Rabeprazole sodium (EC) and domperidone (SR) capsule
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Here is a comprehensive overview of the Rabeprazole Sodium (EC) + Domperidone (SR) combination capsule, covering each component and the rationale for combining them.
Rabeprazole Sodium (EC) + Domperidone (SR) Capsule
This is a fixed-dose combination used widely in gastroenterology. The enteric-coated (EC) rabeprazole targets acid suppression, while the sustained-release (SR) domperidone provides prokinetic and antiemetic support.
Rabeprazole Sodium (EC)
Class
Proton Pump Inhibitor (PPI)
Mechanism of Action
Rabeprazole is a prodrug. After oral absorption, it diffuses into the parietal cells of the gastric mucosa and accumulates in the acidic secretory canaliculi, where it is activated by proton-catalyzed formation of a tetracyclic sulfenamide. The activated form covalently binds to sulfhydryl groups of cysteines in the H⁺/K⁺-ATPase (proton pump), irreversibly inactivating it.
Acid secretion resumes only after new pump molecules are synthesized, providing prolonged suppression of up to 24–48 hours despite a short plasma half-life of ~0.5–3 hours.
Why Enteric-Coated (EC)?
PPIs are acid-labile — they degrade in gastric acid before reaching the small intestine. Enteric coating dissolves only at alkaline pH, protecting the drug and improving oral bioavailability. Rabeprazole is specifically formulated as enteric-coated pellets within gelatin capsules.
Pharmacokinetics
- Should be taken before the first meal of the day (fasting increases H⁺/K⁺-ATPase availability)
- Once-daily dosing is usually sufficient
- Metabolism: Unlike other PPIs, rabeprazole is cleared predominantly through nonenzymatic reduction to a thioether metabolite, with a smaller contribution from CYP3A4. This means CYP2C19 genetic variation has less influence on rabeprazole compared to omeprazole/lansoprazole — a clinical advantage in variable metabolizers.
Drug Interactions
- PPIs can interact with warfarin, diazepam, atazanavir/nelfinavir, and cyclosporine
- When co-prescribed with clopidogrel, agents with minimal CYP2C19 inhibition — such as rabeprazole or pantoprazole — are preferred to avoid reducing clopidogrel's antiplatelet effect.
Dose
Standard adult oral dose: 20 mg once daily
Domperidone (SR)
Class
Prokinetic agent / Dopamine D2-receptor antagonist
Mechanism of Action
Domperidone antagonizes peripheral D2 receptors in the GI tract. Dopamine normally inhibits cholinergic smooth muscle stimulation; blocking this effect:
- Enhances gastroduodenal contractions and coordination
- Stimulates upper GI motility (similar to metoclopramide)
- Acts as an antiemetic via D2 blockade in the chemoreceptor trigger zone (CTZ), which lies outside the blood-brain barrier (BBB)
Unlike metoclopramide, domperidone does not readily cross the BBB, greatly reducing extrapyramidal side effects.
Why Sustained-Release (SR)?
The SR formulation provides steady plasma concentrations over the day, reducing peak-trough fluctuations and improving tolerability and compliance compared to immediate-release dosing.
Pharmacokinetics
- Rapidly absorbed; peak concentration in ~30 minutes
- Half-life: ~7 hours
- Metabolized via hepatic CYP3A4, N-dealkylation, and hydroxylation
- Excreted: ~2/3 in feces, ~1/3 in urine
Therapeutic Uses
- Gastroparesis (doses: 10 mg TID, up to 20 mg TID if needed)
- Nausea and vomiting
- Gastroesophageal reflux (as a prokinetic adjunct)
- Occasionally used to promote postpartum lactation (stimulates prolactin release)
Adverse Effects
| Effect | Details |
|---|---|
| Cardiac arrhythmias | Risk of serious ventricular arrhythmias/sudden cardiac death, especially in patients >60 years or doses >30 mg/day |
| Prolactin elevation | Galactorrhea, gynecomastia, amenorrhea, impotence |
| CNS effects | Minimal (does not cross BBB), but can affect areas lacking BBB (e.g., CTZ); caution in dementia |
| QT prolongation | Metabolized by CYP3A4; arrhythmia risk higher with specific CYP3A4 polymorphisms |
Due to cardiac concerns, Europe has limited domperidone to short-duration treatment only.
Rationale for the Combination
| Rabeprazole (EC) | Domperidone (SR) |
|---|---|
| Suppresses gastric acid | Accelerates gastric emptying |
| Treats mucosal damage | Reduces nausea/vomiting |
| Addresses acid hypersecretion | Improves gastroduodenal motility |
Indications for the Combination
- GERD (gastroesophageal reflux disease) with associated dysmotility
- Functional dyspepsia with bloating, nausea, early satiety
- Peptic ulcer disease with associated gastroparesis
- Non-ulcer dyspepsia where acid suppression alone is insufficient
The combination addresses both the acid component and the motility/nausea component simultaneously, making it more effective than either agent alone for conditions like GERD with delayed gastric emptying.
Key Clinical Points
- Take before meals (rabeprazole requires meal-stimulated acid to activate pump molecules)
- Avoid in patients with cardiac arrhythmias, QT prolongation, or those on CYP3A4 inhibitors (increases domperidone levels)
- Rabeprazole's CYP2C19-independent metabolism makes this combination suitable for patients on clopidogrel
- Domperidone's limited CNS penetration makes it better tolerated than metoclopramide for long-term prokinetic use
Sources: Goodman & Gilman's Pharmacological Basis of Therapeutics; Katzung's Basic and Clinical Pharmacology, 16th Ed.; Yamada's Textbook of Gastroenterology, 7th Ed.
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