Tramadol
Tramadol is an analgesic agent with a complicated mechanism of action:
- Action at all opioid receptors, but particularly MOP, causing analgesia as well as nausea and vomiting
- Inhibits 5-HT reuptake which provides descending inhibitory analgesia
- Inhibits NA reuptake descending inhibitory analgesia
- NMDA receptor antagonist
| Properties | Tramadol |
|---|---|
| Class | Cyclohexanol derivative. Racemic mixture of (+)Tramadol which has greater MOP and 5HT reuptake effects, and (-)Tramadol, which mediates NA reuptake inhibition |
| Uses | Analgesia |
| Presentation | Racemic mixture - each isomer has complementary effects. IV solution is clear at 50mg.ml-1 |
| Route of Administration | PO/IV/Topical |
| Dosing | 50-100mg QID. Potency 1/5th that of morphine. |
| Absorption | Bioavailability 70% |
| Distribution | VD 4L.kg-1 |
| Metabolism | Hepatic to active and inactive metabolites |
| Excretion | Urinary of predominantly inactive metabolites, t1/2β 300 minutes |
| Respiratory | Minimal respiratory depression |
| CVS | Avoid concomitant MAO-I use given NA reuptake inhibition |
| CNS | Increased seizure risk in those with epilepsy or concurrent SSRI/SNRI/TCA use. Minimal addiction potential |
| GIT | N/V |
References
- Peck TE, Hill SA. Pharmacology for Anaesthesia and Intensive Care. 4th Ed. Cambridge University Press. 2014.