Ondansetron Use for Preventing Pruritus in Patients Undergoing Cesarean Section

Opioids are often added with a local anesthetic to enhance the duration and quality of spinal anesthesia for cesarean delivery patients. However, spinal opioids are associated with a wide variety of side effects such as nausea, vomiting, (N/V) and pruritus (itching). The occurrence of pruritus can vary between 30% and 100% making pruritus the most common side-effect of intrathecal opioids and this rate is even higher in pregnant patients. Pruritus may require treatment which can be ineffective or sometimes reverse the analgesic effect of the opioids. Ondansetron is a safe and very commonly used Serotonin receptor antagonist treatment for local anesthetic opioid-induced pruritus used in pregnancy. The effect of different administration times of ondansetron in reducing pruritus or N/V in cesarean section (CS) cases has not been extensively studied and thus, this prospective study can help guide future clinical management of side effects caused by spinal intrathecal morphine administration.

The primary aim of this study is to observe in a randomized double-blinded trial if the timing of prophylactic administration of intravenous ondansetron can reduce the incidence and severity of intrathecal morphine-induced pruritus in patients undergoing Cesarean section (CS). The secondary aim is to establish the effect of intravenous ondansetron given at different time intervals following CS for postoperative nausea and vomiting (PONV). The primary study hypothesis is that patients receiving prophylactic intravenous ondansetron (15-30 minutes prior to intrathecal morphine) will experience a lower incidence and severity of intrathecal morphine-induced pruritus than patients receiving ondansetron administered at the time of umbilical cord clamping. The secondary study hypothesis is that CS patients receiving intravenous ondansetron 15-30 minutes prior to intrathecal morphine will have less nausea and vomiting than patients receiving ondansetron administered at the time of umbilical cord clamping.

As the effect of prophylactic administration of ondansetron in reducing pruritus or Nausea/Vomiting in cesarean section (CS) cases has not been studied and thus, this prospective study may help guide future clinical management of side effects caused by intrathecal morphine administration.

Inclusion criteria

• American Society of Anesthesiologists (ASA) physical status 1-3
• Adult parturient (18 -50 years of age) scheduled to undergo elective cesarean delivery under spinal anesthesia
• Patients must be willing and cognitively able to give written informed study consent

Exclusion criteria

• Patients with an ASA physiological assessment greater than grade 3
• Allergies to local anesthetics, opioids, or ondansetron
• Coagulopathies precluding provision of spinal anesthesia
• Pre-eclampsia with severe features
• Eclampsia
• Pre-intrathecal pruritus
• Psychiatric or language deficiencies affecting assessment of pain
• Insufficient understanding of the pain scoring system
• Patients who receive any other regional anesthesia techniques
• Patients on higher than a 100mg of daily morphine equivalent
• Cardiac issues that would preclude spinal anesthesia (Congestive heart failure, Mitral or Aortic valve pathology.
• Confounding neural issues that would preclude spinal anesthesia.
• Coadministration of drugs that would potentially interact with ondansetron. Including Apomorphine, Phenytoin, Carbamazepine, Rifampicin, Tramadol and Chemotherapy drugs.
• Coadministration of drugs that would potentially prolong QTc interval. Including Antiarrhythmic, Antidepressants, Antipsychotics, and the following list of medications.

a. Levofloxacin, Ciprofloxacin, Gatifloxacin, Moxifloxacin, Clarithromycin, Erythromycin, Ketoconazole, Itraconazole, Cisapride, Sumatriptan, Zolmitriptan, Arsenic, Dolasetron, Methadone

• Coadministration of drugs that would potentially lead to the development of serotonin syndrome. Including the following:

a. Selective serotonin reuptake inhibitors, Serotonin and norepinephrine reuptake inhibitors, antidepressants, carbamazepine , valproic acid, triptans, Chronic pain medications prior to procedure (Fentanyl, Hydrocodone, Meperidine, Oxycodone, tramadol),Lithium, dextromethorphan, Linezolid and Ritonavir

• Patients having the following

• Patients known to have hypersensitivity (e.g., anaphylaxis) to ondansetron or any components of the formulation
• Concomitant use of apomorphine
• History of QTc interval prolongation (QTc >440) and Torsade de Pointes
• Serotonin syndrome
• Phenylketonuric patients
• Concurrent use of selective serotonin reuptake inhibitors (SSRIs) and serotonin and noradrenaline reuptake inhibitors (SNRIs)