Comparison of Analgesic Effect between Gabapentin and Diclofenac on Post-Operative Pain in Patients Undergoing Tonsillectomy

Dear Editor, We have examined attentively the latest manuscript by Yeganeh Mogadam et al. entitled " Comparison of Analgesic Effect between Gabapentin and Diclofenac on Post-Operative Pain in Patients Undergoing Tonsillectomy " available in Archives of Trauma Research (1). Ninety patients were included to receive 20 mg/kg oral gabapentin (n = 30), 1.0 mg/kg rectal diclofenac (n = 30) or placebo (n = 30) preoperatively. Pain was evaluated postoperatively at 2, 6, 12 and 24 hours. Authors concluded that gabapentin and diclofenac reduced postoperative pain and opioid consumption without any obvious side effects. Diclofenac is highly bound to serum proteins (≥ 99.5%) and has a relatively low volume of distribution (0.12 to 0.17 L/kg) (2, 3). Diclofenac easily penetrates the synovial fluid and crosses the placenta (2,3). However, diclofenac does not easily cross the blood-brain barrier. It has been proved that the diclofenac concentrations in cerebro-spinal fluid is 8.22% compared to its value in plasma (4). There are reports wherein the anti-inflammatory and antinociceptive effect of diclofenac cannot be directly explained by circulating concentrations in humans (2, 3). Therefore, it has been suggested that diclofenac effects are mainly mediated via a local action in target tissues. In the present study, it is probable that diclofenac produced prostaglandins inhibition to oropharynx level and with that decreasing the sensitization of nociceptors at this level. On the other hand, although gabapentin is a structural analogue of GABA, which does not cross the blood-brain barrier, gabapentin penetrates into the central nervous system (5). Gabapentin binds to plasma proteins and it is not metabolized by nor inhibits hepatic enzymes that are responsible for the metabolism of other drugs (6). It is well known that gabapentin has analgesic and antihyperalgesic effects and is used in the control of clinical pain (6, 7). In this sense, the properties of gaba-pentin have been attributed to an action on the central and peripheral nervous system. Therefore, it is suggested that the gabapentin-induced analgesic effect in the present study was mediated by pain modulation at local level and on the descending pathways. In the present study, children and adult patients were evaluated together. It has been suggested that children may need moderately higher dosages of gabapentin to reach plasma concentrations comparable with those found in adults (8). Likewise, differences have been found in the volume of distribution, Cmax and clearance of diclofenac between children and adults (9, 10). Therefore, all …