IT IS A SYNTHETIC OPIOID AGONIST-ANTAGONIST ANALGESIC OF THE PHENANTHRENE SERIES. NALBUPHINE IS A POTENT ANALGESIC. ITS ANALGESIC POTENCY IS ESSENTIALLY EQUIVALENT TO THAT OF MORPHINE ON A MILLIGRAM BASIS. RECEPTOR STUDIES SHOW THAT NALBUPHINE BINDS TO MU, KAPPA, AND DELTA RECEPTORS, BUT NOT TO SIGMA RECEPTORS. NALBUPHINE IS PRIMARILY A KAPPA AGONIST/PARTIAL MU ANTAGONIST ANALGESIC.
THE ONSET OF ACTION OF NALBUPHINE OCCURS WITHIN 2 TO 3 MINUTES AFTER INTRAVENOUS ADMINISTRATION, AND IN LESS THAN 15 MINUTES FOLLOWING SUBCUTANEOUS OR INTRAMUSCULAR INJECTION. THE PLASMA HALF-LIFE OF NALBUPHINE IS 5 HOURS, AND IN CLINICAL STUDIES THE DURATION OF ANALGESIC ACTIVITY HAS BEEN REPORTED TO RANGE FROM 3 TO 6 HOURS.
NALBUPHINE MAY PRODUCE THE SAME DEGREE OF RESPIRATORY DEPRESSION AS EQUIANALGESIC DOSES OF MORPHINE. HOWEVER, NALBUPHINE EXHIBITS A CEILING EFFECT.