Tramadol
Second line weak opioid
Mechanism of action: mu-opioid agonist and inhibition of the reuptake of norepinephrine and serotonin. Tramadol consists of two enantiomers: R(+)-tramadol is an agonist of the mu opioid receptor and inhibits serotonin reuptake, while S(-)-tramadol inhibits norepinephrine reuptake.
Presentation: tablet, dispersible tablet, injection
Suggested dose: 50-100mg orally four times a day for adults over 50kg with normal hepatic and renal function.
Caution:
- in elderly patients as can cause confusion
- in patients with epilepsy as can lower seizure threshold
- in patients co-prescribed antidepressants due to risk of serotonin syndrome
Serotonin syndrome is caused by excessive stimulation of serotonin receptors in the central and peripheral nervous system, and may be precipitated when tramadol is co-prescribed with an SSRI. The features include:
- neuromuscular hyperactivity (tremor, clonus, myoclonus, hyperreflexia, rigidity);
- autonomic hyperactivity (sweating, fever, tachycardia, tachypnoea); and
- altered mental status (agitation, confusion).
Co-prescribe prn Naloxone
Oral absorption: rapid and almost complete absorption after oral administration. Bioavailability of approx. 75%
Protein binding: 20%
Metabolism: Hepatic. The O-desmethyl-tramadol derivative (designated M1) produced by CYP2D6 has a 6 times higher affinity for the mu opioid receptor than the parent compound.
Elimination: excreted by the kidneys: 30% is excreted unchanged in the urine, with 60% excreted as metabolites.
Half-life: 6 hours
Further prescribing information (side effects, contraindications, interactions):