Does Postoperative Gabapentin Reduce Pain, Opioid Consumption and Anxiety and Have a Positive Effect on Health Related Quality of Life After Radical Prostatectomy?

The Acute Pain Service (APS) at Sunnybrook has been using Gabapentin 200 mg three times a day (TID) resulting in anecdotal benefits in terms of analgesia and opioid sparing effects. Higher doses of Gabapentin were associated with an increased incidence of sedation. The purpose of the study is to investigate if Gabapentin 200 mg given three times a day for 72 hours (9doses) results in a reduction in the total amount of opioid required after radical prostatectomy surgery as compared to placebo, and if analgesia is improved. This study will also examine the possible anxiety sparing effects and any health related quality of life (HRQL) changes, which may be a result of our perioperative use of gabapentin.

Gabapentin Gabapentin is an anti-epileptic agent originally developed to treat spasticity (1), and eventually was found to be effective against chronic neuropathic pain (1,2). Gabapentin is available as an oral preparation and is primarily absorbed in the small intestine (1). Gabapentin is not metabolized in humans and is eliminated unchanged via the kidneys. It has no known drug-drug interactions, but it is reported that antacids can reduce the bioavailability of Gabapentin by about 20%, and Cimetidine can decrease the clearance of Gabapentin from the body by about 12% (1,2). Side effects of Gabapentin tend to be mild with somnolence (20%), dizziness (18%), ataxia (13%), and fatigue (11%) being the most common (1). The exact mechanism of Gabapentin in pain management is unknown, but it has demonstrated inhibition of mechanical hyperalgesia, and mechanical/thermal allodynia in those with neuropathic pain (1).

Over the past 5 years, there have been 20 studies examining the effect of Gabapentin on postoperative pain (1 \& 3-22). All but one of these studies (16) has found that Gabapentin demonstrated a significant reduction in the amount of postoperative opioid required (16-67%) and a simultaneous reduction in pain scores. There was no difference in side effect profile between the Gabapentin and the control groups in 11 studies(3-5,7,8,10,14-16,18,20), while one(18) found a higher incidence of nausea and urinary retention in the control groups, and two studies(11,13) found a higher incidence of nausea/vomiting in the Gabapentin group. The most common side effect of increased sedation was found in only 4 studies when doses greater than 900 mg per day were given (9,11-13). The daily dose of postoperative Gabapentin in the current protocol is 200 mg TID (600 mg/day) which we currently use in our clinical population with minimal side effect issues.

There have been 8 studies looking at the administration of Gabapentin in the postoperative period (4,6-8,11,20,22,23). Fassoulaki and colleagues (6) examined pain scores and opioid consumption in postoperative breast cancer patients. Seventy-five patients undergoing surgery for breast cancer were randomized to receive Mexiletine 600 mg/day, Gabapentin 1200 mg/day or placebo for 10 days. Opioid consumption was reduced by 50% in the Gabapentin and Mexiletine groups vs. the placebo group on days 2-10. Only the Gabapentin group had decreased pain after movement from the 2nd to the 5th postoperative day. There were no adverse effects reported in the Gabapentin group. Dierking and his colleagues randomized 80 patients to receive either 1200 mg of Gabapentin or placebo 1 hr preoperatively, then either Gabapentin 600 mg or placebo at hours 8, 16, and 24 postoperatively following abdominal hysterectomies(4). Opioid consumption was reduced by 32% in this study and there was no significant difference between side effects in either group. Another study looking at postoperative outcomes and Gabapentin was published by Gilron and his colleagues who randomized 110 patients to 4 study groups: (A) placebo (B) Gabapentin 600 mg TID (C) Rofecoxib 50 mg/day (D) Gabapentin 600 mg TID \& Rofecoxib 50 mg/day starting 1hr preoperatively and continuing for 72 hours postoperatively (9). This study was unique because it went further than simply looking at pain scores and morphine consumption data. Gilron and his colleagues demonstrated that the Gabapentin and the Gabapentin and Rofecoxib groups also significantly decreased movement associated pain evoked by sitting and coughing post abdominal hysterectomy. Adverse events were similar in all groups except sedation, which was more frequent with Gabapentin. Consistent with previous literature, the multimodal Gabapentin/Rofecoxib combination demonstrated opioid sparing, lower pain scores, but most importantly, decreased movement associated pain, which may be a significant factor in faster rehabilitation. In our study we have chosen to use Gabapentin 200 mg TID (bioequivalence of 600 mg/day) based on our extensive clinical experience with our patient population. This appears to be the dose at which most patients do not exhibit the Gabapentin related side effects described earlier. Only four studies have prescribed Gabapentin beyond 72 hours postoperatively (6-8,11). This is an area in which further research is needed to determine whether prolonged postoperative administration and its benefits translate into earlier hospital discharge, decreased chronic pain rates and increased functional recovery even beyond the acute post surgical time period. By following patients to 4 weeks post surgery, this study will aim to answer some of the questions regarding the perioperative use of gabapentin and its possible role ameliorating functional recovery beyond the acute hospitalization period.

