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.

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]

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.

Analysis of isoxazolyl penicillins and their metabolites in body fluids by high-performance liquid chromatography

A high-performance liquid chromatographic assay method to quantitate the isoxazolyl penicillins, their active metabolites, and their penicilloic acids in serum or urine is described. Separation and analysis is performed using reversed-phase chromatography. Urine samples, after the appropriate dilution, can be assayed directly. Serum samples (0.1 ml) are either extracted with methylene chloride or treated with perchloric acid--methanol. Serum levels as low as 0.4 microgram/ml (extraction procedure) can be assayed accurately.

Dicloxacillin and flucloxacillin twice daily with probenecid in staphylococcal infections. A clinical and pharmakokinetic evaluation

The therapeutic efficacy of decloxacillin or flucloxacillin, 1--2 g orally with probenecid twice daily was evaluated in staphylococcal infections. Excellent results were obtained with this as long-term maintenance therapy in 4 patients with relapsing chronic osteomyelitis and in 6 patients with postoperative infections. No side effects were observed in these patients. In 35 patients with furunculosis twice daily administration of dicloxacillin was used as a primary therapeutic regimen. All healed, but 4 recurrencies occurred during a 3-month observation period after therapy. In 5 patients allergic reactions were noted. The unbound fraction of flucloxallin in serum exceeded MIC values of methicillin-susceptible Staphylococcus aureus during 11 of 24 h. Pharmacokinetic data on flucloxallin with and without probenecid are given.

Concentration of dicloxacillin and benzylpenicillin in fracture haematoma

Prophylaxis with loading doses of dicloxacillin (3 patients) and benzylpenicillin (5 patients) has been used preoperatively for malleolar fractures treated in a standardized manner. Postoperatively, the same dose was given every 6 h for a total period of 48 h. The concentration of antibiotics was measured in serum before and after operation and 6 h after the first infusion. Samples from the haematoma were taken during operation and from the drainage collected during 24 h. Satisfactory concentrations were found in serum pre- and postoperatively and in the haematoma.

Use of the serum bactericidal titer to assess the adequacy of oral antibiotic therapy in the treatment of acute hematogenous osteomyelitis

Serum bactericidal titers against Staphylococcus aureus were measured in 63 children who were receiving mafcillin or methicillin intravenously, or dicloxacillin, penicillin, or cephalexin orally. The SBTs obtained following unit does of 25 mg/kg of dicloxacillin, 35 mg/kg of penicillin, or 25 mg/kg of cephalexin with probenecid were comparable to those seen following intravenous doses of 40 mg/kg nafcillin or methicillin. Twenty-two children with acute hematogenous osteomyelitis proven or presumed to be due to S. aureus were treated intravenously until point tenderness and fever had resolved, and then with oral therapy. The mean duration of intravenous therapy was 14 days. Oral doses were adjusted so that a peak SBT of greater than or equal to 1:16 and a trough SBT of greater than or equal to 1:2 were obtained in most children. No recurrences occurred. The SBT proved to be a practical means of assessing the adequacy of oral therapy in children with infections due to S. aureus.

Prediction of the concentration of penicillins in ascitic fluid from serum kinetics and protein binding of the antibiotics in serum and ascitic fluid of dogs

Ascites was induced in dogs by partial ligation of the inferior vena cava. Concentrations of ampicillin, penicillin G, oxacillin, cloxacillin, dicloxacillin, nafcillin, and methicillin in ascitic fluid and serum were each determined in three animals. All antibiotics were administered intramuscularly in a dose of 15 mg/kg (dry weight) for both single-dose and multiple-dose (eight doses at 4-hr intervals) studies. Binding of antibiotics to serum and ascitic fluid proteins was measured by ultracentrifugation. After single doses the highly protein-bound drugs (oxacillin, cloxacillin, dicloxacillin, and nafcillin) had lower percentages of penetration (ratio of peak in ascitic fluid to that in serum, multipled by 100) than did methicillin, ampicillin, and penicillin G, which have a lower degree of protein binding. The effect was partially overcome by repetitive doses, but five to six doses were usually required to reach equilibrium. In addition to protein binding, serum kinetics (particularly the log mean total concentration of drug in serum after multiple doses) were important determinants of antibiotic concentrations in ascitic fluid. The total antibiotic concentration in ascitic fluid at equilibrium can be accurately calculated from the log mean serum concnetration and the percentages of protein binding in serum and ascitic fluid.

