The invention relates to a pharmaceutical composition suitable for injection as an aqueous suspension for sustained release of a bisphosphonate drug, the composition comprising: a sosoloid containing a salt of a bisphosphonate drug; and a salt of a pentavalent phosphorus oxoacid, the sosoloid having a solubility in saline of less than 0.05% by weight as bisphosphonic acid for use as a medicament and for use in the prevention or treatment of a bone disease in a patient, in particular osteoporosis.