Prophylactic antibiotic therapy for Staphylococcus aureus
If Staphylococcus aureus grows repeatedly from respiratory secretions, antibody studies suggest that it is almost certainly present in the lower airways (Strandvik et al, 1990). Comparison of cultures from the throat and bronchial tubes of the same patients with cystic fibrosis (CF) supports this finding. When patients are receiving long term prophylactic flucloxacillin, S. aureus is no longer a significant problem and is cultured infrequently (Southern et al, 1993; Littlewood et al, 1995).
A comparison of screened infants with CF in East Anglia on long term flucloxacillin or episodic antibiotics from the time of diagnosis showed those on long term flucloxacillin had significantly less cough, fewer S. aureus isolates, less often required in-patient treatment, had shorter hospital admisions and needed fewer courses of additional antibiotics (Weaver et al, 1994). Although the CF Foundation’s 4-year trial of cephalexin failed to demonstrate clinical differences between the treated and control children, the treated group had fewer positive cultures for S. aureus, 6% vs 30% but more P. aeruginosa, 25% vs 6% (Stutman & Martell, 1992). A recent systematic review of the diversity of treatments for S. aureus found that anti-staphylococcal treatment achieved sputum clearance of S. aureus and concluded that prophylactic treatment in young children is likely to be of clinical benefit (McCaffery et al, 1999).
Some CF clinics (e.g. Copenhagen) do not recommend long term flucloxacillin, but perform regular throat swabs or sputum cultures. Any potentially harmful organisms isolated from the cultures, including S. aureus, are treated with a course of an appropriate antibiotic. Further cultures are taken in two or three weeks to ensure the organism has cleared (Szaff & Hoiby, 1982). A major disadvantage of this approach is that throat cultures are an insensitive method of detecting organisms in the lower airways. Recent studies comparing throat/sputum cultures and cultures obtained at bronchoscopy revealed many potential pathogens in the lower airways which had not been detected by cultures from the upper respiratory tract (Wood, 1989; Ramsey et al, 1991; Armstrong et al, 1995; Armstrong et al, 1996). Also cultures are performed infrequently in some clinics and therefore S. aureus or other pathogens are not identified and thus not treated.
No clinical trial has yet answered the question whether prophylactic or intermittent anti-staphylococcal therapy results in improved lung function tests or chest x-rays, an increase in bacterial resistance or earlier P. aeruginosa infection (McCaffrey et al, 1999).
Our present policy is to recommend long term prophylactic flucloxacillin and this is continued indefinitely (50-100mg/kg/day in divided doses to a maximum of 1 gram four times a day in adults). Experience of patients referred to Leeds for CF assessments indicates that S. aureuscontinues to be a cause of significant lung damage in some individuals with CF who have not received, or have failed to comply with, such preventative treatment. We believe that the lungs of treated patients have some protection from S. aureus infection. When patients are receiving long term prophylactic flucloxacillin, S. aureus is cultured infrequently (Southern et al, 1993; Littlewood et al, 1995).
If S. aureus grows repeatedly from a patient who is prescribed long term flucloxacillin one should first confirm that the drug is being taken. Another anti-staphylococcal antibiotic should be added for two weeks e.g. fucidin or rifampicin. Before accepting that it is not possible to eradicate S. aureus, the patient should receive a two week course of intravenous antibiotics e.g. flucloxacillin.
Some older patients have entrenched S. aureus for many years. It is reasonable to treat them with long term flucloxacillin to minimise tissue damage. Some clinics will not specifically treat the S. aureus unless its appearance is associated with an obvious change in symptoms and signs. In Leeds we do not agree with that policy.
•If Staphylococcus aureus grows repeatedly from respiratory secretions, antibody studies suggest that it is almost certainly present in the lower airways
• Prompt and effective antibiotic treatment of respiratory infection has played a major part in the improved prognosis for people with CF
• No clinical trial has yet answered the question whether prophylactic or intermittent anti-staphylococcal therapy results in improved lung function tests or chest x-rays, an increase in bacterial resistance or earlier P. aeruginosa infection
• It is our policy to prescribe prophylactic flucloxacillin from diagnosis and continue indefinitely
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