Liposome Bupivacaine Femoral Nerve Block for Postsurgical Analgesia after Total Knee Arthroplasty

PATIENTS undergoing total knee arthroplasty (TKA) typically experience moderate to severe postsurgical pain^1–3  that can last for several days. Effective pain management facilitates early ambulation and rehabilitation,^4,5  which in turn hastens recovery, reduces length of stay, and decreases patient risk for complications including thromboembolism and nosocomial infection.⁶  Use of femoral nerve block improves postsurgical analgesia and reduces parenteral opioid requirements in patients undergoing TKA.^1,6–10  However, single-injection femoral nerve blocks are limited by the relatively short duration of analgesia provided by the currently available formulations of local anesthetics (typically 24 h or less).^6,11  Duration of analgesia can be prolonged with continuous peripheral nerve blocks. However, this requires placement of a perineural catheter,^11,12  continuous infusion of local anesthetic, inconvenience of carrying catheter and local anesthetic reservoir/pump, infusion management and catheter site care, infection, leakage, accidental dislocation, and cost and maintenance of equipment.^11,13 

Liposome bupivacaine (bupivacaine liposome injectable suspension; EXPAREL^®; Pacira Pharmaceuticals, Inc., USA) is a multivesicular formulation of bupivacaine indicated for administration into the surgical site to produce postsurgical analgesia.¹⁴  Liposome bupivacaine has been shown to provide postsurgical analgesia across a range of surgical models, with a safety profile that is similar to that of bupivacaine HCl.^15–17  While available data in volunteers suggest that liposome bupivacaine in a femoral nerve block results in prolonged blockade,¹⁸  its analgesic effects when used in a peripheral nerve block in a setting of acute postsurgical pain remain unknown.

This was a multicenter, randomized, double-blind, parallel-group, placebo-controlled, dose-ranging study designed to meet the U.S. Food and Drug Administration (FDA) standard for approval of analgesic agents, which rests on comparison of investigational agents versus placebo in well-matched populations. The objective was to assess efficacy, safety, and pharmacokinetics of liposome bupivacaine when administered as a single injection in a femoral nerve block in subjects undergoing primary unilateral TKA under general, spinal, or epidural anesthesia (Study Director: Erol Onel, M.D.; U.S. National Institutes of Health [www.clinicaltrials.gov] study identifier: NCT01683071; prospectively registered on September 7, 2012). The study was conducted in two parts at 23 U.S. medical centers: dose ranging (part 1) and treatment (part 2). In part 1, the primary objective was to evaluate three liposome bupivacaine doses versus placebo and select an optimal dose from among these for part 2. In part 2, the primary objective was to evaluate the selected dose of liposome bupivacaine versus placebo with respect to efficacy and safety.

Because this study involved an off-label use of liposome bupivacaine, an Investigational New Drug application (No. 69,198) was approved by the FDA before subject enrollment. Individual enrolling centers obtained approval of an institutional review board/independent ethics committee (appendix) that complied with International Council for Harmonisation Good Clinical Practice guidelines and/or the FDA Title 21 of the Code of Federal Regulations Part 56. Written informed consent was obtained from all subjects before undergoing any study-related procedures.

Male and female subjects aged 18 yr or older scheduled to undergo primary, unilateral TKA under general, spinal, or epidural anesthesia were eligible if classified as American Society of Anesthesiologists physical status classification of 1, 2, or 3; demonstrated adequate motor function by being able to walk unassisted at least 20 m (use of four-legged walker optional); and had no sensory deficit in the distribution of the femoral nerve, as tested by sensitivity to cold. Subjects were excluded if they were pregnant or nursing; were undergoing a concurrent surgical procedure (e.g., bilateral TKA); had a concurrent painful condition that may have required analgesic treatment in the postsurgical period that was not strictly related to study treatment and may have confounded the postsurgical assessments; or had used long-acting opioids, nonsteroidal antiinflammatory drugs, acetaminophen, or aspirin (except low-dose aspirin for cardioprotection) within 3 days before surgery or any opioids within 24 h before surgery. Subjects who had initiated treatment with selective serotonin or norepinephrine reuptake inhibitors, gabapentin, pregabalin, or duloxetine within 1 month before surgery were also excluded.

