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Miscellaneous antibiotics are antibiotics which are the only agent available in their class. This means that they are unique in their action and not comparable to other antibiotics, although their spectrum of activity or certain side effects may be similar to other antibiotics.

Antibiotics are medicines that are used to treat infections by killing bacteria or other susceptible organisms or inhibiting their growth.

What are miscellaneous antibiotics used for?

Miscellaneous antibiotics are used to treat infections caused by susceptible bacteria or other susceptible organisms, usually when other more common agents are not effective or not tolerated. There is not a single antibiotic that will treat all infectious disease scenarios.

Laboratory culture determines which antibiotic will be the most effective at killing or inhibiting the growth of the bacteria causing the infection. Examples of infections for which miscellaneous antibiotics may be used for include:

• Atovaquone: For the treatment or prevention of pneumonia caused by Pneumocystis carinii (also called P. jiroveci)
• Bacitracin: Use is restricted to infants with pneumonia and empyema (a collection of pus within the layers of the lungs)
• Chloramphenicol: Serious infections when less hazardous antibiotics are ineffective or contraindicated
• Colistimethate: Infections caused by gram negative bacilli, particularly Pseudomonas aeruginosa, Enterobacter aerogenes, Escherichia coli, Klebsiella pneumoniae
• Daptomycin:
  • Infections caused by resistant gram-positive bacteria such as multi-resistant Staphylococcus aureus (MRSA) or vancomycin-resistant enterococci (VRE)
  • Typically, bacteremia’s, endocarditis, skin and soft tissue infections.
• Metronidazole:
  • Anaerobic infections such as bacteroides infections, Clostridium difficile-associated diarrhea, Helicobacter pylori-associated peptic ulcer disease
  • Parasitic infections such as trichomonas, giardia.
• Pentamidine: This is actually an antifungal agent that has been included in the list of miscellaneous antibiotics. It may be used for the treatment or prevention of pneumonia caused by P. carinii (also called P. jiroveci)
• Rifaximin:
  • travelers diarrhea caused by E. coli in adults and children over the age of 12
  • Irritable bowel syndrome in adults whose main symptom is diarrhea
  • Hepatic encephalopathy.

What are the differences between miscellaneous antibiotics?

Each miscellaneous antibiotic has a different way of killing or inhibiting the growth of bacteria, so they are all unique, although their spectrum of activity or certain side effects may be similar to other antibiotics.

In addition, they can differ by their preferred route of administration (eg, oral, rectal, vaginally, or by injection).

Please refer to individual drug monographs for their mechanism of action, route of administration, and antibiotic spectrum.

Are miscellaneous antibiotics safe?

Each miscellaneous antibiotic works in a different way, which means their risk of severe side effects differs. Examples of severe side effects associated with miscellaneous antibiotics include:

• Allergic reactions. These have been reported with most antibiotics; symptoms may include a rash, hives (urticaria), swelling, or rarely, anaphylaxis
• Rarely, some people may develop a super-infection due to overgrowth of a naturally occurring bacterium called Clostridium difficile, following use of any antibiotic. Symptoms include severe diarrhea
• Atovaquone: Increased liver enzymes and liver damage have been reported in people taking atovaquone
• Bacitracin: May cause kidney failure. Infants should be monitored during use, the daily dose should not be exceeded, and it should not be given with other drugs that have the potential to cause kidney damage
• Chloramphenicol: Serious, potentially fatal, blood disorders have occurred after chloramphenicol administration. “Gray Baby Syndrome” – a potentially fatal condition associated with chloramphenicol administration to newborns or pregnant women may occur because newborns lack the liver enzymes necessary to metabolize the drug
• Colistimethate: short-lasting neurological disturbances, kidney damage (usually reversible), and breathing difficulties have been reported
• Daptomycin:  Muscle aching or muscle weakness in conjunction with increases in laboratory values of creatine phosphokinase over 10 times the upper limit of normal. Rhabdomyolysis (the destruction of muscle fibers), with or without kidney damage has also been reported. Daptomycin has also been associated with eosinophilic pneumonia (the accumulation of white blood cells in the lung), peripheral neuropathy and other nervous system effects
• Metronidazole:  Has been shown to be carcinogenic in mice and rats; association with cancer in humans is unknown but unnecessary use of the drug should be avoided
• Pentamidine: Fatalities due to severely low blood pressure, low blood sugar, acute pancreatitis or cardiac arrhythmias have been reported. Severe skin reactions, resulting in surgery and skin grafting have also been associated with injection extravasation.

For a complete list of severe side effects, please refer to the individual drug monographs.

What are the side effects of miscellaneous antibiotics?

Each miscellaneous antibiotic works in a different way, which means their risk of side effects differ. An example of side effects associated with some miscellaneous antibiotics include:

• Atovaquone: diarrhea, fever, headache, nausea, rash, rhinitis
• Aztreonam: diarrhea, injection-site reactions, nausea, vomiting
• Bacitracin: kidney damage, nausea, vomiting, skin rashes
• Chloramphenicol: headache, nausea, vomiting
• Colistimethate: gastrointestinal effects, tingling of the extremities, urinary problems
• Daptomycin: diarrhea, dizziness, headache, muscle pain or weakness, urinary problems
• Metronidazole: loss of appetite, metallic taste, nausea, vomiting, interacts with alcohol (causing nausea, vomiting, skin flushing fast heartbeat), interacts with some medicines (such as warfarin)
• Pentamidine: low blood pressure, nausea, blood disorders, low blood sugar, changes in laboratory tests
• Rifaximin: abnormal liver function tests, dizziness, fatigue, headache, nausea, swelling.

For a complete list of side effects, please refer to the individual drug monographs.