.

Dicloxacillin and flucloxacillin: pharmacokinetics, protein binding and serum bactericidal titers in healthy subjects after oral administration.

The pharmacokinetics of dicloxacillin and flucloxacillin were studied in 12 healthy volunteers after oral administration. The participants received a single dose of either dicloxacillin (0.5 g, 0.75 g or 1.0 g) or flucloxacillin (0.75 g) in a cross-over fashion. Antibiotic concentrations were determined in serum and urine by bioassay and followed for 8 and 24 h, respectively. The three dicloxacillin dosages showed no significant differences for the serum elimination half-lives (t1/2 beta, median: 72 min). Comparing 0.75 g flucloxacillin with the same dose of dicloxacillin, no significant differences between the values of Cmax, t1/2 beta and AUC were found. Protein binding as determined by ultrafiltration in pooled serum was 94.7-96.2% for flucloxacillin and 96.4-97.2% for dicloxacillin. The serum bactericidal titers were similar for the two drugs. In conclusion, dicloxacillin and flucloxacillin showed similar pharmacokinetic behavior after 0.75 g doses in human volunteers.

Should probenecid be used to reduce the dicloxacillin dosage in orthopaedic infections? A study of the dicloxacillin-saving effect of probenecid.

Reduction in the dosage of dicloxacillin from 500 mg to 250 mg 3 times a day would mean lowering of costs and less side-effects in orthopaedic infections. In this cross-over study, the serum concentrations of dicloxacillin were measured in 9 patients after administration of dicloxacillin 500 mg 3 times a day (dicloxacillin 500 mg) and after co-administration of 250 mg dicloxacillin and 250 mg probenecid 3 times per day (dicloxacillin 250 mg+probenecid 250 mg). Concentrations were measured every hour after the tablet intake. The mean maximum serum concentrations of dicloxacillin were 17.1 micrograms/ml (dicloxacillin 500 mg) and 12.2 micrograms/ml (dicloxacillin 250 mg+probenecid 250 mg), respectively (P < 0.05). Serum concentrations above 3 micrograms/ml were obtained during 285 min. in both regimes, but the individual variations were biggest during in the dicloxacillin 250 mg+probenecid 250 mg treatment. Serum concentrations above 5 micrograms/ml were in mean measured during 228 min. (dicloxacillin 500 mg) and 190 min. (dicloxacillin 250 mg+probenecid 250 mg), respectively (P < 0.05). The clinical significance of these findings is being discussed. In theory, treatment with dicloxacillin 250 mg+probenecid 250 mg may be as sufficient as dicloxacillin 500 mg.

Comparison of bactericidal activity of five antibiotics against Staphylococcus aureus.

Ten volunteers were given each of five antibiotics, sequentially, until steady state was reached. Peak and trough sera were then drawn, and bactericidal titers were determined to two different isolates of Staphylococcus aureus, both sensitive in vitro to all antibiotics tested. The antibiotics were cephalexin, trimethoprim/sulfamethoxazole (TMP/SMZ), clindamycin, dicloxacillin, and ciprofloxacin. Mean peak serum bactericidal titers (SBT) were significantly higher for cephalexin than for dicloxacillin, ciprofloxacin, and TMP/SMZ (P less than .05). The difference between cephalexin and clindamycin did not achieve statistical significance. Dicloxacillin, clindamycin, and ciprofloxacin were not statistically different from each other. Mean SBT for TMP/SMZ was less than 1:2, significantly less than that achieved by the other antibiotics. Only clindamycin achieved a trough SBT greater than 1:2. This was statistically significant compared with each of the other antibiotics.

Significance of "extravascular" protein binding for antimicrobial pharmacodynamics in an in vitro capillary model of infection.

The effect of protein binding in an "extravascular" space on antimicrobial pharmacodynamics was studied in an in vitro capillary model of infection. Simulated 500-mg oral doses of dicloxacillin (approximately 96% bound) or cephalexin (less than 5% bound) were administered every 6 h for four doses. A 10-fold-higher dose of dicloxacillin was also studied to determine the effect of drug concentration on the reduction of bacterial killing in the presence of protein. Staphylococcus aureus ATCC 25923 was inoculated into peripheral chambers filled with either Mueller-Hinton broth or Mueller-Hinton broth plus 25% human serum. Serial samples for bacterial counts were collected over 24 h. The presence of serum in the chambers significantly reduced bacterial killing by dicloxacillin but not by cephalexin during the first 6 h (two-way analysis of variance, F = 6.04, P less than 0.05) but not at 24 h. Reduction of dicloxacillin activity in serum-containing chambers persisted with the higher dose. These data suggest that despite attaining higher total drug concentrations in protein-containing extravascular spaces with highly bound drugs, protein binding reduces bactericidal activity during the early stages of treatment in this model.

Optimization of high-performance liquid chromatographic analysis for isoxazolyl penicillins using factorial design.

A 3 X 3 factorial design has been used to study the effects of pH and acetonitrile concentration of the eluents on the retention and resolution of cloxacillin, flucloxacillin and dicloxacillin on a C18 column. The logarithm of the capacity factors of these solutes have been found to vary linearly with the pH and quadratically with the acetonitrile content. The equations generated have been employed to predict experimental conditions necessary for an optimum separation. The chromatographic condition selected has been applied to the quantitation of flucloxacillin in human plasma using dicloxacillin as the interval standard. Sample preparation consists of protein precipitation and solid-phase extraction. The detection limit of the assay at 220 nm for flucloxacillin is in the region of 0.1 microgram/ml. This assay has been employed in a study of the relative bioavailability of two commercial flucloxacillin sodium capsules in ten healthy volunteers.

