A prefilled plastic syringe comprising an aqueous botulinum toxin formulation, the plastic syringe comprising (a) a plastic syringe barrel including a proximal end and a distal end, and a generally cylindrical wall extending therebetween and defining a barrel lumen, the syringe barrel having a distally projecting tip with a fluid passage extending therethrough and communicating with the barrel lumen, wherein the generally cylindrical wall has an interior surface coated with a barrier layer, (b) a capping device having an outlet engaging portion sealingly engaging and closing the distal open outlet end of the syringe, wherein the outlet engaging portion is made of an elastomeric material, and (c) a plunger rod assembly which extends into the proximal end of the syringe barrel and includes a plunger stopper in sliding fluid-tight engagement with the cylindrical wall of the barrel lumen, wherein the plunger stopper is made of an elastomeric material, which has a coating on at least a portion of the plunger stopper contacting the aqueous botulinum toxin formulation during storage and/or injection, wherein the barrier layer of the syringe barrel is a silicone layer, wherein the elastomeric material of the outlet engaging portion is chlorinated butyl rubber, wherein the elastomeric material of the plunger stopper is chloro butyl rubber and the coating on the plunger stopper is a crosslinked silicone coating, or the elastomeric material of the plunger stopper is bromo butyl rubber and the coating on the plunger stopper is a fluorinated ethylene-ethylene copolymer coating, wherein the aqueous botulinum toxin formulation comprises water, botulinum toxin at a concentration of 10 U/ml to 150 U/ml, sodium chloride at a concentration of 0.5% to 1.5% w/v, a sugar at a concentration of 0.1% to 2% w/v, and albumin at a concentration of 0.01% to 1% w/v, and the pH of the aqueous botulinum toxin formulation is between 6.1 and 7.3 during storage, and wherein the biological activity of the botulinum toxin expressed in Mouse Units is not reduced by more than 25%, relative to the initial toxin activity, upon storage of the prefilled plastic syringe for 12 months at 5°C or 3 months at 25°C. (a) a plastic syringe barrel including a proximal end and a distal end, and a generally cylindrical wall extending therebetween and defining a barrel lumen, the syringe barrel having a distally projecting tip with a fluid passage extending therethrough and communicating with the barrel lumen, wherein the generally cylindrical wall has an interior surface coated with a barrier layer, (b) a capping device having an outlet engaging portion sealingly engaging and closing the distal open outlet end of the syringe, wherein the outlet engaging portion is made of an elastomeric material, and (c) a plunger rod assembly which extends into the proximal end of the syringe barrel and includes a plunger stopper in sliding fluid-tight engagement with the cylindrical wall of the barrel lumen, wherein the plunger stopper is made of an elastomeric material, which has a coating on at least a portion of the plunger stopper contacting the aqueous botulinum toxin formulation during storage and/or injection, wherein the barrier layer of the syringe barrel is a silicone layer, wherein the elastomeric material of the outlet engaging portion is chlorinated butyl rubber, wherein the elastomeric material of the plunger stopper is chloro butyl rubber and the coating on the plunger stopper is a crosslinked silicone coating, or the elastomeric material of the plunger stopper is bromo butyl rubber and the coating on the plunger stopper is a fluorinated ethylene-ethylene copolymer coating, wherein the aqueous botulinum toxin formulation comprises water, botulinum toxin at a concentration of 10 U/ml to 150 U/ml, sodium chloride at a concentration of 0.5% to 1.5% w/v, a sugar at a concentration of 0.1% to 2% w/v, and albumin at a concentration of 0.01% to 1% w/v, and the pH of the aqueous botulinum toxin formulation is between 6.1 and 7.3 during storage, and wherein the biological activity of the botulinum toxin expressed in Mouse Units is not reduced by more than 25%, relative to the initial toxin activity, upon storage of the prefilled plastic syringe for 12 months at 5°C or 3 months at 25°C.