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, which are commonly prescribed for bacterial infections including respiratory, skin and urinary infections. This group of antibiotics includes Cipro, Levaquin, Avelox and others. A full 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. This was followed by a labeling requirement 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 muscle weakness that is progressive. 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 under diagnosis of this condition (http://www.myasthenia.org/HealthProfessionals/ClinicalOverviewofMG.aspx).
Use of fluoroquinolones may worsen symptoms of muscle weakness or respiratory problems in patients with Myasthenia gravis.
A retrospective study published in October reported on adverse event data collected by the US FDA on fluoroquinolones. The authors found 37 cases of exacerbation of 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 1 day of administration of the antibiotic. In 5% of these cases, the outcome was death of the patient.
Concerns with use of specific fluoroquinolones (e.g. ciprofloxacin and norfloxaxcin) in patients with Myasthenia gravis have been reported in peer reviewed scientific journals for decades, dating back 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 certainly come at a high cost for a lot of people.