[Objective] Various vaccines and protein drugs including antibody drugs are mainly used as injectable drug such as subcutaneous or intramuscular injection. Pain caused by administration of these injections is a side effect in a broad sense. Therefore, it is necessary to select "less painful" in consideration of improvement of QOL of patients from multiple drugs having equivalent efficacy, but it was not easy to predict and evaluate pain at the preclinical phase. Thus, we report the quantification of pain using the electromyogram generated at the injection. [Materials, Methods] Rats were anesthetized with pentobarbital. A bipolar stainless-steel electrode was placed into the semitendinosus muscle. The EMG signals were recorded in Power Lab 8/35. After inserting the electrode, the fingertip of hind limb was pinched strongly by clamp, and confirmed the EMG amplitude was increased. 0.9% Saline ( 50µL, pH 6.5 ) was served as negative controls.  10 % salt solution (50µL), dilute hydrochloric acid (50 µL, pH 3), and 0.9% saline solution (200µL) as expected to cause pain were injected into the rat plantar aspect subcutaneously. [RESULTS] EMG amplitude was increased in each solution immediately after injection. These results suggested the quantification of pain associated with parenteral injection is a useful evaluation system.

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