The Sunnybrook Health Sciences Acute Pain Service (APS) does not know if 200 mg of Gabapentin is effective at reducing morphine consumption, and improving analgesia. Much higher doses (i.e. greater than 1800 mg/day) published in the literature were initially used at Sunnybrook, but many patients (anecdotally) became too sedated. We are currently using the dose suggested in our protocol 200 mg TID without any major problems. Therefore our goal is to assess if Gabapentin 200 mg does in fact have opioid reducing and analgesic benefits in the radical prostate population. Our pilot data from 15 patients indicates these benefits might exist. Furthermore, examining the role of gabapentin in regards to perioperative anxiety and following patients beyond the acute post surgical time period and following any changes related to their functional recovery and quality of life will help to close some of the gaps in the literature regarding the perioperative usefulness of gabapentin.

Gabapentin and Anxiety

The preoperative effectiveness of Gabapentin in decreasing anxiety scores and improving early functional recovery after anterior cruciate ligament knee surgery (n=40) has recently been demonstrated(10). Premedication with Gabapentin 1200 mg improved preoperative anxiolysis, postoperative analgesia, and early knee mobilization. By including a physical measure (active and passive knee flexion), Menigaux and colleagues also demonstrated that adequate postoperative analgesia enhances mobilization of the knee joint, thus potentially improving functional recovery. This French study examined patient's preoperative anxiety levels by administering an anxiety Visual Analogue Score prior to induction of anesthesia in the operating room. Since this method of anxiety testing has not been validated, we will use four reliable and well-validated anxiety tools in our present study. These measures are all one page questionnaires that are of little burden to patients. The anxiety measures are: The Spielberger State-Trait Anxiety Inventory, The Pain Catastrophising Scale, The Pain Anxiety Symptoms Scale and a 7 Item Modified Hospital Anxiety \& Depression Scale.

The State-Trait Anxiety Inventory (STAI) consists of two self-report scales, one measuring state anxiety and the other measuring trait anxiety (24). Each scale consists of 20 statements about how the respondent may feel, and they are asked to rate how strongly they agree ("very much so") or disagree ("not at all") with the item. The S-Anxiety scale evaluates how respondents feel "right now, at this moment", whereas the T-Anxiety scale evaluates how they feel "generally". This scale has been used extensively in research and clinical practice, and has been shown to be valid and reliable (24).

Catastrophising or catastrophic thinking refers to "an exaggerated negative 'mental set' brought to bear during actual or anticipated pain experience" (25). The PCS is a 13 item self-report inventory that measures catastrophic thinking in relation to pain (26). Respondents are asked to reflect on past painful experiences and to indicate the degree to which they experience each of 13 thoughts or feelings when experiencing pain. Each item is rated on a 5-point rating scale with the end points 0 = not at all and 4 = all the time. The PCS yields a total score and three subscale scores assessing rumination (i.e., excessive focus on pain sensations), magnification (i.e., exaggerating the threat value of pain sensations) and helplessness (i.e., perceiving oneself as unable to cope with pain symptoms). The PCS has been shown to have high internal consistency {coefficient alphas: total PCS = .87, rumination = .87, magnification = .66, and helplessness = .78 (26). The PCS has been shown to predict pain intensity in patients with acute postoperative pain (27) and pain related disability in chronic neuropathic pain patients even after controlling for pain severity (28).

The Pain Anxiety Symptoms Scale (PASS) is a 40-item assessment tool that measures fear and anxiety responses to pain, and the short form of the PASS is a condensed version of the full PASS with only 20 items (29). The PASS-20 is a reliable and valid scale with adequate psychometric properties.

