Rapid growth for Pacira Pharmaceuticals' (PCRX 0.13%) time-release surgical painkiller Exparel is lifting profit as sales are leveraged against fixed costs, but a bigger opportunity may be ahead if the company can execute on plans to boost Exparel's addressable market. If so, the rapid run-up in Pacira Pharmaceuticals shares in October may be the start, rather than the end, for this company.