Pharmacodynamics and Key Effects
Prostaglandin-based medications have a pronounced stimulating effect on the myometrium. Under their influence, the smooth muscle of the uterus begins to contract rhythmically, and its baseline tone increases significantly and stably.
A crucial pharmacological feature of prostaglandins is their temporal universality. Unlike oxytocin, to which the uterus becomes sensitive only in the late stages of gestation, prostaglandins work effectively at all stages of pregnancy.
In addition, they have a specific effect on the cervix: they cause its relaxation, effacement, and dilation (a clinical process known as "cervical ripening"). Due to this dual effect (active stimulation of the uterine body and parallel relaxation of the cervix), these agents are successfully used for both elective labor induction and medical termination of pregnancy.
The pharmacokinetics of these drugs is characterized by rapid metabolism. They are quickly inactivated in the pulmonary vascular bed, as well as in the tissues of the kidneys, spleen, intestines, and adipose tissue. The half-life is so short that upon intravenous administration, 97% of PGE_2 disappears without a trace from the blood plasma in just 90 seconds.
Dinoprost (PGF2α Analog)
Dinoprost (known by the trade name Enzaprost-F) is a prostaglandin PGF_{2\alpha} preparation. It reliably stimulates the myometrium at any gestational age and promotes cervical effacement.
Main indications and routes of administration:
- Medical abortion: up to 15 weeks of pregnancy, the drug is administered intra-amniotically (directly into the amniotic sac), and after 15 weeks, extra-amniotic administration is used.
- Labor dystocia ( uterine inertia): used as intravenous drip infusions to enhance contractions.
Characteristic side effects:
- Respiratory system: the drug increases pulmonary vascular tone and can trigger bronchospasm. For this reason, it is prescribed with extreme caution to patients with bronchial asthma.
- Gastrointestinal tract: a sharp increase in motility is observed, often leading to diarrhea.
- Cardiovascular system: marked fluctuations in blood pressure are possible (at high doses, the drug causes hypertension) and various cardiac arrhythmias.
Dinoprostone (PGE2 Analog)
Dinoprostone (found under the names Prepidil, Prostin E_2) is a synthetic analog of prostaglandin PGE_2.
Its stimulating effect on the uterus and gastrointestinal tract is largely similar to the effects of dinoprost, but its influence on other body systems is radically different:
- Respiratory system: unlike dinoprost, dinoprostone dilates the bronchi and pulmonary blood vessels, acting as a bronchodilator.
- Hemodynamics: it has a noticeable hypotensive effect, meaning it lowers blood pressure.
Indications and dosage forms: To induce labor, the drug may be prescribed orally, via intravenous infusion, or intravaginally (in the form of a special gel). For medical abortion, exclusively intravenous infusions are used.
Specific side effects: In addition to standard nausea, vomiting, diarrhea, headache, and hypotension, dinoprostone actively affects thermoregulation. It directly stimulates the corresponding center in the hypothalamus, causing severe chills and fever in patients.
Complications and Emergency Management
The primary risk when using any prostaglandin preparation is the development of hyperstimulation (excessive, uncontrolled stimulation of myometrial contractions). Excessive and prolonged uterine activity critically disrupts the blood supply to the placenta and the uterus itself, creating an immediate threat of acute fetal hypoxia.
Emergency management algorithm for hyperstimulation:
- Immediate discontinuation: completely stop the administration of the medication.
- Removal of the drug: if local forms were used (e.g., vaginal gel), thoroughly remove any remaining drug from the vagina.
- Supportive therapy: initiate oxygen therapy to combat hypoxia.
- Pharmacological correction: intravenously administer $\beta_2$-adrenergic agonists to rapidly relax the myometrium.