Plasma concentration following oral administration of di- and flucloxacillin in infants and children.

The bioavailability of commercial liquid preparations of di- and flucloxacillin was compared in infants and children. The plasma concentrations following a dose of 12.5 mg/kg were equal within the two age groups. Infants 0-1 months old, however, demonstrated a better absorption than older children.

[Microcalorimetric study of the parameters of dicloxacillin binding with human serum albumin at different temperatures]. / Mikrokalorimetricheskoe izuchenie parametrov sviazyvaniia dikloksatsillina s syvorotochnym al'buminom cheloveka pri razlichnykh temperaturakh.

The thermodynamic parameters of human serum albumin (HSA) binding with dicloxacillin, an antibiotic widely used in clinical practice, were determined with the method of differential flow microcalorimetry at 18, 25, 30, 37 and 45 degrees C. The experiments were performed at two ionic strengths: 0.02 and 0.15. Two hypothetic models of interaction in the HSA-drug system were considered in processing the data for the curves of calorimetric titration. The first model implies the presence of independent homogeneous active sites on the protein. In accordance with the second model there are one primary and secondary independent homogeneous active sites on the biopolymer molecule. It is shown that dicloxacillin association with HSA proceeds according to the mechanism suggesting the presence of one primary and one secondary active sites on the protein molecule. The binding process in the system studied is exothermic, the enthalpy increasing at the temperature change from 18 to 45 degrees C. At the same time the binding constant and enthropy of the system decrease. The influence of the solution ionic strength on the binding process was practically lacking. On the basis of the analysis of the thermodynamic data it is concluded that the character of the binding in the HSA-dicloxacillin system at 18-30 degrees C is hydrophobic. With an increase in the temperature the hydrophoby level decreases.

Pharmacokinetics of dicloxacillin in serum and aortic wall during aneurysmal surgery.

Twenty-one patients undergoing elective surgery for abdominal aortic aneurysm were randomly assigned to receive 2 grams of dicloxacillin as an intravenous infusion either at the induction of anaesthesia, 3 hours or approximately 6 hours before surgery. Samples from serum and aortic tissue were simultaneously obtained so that antibiotic levels could be compared as a function of time. High concentrations of dicloxacillin in serum and aortic tissue were present already shortly after infusion and active levels were maintained in aortic tissue for approximately six hours. The kinetics of dicloxacillin was similar in serum and aortic tissue. These results support the need for antibiotic administration shortly before surgery to ensure adequate tissue levels of antibiotics.

Comparison of oral penicillinase-resistant penicillins: contrasts between agents and assays.

We observed the comparative serum levels and mean peak serum antistaphylococcal activity in eight fasting adults who received 500 mg each of dicloxacillin, cloxacillin, oxacillin, and nafcillin. Dicloxacillin achieved higher and more prolonged serum levels and greater peak serum antistaphylococcal titers than the other drugs studied. The higher degree of protein binding of dicloxacillin was reflected in a greater disparity between the peak antistaphylococcal activity observed when dilutions were done in serum compared to broth. The lesser protein-bound penicillins showed less disparity, but this effect was offset by the higher serum levels obtained by dicloxacillin. The higher protein binding of dicloxacillin did not prevent its having equal or superior antistaphylococcal activity in serum when the drugs were given in equal doses.

Concentrations of cloxacillin, dicloxacillin and flucloxacillin in dental alveolar serum and mandibular bone.

Deep infections caused by staphylococci are serious complications after oral surgery. Intensive antibiotic treatment is always necessary in these infections. Isoxazolylpenicillins are often used. Levels of three isoxazolylpenicillins, namely, cloxacillin, dicloxacillin and flucloxacillin, were measured in serum, dental alveolar serum and mandibular bone in 60 patients undergoing surgical removal of impacted third molars after a single dose of 500 mg. The systemic serum concentrations were higher than the dental alveolar serum concentrations in most patients. The maximum concentration in the alveolar serum was 3.8-6.4 microgram/ml for cloxacillin, 6.0-15.0 microgram/ml for dicloxacillin and 10.0-15.0 microgram/ml for flucloxacillin. The concentration in mandibular bone was 2.0 +/- 0.4 microgram/g for cloxacillin, 2.0 +/- 0.5 microgram/g for dicloxacillin and 2.0 +/- 0.5 microgram/g for flucloxacillin.

Concentrations of semi-synthetic penicillins in the plasma and in the expectoration, administered by means of intermittent vein perfusion.

We report the levels of concentration of ampicillin, dicloxacillin, and carbenicillin reached in the blood and in the expectoration following the administration of these drugs by rapid venous infusion, once every 24 h. The concentration of ampicillin in the blood serum varied from 150 to 180 micrograms/ml at the end of the infusion and from 30 to 3 micrograms/ml 4 afterwards and the dicloxacillin concentration from 150 to 120 micrograms/ml, and from 24 to 6 micrograms/ml. The concentration of ampicillin in purulent expectoration was 5-7 micrograms/ml and that of dicloxacillin 2.5-4 micrograms/ml. The concentration of carbenicillin in the plasma varied from 1,040 to 130 micrograms/ml, and in the expectoration it was around 15 micrograms/ml. Several cases of acute and chronic lung and bronchial diseases caused by bacteria have been treated by means of venous infusion once every 24 h and results were excellent.