A hazardous agent injection system including from about 0.02 ml to about 4.0 ml of methotrexate at a concentration of from about 7.5 mg/ml to about 150 mg/ml; a needle-assisted jet injector including a container configured to contain the methotrexate; a injection outlet member associated with the container; an injection-assisting needle coupled to the injection outlet member; a firing mechanism associated with the container; an energy source associated with the firing mechanism; and a trigger mechanism associated with the firing mechanism, wherein the needle-assisted jet injector is configured to eject the methotrexate from the injection outlet member such that the Cmax, Tmax and bioavailability of the needle-assisted jet injected methotrexate falls between about 80% and about 125% of the Cmax, Tmax and bioavailability of methotrexate delivered by a hand-powered syringe.