ZURICH, April 20 (Reuters) - The composition of the top Swiss stock index is due to change as early as this month, with Actelion poised to fall out of the Swiss Market Index (SMI) ahead of the completion of the biotechnology company's takeover by Johnson & Johnson.
Friday is the next deadline for Actelion shareholders to take J&J's $30 billion, $280 per share offer.
If more than 80 percent of shares are tendered, then Actelion's free float would slip below the 20 percent threshold required for inclusion in not only the benchmark SMI but also the broader Swiss Performance Index, Stephan Meier, a spokesman for the SIX Swiss Exchange, said on Thursday.
The chances of J&J's stake topping 80 percent are good, since it held 77 percent of Actelion shares at the end of March when it declared the takeover a success.
Should that happen, the SIX Swiss Exchange could make an announcement as early as Friday about future steps leading to another company filling Actelion's place in the SMI.
Candidates include drug ingredients maker Lonza, adhesives maker Sika and asset manager Partners Group , as well as hearing aid maker Sonova .
There will almost certainly be further SMI changes later this year, after ChemChina's takeover of Swiss chemicals maker Syngenta is completed. (Reporting by Rupert Pretterkleber; Writing by John Miller; Editing by Mark Potter)