One might speculate that L-Dromoran is superior to morphine in the following respects:
A low(er) capacity to induce tolerance
An enhanced action on descending inhibitory pathways
Its multi-modal synergystic properties
Actions against hyperalgesia
Its unique applicability to severe chronic pain including cancer-related and neuropathic pain.
Its long duration of action and accumulative phartmacokinetic properties; when dosed correctly this accumulation allows chronic doses to be reduced to as little as half the induction dose.
Often better tolerated than morphine, with less nausea & vomiting, pruritis, constipation, and very little to no clouding or sedation.
Its Pharmacodynamic Mechanisms of Action (A lower numerical value indicates a higher binding affinity for a particular site)
Very high affinity mu agonist - 0.21nM
High affinity kappa agonist - 2.3nM
Moderate affinity delta agonist - 4.2nM
High affinity NMDA antagonist - 0.6uM (methadone is 6.0uM, ketamine is 0.8uM)
5HT (i.e. serotonin) reuptake inhibitor
Norepinephrine reuptake inhibitor
For Some Good Literature on Levorphanol Tartrate: