On this podcast, I cover ciprofloxacin pharmacology. Ciprofloxacin is one of the most widely recognized fluoroquinolone antibiotics and has been on the market for decades. Because of its broad utility, it often comes up in practice, but it also carries significant adverse effect concerns and boxed warnings that pharmacists and prescribers need to keep in mind.

From a pharmacology standpoint, ciprofloxacin works by inhibiting bacterial DNA gyrase and topoisomerase IV, enzymes that are essential for bacterial DNA replication, transcription, and repair. This action gives ciprofloxacin bactericidal activity against a variety of gram-negative organisms, including E. coli, Klebsiella, Enterobacter, and Pseudomonas aeruginosa. It also has some gram-positive activity, though it is generally not the best choice for strep infections.

Ciprofloxacin comes in multiple dosage forms, including oral tablets, oral suspension, and intravenous formulations, which makes it flexible across care settings. I discuss the conversion of IV and PO formulations.

Pharmacokinetics are important to consider. Ciprofloxacin is primarily renally eliminated, so dose adjustments are necessary in patients with impaired kidney function. Distribution into tissues is generally good, but it has limited activity in the lungs against Streptococcus pneumoniae, which is why it is not a first-line option for community-acquired pneumonia.

Adverse effects are a major concern. The fluoroquinolone class carries multiple boxed warnings. Ciprofloxacin has been associated with tendon rupture, peripheral neuropathy, CNS effects such as agitation or seizures, and exacerbation of myasthenia gravis. More recent warnings include the risk for aortic aneurysm and hypoglycemia or hyperglycemia, particularly in older adults or those with comorbidities. On top of these boxed warnings, ciprofloxacin can also prolong the QT interval and cause GI upset.

Drug interactions are another big factor in practice. Ciprofloxacin is a CYP1A2 inhibitor, which can raise levels of drugs like theophylline, tizanidine, and clozapine. It also interacts with polyvalent cations such as calcium, magnesium, iron, and aluminum, which can dramatically reduce its absorption—sometimes by more than 50%. This is a common reason for treatment failure if counseling isn’t provided.

From a dosing perspective, ciprofloxacin is usually given 250–750 mg orally twice daily or 400 mg IV every 8–12 hours depending on the indication and severity of infection. Renal dosing adjustments are needed as kidney function declines.

In summary, ciprofloxacin is a powerful antibiotic when used appropriately. It remains an option for urinary tract infections, complicated intra-abdominal infections, and some cases of hospital-acquired pneumonia, but its use must be balanced with the potential for significant adverse effects and interactions. For pharmacists, educating patients on drug interactions, counseling about boxed warnings, and ensuring correct dosing in renal impairment are some of the most valuable interventions when ciprofloxacin shows up on a medication list.

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