For parts 1 and 2, each subject received a unique randomization code and subject identifier issued by a centralized randomization system. Synteract, Inc. (USA) created the randomization schedule using SAS^®, and Premier Research (USA) incorporated the schedule into their interactive Web response system. During part 1, 101 subjects undergoing TKA were randomized in a 1:1:1:1 ratio to receive one of three single-dose administrations (67, 133, or 266 mg) of liposome bupivacaine in a total volume of 20 ml or preservative-free normal saline for injection (placebo) administered in a femoral nerve block under ultrasound guidance. At the conclusion of the block, a femoral nerve catheter was left in place to allow access for administration of perineural local anesthetic as a rescue treatment, if needed. Blood samples for pharmacokinetic analysis were also obtained during part 1. An unblinded dose selection committee reviewed the area under the curve for numeric rating scale score for pain intensity at rest through 72 h (AUC NRS-R_0–72), total postsurgical opioid consumption, time to first opioid rescue medication, and safety data through 72 h postoperatively. The unblinded dose selection committee then selected the optimal dose for part 2.

During part 2, 196 subjects (none of whom participated in part 1) were randomized in a 1:1 ratio to receive the selected dose of liposome bupivacaine or placebo in a total volume of 20 ml in a single-injection femoral nerve block under ultrasound guidance. At the conclusion of the block, a femoral nerve catheter was left in place to allow access for administration of perineural local anesthetic as a rescue treatment, if needed.

Preoperatively, a single-injection femoral nerve block and perineural catheter were administered under ultrasound guidance, as previously described.¹⁹  All surgeries were conducted under general, spinal, or epidural anesthesia. Bupivacaine was not used as the spinal anesthetic. The choice of other spinal anesthetic agent or agents was left to the discretion of the attending anesthesiologist. Use of short-acting and ultra–short-acting IV opioids (e.g., fentanyl) was permitted during surgery. However, intraoperative administration of other opioids (including intrathecal opioids) or any other analgesics, local anesthetics (except for spinal anesthesia), or antiinflammatory agents was not permitted except for emergency use to treat an adverse event (AE).

In parts 1 and 2, postsurgical rescue analgesic medications were administered only upon subject request according to a protocol-defined sequence. No other analgesics (including nonsteroidal antiinflammatory drugs) were permitted during the 72-h postsurgical observation period. If a first rescue medication was required, the subject was given a single IV bolus of hydromorphone 0.5 mg. If a second rescue medication was required, the subject was provided with on-demand IV morphine or hydromorphone, administered by a patient-controlled analgesia pump for the remainder of the 72-h study period or until a third rescue medication was requested; if the subject was able to tolerate oral medications, immediate-release oxycodone tablets (no more than 10 mg every 4 h) were available. If a third rescue medication was required, the subject received a continuous femoral nerve block of bupivacaine HCl 0.125% (1.25 mg/ml), administered via the previously inserted femoral nerve catheter at a rate of 8 ml/h for up to 12 h. Any subject who failed to achieve adequate analgesia after three rescue treatments was withdrawn from the study and followed only for safety. For subjects who were withdrawn, analgesia was provided in accordance with standard practice at the individual study site.

During part 1 only, blood samples for pharmacokinetic assessments were drawn at baseline, 15 min, 30 min, and 1, 2, 4, 8, 12, 24, 36, 48, 60, and 72 h after starting administration of study medication.

Pain intensity assessments were conducted at baseline (before nerve block administration), at 2, 4, 8, 12, 24, 36, 48, 60, and 72 h postsurgery, and at the first request for rescue analgesia. Pain was assessed using an 11-point NRS (0 = no pain; 10 = worst possible pain) at rest and upon activity, the latter defined as active flexion of involved knee 45 degrees or less. Sensitivity to cold was assessed at baseline and at 2, 4, 12, 24, 36, 48, 60, and 72 h after surgery or until sensitivity to cold had returned in two consecutive evaluations. Motor function was assessed during the acute postsurgical period and on day 30 by measuring the subject’s ability to walk 20 m on a level surface with or without use of a four-legged walker. Long-term rehabilitation outcomes were not assessed.

