Quinolones Flashcards
Example of a Quinolone
Ciprofloxacin
How do Quinolones work?
Quinolones kill bacteria by inhibiting DNA synthesis. They are particularly active against aerobic Gram-negative bacteria, which explains their utility in treatment of urinary and gastrointestinal infections. Moxifloxacin and levofloxacin are newer quinolones with enhanced activity against Gram-positive organisms. They can therefore be used to treat LRTI, which may be caused by either Gram-positive or Gram-negative organisms.
Bacteria rapidly develop resistance to quinolones. Some bacteria prevent intracellular accumulation of the drug by reducing permeability and/or increasing efflux. Others develop protective mutations in target enzymes. Quinolone resistance genes are spread horizontally between bacteria by plasmids, accelerating acquisition of resistance.
Indications for Quinolones
Quinolones are generally reserved as second or third-line treatment due to the potential for rapid emergence of resistance and an association with Clostridium difficile infection. With these caveats in mind, they are used in:
Urinary tract infection (UTI).
Severe gastrointestinal infection, e.g. with Shigella, Campylobacter.
Lower respiratory tract infection (LRTI) (moxifloxacin, levofloxacin).
Ciprofloxacin is the only oral antibiotic in common use with activity against Pseudomonas aeruginosa.
Moxifloxacin and levofloxacin do not have this property.
Side effects of Quinolones
GI upset (including nausea and diarrhoea) and immediate and delayed hypersensitivity reactions.
Class-specific adverse reactions include neurological effects (lowering of the seizure threshold and hallucinations), and inflammation and rupture of muscle tendons.
Quinolones (particularly moxifloxacin) prolong the QT interval and therefore increase the risk of arrhythmias.
They promote Clostridium difficile colitis, particularly with the hypervirulent 027 strain.
Interactions of Quinolones
Drugs containing divalent cations (e.g. calcium, antacids) reduce absorption and efficacy of quinolones. Ciprofloxacin inhibits certain cytochrome P450 enzymes, increasing risk of toxicity with some drugs, notably theophylline. Co-prescription of NSAIDs increases the risk of seizures, and of prednisolone increases the risk of tendon rupture. Quinolones should be prescribed with caution in patients taking other drugs that prolong the QT interval or cause arrhythmias, such as amiodarone, antipsychotics, quinine, macrolide antibiotics and SSRIs.
Elimination of Quinolones
Renal
Patient information on Quinolones
Explain that the aim of treatment is to get rid of infection and improve symptoms. For oral treatment, encourage the patient to complete the prescribed course. Before prescribing, always check with your patient personally or get collateral history to ensure that they do not have an allergy to quinolones (any ‘floxacin’).
Warn them to seek medical advice if a rash or other unexpected symptoms develop. If an allergy develops during treatment, give the patient written and verbal advice not to take this antibiotic in the future and make sure that the allergy is clearly documented in their medical records.
Explain that the aim of treatment is to get rid of infection and improve symptoms.
For oral treatment, encourage the patient to complete the prescribed course.
Before prescribing, always check with your patient personally or get collateral history to ensure that they do not have an allergy to quinolones (any ‘floxacin’).
Warn them to seek medical advice if a rash or other unexpected symptoms develop. If an allergy develops during treatment, give the patient written and verbal advice not to take this antibiotic in the future and make sure that the allergy is clearly documented in their medical records.
Contraindications of Quinolones
Quinolones should be used with caution in people at particular risk of adverse effects including those with or at risk of seizures, who are growing (potential risk of arthropathy); and with other risk factors for QT prolongation (such as cardiac disease or electrolyte disturbance).
