PTCB Guide to Fluoroquinolones

Also called quinolones, the -floxacin antibiotics · suffix -floxacin · updated August 4, 2026

What gets tested

• Recognizing the -floxacin suffix and matching brand to generic (Cipro is ciprofloxacin, Levaquin is levofloxacin)
• The mechanism: DNA gyrase and topoisomerase IV inhibition, and that the class is bactericidal
• The boxed warnings, especially tendinitis and tendon rupture in the Achilles tendon
• The chelation interaction with antacids, dairy, and mineral supplements, and the timing rule that follows
• QT prolongation and photosensitivity as class effects
• That fluoroquinolones are generally avoided in children and pregnancy

What is not tested

You are not expected to select a fluoroquinolone for a specific organism or to know resistance patterns. What matters is stem recognition, the brand and generic pairs, the mechanism in one line, and above all the safety profile: the boxed warnings, the chelation timing rule, and the counseling points. Strengths, dosage forms, routes, special handling, and duration of therapy fall under PTCE knowledge area 1.4 and remain testable.

Why fluoroquinolones matter

Ciprofloxacin and levofloxacin are widely dispensed, and the class carries one of the most heavily counseled safety profiles in the pharmacy. The chelation interaction is also one of the clearest examples on the exam of an interaction that a technician can catch at the point of sale, because the offending products are often over-the-counter antacids and supplements sitting in the same basket.

Fluoroquinolones at a glance

Mechanism of action

Bacterial DNA is a long molecule packed into a small cell, and unwinding it for replication introduces mechanical strain. Bacteria solve this with two enzymes: DNA gyrase, which relieves supercoiling ahead of the replication fork, and topoisomerase IV, which separates the two finished daughter chromosomes. Fluoroquinolones inhibit both, trapping the enzymes on the DNA at the point where they have cut the strand but not resealed it. The bacterium is left with fragmented chromosomal DNA it cannot repair, so the effect is bactericidal rather than merely growth-halting. Human cells use a different topoisomerase, which is the basis for selectivity, although the class's characteristic tendon, nerve, and central nervous system effects show that the selectivity is not absolute. Absorption is excellent by mouth, so oral and intravenous doses are often comparable, but the molecule carries chemical groups that bind avidly to divalent and trivalent metal cations. Calcium, magnesium, aluminium, iron, and zinc form a complex called a chelate that the gut cannot absorb, which is why an antacid or a mineral supplement taken at the same time can cut absorption enough to cause treatment failure.

Common and important side effects

• Tendinitis and tendon rupture, most often the Achilles tendon, with the risk highest in patients over 60, on corticosteroids, or with a transplant
• Peripheral neuropathy, which can be rapid in onset and may be permanent
• Central nervous system effects: confusion, agitation, insomnia, and rarely seizures
• QT interval prolongation and the arrhythmia risk that follows
• Photosensitivity, meaning an exaggerated sunburn response
• Nausea, diarrhea, and Clostridioides difficile associated diarrhea
• Blood glucose disturbances, both low and high, particularly in patients on diabetes medicines

Key interactions

• Antacids, calcium, magnesium, aluminium, iron, zinc, sucralfate, and dairy products chelate fluoroquinolones and block their absorption
• Other QT-prolonging drugs raise the arrhythmia risk when combined with a fluoroquinolone
• Corticosteroids taken alongside a fluoroquinolone increase the risk of tendon rupture
• Warfarin's effect may be increased, so INR is monitored
• Ciprofloxacin inhibits CYP1A2 and raises theophylline and caffeine levels
• Blood glucose lowering agents may interact, so diabetic patients monitor more closely

Patient counseling notes

• Take the dose at least 2 hours before, or 6 hours after, any antacid, calcium, iron, magnesium, or zinc product. Check the exact interval on the label being dispensed
• Stop the drug and contact the prescriber at the first sign of tendon pain, swelling, or inflammation, especially at the back of the ankle, and rest the joint
• Report numbness, tingling, burning, or weakness in the hands or feet promptly, because nerve damage can become permanent
• Use sunscreen and protective clothing, because the skin burns more easily during therapy
• Drink plenty of fluids throughout the course
• Report confusion, severe mood changes, palpitations, or fainting

Practice questions

Work the Fluoroquinolones questions below first, then widen out. Two skills carry most of the Medications domain, and each has its own quiz. The first is drug class identification: recognising which class a drug belongs to from its name or its stem, which is what the drug class identification quiz drills across every class. The second is brand and generic recall, because the exam switches between the two names freely and expects you to follow. Pair this guide with the brand and generic quiz until the brand and generic pairs in the table above come back without effort.

Related drug-class guides

Official sources

• MedlinePlus: Ciprofloxacin
• MedlinePlus: Levofloxacin
• MedlinePlus: Moxifloxacin
• MedlinePlus: Antibiotics (topic overview)
• ClinCalc DrugStats: Ciprofloxacin (dispensing data)

PTCB Quiz Prep is an independent study resource, not affiliated with the Pharmacy Technician Certification Board. This guide is for exam preparation, not medical advice. Part of the PTCB Medications domain.