Abstract: A pharmaceutical composition or dosage form is described for the delivery of at least one pharmaceutically active agent or drug in a sustained and controlled manner. The pharmaceutical composition is an injectable formulation which is capable of responding to local stimuli at the site of injection, such as pH and temperature, and comprises a thermoresponsive polymer composition with a suspension of pH responsive micro- or nano-particles which contain the at least one pharmaceutically active agent or drug. The thermoresponsive polymer composition is formed from poly(methyl vinyl ether) (PMVE), and an inorganic salt, and the micro- or nano-particles are formed from chitosan and eudragit. The composition can be used to treat any disease or condition which results in a decrease in pH, such as for treating a solid tumour, gout, acidosis, ketosis and the like.