Drug binding to plasma proteins during human pregnancy and in the perinatal period. Studies on cloxacillin and alprenolol

Plasma protein binding of one acidic drug, cloxacillin, and one basic drug, alprenolol, was determined by equilibrium dialysis at +37 degrees C during pregnancy and the 1st postnatal week in 12 women and their newborn infants and in 7 nonpregnant women (controls). A significant increase in fraction free cloxacillin in maternal plasma occurred during pregnancy already from the 2nd trimester compared to the controls (p less than 0.01) and was most pronounced at delivery (median values 0.126 and 0.069, respectively). A similarly increased fraction free cloxacillin was found in cord blood (median value 0.108) which further increased during the 1st postnatal week (range 0.112-0.164). In maternal plasma the binding capacity returned to the values of the controls during the same time period. The binding of cloxacillin was significantly correlated with the concentration of albumin (p less than 0.01). High correlation was also found between binding of the basic drug alprenolol and concentration of orosomucoid (p less than 0.005). This was most obvious in the newborn infants with low concentrations (range 0.1-0.3 g/l) and in the mothers during the puerperium with high concentrations of orosomucoid (range 0.7-2.5 g/l). On the basis of plasma protein binding data in the mother and her child, a maternal to fetal plasma concentration ratio was calculated. For cloxacillin this ratio was close to unity (1.03), while it was significantly above unity for alprenolol (1.72). At equilibrium, therefore, the total plasma concentration of alprenolol in the mother can be expected to exceed the concentration in her infant.

[Penetration of cloxacillin into human bone tissue after oral administration (author's transl)]

Cloxacillin diffusion into spongious and cortical bone was studied in 20 patients undergoing total replacement of the hip, after an oral single-dose of 1 g (10 patients) or an oral dose of 1 g every 8 hours (10 patients). Serum and bone samples were collected 2 and 3 hours after the last dose and assayed for antibiotic concentration by a microbiological method. Bone levels were similar in any group of patients, but significantly higher in spongious bone than in cortical bone. The bone/serum concentration ratios were 0.15 for spongious bone and 0.10 for cortical bone. Calculations from these data showed that adequate local levels inhibitory to Staphylococcus aureus, would be achieved by cloxacillin administration of 1 g dose every 4 hours orally.

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.

Drug distribution in whole blood of mothers and their newborn infants: studies of cloxacillin and flucloxacillin

The distribution of cloxacillin and flucloxacillin in whole blood from seven newborn infants and their mothers was determined in vitro by equilibrium dialysis at 37 degrees C. Seven healthy, non-pregnant women of reproductive age served as controls. The distribution of the penicillins to erythrocytes was the same in the infants as in the adults. It was significantly lower in the presence of plasma albumin than when plasma was replaced by isotonic phosphate buffer. The plasma protein binding of cloxacillin and flucloxacillin in 22 infants was significantly lower than in the controls, but was slightly higher than in the mothers. A significant correlation between binding of cloxacillin and flucloxacillin in the same individual suggested that the two drugs were bound to similar sites. During the first postnatal week binding in infant plasma decreased. This change was correlated with an increase in the bilirubin levels. In the mothers, the binding increased during the first week after delivery. On the basis of the distribution data, maternal to fetal plasma and whole blood concentration ratios at equilibrium were calculated. These ratios were lower for flucloxacillin (medians 0.770 and 0.821, respectively) than for cloxacillin 0.996 and 1.094). Accordingly, at equilibrium somewhat higher levels of flucloxacillin should appear on the fetal than on the maternal side, whereas the concentrations of cloxacillin would be expected to be approximately the same.

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.

The effect of semisynthetic penicillins on the binding of bilirubin by neonatal serum

1. The effect of ampicillin, cloxacillin, flucloxacillin and sulphafurazole on bilirubin on bilirubin binding by pooled human umbilical cord serum and bovine serum albumin was studied in vitro using Sephadex gel filtration. 2. Sulphafurazole displaced bilirubin from binding; both cloxacillins displaced bilirubin from pooled cord serum but not bovine serum albumin. 4. No displacement of bilirubin by the cloxacillins from pooled cord serum could be detected at therapeutic plasma concentrations of these drugs. 5. Scatchard analysis of the interactions showed that displacement of bilirubin by these drugs occurred principally at the primary, high affinity, low capacity binding site.

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.

