Cystic fibrosis (CF) is a disease caused by the dysfunction of the cystic fibrosis transmembrane conductance regulator (CFTR) protein. This protein, which functions as a channel, is normally found on the surface of various secretory cells in different parts of the body such as the lungs, gastrointestinal tract, and reproductive organs.
Specific mutations within the gene that encodes for this channel protein compromise the transport of chloride and water across cell membranes and affects the consistency of mucus that is produced by secretory cells. This leads to the accumulation of thick, sticky mucus in organs.
The mucus that accumulates in CF is rich in polysaccharides and proteins, presenting an ideal culture medium for the growth of different kinds of bacteria. The lungs are particularly vulnerable in patients with CF, making them susceptible to a wide range of acute and chronic bacterial infections.
There is a complex arsenal of antibiotics to combat these infections. Based on the route of administration these antibiotics can be classified into four categories: oral (taken by mouth), intravenous (injected into the bloodstream), intramuscular (injected into a muscle), or inhaled. The antibiotics can be sub-classified further based on their origin, the class of bacteria they target, and their mechanism of action. Staphylococcus aureus, Haemophilus influenzae, Pseudomonas aeruginosa, and Burkholderia cepacia are some common bacterial species that can infect CF patients and are the target of the most commonly used antibiotics.
Decisions related to antibiotic use
Since CF patients are susceptible to a wide variety of bacterial infections, it is important to identify the right combination of antibiotics that a patient may need early on to prevent the infection from spreading. Bacterial species can quickly become antibiotic resistant, making a certain class of antibiotics ineffective. That is why optimizing antibiotic doses, and why combinations of one or more antibiotics may be required. The type, dose, and frequency of antibiotics prescribed can vary from patient-to-patient and on clinical recommendations of the physician. Specific guidelines regarding antibiotic use are followed by clinicians to reach a decision regarding the details of antibiotic use.
Below are popular classes of antibiotics used to treat CF with common examples for each class, their prevailing routes of administration, and the pathogens they are directed against.
Penicillins usually administered orally, and in some cases intravenously, are frequently used to treat S. aureus infections. P. aeruginosa infections also can be treated with intravenous penicillin. Examples of penicillins include methicillin, oxacillin, nafcillin, carbenicillin, ticarcillin, piperacillin, mezlocillin, azlocillin, ticarcillin, clavulanic acid, and piperacillin-tazobactam.
Aminoglycosides, such as tobramycin, amikacin, and gentamicin, administered intravenously and more commonly by inhalation, are one of the most popular choices for treating P. aeruginosa infections. The use of inhalation is preferred because this way the antibiotic is delivered directly to the site of the infection and is more effective.
In addition to Penicillin, oral cephalosporins (e.g., cephalexin, cephalexin, cefdinir, cefprozil, and cefaclor) can be used to treat S. aureus and P. aeruginosa infections.
Vancomycin and linezolid
The emergence of methicillin-resistant S. aureus (MRSA) is observed in many CF cases. These genetically distinct strains of S.aureus are notoriously difficult to treat because they lack many properties that usually make S.aureus sensitive to common antibiotics. However, many years of research has led to the identification of some options that can be tried. Vancomycin administered intravenously is the prevalent choice to treat MRSA.
Linezolid (brand name, Zyvox) is another option for treating MRSA infections. Linezolid belongs to a class of antibiotics called oxazolidinones and acts by targeting bacterial protein synthesis.
Although their use is now on the decline, sulfonamides are still used to treat some specific types of bacterial infections. For instance, P. aeruginosa infections can be treated by sulfisoxazole, a sulfonamide that can be administered alone or in combination with erythromycin. S. aureus infections can be treated with sulfamethoxazole/trimethoprim, and macrolides (e.g., erythromycin, clarithromycin, and azithromycin) usually given orally, although other routes of administration also may be used based on the physician’s recommendations.
Tetracyclines (e.g., doxycycline, minocycline, and tigecycline), which also are used to treat S. aureus infections, can be administered by oral, intravenous, and intramuscular routes.
Macrolides and quinolones (ciprofloxacin and levofloxacin) administered orally or intravenously also have been used to treat P. aeruginosa infections. Some other antibiotics such as aztreonam and colistimethate often are administered by inhalation and intravenously to treat P. aeruginosa infections.
Most antibiotics start acting within 48 to 72 hours from the time of administration. However, it is imperative that patients complete the prescribed course of antibiotics to prevent the resurgence of antibiotic-resistant strains.
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