Subjects also completed an overall benefit of analgesic score (OBAS) questionnaire at 24, 48, and 72 h. The OBAS questionnaire is a validated, multidimensional tool that assesses pain intensity, opioid-related AEs, and overall subject satisfaction with pain treatment (table 1).²⁰  Subject satisfaction with pain control and physician satisfaction with return of sensory/motor function were assessed using a 5-point Likert scale (from “extremely dissatisfied” to “extremely satisfied”) at 72 h and on day 30. During part 1 only, subjects were also assessed for predefined treatment-emergent opioid-related AEs.

Efficacy outcomes were assessed for all subjects who received study drug and underwent the surgery as planned and consisted of the primary outcome (AUC NRS-R_0–72), secondary outcomes (total opioid consumption through 72 h and time to first use of opioid rescue medication), and tertiary outcomes (NRS-R and NRS with activity [NRS-A] scores at each assessed time point; AUC of NRS-R scores from 0 to 24, 24 to 48, and 48 to 72 h; total opioid consumption from 0 to 24, 24 to 48, and 48 to 72 h; AUC of NRS-A scores from 0 to 24 and 0 to 72 h; proportion of subjects who were pain-free [NRS-R score of 0 or 1] at each time point; cumulative total opioid consumption at 24, 36, 48, and 60 h; OBAS questionnaire results at 24, 48, and 72 h; subject satisfaction with postsurgical pain control at 72 h and at day 30; and time to subject’s return of sensitivity to cold). Specific opioid doses were converted to IV morphine equivalent doses.

Pharmacokinetic parameters (assessed only during part 1 of the study) were calculated from the plasma bupivacaine concentration–time profiles by noncompartmental analysis and included plasma concentration (C_max), time to peak plasma concentration (T_max), AUC from time 0 to last collection time after drug administration (AUC_0–tlast), AUC from time 0 extrapolated to infinity after drug administration (AUC_0–∞), apparent terminal elimination rate constant (λ_z), and apparent terminal elimination half-life (t_{1/2 el}). Blood samples were drawn at baseline, 15 min, 30 min, and 1, 2, 4, 8, 12, 24, 36, 48, 60, and 72 h after starting administration of study medication. Placebo samples were collected to maintain blinding but were not analyzed.

Safety outcomes were assessed separately, and combined, for all subjects who received study drug in parts 1 or 2 and consisted of AEs (through day 30), vital sign assessments (at baseline and 30 min, 1 h, and 2 h postsurgery), neurologic assessments (at baseline and 15 min, 30 min, and 1, 2, 4, 8, 12, 18, 24, 30, 36, 42, 48, 60, and 72 h postsurgery), cardiac assessment (electrocardiogram recordings from baseline through 72 h postsurgery), motor function assessments (at baseline and 24 and 72 h postsurgery and on day 30), and assessment of physician satisfaction with return of sensory/motor function (at 72 h and day 30 postsurgery). Electrocardiogram data were continuously recorded via a 12-lead electrocardiogram device and interpreted by a centralized reference cardiologist. Electrocardiogram changes were examined using data obtained at the time closest to the actual T_max (when available), mean T_max, and median T_max from each dose group.

Sample size for part 1 was based on the statistician’s estimate of a reasonable sample size from extrapolation of data compiled across phases 2 and 3 wound infiltration studies of liposome bupivacaine.^15,17  Sample size for part 2 was based on results from a phase 3 study of liposome bupivacaine versus placebo in subjects undergoing hemorrhoidectomy, where mean (SD) AUC of NRS-R_0–72 scores were 141.6 (100.6) and 202.3 (104.1), respectively.²¹  An estimated enrollment of approximately 180 subjects (90 per treatment group) was needed to achieve more than 97% power to detect a difference in means of 61 for the primary efficacy analysis (assuming the common SD is 104) using a two-group t test with a significance level of 0.05.

