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Cough and Cold Medications |   |
Antiinfective Agents
Respiratory infections caused by bacterial, fungal, protozoal, and viral organisms occur in patients with pneumonia, acute and chronic bronchitis, bronchiectasis, sunusitis, and cystic fibrosis. Antibiotics represent one of the most commonly used antiinfective agents in the respiratory therapist's arsenal.
The term antibiotic means a substance that is produced by microorganisms (bacteria, fungi, molds) that is capable of inhibiting or killing bacteria and other microorganisms. The mechanisms by which antibiotics inhibit or kill microorganisms include:
- Inhibition of cell wall synthesis. Bacterial cells have rigid protective walls, without which they explode. Antibiotics that inhibit bacterial cell wall synthesis include: penicillins, bacitracin, cephalosporins, vancomycin, and cycloserine.
- Alteration of cell membrane permeability. Disruption of the cell's membrane function upsets the necessary flow and storage of cell material required for growth. Membranes of certain bacteria and fungi are especially susceptible to antibiotics such as polymyxins.
- Inhibition of protein synthesis. Antibiotics that interfere with the ribosome's ability to synthesize needed proteins include: chloramphenicol, tetracyclines, erythromycin, lincomycin, streptomycin, kanamcin, and gentamicin.
- Inhibition of nucleic acid synthesis. Antibiotics that attach to the DNA strands and block further DNA replication or formation of messenger RNA include: fluoroquinolones (like ciprofloxacin), trimethoprim, sulfonamides, and rifampicin.
Antibiotics are usually administered systemically, but several (carbenicillin, gentamicin, streptomycin) have been aerosolized for localized infections (lung abscess and bronchiectasis). Tobramycin has been used for chronic infections in cystic fibrosis. Parenteral medications are often ineffective in lung infections because the presence of edema, fibrosis, or thick exudates limit diffusion of the drug into the lung.
Aerosolized antibiotics also may be useful when infections appear resistant to systemic therapy. However, aerosolized antibiotics should be considered a supplement to systemic therapy, not a replacement. They are probably most useful for stubborn gram-negative infections.
Results on aerosolized antibiotics have been mixed, and there are several disadvantages to aerosolized antibiotics, including:
- Bronchospasm is very common.
- Some antibiotics are inactivated by DNA and enzymes found in mucus.
- Doses for aerosolized administration have not been clearly established.
- Resistant microorganisms are created, as mentioned above.
- Expensive equipment may be needed and considerable staff time required for administration.
Despite these above, aerosolized antibiotics may be considered for children with cystic fibrosis, fungal infections (pulmonary coccidioidomycosis, endobronchial histoplasmosis), and when systemic therapy appears ineffective or toxicity has been reached.