Researchers believe that Zadaxin, SciClone’s thymosin alpha-1, a synthetic polypeptide, works by boosting the ability of the body's immune system to produce T cells.
In November 1996, SciClone Pharmaceuticals, Inc. commented on results from a randomized, placebo-controlled, double-blind phase III study in chronic hepatitis C patients receiving a combination therapy of thymosin alpha 1 and interferon alpha-2B. A life-table analysis showed almost 50% of the 65 patients had complete normalization of ALT in the thymosin combination treated group and in less than 20% of the interferon-only treated group. The study showed a statistically significant reduction in ALT levels in the combination group and significant complete normalization of ALT levels, as compared to the interferon only and placebo groups. Also observed were significant early virologic responses in patients treated with combination therapy when compared to the interferon arm.
In 1998, the University of Cincinnati Medical Center reported sustained biochemical responses in 14.2% of patients treated with the combination treatment for 26 weeks, compared to 8.1% in patients taking IFN alone.
In another U.S. hepatitis C trial, 41.9% of those treated with Zadaxin combined with interferon responded while only 16.6% patients responded when treated with interferon alone, according to the SciClone website.
When used in combination with IFN, fever, fatigue, muscle aches, nausea, vomiting, and neutropenia were reported at a significantly higher rate than with IFN alpha 2b alone or with placebo Hepatology 1998; 27:1128-35).
Zadaxin is not yet approved in the US, Canada or Europe, although it is available in 13 other countries, including Mexico (http://www.scicloneinternational.com/ A phase III trial for non-responders, combining Pegasys with Zadaxin, is underway (http://www.scliver.com/trial.html Early response rates show 20-36% in previous non-responders (www.businesswire.com 11/04/2002).
In a study combining Zadaxin with pegylated IFN and ribavirin, 61% of non-responders improved. Researchers say is too soon to know if this combination is more effective than the two-drug Zadaxin plus interferon regimen being evaluated in the phase III trials. Findings will be in 2005 (Salynn Boyles, Experimental Hepatitis C Drug 'Promising', WebMD Medical News, October 27, 2003).