Why Hyoscine is Given to Pregnant Women
Hyoscine (hyoscine butylbromide) is primarily administered to pregnant women as a labor analgesic and cervical spasmolytic agent to shorten the duration of active labor, not for typical gastrointestinal indications during pregnancy.
Primary Indication: Labor Management
Mechanism During Labor
- Hyoscine butylbromide acts by inhibiting cholinergic transmission in the abdomino-pelvic parasympathetic ganglia, specifically targeting the cervico-uterine plexus to relieve smooth muscle spasm and aid cervical dilatation 1
- The drug's anticholinergic action produces smooth-muscle relaxation in the female genital organs, facilitating labor progression 1, 2
Clinical Efficacy in Labor
- Intravenous hyoscine butylbromide (40 mg) significantly shortens the active phase of labor by approximately 84 minutes compared to placebo 3
- In primiparous women specifically, the reduction is approximately 55 minutes 3
- Pain relief of up to 35.6% has been documented on visual analog scales when used during labor 1
- Mean duration of labor was reduced from 8 hours 16 minutes (control) to 3 hours 46 minutes (treatment group) in one randomized trial 1
Safety Profile in Pregnancy
Maternal Safety
- No adverse maternal effects were noted in clinical trials of hyoscine butylbromide use during labor 1
- The drug has minimal systemic absorption (bioavailability <1% after oral administration), which limits systemic side effects 2
- Hyoscine butylbromide does not penetrate the blood-brain barrier, reducing central nervous system effects 2
Fetal Safety
- Neonatal outcomes were comparable between treatment and control groups, with no short-term adverse fetal effects documented 1
- Mode of delivery was not adversely affected by hyoscine butylbromide administration 1
Important Clinical Caveats
Formulation Matters
- Hyoscine butylbromide (quaternary ammonium compound) is poorly absorbed from the gastrointestinal tract and less likely to cross the blood-brain barrier compared to scopolamine (tertiary amine) 4
- Intramuscular preparations may be more effective than oral formulations due to poor oral absorption 4
Scopolamine vs. Hyoscine Butylbromide
- Scopolamine (the tertiary amine form) readily crosses the placenta and should be administered to pregnant women only under observation 5
- Scopolamine is considered compatible with nursing and nonteratogenic, but requires more caution than hyoscine butylbromide 5
Timing of Administration
- Hyoscine butylbromide is typically administered during the active phase of labor (not throughout pregnancy) 1
- The standard dose is 40 mg as a slow intravenous injection 1
Not a Primary Antiemetic in Pregnancy
While hyoscine compounds have antiemetic properties, they are not recommended as first-line agents for nausea and vomiting in pregnancy. For pregnancy-related nausea:
- First-line options include vitamin B6, doxylamine, and promethazine 6, 7
- Metoclopramide is preferred as a second-line agent 6, 7
- Phenothiazines like prochlorperazine are reserved for severe, intractable cases 6
Clinical Bottom Line
Hyoscine butylbromide serves a specific obstetric purpose: accelerating labor and providing analgesia during active labor through its cervical spasmolytic effects, with demonstrated safety for both mother and neonate 1, 3. It is not used for routine pregnancy symptoms but rather as an active labor management tool.