Efficacy of Repeat Dosing of Liposomal Bupivacaine on Postoperative Pain in Patients With Anal Fistula: A Multicenter, Randomized, Open-Label, Controlled Study
Phase: NA
Conditions: Anal Fistula
Sponsor: Sixth Affiliated Hospital, Sun Yat-sen University

Study Protocol
Version 1
26 June 2025
Title:
Efficacy of repeat dosing of liposomal bupivacaine on postoperative pain in patients
with anal fistula: a multicenter, randomized, open-Label, controlled study
Design:
A multicenter, randomized, open-Label, controlled study.
Settings:
The Sixth Affiliated Hospital of Sun Yat-sen University; The First Affiliated Hospital
of Guizhou University of Traditional Chinese Medicine; Maoming People's Hospital;
Nanjing Hospital of C. M.; Dongguan TCM Hospital; Xingyi People's Hospital;
People's Hospital of Xinjiang Uygur Autonomous Region.
Patients:
Patients diagnosed with anal fistulas and undergoing surgical treatment.
Intervention:
Liposomal
Bupivacaine
Repeat
Dosing
Group: A single
dose
of liposomal
bupivacaine is administered at the conclusion of surgery without adjunctive analgesics,
followed by a supplemental dose 72 hours postoperatively.
Liposomal
Bupivacaine
Single-Injection
Group: A single
dose
of
liposomal
bupivacaine is administered at the conclusion of surgery without adjunctive
analgesics.
Primary Outcome Measure:
Area Under the Curve (AUC) of the Numerical Rating Scale (NRS) for pain within 7
Days postoperatively (NRS-AUC0-168h)

Secondary Outcome Measures:
1. Numerical Rating Scale (NRS) for pain during wound dressing changes within 7
days postoperatively.
2. Area Under the Curve (AUC) of the Numerical Rating Scale (NRS) for pain from
96 to 168 hours postoperatively (NRS-AUC96h-168h).
3. Number of breakthrough pain episodes and corresponding Numerical Rating Scale
(NRS) scores during episodes.
4. Postoperative 7-day cumulative consumption of all analgesic drugs (calculated as
morphine equivalents).
5. Postoperative 7-day cumulative consumption of rescue analgesic drugs (calculated
as morphine equivalents).
6. Safety (including incidence of postoperative adverse events and serious adverse
events): Adverse events and serious adverse events occurring within 14 days after
medication were assessed.
7. Postoperative heart rate and blood pressure monitoring: Heart rate, systolic blood
pressure, and diastolic blood pressure at 24h, 48h, 72h, 96h, 120h, 144h, and 168h
postoperatively.
8. SF-12 scores at preoperative, 1 week, 1 month, and 2 months postoperatively.
9. Postoperative 8-week wound healing outcomes: Healing rate, healing time, edema
score, granulation tissue color score, presence of infection, presence of bleeding, and
other relevant parameters.
10. Preoperative,
14-day
postoperative,
and
1-month
postoperative
Wexner
Incontinence Scores.
11. Analgesia satisfaction: Postoperative analgesic satisfaction was assessed using a
5-point categorical scale at 24h, 96h, and 168h postoperatively.
Study Participants:

Patients diagnosed with anal fistulas and undergoing surgical treatment were recruited
and screened through a multi-center collaboration involving the following institutions:
the Department of Colorectal Surgery at the Sixth Affiliated Hospital of Sun Yat-sen
University, the Department of Proctology at the First Affiliated Hospital of Guizhou
University of Traditional Chinese Medicine, the Department of Traditional Chinese
Medicine Proctology at Maoming People's Hospital, the Department of Proctology at
Nanjing Hospital of C. M., the Department of Proctology at Dongguan TCM Hospital,
the Department of Colorectal Surgery at Xingyi People's Hospital of Guizhou
Province, and the Department of Colorectal Surgery at People's Hospital of Xinjiang
Uygur Autonomous Region.
Inclusion Criteria:
1. Diagnosed with anal fistula and scheduled to undergo anal fistula surgery;
2. Aged between 18 and 60 years;
3. ASA (American Society of Anesthesiologists) physical status class I-II;
4. Patient provides written informed consent after understanding the study protocol.
Exclusion Criteria:
1. Anal fistula caused by specific etiologies (e.g., tuberculosis);
2. Concurrent acute perianal skin infection;
3. Poorly controlled diabetes (HbA1c >9%);
4. Chronic use of corticosteroids;
5. History of radiotherapy or chemotherapy within the past 2 weeks;
6. Pregnancy or lactation;
7. Hypersensitivity to local anesthetics or any component of the investigational drug;
8. History of substance abuse, illicit drug use, or alcohol abuse;
9. Use or planned use of non-opioid/opioid analgesics within 12 hours before/during
surgery;