Three subsets of the enrolled study population were analyzed. Safety analyses included all subjects who received study drug and were based on actual treatment received. Efficacy analyses included all subjects in the safety analysis set who underwent surgery as planned and were based on randomized treatment, regardless of actual treatment received. Pharmacokinetic analysis (part 1 only) included all subjects in the safety analysis set who received liposome bupivacaine, provided sufficient blood samples to permit calculation of pharmacokinetic parameters, and did not receive perineural bupivacaine HCl as rescue medication.

Statistical analyses were performed using SAS^® Version 9.2 (SAS Institute Inc., USA, 2009). To account for the use of rescue medication and missing NRS pain intensity score data, windowed worst observation carried forward (wWOCF) plus last observation carried forward (LOCF) imputation method was used to calculate the primary efficacy measure (AUC NRS-R_0–72). The wWOCF plus LOCF imputation procedure was used as follows: wWOCF—for subjects who took rescue medication, NRS scores recorded within a half-life (“window”) of the opioid rescue medication given were replaced by their highest (“worst”) NRS scores before taking their first rescue medication. For subjects who required bupivacaine HCl infusion, the “window” for highest NRS scores was considered from start of infusion until 24 h afterward; LOCF—in cases where subjects had missing NRS pain intensity scores, the scores were interpolated in one of three ways: (1) By the median score from other subjects at the same time point in the same treatment group if before the first nonmissing score; (2) By LOCF if after the last nonmissing score; and (3) By linear interpolation if between two nonmissing scores. Liposome bupivacaine was compared with placebo in parts 1 and 2 using analysis of covariance, with treatment as the main effect and baseline NRS-R pain intensity score as the covariate.

Continuous variables were summarized using standard statistical measures including mean, median, SD, minimum/maximum, P values, and two-sided 95% CIs, along with number of subjects included in each analysis, and were reported by treatment group. Categorical variables were summarized by treatment group using counts and percentages. Between-group differences were reported using least-squares means (for NRS scores) or as geometric least-squares means (for postsurgical opioid amounts used).

For secondary efficacy measures in parts 1 and 2, total postsurgical opioid consumption through 72 h was compared between the liposome bupivacaine and placebo groups using ANOVA with treatment as the main effect. Opioid medications were first converted to IV morphine equivalents for each subject, and natural logarithmic transformation was applied to the total amount before analysis. Between-group differences were reported using geometric least-squares means. Time to first opioid rescue was computed in hours as the date and time of first opioid rescue minus date and time of end of surgery; these data were analyzed using the Kaplan–Meier method.

For part 2, no multiple comparisons of the primary efficacy variable (AUC NRS-R_0–72) were made. The two secondary efficacy variables (total opioid consumption through 72 h and time to first opioid use) were only to be analyzed using a hierarchical fixed-sequence stepwise testing procedure if the primary efficacy variable was statistically significant (P ≤ 0.05). To avoid a type 1 error, the testing was performed in a sequentially rejective fashion. First, total postsurgical opioid consumption through 72 h was tested. If the test of opioid consumption was significant (P ≤ 0.05), time to first opioid rescue medication was tested. Each test was declared positive at the two-sided 0.05 significance level. The significance level for probability values from between-group comparisons of tertiary efficacy variables were adjusted for multiplicity using the Bonferroni correction method. In order to determine whether imputed pain scores had a meaningful effect on cumulative pain scores at rest, a post hoc analysis was conducted to calculate AUC NRS-R_0–72 (the primary end point), as well as AUC NRS-R_0–24, AUC NRS-R_24–48, and AUC NRS-R_48–72, using only unimputed pain scores.

