Four basic factors affect the success of drugs: efficacy, safety, convenience of administration and price. Investors in Genzyme General have been watching the progress of Oxford GlycoSciences plc's Vevesca to treat Gaucher disease to determine whether Vevesca will pose a threat to GENZ's Cerezyme franchise.

Last week Oxford GlycoSciences (LSE:OGS, OGSI, Abingdon, U.K.) reported positive 24-month results from an ongoing open-label extension of its completed Phase II trial of Vevesca (Study 001). But a true side-by-side comparison is not yet available to allow investors to make a clear judgment call.