Subtherapeutic dicloxacillin levels in a neonate: possible mechanisms

A neonate treated initially with oxacillin intravenously for two weeks and who was receiving phenobarbital for a seizure disorder subsequently failed to achieve therapeutic levels of orally administered dicloxacillin, even when the dosage was as high as 175 mg/kg/day. Intestinal absorption was documented by high serum peak levels. The low trough levels correlated with a high urinary excretion rate. The possibillity that renal tubular transport of dichloxacillin was stimulated by administration of penicillin derivatives (and/or phenobarbital) is suggested, and the need for careful monitoring of serum levels of antibiotics in neonates is emphasized.

Correction of protein binding defect in uremic sera by charcoal treatment

Protein binding of numerous drugs, primarily organic acids, is decreased in sera from uremic patients. The defect in binding is (1) greater than can be accounted for by hypoalbuminemia alone; (2) unchanged by prolonged in vitro dialysis; (3) transferred in the protein but not the ultrafiltrate fraction of uremic serum; and (4) not reproduced by addition of low and middle molecular weight compounds known to accumulate in uremia. However, treatment with activated charcoal at pH3 was found to significantly increase drug protein binding in uremic sera. This effect was studied with six different drugs in sera from groups of 6 normal subjects and 8 patients on chronic hemodialysis. The percentage of sulfamethoxazole, dicloxacillin, diphenylhydantoin, salicylate, and digitoxin bound to protein in normal sera (65.9, 97.1, 93.1, 96.7, and 92.7, respectively) was unchanged by charcoal treatment. In contrast, charcoal treatment significantly (p less than 0.01) increased the percentage of drug bound to protein in uremic sera from 41.7 to 59.0 for sulfamethoxazole, 90.7 to 96.3 for dicloxacillin, 84.3 to 90.8 for diphenyhydantoin, 86.4 to 93.8 for salicylate, and 89.5 to 90.9 for digitoxin. Charcoal treatment significantly (p less than 0.05) reduced penicillin protein binding in normal sera and failed to correct the binding defect for penicillin in uremic sera. The effect of charcoal can be explained by removal of an inhibitor which accumulates in uremia and (1) occupies the binding site of certain drugs, (2) changes the configuration of the albumin molecule, or (3) both. Free fatty acid (FFA) concentrations in uremic patients were similar to those in normal subjects and were not the cause of the binding defect.

Uptake of antibiotics by human erythrocytes

Human erythrocytes have been used as a model system for the study of uptake and release of antibiotics. Penicillin G, dicloxacillin, tetracycline, and minocycline were all taken up by the cells, but each showed a characteristic ratio of distribution between the extracellular and intracellular compartments. Comparison of the penicillin analogues indicated that dicloxacillin, the more lipid-soluble compound, reached higher intracellular concentrations than did penicillin G. Use of human plasma as the incubation medium markedly decreased antibiotic uptake and enhanced antibiotic egress from preloaded cells. These effects were related to the binding of drugs to serum proteins. In vivo studies in which penicillin G was injected intravenously by bolus and was then given by constant infusion showed that intraerythrocytic concentrations of drug after 2 hr approached or exceeded those in plasma. These results can be explained, in part, by the fact that the slower rate of efflux of penicillin G from the cells than of clearance from plasma serves to maintain the high initial levels of drug for a longer period.

Comparative studies of the activity of ciclacillin and dicloxacillin

The penicillins ciclacillin and dicloxacillin demonstrate marked similarities in biological activity but, as far as can be determined, differ substantially in respect to the degree of protein binding, which is relatively low for ciclacillin and relatively high for dicloxacillin. In mice infected with Staphylococcus aureus Smith, ciclacillin is considerably more active than dicloxacillin, although both drugs are similarly effective in vitro and similarly absorbed and eliminated in vivo. The high degree of protein binding exhibited by dicloxacillin could therefore very probably explain its relatively low chemotherapeutic activity. Moreover, the in vitro and in vivo findings of the study are inconsistent with the tenets of the tau/2 thesis.