A total of 94 subjects received 67 mg (n = 22), 133 mg (n = 24), or 266 mg (n = 24) liposome bupivacaine or placebo (n = 24). For the primary efficacy measure, AUC NRS-R_0–72, least-squares mean (standard error [SE]) values were 533 ([33] P = 0.949), 427 ([32] P = 0.024), and 436 ([32] P = 0.039) in the liposome bupivacaine 67-, 133-, and 266-mg groups, respectively, compared with 531 (32) in the placebo group (table 2). Regarding secondary efficacy measures, distribution of time to first opioid rescue medication was significantly longer in the liposome bupivacaine 266-mg group compared with placebo (table 3). Several other assessments suggested a better response to the 266-mg dose, most notably at earlier time points tested (table 3). Overall, 86 subjects (92%) experienced an AE during part 1 of the study, 20 (91%) in the liposome bupivacaine 67-mg group, 22 (92%) in the 133-mg group, 21 (88%) in the 266-mg group, and 23 (96%) in the placebo group (table 4). Nausea (47%), pyrexia (28%), dizziness (17%), constipation (13%), and anemia (12%) were the most frequently reported AEs. No subject discontinued study participation due to an AE. Despite no difference in the primary outcome measure between the 133-mg and 266-mg doses, the liposome bupivacaine 266-mg dose was chosen for part 2 of the study, based on a suggestion of a better response earlier not accompanied by meaningfully increased risk of AEs.

Dose-related increases were observed in mean plasma bupivacaine levels, C_max, and AUC values (table 5). The relationship between dose and bupivacaine plasma exposure over time suggests that liposome bupivacaine demonstrates linear pharmacokinetics (fig. 1).

A total of 184 subjects received liposome bupivacaine or placebo (liposome bupivacaine, n = 92; placebo, n = 92) and 164 completed the study (table 6 and fig. 2). In the liposome bupivacaine group, 26% of NRS-R pain intensity scores were not imputed, 69% were imputed due to use of rescue medication, and 5% were interpolated due to a missing value. In the placebo group, 24% of NRS-R scores were not imputed, 70% were imputed due to use of rescue medication, and 6% were interpolated due to a missing value.

Least-squares mean (SE) AUC NRS-R_0–72 was lower in the liposome bupivacaine group than in the placebo group (419 [17] vs. 516 [17], respectively; P < 0.0001; table 7). In the analysis without imputation, least-squares mean AUC NRS-R_0–72 remained significantly lower with liposome bupivacaine versus placebo (221 [12] vs. 282 [12]; P = 0.0005).

Subjects in the liposome bupivacaine group used less total postsurgical opioids through 72 h than those in the placebo group (geometric least-squares mean IV morphine equivalents 76 vs. 103 mg, respectively; P = 0.0016); between-group differences in cumulative opioid consumption were maintained through 24 h (46 vs. 60 mg, respectively), 36 h (58 vs. 77 mg, respectively), 48 h (66 vs. 89 mg, respectively), and 60 h (72 vs. 98 mg, respectively; P ≤ 0.0058 for each comparison). Median time to first use of opioid rescue medication was similar between the liposome bupivacaine and placebo groups (0.44 vs. 0.43 h; P = 0.9556).

Between-group differences in mean (SD) NRS-R at first request for rescue pain medication, AUC of NRS-R_0–24, AUC of NRS-A_0–24, and AUC of NRS-A_0–72 scores, and geometric least-squares mean amount of postsurgical opioid rescue medications consumed from 0 to 24 h were lower in the liposome bupivacaine group versus placebo (table 8). Least-squares mean (SE) AUCs of NRS-R scores were significantly lower (P < 0.0083) in the liposome bupivacaine group during each 24-h interval (0 to 24, 24 to 48, and 48 to 72 h) after surgery (fig. 3). Between-group differences in the least squares mean (SE) in favor of liposome bupivacaine versus placebo were −29.0 (7.6) (P = 0.0002) during the first 24 h postsurgery, −29.1 (8.6) (P = 0.0009) during 24 to 48 h postsurgery, and −38.4 (10.2) (P = 0.0002) during 48 to 72 h postsurgery. In the analysis without imputation, least-squares mean (SE) cumulative pain scores at rest remained significantly lower in the liposome bupivacaine group versus placebo during the first day (AUC NRS-R_0–24, 68 [3] vs. 80 [3], respectively; P = 0.0051) and second day after surgery (AUC NRS-R_24–48, 82 [5] vs. 112 [5], respectively; P< 0.0001), but not on day 3 (AUC NRS-R_48–72, 66 [7] vs. 83 [7], respectively; P = 0.0736).