Finally, The Hospital Anxiety and Depression Scale (HADS, 30) is a widely used scale for measuring the symptoms of anxiety and depression among medical inpatients, outpatients and in the general population (31). The HADS is a 14-item questionnaire that measures symptoms of anxiety (7 items) and depression (7 items). For each item, the patient is asked to select from among 4 possible choices (scored from 0 to 3) the one that best describes how they have been feeling over the past week. The HADS yields an anxiety (HADS-A) and a depression (HADS-D) subscale score. We have chosen to administer only the (HADS-D) component because we feel that the other anxiety measure provide enough information in regards to anxiety. In general, the psychometric properties of the HADS are excellent. It has been administered in more than 700 studies to more than 35,000 individuals. Internal consistency for the anxiety and depression subscales show Chronbach alphas of between 0.80-0.93 for the anxiety subscale and between 0.81 and 0.90 for the depression subscale (31,32). Concurrent validity of the HADS is very good as measured by correlation coefficients of between 0.62 and 0.73 for the HADS-D with various well-validated depression scales (e.g., Beck Depression Inventory, SCL-90 Depression subscale (31,32). The HADS has been demonstrated to be sensitive to changes due to disease progression and in response to therapeutic interventions (32). The 7 item modified HADS will take less than 2 minutes to fill out (33).

The burden to patients will be minimal because all of the above measures can be completed in 15-20 minutes. Patients will be asked to complete these items at baseline (prior to surgery), on the day of hospital discharge (likely POD 3) and at the 3 month follow up post surgery.

Health Related Quality of Life

Outcomes pertaining to health related quality of life (HRQOL) are gaining importance when assessing the impact that interventions have on various disease states (34). Many tools are available, however it has been recommended that both a general and disease specific HRQOL tool be used to help ensure any changes in HRQOL status are captured (34,35). Regardless of the instrument(s) chosen they should be valid \& reliable, as well as sensitive and responsive to change (35, 36). Other key considerations include utilizing a tool that captures the key dimensions of HRQOL, specifically physical, psychological, \& social/role functioning (35, 37). A critical component to assessing HRQOL is that, given the subjective nature of quality of life, the data should be assessed by the patient, not the health care provider (37).

In order to meet all of these criteria, this study will utilize the SF-36 Health Outcomes questionnaire (SF-36), the UCLA Prostate Cancer Index, (UCLA-PCI) and the Brief Pain Inventory (BPI).

The SF-36 is a widely used general HRQOL tool, with extensive validity and reliability and responsiveness across many populations (38, 39). The SF-36 is a 36 question survey used to describe overall health status. It has 8 subscales (physical functioning, role limitations, bodily pain, general health perception, vitality, social function, role limitation as a result of emotional problems, and general mental health). It takes 5-10 minutes to complete and can be used with persons 14 and older.

The UCLA Prostate Cancer Index (UCLA-PCI) is also a valid and reliable tool, measuring health related outcomes specific to the prostate cancer population (40). It takes about 10 minutes to complete. In a recent review of HRQL in prostate cancer studies, the SF-36 and UCLA-PCA were the most frequently used general and disease specific tools used (41)

In order to make the measurement of pain more robust, a valid and reliable tool should be used. The Numeric Rating Scale (NRS) \& Brief Pain Inventory will be used. The Brief Pain Inventory (BPI) is a widely used tool that has been validated in a wide variety of clinical and research populations, including the cancer population (42) and post operative population (43). It takes about 5 minutes to complete. The BPI measures pain intensity and pain interference on work, activity, mood, enjoyment sleep, walking, and relationships. It is important to assess baseline pain when undertaking a trial to assess pain or analgesia related outcomes.

Recently published articles have examined the effect of post operative pain on HRQOL after discharge, and have found that pain contributes to lower scores on HRQOL indices (44-46), at one week and one month post discharge.

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Eligibility Criteria:
Inclusion Criteria:

* Undergoing radical prostatectomy
* Able to read and write english (assistance is allowed)
* Normal creatinine blood serum level
* No known allergies to study medications

Exclusion Criteria:

* Patients not providing informed consent
* Patients less than 18 years of age or greater than 75 years of age
* Known allergy to any of the medications being used
* History of drug or alcohol abuse
* Preoperative pain
* Patients unable or unwilling to use PCA
* Patients with impaired renal function (Creatinine \>106)