On Monday, Health Canada issued an advisory that requires manufacturers of some antibiotics to revise labels to include a warning that use may increase problems in patients with Myasthenia gravis. The advisory applies to a class of antibiotics known as fluoroquinolones, broad-spectrum antibiotics commonly prescribed for bacterial infections, including respiratory, skin, and urinary infections. This group of antibiotics includes Cipro, Levaquin, Avelox, and others. A complete list of affected products on the market in Canada can be found here.
In 2008, the FDA dealt with these drugs by issuing an alert requiring black box warnings for fluoroquinolone antibiotics, addressing the risk of tendon ruptures and tendonitis (http://www.fda.gov/Drugs/DrugSafety/PostmarketDrugSafetyInformationforPatientsandProviders/ucm126085.htm). This type of warning is the strongest warning that can be applied to prescription drugs. A labeling requirement followed this in February 2011, which required a black box warning advising that fluoroquinolones not be used in patients with a known history of Myasthenia gravis.
Both Health Canada and the FDA have limited labeling changes to oral dosage formats (e.g., tablets) and intravenous antibiotics, stating that eye and ear drops do not seem to pose the same risk.
Myasthenia gravis is a chronic disorder causing progressive muscle weakness. Muscle weakness can occur in the face, eyes, neck, throat, and limbs. Symptoms are often exacerbated by activity and regress with rest. The prevalence of Myasthenia gravis estimated to be 14 to 20 per 100,000, with an estimated 36,000 to 60,000 cases in the US. It is suggested that these values may be underestimated due to the under-diagnosis of this condition (http://www.myasthenia.org/HealthProfessionals/ClinicalOverviewofMG.aspx).
The use of fluoroquinolones may worsen symptoms of muscle weakness or respiratory problems in patients with Myasthenia gravis.
A retrospective study published in October reported adverse event data collected by the US FDA on fluoroquinolones. The authors found 37 cases of worsening symptoms in patients with Myasthenia gravis. Reports of suspected fluoroquinolones in order or prevalence included levofloxacin, moxifloxacin, ciprofloxacin, ofloxacin, gatifloxacin, norfloxacin, trovafloxacin, pefloxacin, and prulifloxacin. In half of these cases, adverse effects were seen within one day of antibiotic administration. In 5% of these cases, the outcome was the patient’s death.
Concerns with the use of specific fluoroquinolones (e.g., ciprofloxacin and norfloxacin) in patients with Myasthenia gravis have been reported in peer-reviewed scientific journals for decades as early as 1988. Crazy, right? Unfortunately, it has taken over twenty years for this scientific evidence to receive recognition and public awareness, which has undoubtedly come at a high cost for many people.