Zanaflex is approved by the Food and Drug Administration (FDA) for the management of spasticity in conditions such as multiple sclerosis and spinal cord injury. It has been available in Japan and Europe since 1985 for use as a short-term muscle relaxant.
An April 2007 public advisory issued by the FDA said using Zanaflex together with certain drugs (including fluvoxamine [LUVOX] and ciprofloxacin [CIPRO]), can result in drowsiness and extremely low blood pressure.
Zanaflex is related chemically to the blood-pressure-lowering drug clonidine (CATAPRES). Because Zanaflex can lower blood pressure, patients should be cautious when using this drug in combination with blood pressure-lowering drugs. Even when used alone, patients may experience dizziness, lightheadedness, or fainting when getting up suddenly from a sitting or lying position because of the blood pressure-lowering effect of this drug.
Drowsiness was reported by almost half (48 percent) of patients taking Zanaflex in clinical trials. In 10 percent of these cases, the drowsiness was severe.
A small percentage (about 5 percent) of patients participating in controlled clinical trials experienced liver function test (LFT) results greater than three times the upper limit of what is considered normal. This level of LFT elevation is an early indicator of possible liver toxicity. In postmarketing reports, the use of Zanaflex has been associated with three deaths from liver failure. LFT monitoring should be done before and during the first six months of Zanaflex treatment.