Solvent systemSolvent systems used in parenteral suspension are classified as either aqueous or non-aqueous vehicles. Choice of a typical solvent system depends on solubility, stability & desired release characteristics of the drug. Non-aqueous vehicles include both water miscible and water immiscible vehicles. Water for injection is generally the preferred solvent system. However, non-aqueous water miscible agents are used as co-solvents with water for injection to promote the solubility & stability in parenteral preparation. Examples of water miscible non-aqueous vehicles include ethanol, glycerin, propylene glycol and nlactamide. The use of water miscible co-solvents can lead to undesirable side effect for eg intramuscular injection of propylene glycol- water, ethyl alcohol-water & polyethylene glycol (PEG) 400 water mixtures was found to cause muscle damage as measured by in vitro release of creatinine kinase from isolated rat skeletal muscle (37).