Least-squares mean (SE) NRS-R and NRS-A scores through 72 h are shown in figures 4 and 5, respectively. Least-squares mean NRS-R scores were lower in the liposome bupivacaine group than in the placebo group at 2, 4, 12, and 24 h postsurgery (fig. 4). The between-group difference in least-squares mean NRS-R scores ranged from as high as 1.6 at 2 h after surgery to as low as 0.5 at 60 h after surgery. Least-squares mean NRS-A scores were lower in the liposome bupivacaine group than in placebo groups at 24 and 60 h after surgery (fig. 5). The between-group difference in least-squares mean NRS-A scores ranged from as high as 1.3 at 2 and 24 h after surgery to as low as 0.5 at 36 h after surgery. The mean NRS-A pain intensity scores remained in the moderate range in both the liposome bupivacaine and placebo groups throughout the part 2 study period.

All subjects required at least some rescue medication (table 9), with no difference between groups (P = not significant [NS]). Pain was sufficiently severe to require the first and then a second opioid rescue medication in 92% of subjects in the liposome bupivacaine group compared with 81% in the placebo group.

More subjects treated with liposome bupivacaine were pain-free at 12 h postsurgery (fig. 6; P = 0.0038). The proportion of subjects treated with liposome bupivacaine who were pain-free increased steadily after 8 through 60 h postsurgery, while the proportion of subjects treated with placebo who were pain-free decreased between 2 and 8 h before increasing at 12 h after surgery.

With respect to subject-reported outcomes, mean OBAS was lower (indicating superior analgesia) among subjects receiving liposome bupivacaine compared with placebo at 24 (5.6 vs. 7.3, respectively; P = 0.0011) and 72 h (3.1 vs. 4.1; P = 0.0072) postsurgery. In contrast, there was no difference in the proportion of subjects who were “satisfied” or “extremely satisfied” with their pain control at 72 h (92 vs. 84%; P = NS) and at day 30 (89 vs. 83%; P = NS). Median time to sensitivity to cold was 1.85 h (95% CI, 0.48 to 2.02) in the liposome bupivacaine group compared with 1.88 h (95% CI, 0.45 to 2.00) in the placebo group (P = NS).

In part 2, 176 subjects (96%) experienced at least one AE, 88 (96%) in each treatment group. Frequency of specific AEs was generally similar between treatment groups (table 4). Nausea (60%), constipation (35%), pruritus (35%), vomiting (35%), and pyrexia (28%) were the most frequently reported AEs. At least one serious AE was reported by eight subjects (9%) receiving liposome bupivacaine 266 mg and nine subjects (10%) receiving placebo. Each of the serious AEs was judged by the study investigator to be unrelated to study drug. There were no discontinuations due to an AE, and there were no deaths during the study.

In parts 1 and 2 combined, physician satisfaction with return of sensory/motor function was rated as “satisfied” or “extremely satisfied” for 89% of subjects receiving liposome bupivacaine 266 mg at 72 h postsurgery versus 95% of subjects who received placebo. On day 30, proportions of “satisfied” or “extremely satisfied” ratings were 96 and 97%, respectively. Overall, the proportion of subjects completing the 20-m walk test was similar between treatment groups at 24 h after surgery (51% [55 of 107], liposome bupivacaine 266 mg vs. 56% [58 of 103], placebo), at 72 h after surgery (83% [86 of 104] vs. 89% [90 of 101]), and on day 30 (99% [103 of 104] vs. 100% [100 of 100]). No falls occurred during part 1 of the study. Three falls were reported during part 2, and each occurred in the liposome bupivacaine group (3.3% of subjects treated with liposome bupivacaine). One 63-yr-old female subject fell after getting up from the toilet. The second fall occurred when an 81-yr-old male subject attempted to walk to the bathroom without assistance. The third fall occurred when a 66-yr-old male subject was attempting to sit on the toilet but missed the seat. None of the subjects sustained injuries or complications due to their fall; investigators judged that the study drug was related to the fall only in one subject. All subjects who experienced a fall were nonetheless able to complete a 20-m walk test at 24 h, 72 h, and 30 days after surgery and reported that they were “satisfied” and/or “extremely satisfied” with their pain control at 72 h and on day 30. The treating physicians for these three subjects reported that they were satisfied with return of motor function at all timed assessments.

