By James Loh/HBO/Reuters US-listed Horizon Pharmaceuticals said on Wednesday it had reached an agreement to sell a blockbuster drug to its main rival, New Jersey-based Meridian Health.In a statement, Horizon said it had agreed to pay $1.9bn (£1.4bn) for Horizon’s new super-smart drug, which has been dubbed the ‘smart pill’.Horizon’s drug is currently available in…