The present invention relates to injectable pharmaceutical compositions comprising therapeutically effective amount of succinylcholine chloride, one or more pharmaceutically acceptable aqueous solvents, and one or more stabilizing agents selected from aliphatic polyols; lower alkyl alcohols; amino acids having at least one additional amino, carboxyl or hydroxyl group; amino alcohols; and aliphatic dicarboxylic acids having at least one hydroxyl or amino group, or α-β unsaturation. The compositions are stable at room temperature for at least 30 days. Methods of manufacturing the injectable pharmaceutical compositions are also provided. The composition may be provided in a sealed container, e.g., an ampoule, vial and pre-filled syringe, and are suitable for subcutaneous, intravenous or intramuscular administration as an adjunct to general anesthesia, to facilitate tracheal intubation, and/or to provide skeletal muscle relaxation during surgery or mechanical ventilation.