It is not useful for spasticity due to neurologic conditions such as cerebral palsy.A 2004 review found benefit for fibromyalgia symptoms, with a reported number needed to treat of 4.8 (meaning that 1 person out of every 4.8 benefits from treatment) for pain reduction, but no change in fatigue or tender points. A 2009 Cochrane review found insufficient evidence to justify its use in myofascial pain syndrome. It may also be used along with other treatments for tetanus. Side effects
Cyclobenzaprine results in increased rates of drowsiness (38%), dry mouth (24%), and dizziness (10%). Drowsiness and dry mouth appear to intensify with increasing dose. The sedative effects of cyclobenzaprine are likely due to its antagonistic effect on histamine, serotonin, and muscarinic receptors.Agitation is a common side effect observed, especially in the elderly. Some experts believe that cyclobenzaprine should be avoided in elderly patients because it can cause confusion, delirium, and cognitive impairment. In general, the National Committee for Quality Assurance recommends avoiding the use of cyclobenzaprine in the elderly because of the potential for more severe side effects.Dysphagia, a life-threatening side-effect, may rarely occur. Treatment protocols and support should follow the same as for any structurally related tricyclic, such as tricyclic antidepressants. Overdose
The most common effects of overdose are drowsiness and tachycardia. Rare but potentially critical complications are cardiac arrest, abnormal heart rhythms, severe low blood pressure, seizures, and neuroleptic malignant syndrome. Life-threatening overdose is rare, however, as the median lethal dose is about 338 milligrams/kilogram in mice and 425 mg/kg in rats.
Host genetic factors
For genotype 1 hepatitis C treated with pegylated interferon alfa-2a or pegylated interferon alfa-2b combined with ribavirin, it has been shown that genetic polymorphisms near the human IL28B gene, encoding interferon lambda 3, are associated with significant differences in response to the treatment. This finding, originally reported in Nature, showed genotype 1 hepatitis C patients carrying certain genetic variant alleles near the IL28B gene are more likely to achieve sustained virological response after the treatment than others. Another report in Nature  demonstrated the same genetic variants are also associated with the natural clearance of the genotype 1 hepatitis C virus. Other infections
Has also been used for Middle East respiratory syndrome and hepatitis E.

Manufacture
It is pegylated with a branched 40 kg/mol PEG chain. The drug has been manufactured under the brand name Pegasys by Roche Pharmaceuticals. Due to changes in clinical practice - antiviral hepatitis drugs such as sofosbuvir have become much more important - Roche announced in 2020 that it would withdraw Pegasys from the market worldwide, but subsequently sold the worldwide rights to pharma&, an Austrian / Swiss pharmaceutical company that ensures supply in the medium and long term almost worldwide (excluding China and Japan). Research
A Cochrane Review sought to determine whether interferon alfa-2a could be used as a treatment for individuals with neovascular age-related macular degeneration. They found no evidence of improved visual acuity with potential harm. References
External links

"Peginterferon alfa-2a". Drug Information Portal. U.S. National Library of Medicine. Pegasys at the US National Library of Medicine Medical Subject Headings (MeSH)