The most common adverse events observed in clinical trials in patients treated with NAGLAZYME were headache, fever, arthralgia, vomiting, upper respiratory infections, abdominal pain, diarrhea, ear pain, cough, and otitis media. Severe reactions included angioneurotic edema, hypotension, dyspnea, bronchospasm, respiratory distress, apnea, and urticaria. The most common symptoms of infusion reactions included fever, chills/rigors, headache, rash, and mild to moderate urticaria. Nausea, vomiting, elevated blood pressure, retrosternal pain, abdominal pain, malaise, and joint pain were also reported. No patients discontinued infusions of NAGLAZYME for adverse events and all patients who completed the double-blind portion of the trial continued to receive weekly infusions of NAGLAZYME. Nearly all patients developed antibodies as a result of treatment, but the level of the immune response did not correlate with the severity of adverse events. Because antihistamine use may increase the risk of apneic episodes, evaluation of airway patency should be considered prior to the initiation of treatment. Consideration to delay infusion of NAGLAZYME should be given when treating patients who present with an acute febrile or respiratory illness.