10. Concurrent treatment with anticonvulsants, MAO inhibitors, antidepressants,
neuromuscular blockers, or anticholinergics within 2 weeks prior to surgery;
11. Severe hepatic/renal impairment, cardiopulmonary dysfunction, coagulation
disorders, or comorbidities contraindicating surgery;
12. History of severe psychiatric disorders or cognitive impairment;
13. Sensory disorders (e.g., hyperalgesia) or preexisting pain interfering with
postoperative pain assessment;
14. Contraindications to amide-type local anesthetics, opioids, or propofol;
15. Participation in investigational drug trials within 90 days prior to enrollment;
16. Other clinical/laboratory conditions deemed by investigators to preclude trial
participation.
Study Intervention And Post-Intervention Care:
The Liposomal Bupivacaine Repeat Dosing Group: a single 20 mL (266 mg)
undiluted liposomal bupivacaine injection was administered at surgical conclusion
without adjunctive analgesics. The solution was divided into six equal aliquots (≈3.3
mL each) and infiltrated circumferentially around the incision using a 25-gauge or
larger needle, targeting supra- and subfascial planes as well as subcutaneous tissue,
with frequent aspiration to minimize intravascular risk. At 72 hours postoperatively,
topical lidocaine cream was applied peri-incisionally for ≥20 minutes followed by
repeat administration of 20 mL (266 mg) undiluted liposomal bupivacaine via
identical infiltration technique (both provided at no cost).
The Liposomal Bupivacaine Single-Dose Group: received identical intraoperative
administration (20 mL undiluted solution, six-point infiltration, fascial/subcutaneous
injection with aspiration) without postoperative bupivacaine re-dosing. At 72 hours,
these patients underwent lidocaine cream application only prior to subsequent
procedures.
Postoperative management followed standard anal fistula protocols, including

prophylactic antibiotics, liquid diet initiation, hemostatic measures, and continuous
monitoring of vital signs (e.g., blood pressure, heart rate). For breakthrough pain
(defined as sudden, transient severe pain with Numerical Rating Scale [NRS] ≥4
occurring despite stable background pain control), a stepwise rescue analgesia
protocol was implemented: 1) Oral acetaminophen or NSAIDs were administered as
needed; 2) If insufficient, tramadol (50-100 mg intramuscularly/orally) was added,
with a maximum daily cumulative dose of 400 mg; 3) For tramadol-refractory pain,
meperidine intramuscular injection was administered. All breakthrough pain episodes
were documented with NRS scores and duration.
A standardized follow-up protocol was implemented for 8 weeks post-discharge, with
biweekly assessments. Evaluations included wound healing status, adverse events
(AEs), and serious adverse events (SAEs). Wound healing was defined as complete
mucosal coverage with full re-epithelialization and absence of discharge, assessed by
an independent blinded observer (unaffiliated with the surgical team) during clinic
visits. The observer recorded wound parameters using a numerical scoring system at
each visit, continuing for up to 8 weeks postoperatively or until complete healing
(whichever occurred first). Specific metrics included: 1) Healing rate: Calculated as
[(Original area - Current area)/Original area] × 100%, with area determined by
maximal length × width measurements (baseline established on postoperative day 1);
2) Healing time: Days from initial dressing change to complete epithelialization;
3) Edema score: 0 (none), 1 (mild), 2 (moderate; requiring dressing intervention), or 3
(severe; requiring surgical excision); 4) Granulation tissue color score: 1 (bright red),
2 (pale red), or 3 (purplish); 5) Infection presence; and 6) Bleeding severity (none,
oozing, active bleeding). A comprehensive electronic database was maintained by
dedicated personnel, supplemented by remote tracking via telephone, mailed
questionnaires, and email between scheduled visits.
Sample Size Justification:
This randomized controlled trial (RCT) was designed to detect a projected 56-unit
difference in the area under the curve (AUC) of Numerical Rating Scale (NRS) scores

(0–168 hours postoperatively) between the liposomal bupivacaine repeat-dosing and
single-dosing groups, with an estimated pooled standard deviation (SD) of 160 based
on prior studies. Using a two-sample t-test module in NCSS PASS 21 software (LLC.
Kaysville, Utah, USA; ncss.com/software/pass) with a two-sided significance level (α)
of 0.05, a minimum of 173 subjects per group was required to achieve 90% power
(1-β). Accounting for an anticipated 15% dropout rate, the final enrollment target was
set at 204 subjects per group (total N=408).
Statistical Analysis:
Primary Efficacy Analysis:
All enrolled subjects underwent an 8-week follow-up period. The primary endpoint,
NRS-AUC<sub>0-168h</sub> over the initial postoperative week, was calculated
using the trapezoidal rule. Treatment effects were evaluated through an analysis of
covariance (ANCOVA) model, providing least-squares means with standard errors
and 95% confidence intervals. This model adjusted for baseline NRS scores and
randomization stratification factors to enhance precision.
Missing Data Handling for Primary Endpoint:
Missing resting NRS scores occurring during sleep periods were imputed using the
last non-missing presleep value if below 3; otherwise, a conservative score of 3 was
assigned. For other missing NRS assessments: 1) Baseline or critical timepoint (e.g.,
72h redosing) missingness was addressed through group-level median imputation; 2)
Intermittent missing values underwent linear interpolation; 3) Terminal missing
observations utilized last observation carried forward (LOCF). All AUC calculations
relied on scheduled assessment times when actual recording times were unavailable.
Secondary Endpoint Categorization and Analysis:
Secondary outcomes were classified into three domains. Continuous variables
included late-phase NRS-AUC<sub>96-168h</sub>, analgesia consumption metrics,
healing duration, and serial Wexner incontinence scores. Categorical measures
encompassed adverse event incidence, cardiorespiratory symptom rates, and binary
healing outcomes (infection/bleeding status). Longitudinal parameters featured vital

signs, quality-of-life (SF-12) trajectories, wound assessment scores, and analgesia
satisfaction surveys.
Statistical Testing Framework:
Continuous secondary endpoints underwent ANOVA or ANCOVA (covariate-adjusted)
for between-group comparisons. Categorical outcomes were analyzed through
frequency distributions with Clopper-Pearson 95% CIs, rate differences with
corresponding CIs, and chi-square/Fisher's exact tests. Repeated measures employed
mixed-effects modeling (MMRM) to account for temporal correlations. All inferential
analyses were conducted using SAS® with two-sided testing at α=0.05.