opioid drug pathway levorphanol drug pathway 2016-03-02T08:45:44Z PW:0002554 The pharmacokinetics and pharmacodynamics pathway of levorphanol, an opioid used for the treatment of moderate to severe pain. Primarily an agonist of the mu opioid receptor, levorphanol acts as an agonist or antagonist for several other receptors. Genetic variations can result in changes in drug availability and can cause differences in the response of the organism to the drug. pathway vpetri