Cloxacillin distribution in the rabbit eye after intravenous injection

Distribution of isotopically labelled and intravenously injected cloxacillin was studied in rabbit eye. The antibiotic concentration determined by liquid scintillation counting proved to be a reliable measure of the total antibiotic concentration when controlled by microbiological assay. In the rabbit eye after an intravenous injection of 50 mg/kg of cloxacillin sodium, longlasting antibiotic concentration regarded as therapeutic against penicillinase producing staphylococci was obtained in all vascularized ocular structures and in the cornea. The antibiotic present in the iris and ciliary body, and in the retina and choroid preparations, proved to be partly intravascular, whereas it penetrated better into the extravascular tissue compartment of the sclera and limbal area. Cloxacillin failed to achieve a therapeutic antibiotic concentration in the vitreous body and in the lens. Administration of probenecid had an enhancing effect on ocular cloxacillin concentration allowing improved drug diffusion into the eye by means of an elevated plasma concentration. No specific ocular effect of probenecid was noticed. Therapeutic concentration of cloxacillin in the aqueous humour, otherwise barely achieved, was more satisfactorily obtained with a previous injection of probenecid.

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.

Bactericidal activity and pharmacology of flucloxacillin

Flucloxacillin, a recent addition to the group of isoxazolyl penicillins, was studied in vitro and in normal volunteers. The bactericidal activity of the drug against most strains of gram-positive bacteria including penicillin-resistant Staphylococcus aureus was similar to that of oxacillin and approximately fourfold greater than that of cloxacillin. Each of the three penicillins was administered orally to a group of ten volunteers for eight days in a dose of 500 mg four times a day. The mean concentrations of flucloxacillin in the serum were two- to sixfold higher than those of the other two agents on the first, fourth and eighth days of therapy. The percentage of flucloxacillin bound by serum protein was 94.6 per cent; for cloxacillin and oxacillin the values were 93.5 and 91.5 per cent, respectively. Using these data, the concentrations of free flucloxacillin in serum were found to be twice as high as those of cloxacillin and oxacillin. These findings suggest that, when administered orally, this new agent may offer some therapeutic advantage over oxacillin and cloxacillin.

Antibiotics in the treatment of chronic staphylococcal osteomyelitis

Fourteen patients with chronic osteomyelitis were treated with oral penicillin, oxacillin, or cloxacillin at a dose of 5 gm/day, plus 0.5 gm of probenecid (Benemid) three or four times per day. Treatment was continued for 2 1/2 to six months. In ten patients, evidence of osteomyelitis disappeared and there has been no recurrence during follow-up periods varying from six months to 2 1/2 years. Significant hepatotoxicity was encountered in two patients; one similar patient, not in this series but receiving a similar regimen of antibiotic, developed leukipenia. Thus, patients with chronic osteomyelitis appear to benefit from such a therapeutic program, but they must be monitored closely for hepatic or hematologic toxicity.

Pharmacokinetics of flucloxacillin and cloxacillin in healthy subjects and patients on chronic intermittent haemodialysis

1 A pharmacokinetic study on flucloxacillin and cloxacillin was performed to investigate the factors contributing to the higher serum concentrations reported for the former after oral administration. 2 The results obtained in a study performed in a group of volunteers with flucloxacillin administered orally and by continuous infusion, were compared with the results of a similar investigation with cloxacillin. Patients on chronic intermittent haemodialysis received flucloxacillin orally and as a single i.v. injection. The results of this part of the study were compared with those of an earlier study on cloxacillin in haemodialysis patients. Serum and urine concentrations of flucloxacillin and cloxacillin were determined by bio-assay, and a one-compartment model was used for the calculations. 3 Higher serum concentrations reached after oral administration of flucloxacillin as compared with cloxacillin were based not only on better oral absorption (53.7% and 32.9%, respectively) but also on slower (renal and extra-renal) elimination (T1/2 : 46 and 32 min, respectively). A significant difference between the apparent volumes of distribution of flucloxacillin and cloxacillin, which could contribute to higher serum concentrations, could not be demonstrated. Considerable individual variation occurs in the rate and amount of oral absorption, especially in patients. The elimination rate of flucloxacillin in haemodialysis patients (T1/2 : 2h 53 min) corresponds with the extra-renal elimination rate in healthy subjects. No influence of haemodialysis on the elimination rate constant of flucloxacillin was found; total plasma clearance was, however, slightly but significantly higher during dialysis.

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.