** PTC Therapeutics' PTCT.O shares down 2.8% premarket on Mon to $73 as it looks to refinance convertible debt

** Warren, New Jersey-based PTCT offering privately $500 mln convertible bonds (CBs) due 2031

** Intends to use net offering proceeds for repurchases of a portion of its 1.5% CBs due 2026, and for repayment/retirement of any remaining 2026 CBs at maturity

** Also expects to repurchase its shares in amount of approx $50 mln to facilitate hedging by investors in the new CBs

** PTCT has roughly $6.2 bln market cap

** Through Fri close, stock down 1% YTD

** Avg rating of 15 analysts is "buy"; median PT $92.50, according to LSEG data