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Pharmacology: Pharmacodynamics: The analgesic effect of butorphanol is influenced by the route of administration. Onset of analgesia is within a few minutes for intravenous administration and within 15 minutes for intramuscular injection. Peak analgesic activity occurs within 30 to 60 minutes following intravenous and intramuscular administration. The duration of analgesia varies depending on the pain model as well as the route of administration, but is generally 3 to 4 hours with IM and IV doses as defined by the time 50% of patients required remedication. In postoperative studies, the duration of analgesia with IV or IM butorphanol was similar to morphine, meperidine. and pentazocine when administered in the same fashion at equipotent doses.
Pharmacokinetics: Butorphanol Tartrate Injection is rapidly absorbed after IM injection and peak plasma levels are reached in 20 to 40 minutes.