Pharmacokinetic interpretation of dicloxacillin levels in serum after extravascular administration

Evidence was found for the existence of an episome-specified variant of the enzyme dihydropteroate synthase involved in folic acid formation. Since the plasmid-borne enzyme showed a decreased susceptibility for sulfonamide inhibition and was transferable together with resistance to this drug, it is proposed that diploidy for the target enzyme in some cases could be the mechanism of R-factor-mediated resistance to sulfonamides. Two types of evidence were obtained. One was the rescue from temperature sensitivity of bacterial mutants with a lesion in the chromosomal dihydropteroate synthase by the R factor R1dr19 mediating sulfonamide resistance. The other evidence was found by the determination of dihydropteroate forming activity in extracts from R⁻ and R⁺ bacteria. Cells harboring R1dr19 were found to contain an enzyme activity which was far less susceptible to sulfonamide inhibition than the corresponding activity from R⁻ cells.

Enhanced renal excretion of dicloxacillin in patients with cystic fibrosis

Single oral doses of 6.25 mg/kg of dicloxacillin suspension were given to ten cystic fibrosis (CF) patients and eight normal subjects. Peak serum concentrations and areas under the concentration versus time curves for dicloxacillin were variable and, on average, were 2 1/2 times lower in the CF patients. The time of occurrence of the peak serum concentration was similar in both groups and the total urinary recovery of dicloxacillin was normal or increased in the CF patients, suggesting that the intestinal absorption of the drug was unaffected by the disease. The low serum concentrations in the CF patients were caused by unusually high renal clearances of dicloxacillin which average 282 +/- 135 compared to 95 +/- 28 ml/min/1.73 sq m in the normal subjects. Creatinine clearances were also elevated in the CF patients by 55% on average, while urea clearances were normal. The serum protein binding of dicloxacillin was similar in both groups of subjects. Because the rapid excretion results in low and variable serum concentrations of the antibiotic, treatment of CF patients with dicloxacillin may warrant use of increased or more frequent doses and monitoring of serum antibiotic levels.

Treatment of chronic staphylococcal osteomyelitis with cloxacillin and dicloxacillin--a comparative study in 12 patients

12 patients with chronic staphylococcal osteomyelitis were treated with cloxacillin (6 patients) and dicloxacillin (6 patients) in a prospective, comparative study. The drugs were given perorally in the dose 1 g every 4th hour and serum concentrations were followed. 0.5, 1 and 2 hours after administration the serum level of dicloxacillin was about double that of cloxacillin. The lowest serum level of dicloxacillin at the time of administration of the drugs was nearly 3 times as high as the level of cloxacillin. An evaluation of clinical benefit and side-effects revealed no differences between the drugs. The prolonged serum level of dicloxacillin may permit a longer interval between doses than the administration of cloxacillin.

Flucloxacillin, a new isoxazolyl penicillin, compared with oxacillin, cloxacillin, and dicloxacillin

Flucloxacillin, a new isoxazole penicillin, is active against penicillinase-producing strains of Staphylococcus aureus and is well absorbed in man after oral and intramuscular administration. Compared with isoxazole penicillins in current clinical use-namely, oxacillin, cloxacillin, and dicloxacillin-flucloxacillin has proved as active against Gram-positive cocci, including penicillin-resistant staphylococci. The extent of binding of flucloxacillin to the protein of human serum was similar to that of oxacillin and cloxacillin and less than that of dicloxacillin. In man flucloxacillin given orally produced total and free serum levels higher than those obtained with oxacillin and cloxacillin; total serum levels similar to those of dicloxacillin, and free levels greater than those of dicloxacillin. Similarly, after intramuscular injection the free serum levels of flucloxacillin were higher than those of oxacillin, cloxacillin, and dicloxacillin.