Quinolone antibiotics

Quinolone antibiotics, also known as fluoroquinolones, are a class of broad-spectrum antibiotics commonly used to treat a variety of bacterial infections. These antimicrobial medications are effective against both gram-negative and gram-positive bacteria, as well as some intracellular pathogens and anaerobes. Quinolones are bactericidal, meaning they kill bacteria rather than just stopping their growth.

There are several generations of quinolones, each with a slightly different spectrum of activity and pharmacokinetics. They are used in clinical practice to manage infectious diseases such as urinary tract infections (UTIs), prostatitis, respiratory infections, gastrointestinal infections, and certain life-threatening infections caused by multidrug-resistant bacteria. Some quinolones, like ciprofloxacin, are also used for prophylaxis against anthrax exposure.

Quinolones are a class of antibiotics derived from nalidixic acid, the first quinolone discovered. These medications work against a wide range of bacterial infections by targeting enzymes essential for DNA synthesis.

These antibiotics are recognized for their excellent oral bioavailability, which allows for convenient dosing, and for their broad spectrum of activity against both gram-negative and gram-positive pathogens, including Pseudomonas aeruginosa in some cases.

Quinolone antibiotics work by inhibiting bacterial enzymes called DNA gyrase and topoisomerase IV. These enzymes are crucial for bacterial DNA replication, transcription, repair, and recombination. By blocking their action, quinolones prevent bacteria from reproducing and repairing DNA, ultimately leading to bacterial cell death.

This mechanism makes quinolones effective against a variety of bacterial infections. However, overuse or improper prescribing can lead to quinolone resistance, often due to mutations in the DNA gyrase or topoisomerase IV genes or the acquisition of plasmid-mediated resistance factors.

Common quinolone antibiotics include:

• Ciprofloxacin (Cipro)
• Levofloxacin (Levaquin)
• Moxifloxacin (Avelox)
• Ofloxacin (Floxin)
• Gemifloxacin (Factive)
• Norfloxacin (Noroxin)
• Delafloxacin (Baxdela)
• Gatifloxacin (Zymar)
• Sparfloxacin (Zagam)
• Trovafloxacin (Trovan)

These medications differ in their spectrum of activity, oral bioavailability, pharmacokinetics, and clinical use. Some are first-line treatments for uncomplicated urinary tract infections, while others are reserved for complicated infections, multidrug-resistant pathogens, or specific indications such as anthrax exposure prophylaxis.

Quinolones are prescribed for a variety of bacterial infections, including:

• Urinary tract infections (UTIs), including uncomplicated and complicated cases
• Prostatitis
• Respiratory tract infections such as pneumonia
• Gastrointestinal infections caused by pathogens, including Clostridium species
• Skin and soft tissue infections
• Certain life-threatening and serious infections caused by multidrug-resistant gram-negative bacteria, including Pseudomonas aeruginosa
• Post-exposure prophylaxis for anthrax

Their broad spectrum and bactericidal properties make quinolones valuable in clinical practice, but careful prescribing is essential to reduce the risk of serious side effects and antibiotic resistance.

Common side effects may include:

• Gastrointestinal upset such as nausea, vomiting, diarrhea
• Headache and dizziness
• Rash or phototoxicity

Serious side effects, which require immediate medical attention, may include:

• Tendinitis or tendon rupture, particularly in the Achilles tendon
• Peripheral neuropathy, causing numbness or tingling
• Central nervous system effects, including seizures, confusion, or mood changes
• Aortic aneurysm or aortic dissection in at-risk populations
• QT prolongation and arrhythmias
• Liver toxicity or impairment
• Hypoglycemia or hyperglycemia in some patients

These are not all of the possible side effects with the use of quinolone antibiotics. You should always seek medical advice from your healthcare provider for any questions or concerns about your medical condition or treatment. Read all patient information, medication guides, or drug information sheets that come with this medication. You can also report adverse effects to the Food and Drug Administration at www.fda.gov/medwatch or 1-800-FDA-1088.

Although these medications are generally well-tolerated and safe, there are certain warnings, precautions, and drug interactions you should be aware of.

Warnings

Before starting quinolone antibiotics, it is crucial to discuss any existing health conditions with your healthcare provider. You should be sure that your healthcare provider is aware of all your medical conditions, including if you have:

• History of tendon disorders or recent tendon injury
• Heart problems, including arrhythmias or an aortic aneurysm
• Kidney or liver impairment
• Central nervous system disorders, including seizures
• Myasthenia gravis
• Electrolyte abnormalities

Boxed Warning

Quinolones carry a boxed warning for an increased risk of tendonitis, tendon rupture, peripheral neuropathy, and central nervous system effects.

Contraindications

• Known hypersensitivity to any quinolone or fluoroquinolone antibiotics
• Concomitant use with tizanidine
• History of certain cardiac conditions in patients at risk of QT prolongation

Drug interactions

When quinolone antibiotics are taken with other prescription drugs, over-the-counter medications, vitamins, and supplements, it may change how they work or increase the frequency or severity of side effects. Make sure that you tell your healthcare professional about anything that you are taking to avoid any negative drug interactions, including:

• Antacids or supplements containing magnesium, aluminum, calcium, or iron (which reduce oral absorption)
• Warfarin and other anticoagulants (increasing bleeding risk)
• Antiarrhythmic medications
• Certain antivirals or other enzyme inhibitors or inducers affecting drug metabolism
• Corticosteroids (increasing risk of tendon rupture)