The transition from acute to chronic post-surgical pain - a prospective, randomised controlled trial of two medications (nortriptyline and gabapentin) in 150 participants undergoing hip or knee replacement surgery.

There are two pharmaceutical interventions which will be given simultaneously to the intervention group, as studies have shown these medications to have synergistic analgesic activity. The first is gabapentin, which is a gamma-aminobutyric acid (GABA) analogue, which was developed as an anti-epileptic before becoming widely used in neuropathic pain. This medication is taken orally in three daily doses, and will be titrated up in increments of 300mg/day from 300mg to the maximum tolerated dose for an individual (usually in the range of 1800-2200mg/day, with 2200mg being the ceiling limit in this trial). The other pharmaceutical being trialled is nortriptyline. Nortriptyline is a tri-cyclic antidepressant (TCA) which has recently come into vogue as a treatment for neuropathic pain. Nortriptyline will be taken orally once daily at the maximum tolerated dose for the individual (up to 50mg/day). Like gabapentin, this this dose will be titrated up over the course of 7-10 days, starting at 10mg/day. Both of these medications will be taken by the intervention arm of this study between week 6 post-operatively and 3 months post-operatively (a total of 6 weeks). The possible adverse effects will be explained to the participants in advance, and they will be given the opportunity to ask any questions they may have about the medications. Over the titration period, adherence will be monitored by telephone interviews with participants to monitor any adverse effects they may be experiencing. Participants will be instructed to return any unused medication to the researchers for disposal at the conclusion of their time in the trial.