Gabapentin for Prophylaxis Intrathecal Morphine-Induced Pruritus

Intrathecal morphine provides good postoperative analgesia for up to 18-24 hour after administration. Pruritus is the most common side effect of intrathecal morphine, which the incidence was reported as 20%-100%2 and 63% in Songklanagarind Hospital. Pathophysiology of opioid-induced pruritus remain unclear and more than one mechanism may be involved in the development of opioid-induced pruritus, such as, mediated central µ opioid receptors, Dopamine (D2) receptors, Serotonin (5-HT3) receptors, prostaglandin system, GABA receptors, and glycine receptors, so that why opioid-induced pruritus is difficult to manage. Many medications have been used to treat this side effect included antihistamines, 5-HT3 (serotonin) receptor antagonists, opioid antagonists, opioid agonist-antagonists, propofol, and nonsteroidal antiinflammatory drugs.

Gabapentin is an anticonvulsant, a structural analog of aminobutyric acid, and currently approved by the Food and Drug Administration for the treatment of partial seizures and postherpetic neuralgia. Many studies have shown gabapentin to be effective in the case of brachioradial pruritus, itch of neuropathic in origin, uremic pruritus, multiple sclerosis-induced pruritus,cholestatic pruritus, itch produced by burn, and pruritus of unknown origin. However, there is only one small study in Taiwan shown the effectiveness of gabapentin 1200 mg in prevention of intrathecal morphine-induced pruritus in orthopedic surgery, which could reduce incidence of pruritus from 77.5% to 47.5% (38.7% reduction). Because gabapentin has several side effects especially in high dose such as drowsiness, dry mouth, headache, unsteadiness, reduced co-ordination or slowed reaction, constipation, diarrhea, peripheral edema, dizziness, confusion, loss of concentration, weight gain, and nausea, vomiting, so in our study we decided to reduce the dose of gabapentin. Therefore, we would like to know if gabapentin in a smaller dose (600 mg) used in the wider range of age including the elderly can decrease the incidence of intrathecal morphine-induced pruritus in orthopedic surgery in Songklanagarind Hospital.