Butorphanol is extensively metabolized in the liver. Metabolism is qualitatively and quantitatively similar following intravenous , intramuscular , or nasal administration. The major metabolite of butorphanol is hydroxybutorphanol, while norbutorphanol is produced in small amounts. Both have been detected in plasma following administration of butorphanol. Preliminary evidence suggests the elimination half- life of hydroxybutorphanol may be greater than that of its parent.
Elimination occurs by urine and fecal excretion.
Forty-nine percent is eliminated in the urine as hydroxybutorphanol. No effect was observed on C max or T max after a single dose. The effectiveness of opioid analgesics varies in different pain syndromes. After intramuscular administration, pain relief onset occurred at 30 minutes or less, and peak effect occurred between 30 minutes and 1 hour. The anesthesia regimen included barbiturate induction, followed by nitrous oxide and oxygen with halothane or enflurane, with or without a muscle relaxant.