The Composition and Actions of Syntometrine
To understand why Syntometrine is not the same as oxytocin, it is essential to look at its components. Syntometrine is a fixed-dose combination drug, typically consisting of 5 International Units (IU) of synthetic oxytocin and 0.5 mg of ergometrine maleate in a 1ml ampoule. The combination is designed to combine the distinct therapeutic effects of both agents for maximum benefit in preventing or treating postpartum hemorrhage (PPH).
Oxytocin: The Rapid-Acting Component
- Source: Oxytocin is a hormone produced naturally in the hypothalamus.
- Action: As a medication, it induces rhythmic contractions of the uterus, with a rapid onset of action following intramuscular (IM) administration (3–7 minutes) but a relatively short half-life (3–5 minutes).
Ergometrine: The Sustained-Action Component
- Source: Ergometrine is an ergot alkaloid.
- Action: It causes sustained and forceful uterine contractions and also acts as a vasoconstrictor, narrowing blood vessels. Its effect is more prolonged than oxytocin, lasting for around three hours after IM injection.
Synergy of Syntometrine
When combined, the rapid, rhythmic contractions initiated by oxytocin are quickly followed by the prolonged, sustained contractions from ergometrine. This synergistic effect makes Syntometrine a potent uterotonic agent, effectively controlling uterine bleeding by causing the uterus to contract powerfully and compress the blood vessels at the placental site.
The Roles of Oxytocin and Syntometrine in Obstetrics
While both drugs are used for similar purposes in postpartum care, their properties lead to different clinical considerations.
Oxytocin Alone (e.g., as Syntocinon®)
Oxytocin is often the first-line uterotonic agent for preventing PPH due to its strong safety profile and effectiveness in reducing blood loss. It is also used to induce or augment labor and to stimulate uterine contractions in cases of threatened or incomplete miscarriage. Its shorter duration of action can be an advantage, as effects wear off more quickly if there is an adverse reaction.
Syntometrine (Oxytocin + Ergometrine)
Syntometrine is used for the active management of the third stage of labor and for treating existing PPH. The combination's sustained effect is particularly useful for reducing postpartum blood loss. Clinical reviews have shown it to be slightly more effective than oxytocin alone in preventing blood loss of 500ml or more. However, this is balanced against a higher incidence of side effects, primarily due to the ergometrine component.
Comparison of Syntometrine and Oxytocin
| Characteristic | Oxytocin (as single agent) | Syntometrine (Oxytocin + Ergometrine) |
|---|---|---|
| Composition | Only oxytocin | Oxytocin and ergometrine maleate |
| Mechanism | Rhythmic uterine contractions | Initial rhythmic contractions, followed by sustained, forceful contractions and vasoconstriction |
| Onset of Action (IM) | 3–7 minutes | Faster, around 2.5 minutes |
| Duration of Effect | 0.5–1 hour | Around 3 hours |
| Primary Use | PPH prevention, labor induction/augmentation | PPH prevention and treatment |
| Efficacy in PPH | Highly effective | Slightly more effective for blood loss <1000ml |
| Risk of Side Effects | Lower incidence | Higher incidence of specific side effects |
Side Effects and Contraindications
While both medications can cause nausea and vomiting, the side effect profile of Syntometrine is significantly influenced by the ergometrine component. The vasoconstrictive properties of ergometrine increase the risk of elevated blood pressure, which is a major consideration during use.
Syntometrine specific risks
- Hypertension: A key adverse effect, making it contraindicated in patients with severe hypertension, pre-eclampsia, or eclampsia.
- Nausea and Vomiting: More frequently reported with Syntometrine compared to oxytocin alone.
- Other cardiovascular issues: Rarely, coronary artery spasm has occurred. It is also contraindicated in severe cardiac or circulatory problems.
Oxytocin specific risks
- Excessive contractions: If contractions become too strong, it can lead to fetal distress or, in very rare cases, uterine rupture.
- Water intoxication: Can occur with large doses infused too slowly over a prolonged period, leading to confusion and seizures.
Storage and Administration
Both oxytocin and Syntometrine are heat-sensitive and must be stored under specific, cool conditions, typically refrigerated between 2°C and 8°C. This is crucial for maintaining their efficacy. They are most commonly administered via intramuscular (IM) injection by a healthcare professional.
Conclusion: A Matter of Clinical Choice
In conclusion, asking is syntometrine oxytocin? fundamentally misunderstands the medications. Syntometrine is a distinct, two-drug formulation designed to provide a more rapid and sustained uterotonic effect than oxytocin alone. The clinical decision between using Syntometrine or oxytocin hinges on a balance between efficacy and potential side effects. While Syntometrine may offer better protection against moderate postpartum blood loss, its risk of hypertension and other adverse effects makes it unsuitable for certain patients. Therefore, healthcare providers must carefully weigh the patient's risk factors and medical history before deciding on the most appropriate uterotonic agent.
List of key considerations for clinicians:
- Patient History: A woman with a history of hypertension or heart problems should not receive Syntometrine.
- Severity of PPH: The combined, powerful effect of Syntometrine may be deemed necessary for cases with a higher risk of significant bleeding.
- Side Effect Profile: The higher risk of nausea, vomiting, and hypertension with Syntometrine must be accepted if the benefits outweigh the risks.
- Onset and Duration: The clinical situation may demand the specific onset and duration profile offered by one agent over the other.
