Sputum penetration of fusidic acid in patients with cystic fibrosis

Rifampicin and sodium fusidate reduces the frequency of methicillin-resistant Staphylococcus aureus (MRSA) isolation in adults with cystic fibrosis and chronic MRSA infection

Nosocomial transmission of methicillin-resistant Staphylococcus aureus (MRSA) to patients with cystic fibrosis (CF) frequently results in chronic respiratory tract carriage. This is an increasing problem, adds to the burden of glycopeptide antibiotic use in hospitals, and represents a relative contraindication to lung transplantation. The aim of this study was to determine whether it is possible to eradicate MRSA with prolonged oral combination antibiotics, and whether this treatment is associated with improved clinical status. Adult CF patients (six male, one female) with chronic MRSA infection were treated for six months with rifampicin and sodium fusidate. Outcome data were examined for six months before treatment, on treatment and after treatment. The patients had a mean age of 29.3 (standard deviation=6.3) years and FEV(1) of 36.1% (standard deviation=12.7) predicted. The mean duration of MRSA isolation was 31 months. MRSA isolates identified in these patients was of the same lineage as the known endemic strain at the hospital when assessed by pulsed-field gel electrophoresis. Five of the seven had no evidence of MRSA during and for at least six months after rifampicin and sodium fusidate. The proportion of sputum samples positive for MRSA was lower during the six months of treatment (0.13) and after treatment (0.19) compared with before treatment (0.85) (P<0.0001). There was a reduction in the number of days of intravenous antibiotics per six months with 20.3+/-17.6 on treatment compared with 50.7 before treatment and 33.0 after treatment (P=0.02). There was no change in lung function. Gastrointestinal side effects occurred in three, but led to therapy cessation in only one patient. Despite the use of antibiotics with anti-staphylococcal activity for treatment of respiratory exacerbation, MRSA infection persists. MRSA can be eradicated from the sputum of patients with CF and chronic MRSA carriage by using rifampicin and sodium fusidate for six months. This finding was associated with a significant reduction in the duration of intravenous antibiotic treatment during therapy.

Fusidic acid pharmacology, pharmacokinetics and pharmacodynamics

Fusidic acid comes in a variety of formulations for oral, intravenous and topical use. After oral administration of 500 mg Cmax values range from 14.5-3.3 mg/l and an elimination half-life of 8.9-11.0 h. Similar values are obtained with intravenous administration of the sodium salt, although peaks tend to be higher. Bioavailability for the new film-coated tablet is approximately 91% while that of the suspension formulation appears to be much lower. Repeated dosing results in substantial drug accumulation when given 8-hourly, and to a variable extent depending on dose when administered 12-hourly. One study has demonstrated a modest dose-dependency for pharmacokinetics, with decreased clearance at higher doses. Fusidic acid is primarily eliminated by non-renal mechanisms, and a proportion of the drug is metabolised to seven or more breakdown products that can be detected in bile. Hypoalbuminaemia increases fusidic acid clearance, while clearance is decreased in the presence of severe cholestasis, and essentially unchanged in renal failure. Fusidic acid is highly protein-bound (91-98S), but has good penetration to a number of tissues including skin blisters, burns, infected bone and joints. Topical application of fusidic acid results in poor penetration through skin but good penetration into aqueous and vitreous humour. Little is known about the pharmacodynamics of fusidic acid, apart from the fact that it is slowly bactericidal against Staphylococcus aureus, and produces moderate post-antibiotic effects in vitro.

Pharmacokinetics of fusidic acid after a single dose of a new paediatric suspension

The pharmacokinetics of fusidic acid (Fucidine, Leo Laboratories) were studied in 10 children after single oral dosing with 20 mg/kg of a new banana-flavoured paediatric suspension (titrating at 50 mg/ml). Nine blood samples were drawn from each child at 0, 1, 2, 3, 6, 8, 12, 24 and 48 h following dosing with the antibiotic. Serum fusidic acid levels were measured by high-performance liquid chromatography (HPLC). A model-independent method was used for the pharmacokinetic analysis. Results were compared with those obtained after dosing eight healthy adult volunteers with 500 mg of sodium fusidate by parenteral administration (infusion) then per os. The acceptability of the single dose was good. The terminal elimination half-life t1/2 (h) and the mean residence time (MRT, h) of fusidate were similar to those determined in healthy adults after oral dosing, i.e. 16.0 +/- 14.5 versus 16.0 +/- 3.5 and 17.7 +/- 12.1 versus 17.7 +/- 2.5, respectively. In contrast, the oral bioavailability of the suspension (Fapprox., %) was relatively low: of the order of 22.5 versus 91.0% for tablets in the healthy adult, which justifies the use of a relatively higher dose in the child. This led to the calculation of an estimated total clearance (Clest., ml/min) significantly less than that in the healthy adults, while the estimated apparent volume of distribution (Vd, litre/kg) was significantly increased (10.4 +/- 9.1 versus 21.8 +/- 2.1 and 0.73 +/- 0.53 versus 0.30 +/- 0.04, respectively). Fusidic acid is normally excreted in metabolized form (98%). The decrease in clearance could be attributed to the almost immediate saturation of liver enzymes in immature infants.(ABSTRACT TRUNCATED AT 250 WORDS)

Antimicrobial therapy of Pseudomonas pulmonary exacerbations in cystic fibrosis. A prospective evaluation of netilmicin plus azlocillin versus netilmicin plus ticarcillin

High-dose anti-Pseudomonas chemotherapy is mandatory in the treatment of acute pulmonary exacerbations in patients with advanced cystic fibrosis and Pseudomonas aeruginosa isolated from their sputum. However, neither the regimen itself nor its objective evaluation have been optimized yet. In a prospective controlled evaluation 42 such exacerbations were treated for two weeks with netilmicin combined by randomisation with either azlocillin or ticarcillin. Other aspects of therapy were constant. The two therapy groups were comparable in all aspects. Both regimens produced similar improvements in clinical, radiological, laboratory, bacteriological and pulmonary function measurements. Concentrations of sputum bacteria were significantly reduced; transient eradication was documented in 29% and correlated with antibiotic susceptibility of the initially isolated Pseudomonas strains. The highly dosed antibiotics were well tolerated and emergence of resistance was rarely observed. It is concluded that both antibiotic combinations are beneficial and safe in cystic fibrosis. Monitoring of such intensive hospital treatment must include multiple parameters.