Large or repetitive doses of meperidine can cause anxiety, tremors, muscle twitches, and, rarely, convulsions, due to the accumulation of normeperidine. The drug differs from opioids in that, when given in large doses, it dilates the pupil and causes hyperactive reflexes. Severe hypotension can occur when the drug is administered postoperatively. Due to its antimuscarinic (anticholinergic) action, patients may experience dry mouth and blurred vision. When used with major antipsychotic drugs, depression is greatly enhanced. Administration to patients taking MAOIs or dextromethorphan can provoke severe reactions, such as convulsions and hyperthermia. Meperidine is considered to be inappropriate for use in geriatric patients and patients with impaired renal function, due to the accumulation of normeperidine. It should be avoided in elderly patients. Adverse effects associated with normeperidine are not reversible by administration of naloxone.