Incidence of “solicited neurologic events” (including oral/perioral numbness, metallic taste, hearing problems, vision problems, or muscle twitching) was low in both groups at all tested time points through 72 h. The highest incidence occurred at the 12-h time point in the placebo group (7% [7]; 2% [2] in the liposome bupivacaine 266-mg group). Investigators checked plasma bupivacaine levels at the time of a solicited event if they felt it clinically relevant; maximum plasma concentration for any of these subjects was 829 ng/ml.

Electrocardiogram data demonstrated no clinically relevant signal, suggesting drug-related changes in heart rate, atrioventricular conduction (measured by PR interval duration), cardiac depolarization (measured by QRS interval duration), cardiac wave form morphology, or new arrhythmias.

This two-part study was designed to evaluate efficacy and safety of liposome bupivacaine when administered in a femoral nerve block for analgesia in subjects having unilateral TKA. Based on results from part 1 (dose ranging), the unblinded dose selection committee recommended 266 mg of liposome bupivacaine for part 2 of the study. Dose selection was based on the observation that some secondary and tertiary assessments of the 266-mg dose suggested better analgesia compared with the 133-mg dose although these doses did not differ in the primary outcome measure.

Results from the primary and secondary efficacy analyses showed that liposome bupivacaine 266 mg in a femoral nerve block was associated with a modest but statistically significant reduction in cumulative pain intensity scores and opioid consumption through 72 h postsurgery compared with placebo. Results from the per-protocol tertiary analyses, which included imputed pain scores, showed that AUC of NRS scores for pain at rest were lower in the liposome bupivacaine group during all three of the 24-h intervals (0 to 24, 24 to 48, and 48 to 72 h) after surgery. However, a post hoc analysis of cumulative pain scores, which included only unimputed pain scores, showed a significant difference in favor of liposome bupivacaine only during the 0- to 24-h and 24- to 48-h periods after surgery. In the post hoc analysis, the between-group difference did not reach statistical significance during the 48- to 72-h interval after surgery. It should also be noted that pain was sufficiently severe to require second-step rescue with opioids via intravenously administered patient-controlled analgesia in the vast majority of subjects in both treatment groups, and mean subject-reported pain intensity scores with activity remained in the “moderate” range in both treatment groups during part 2 of the study, even with the use of opioid rescue analgesia in the majority of study subjects.

The proportion of subjects who were pain-free was greater in the liposome bupivacaine group compared with placebo beginning at 2 h after surgery. Interestingly, median time to first use of opioid rescue medication was nearly identical (≈0.4 h) in the treatment groups, in contrast to the longer time (1.29 h) with liposome bupivacaine in the liposome bupivacaine 266-mg group (n = 24) in part 1. This finding may be explained by occurrence of the pain in the sciatic nerve distribution, which could have been unaffected by the study intervention.

The rate of AEs in the liposome bupivacaine group was similar to that in the placebo group. There was no apparent impact on motor function; nor were there any clinically meaningful changes in neurologic or cardiac function. While the study was not powered to detect between-group differences in incidence of patient falls, the observed fall rate in the current study (3.3%) was consistent with rates of 1 to 2% reported recently in a retrospective study of more than 191,000 patients who underwent TKA under general, neuraxial, or combined anesthesia.²²  That study also showed no relationship between use of peripheral nerve block and risk for falls. Subjects in the liposome bupivacaine group consumed a significantly lower mean amount of opioids after surgery than those in the placebo group; the incidences of AEs commonly associated with opioid use (e.g., nausea, constipation, pruritus, vomiting) were similar in the two treatment groups, and this lack of effect of modest reduction in opioid use on opioid-induced side effects has been observed with other adjunctive analgesic treatments.^10,23–27 

Because the knee joint is innervated by both the sciatic and femoral nerves, a combination of femoral and sciatic nerve block may provide superior pain relief and reduced opioid consumption in patients undergoing TKA compared with femoral nerve block alone.²  Thus, a limitation of the current study is that the sciatic block was not used in any subjects enrolled, potentially underestimating the analgesic benefit of long-duration femoral block with liposome bupivacaine. In addition, we could not account for potential effects associated with interactions between liposome bupivacaine and bupivacaine HCl (aqueous bupivacaine) administered into the same tissue space via femoral nerve catheter for rescue analgesia. It should also be emphasized that the study evaluated liposome bupivacaine for postsurgical analgesia only; we did not evaluate its use for intraoperative anesthesia in this study. Also, long-term rehabilitative outcomes were not assessed, and detailed quantitative data on the potential effects of liposome bupivacaine on quadriceps weakness were not collected.

