A 34 year old rickshaw puller has been using heroin for the past ten years. One evening his family members found him unconscious. He was brought to the casualty. On examination he had bradycardia, shallow breathing, constricted pupils. His blood pressure was 100/70 mm of Hg. He had brisk bilateral deep tendon reflexes. The plantar reflexes were flexor on both sides. Which of the following is the best treatment for him ?