Intravenous course

Question

Hello,
Could you please give us scientific explanation on how and where precisely intravenous antibiotics will act on the targeted bacteria? What is the difference compared to aerosols? Thank you.

Answer

Hello,
Antibiotics destroy or stop the growth of bacteria by blocking an essential step in their development (synthesis of their wall, DNA, proteins,…). The choice of antibiotics depends on the causative agent and is guided by antimicrobial susceptibility testing (to different antibiotics in the laboratory).

In cystic fibrosis, intravenous antibiotics are used mainly in patients with a respiratory infection with Pseudomonas aeruginosa (or other similar bacteria) because this bacterium is sensitive to very few oral antibiotics (usually it remains sensitive to ciprofloxacin). The antibiotics most frequently prescribed to fight against infection with Pseudomonas aeruginosa are beta-lactam antibiotics (e.g. ceftazidime) in combination with aminoglycosides (e.g. tobramycin), and the prescription of two antibiotics has a synergistic effect. After intravenous administration, they distribute well into the body, especially to lung and sinuses which are the sites of infection in cystic fibrosis.

In cystic fibrosis, once the initial phase of bronchial colonization has ended, Pseudomonas aeruginosa secretes structured aggregates called biofilms, or matrix of complex polysaccharides in which the bacteria are inserted. These biofilms serve as a barrier against antibiotics that reduce virulence of bacteria but can no longer eradicate them.

Some antibiotics can also be administered directly to the site of lung infection by inhalation (e.g. Tobramycin or Colomycin). The advantage of this mode of treatment is to provide the antibiotic directly to the site of infection with minimal toxicity and reduced inconvenience. But it is only possible if the bronchi are not too congested to allow the inhaled antibiotic to reach the distal airways.

In patients with bronchial colonisation with Pseudomonas aeruginosa, the prescription of intravenous antibiotics is indicated in case of acute respiratory exacerbation (with increased cough and sputum, shortness of breath and reduced lung function). Inhaled antibiotics can be prescribed at the time of first Pseudomonas colonisation if the patient is doing well and later in maintenance treatment of chronic infection in order to reduce the frequency of intravenous treatments.

Best regards.
Dr Dominique Hubert

20.09.2011