Analgesic Efficacy and Obstetric Effects of Tramadol, Paracetamol and Placebo in Active Labor

This is a randomized, double-blind, parallel-group, superiority efficacy trial comparing three interventions: tramadol 100 mg IV, paracetamol 1 g IV, and placebo (10 mL 0.9% saline solution) administered at the onset of active labor (cervical dilation ≥4 cm with regular contractions). The study design follows CONSORT guidelines for randomized controlled trials. Randomization will be performed using REDCap's automated randomization module in variable block sizes, ensuring allocation concealment. Double-blinding is maintained: participants, care providers, and outcome assessors are masked to group assignment. The primary endpoint is duration of active labor (minutes from intervention administration to complete cervical dilation). Secondary endpoints include: duration of expulsive phase (minutes), type of delivery (spontaneous vaginal, instrumental, cesarean), need for oxytocin augmentation, maternal adverse events (nausea, vomiting, somnolence, hypotension, pruritus, dizziness), neonatal Apgar scores at 1 and 5 minutes, birth weight, meconium-stained amniotic fluid, NICU admission, and neonatal asphyxia. Data collection includes sociodemographic variables (age, education, marital status, occupation), obstetric variables (gestational age, prenatal care visits, BMI, membrane status, cervical dilation at intervention, baseline fetal heart rate), and pain scores (Visual Analog Scale pre-intervention, 30 min, 1h, 2h post-intervention). Statistical analysis includes ANOVA or Kruskal-Wallis for continuous variables, chi-square for categorical variables, and logistic regression for binary outcomes, with significance set at p<0.05. A Data Safety Monitoring Board will oversee safety every 3 months. The study is funded by Universidad Nacional Autónoma de Honduras and will be conducted at Hospital Escuela, Tegucigalpa, from Feb. 2026 to June 2026.

• Tramadol Hydrochloride (Drug): Tramadol 100 mg administered as a single intravenous dose at the onset of active labor. Tramadol is an atypical opioid analgesic with serotonin and noradrenaline reuptake inhibition properties. The dose is within standard clinical ranges for obstetric analgesia. Administration is performed by trained medical personnel following institutional protocols. Participants are monitored for adverse effects including nausea, vomiting, somnolence, dizziness, and hypotension.
• Paracetamol (acetaminophen) (Drug): Paracetamol 1 g administered as a single intravenous slow infusion at the onset of active labor. Paracetamol is a central analgesic acting through COX-3 inhibition in the central nervous system. It is widely used during pregnancy and labor due to its favorable safety profile. Administration is performed by trained medical personnel following institutional protocols. Participants are monitored for adverse effects including nausea, vomiting, and allergic reactions (rare).
• Placebo (Saline Solution) (Drug): Placebo consisting of 10 mL 0.9% saline solution administered as a single intravenous dose at the onset of active labor. The appearance and administration procedure are identical to the active interventions to maintain blinding. No pharmacological active ingredients are present. Administration is performed by trained medical personnel following institutional protocols.

Primary outcomes

• Duration of Active Labor [From intervention administration (at active labor onset) up to 12 hours.]: Time in minutes from administration of study intervention (at onset of active labor defined as cervical dilation ≥4 cm with regular contractions) to complete cervical dilation (10 cm) or delivery, whichever occurs first. Measured and recorded by attending obstetric staff using standardized timing protocols.

Secondary outcomes

• Duration of Expulsive Phase (Second Stage) [During delivery, from complete cervical dilation up to 120 minutes.]: Time in minutes from complete cervical dilation (10 cm) to fetal expulsion. Measured and recorded by attending obstetric staff.
• Type of Delivery [At delivery]: Classification of delivery outcome: spontaneous vaginal delivery, instrumental delivery (forceps or vacuum), or cesarean section. Assessed by attending obstetrician.
• Need for Oxytocin Augmentation [During labor (from intervention administration up to 24 hours).]: Requirement for additional oxytocin administration to augment uterine contractions during labor. Recorded as yes/no, including dose and timing if applicable.
• Maternal Adverse Events [From intervention administration up to 24 hours postpartum.]: Occurrence of any adverse events potentially related to the intervention, including: nausea, vomiting, somnolence, dizziness, headache, pruritus, hypotension (systolic BP <90 mmHg), or allergic reactions. Severity graded as mild, moderate, or severe.
• Neonatal Apgar Score at 5 Minutes [At 5 minutes after birth.]: Apgar score assessed at 5 minutes after birth. Score ranges from 0-10, with higher scores indicating better neonatal condition.
• Neonatal Complications [From birth up to 48 hours, through hospital discharge.]: Occurrence of neonatal complications including: Apgar score <7 at 5 minutes, meconium-stained amniotic fluid, need for neonatal resuscitation, NICU admission, or neonatal asphyxia
• Pain Scores (Visual Analog Scale) [Pre-intervention, and at 30 minutes, 1 hour, and 2 hours post-intervention.]: Maternal pain assessed using Visual Analog Scale (VAS) from 0 (no pain) to 10 (worst imaginable pain). Measured at baseline (pre-intervention), 30 minutes, 1 hour, and 2 hours post-intervention.

Other outcomes

• Subgroup Analysis by Maternal Age [Throughout study period, average of six months]: Comparison of primary and secondary outcomes stratified by maternal age categories (<20 years, 20-35 years, >35 years).

Sex: Female, ages: 15 Years to 45 Years, accepts healthy volunteers

Inclusion Criteria:

* Nulliparous pregnant women
* Age between 15 and 45 years
* Singleton pregnancy, term (37-41 weeks gestation)
* Cephalic presentation
* Active labor defined as cervical dilation ≥4 cm with regular contractions
* Signed informed consent

Exclusion Criteria:

* Multiple gestation or high-risk pregnancy (preeclampsia, gestational diabetes, etc.)
* Known allergy or contraindication to tramadol or paracetamol
* Recent use (less than 6 hours) of any analgesic medication
* Previous cesarean section or other uterine surgery
* Active infection or fever at admission
* Inability to provide informed consent due to mental or communication conditions
* Non-cephalic presentation
* Rupture of membranes >18 hours without labor
* Participation in another clinical trial within the last 3 months

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