Preemptive analgesia is a treatment modality which starts even before the surgery, so that the central sensitization is prevented due to incisional injury at the time of surgery, so it covers the period of surgery and initial post-operative period preventing the development of central sensitization.

Gabapentinoid compounds are gabapentin and pregabalin which have been extensively used in seizure disorder patient. Role of gabapentinoid compounds in the management of pain, as a pre-emptive analgesia is yet to be completely evaluated in post operative pain. Opioids have always been the preferred drugs to manage post operative pain. Since opioids have major side effects of nausea vomiting associated with its treatment their use comes with management of these side effects.

Currently, diagnostic and therapeutic approaches to manage pain experienced by individuals are limited especially because there's a lack of bio-markers predictive of therapeutic outcome. In search of an objective method for pain measurement, as pain has always been subjective and it is perceived by different people differently the study will also include finding the use of COX(cyclo-oxygenase)-2 as a bio-marker of pain in post-operative patients.

Although several randomized clinical trials and met-analyses have been conducted comparing the safety and efficacy of tapentadol or pregabalin in post-operative pain, there is no head to head clinical trial conducted comparing the preemptive use of two drugs for postoperative pain following total knee arthroplasty (TKA). Hence the present study is planned.

MATERIALS AND METHODS

After approval of the institutional Ethics committee board, written informed consent will be taken from all the eligible and willing patients.

A. Study design: Randomized double blind active controlled parallel group noninferiority clinical trial.

B. Randomization: A variable block randomization. The allocation ratio will be 1:1 ratio between two interventions arms i.e. tapentadol 100 mg(milligram) and pregabalin 150 mg(milligram) orally.

C. Allocation concealment: This study will be participant and investigator blinded. Allocation concealment will be done by sequentially numbered sealed drug pouches.

D. Study site: Department of Pharmacology and Orthopedics of AIIMS, Bhubaneswar.

Selection Criteria

A. Inclusion criteria

1. Patients both males and females undergoing total knee arthroplasty surgery.
2. Patients are capable of providing an informed consent.
3. Age group between 18-75 years.

B. Exclusion criteria

1. Patients with asthma, COPD(Chronic obstructive pulmonary disease) or any other respiratory disease.
2. Persistent nausea and vomiting at time of randomization
3. Epilepsy.
4. Treated with mono amine oxidase inhibitors, tricyclic antidepressants, serotonin norepinephrine re-uptake inhibitors, gabapentinoids.
5. Patient with known neurological/ neuropsychiatric disorders.
6. Drug or alcohol abuse history
7. Opioid tolerance or opioid dependence.
8. Known history of opioid allergy or pregabalin allergy.
9. Renal disease (creatinine >1.5mg/dl)
10. Liver disease (total bilirubin >1.5mg/dl)
11. Pregnancy and lactation.
12. Cardiovascular insufficiency.
13. Patient with potential serotonin syndrome.
14. Patient with history of constipation and prone to paralytic ileus.

Study procedure, tools & evaluation

1. Consent: Patients will be explained the benefit and harm of joining the study and freedom of withdrawing from the study any moment they would like to. A full voluntary written informed consent will be obtained from each patient. Study will be conducted following the principles of Helsinki after getting written permission of the institutional ethics committee. Before enrolment of first patient in this study registration for clinical trial will be done.
2. All the patients will be screened before enrollment after eliciting detailed history they will undergo complete medical and laboratory examinations.
3. A total of 90 patients of either sex will be selected randomly and will be assigned to receive 100 mg of Tapentadol or 150mg Pregabalin orally 1hr before surgery in a double-blind manner. The patient will be assessed for pain at 0,6,12, and 24hrs, post operatively by visual analogue scale score(VAS) (0-100). Pain measurements will also be done on TOTPAR scale at 0,6,12,24 hours. Total rescue analgesic consumption also will be assessed at 24hrs post operatively. All treatment emergent adverse events will be documented. The time to 1st patient request for supplemental analgesia also will be recorded.
4. A blood sample will be obtained from each of the patients twice once at 0 hrs. and again at 6hrs post operatively to evaluate concentration of COX-2 levels by ELISA with commercially available ELISA kits.

Inclusion Criteria:

• 1. Patients both males and females undergoing total knee arthroplasty surgery. 2. Patients are capable of providing an informed consent. 3. Age group between 18-75 years.

Exclusion Criteria:

• 1.Patients with asthma, COPD or any other respiratory disease. 2. Persistent nausea and vomiting at time of randomization 3. Epilepsy. 4. Treated with mono amine oxidase inhibitors, tricyclic antidepressants, serotonin norepinephrine re-uptake inhibitors, gabapentinoids.

  5. Patient with known neurological/ neuropsychiatric disorders. 6. Drug or alcohol abuse history 7. Opioid tolerance or opioid dependence. 8. Known history of opioid allergy or pregabalin allergy. 9. Renal disease (creatinine >1.5mg/dl) 10. Liver disease (total bilirubin >1.5mg/dl) 11. Pregnancy and lactation. 12. Cardiovascular insufficiency. 13. Patient with potential serotonin syndrome. 14. Patient with history of constipation and prone to paralytic ileus.

This study will be participant and investigator blinded. Allocation concealment will be done by sequentially numbered sealed drug pouches.