In this multicenter, randomized, placebo-controlled study, a single-injection femoral nerve block using liposome bupivacaine provided postoperative analgesia and reduced opioid requirements for 48 h or more in subjects undergoing TKA. Use of a long-acting, single-injection nerve block compared to a continuous infusion can eliminate some catheter-related risks such as dislodgement, infection, and undesired retention. Not having to carry a reservoir of local anesthetic during an infusion could also lead to secondary benefits such as increased ability to conduct rehabilitation therapy and earlier ambulation.^11,28  While the results of this study showed that a single administration of liposome bupivacaine can provide analgesia that lasts at least 2 days when used in femoral nerve block, more information is clearly needed in order to better define the potential role of liposome bupivacaine in this surgical setting. Future prospective studies are required to assess the relative safety and efficacy of liposome bupivacaine compared with current standard-of-care postoperative analgesic regimens. At the writing of this article, liposome bupivacaine is not approved for use in peripheral nerve blocks. Based, in part, on the results of this study, a supplemental new drug application for liposome bupivacaine in support of a nerve block indication has been submitted to the U.S. FDA.

The authors thank Michael D. Morren, R.Ph., M.B.A., Peloton Advantage, LLC, Parsippany, New Jersey, for his editorial assistance supported by Pacira Pharmaceuticals, Inc., Parsippany, New Jersey. The authors were fully responsible for the content, editorial decisions, and opinions expressed in the current article. The authors did not receive an honorarium or other funding related to the development of this article.

Dr. Hadzic has consulted and advised for SkyePharma, London, United Kingdom; GE, Fairfield, Connecticut; SonoSite, Bothell, Washington; Codman & Shurtleff, Inc., a division of Johnson & Johnson Health Care Systems, Inc., Raynham, Massachusetts; Cadence Pharmaceuticals, Inc., San Diego, California; Pacira Pharmaceuticals, Inc., Parsippany, New Jersey; Baxter, Deerfield, Illinois; and B. Braun Medical, Inc., Bethlehem, Pennsylvania. He has also received research funding from Glaxo Smith-Kline, Brentford, United Kingdom; Pacira Pharmaceuticals, Inc.; and Baxter. Dr. Hadzic receives royalty income from B. Braun Medical, Inc. Dr. Minkowitz has been a consultant for Pacira Pharmaceuticals, Inc., Parsippany, New Jersey. He has also received research funding from Pacira Pharmaceuticals, Inc.; Innocoll Pharmaceuticals, Newtown Square, Pennsylvania; and DURECT Corporation, Cupertino, California. Dr. Melson has received research grants from Pacira Pharmaceuticals, Inc. Dr. Berkowitz is a stockholder of Pacira Pharmaceuticals, Inc. Ms. Lookabaugh is a consultant for Pacira Pharmaceuticals, Inc. Dr. Ilfeld’s institution has received funding for his research from SPR Therapeutics, Cleveland, Ohio; Baxter Healthcare, Deerfield, Illinois; Smiths Medical, St. Paul, Minnesota; Summit Medical, Inc., Sandy, Utah; Teleflex Medical, Research Triangle Park, Durham, North Carolina; Myoscience, Fremont, California; and Pacira Pharmaceuticals, Inc. In addition, Dr. Ilfeld has been a consultant for Pacira Pharmaceuticals, Inc. The other authors declare no competing interests.

Full protocol available from Ms. Lookabaugh: janice.lookabaugh@pacira.com. Raw data available from Ms. Lookabaugh: janice.lookabaugh@pacira.com.