1. Clinical Overview
A fixed-dose combination (FDC) of a prokinetic agent (Domperidone) and a proton pump inhibitor (Omeprazole). Domperidone enhances upper gastrointestinal motility and acts as an antiemetic by peripheral dopamine D2 receptor antagonism. Omeprazole provides potent and long-lasting inhibition of gastric acid secretion by irreversibly blocking the H+/K+ ATPase enzyme system (proton pump) of the gastric parietal cell. This combination is primarily used for the symptomatic treatment of conditions where gastroesophageal reflux and delayed gastric emptying coexist, such as severe gastroesophageal reflux disease (GERD) with associated nausea and bloating.
| Onset | Duration | Bioavailability |
|---|---|---|
| Domperidone: 30-60 minutes. Omeprazole: Within 1 hour, with maximum acid suppression occurring within 2 hours of the first dose. | Domperidone: 4-8 hours. Omeprazole: Up to 72 hours, due to irreversible binding to the proton pump; acid secretion recovers as new pumps are synthesized. | Domperidone: Approximately 15% (due to extensive first-pass metabolism). Omeprazole: Approximately 30-40% (oral bioavailability increases with repeated dosing). |
2. Mechanism of Action
Domperidone acts as a selective peripheral dopamine D2 and D3 receptor antagonist. It blocks dopamine receptors in the chemoreceptor trigger zone (CTZ) and the gastric wall. In the CTZ (outside the blood-brain barrier), it inhibits nausea and vomiting signals. In the upper GI tract, it increases lower esophageal sphincter pressure, enhances gastric antral contractions, and improves gastroduodenal coordination, thereby accelerating gastric emptying and reducing gastroesophageal reflux. Omeprazole is a prodrug that accumulates in the acidic environment of the parietal cell canaliculi. It is activated to a sulfenamide derivative, which forms a covalent disulfide bond with cysteine residues on the luminal surface of the H+/K+ ATPase (proton pump), irreversibly inhibiting its function. This blocks the final step of gastric acid secretion, leading to profound and prolonged acid suppression.
3. Indications & Uses
- Severe Gastroesophageal Reflux Disease (GERD) with associated nausea and vomiting
- Reflux Esophagitis (Grade B or above) with delayed gastric emptying
- Severe Non-ulcer Dyspepsia (Functional Dyspepsia) with prominent symptoms of postprandial fullness, early satiety, and epigastric burning
4. Dosage & Administration
Adult Dosage: One tablet (Domperidone 30mg + Omeprazole 20mg) once daily, 15-30 minutes before a major meal (usually breakfast). Maximum duration should be as short as possible, generally not exceeding 4-8 weeks for symptom control. For severe cases, a specialist may guide therapy.
Administration: Swallow the tablet whole with a glass of water. Do NOT crush, chew, or break it. Take on an empty stomach, at least 30-60 minutes before a meal (typically breakfast) for optimal absorption of Omeprazole. If a dose is missed, take it as soon as remembered unless it's almost time for the next dose. Do not double the dose.
5. Side Effects
Common side effects may include:
- Headache
- Dry mouth
- Diarrhea or constipation
- Abdominal cramps
- Flatulence
- Dizziness
- Skin rash or itching
- Increased serum prolactin levels (may lead to galactorrhea, breast enlargement/tenderness, menstrual irregularities)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Ketoconazole, Itraconazole, Fluconazole, Posaconazole | Potent CYP3A4 inhibitors. Markedly increase Domperidone plasma levels, increasing risk of QTc prolongation and serious cardiac arrhythmias. | CONTRAINDICATED |
| Clarithromycin, Erythromycin, Telithromycin | CYP3A4 inhibitors and also prolong QTc. Synergistic risk of life-threatening arrhythmias. | CONTRAINDICATED |
| Protease Inhibitors (Ritonavir, Saquinavir) | Strong CYP3A4 inhibitors. Increase Domperidone levels. | CONTRAINDICATED |
| Amiodarone, Procainamide, Quinidine, Sotalol | QTc prolonging agents. Additive risk of arrhythmias with Domperidone. | Major - Avoid Combination |
| Anticholinergics (e.g., Atropine, Hyoscine) | Oppose the gastroprokinetic effect of Domperidone. | Moderate |
| Warfarin, Acenocoumarol | Omeprazole may inhibit CYP2C19, potentially increasing anticoagulant effect. Monitor INR closely. | Major |
| Diazepam, Phenytoin | Omeprazole may inhibit their metabolism (CYP2C19), increasing plasma levels and risk of toxicity. | Moderate |
| Clopidogrel | Omeprazole (especially high dose) inhibits CYP2C19, the enzyme required to convert Clopidogrel to its active metabolite. This may reduce Clopidogrel's antiplatelet efficacy, increasing cardiovascular risk. Avoid combination if possible. | Major |
| Methotrexate (especially high-dose) | Omeprazole may reduce renal clearance of Methotrexate, increasing toxicity (myelosuppression, nephrotoxicity). | Major |
| Digoxin | Increased gastric pH from Omeprazole may increase Digoxin absorption. Monitor Digoxin levels. | Moderate |
| HIV Protease Inhibitors (Atazanavir, Nelfinavir) | Omeprazole reduces gastric acidity, severely decreasing absorption of these drugs, compromising antiviral efficacy. | Major - Avoid Combination |
| Iron Salts, Ketoconazole, Itraconazole | Omeprazole reduces gastric acidity, which can decrease the absorption of these drugs. Separate administration by 2-3 hours. | Moderate |
7. Patient Counselling
- DO take the tablet whole, 30-60 minutes before breakfast.
- DO inform your doctor about all other medicines, vitamins, and herbal supplements you are taking.
- DO inform your doctor if you have a history of heart, liver, or kidney disease.
- DO report any symptoms of irregular heartbeat, dizziness, or fainting immediately.
- DON'T crush, chew, or break the tablet.
- DON'T take a double dose to make up for a missed one.
- DON'T consume grapefruit or grapefruit juice while on this medication.
- DON'T take this medication for longer than prescribed by your doctor.
8. Toxicology & Storage
Overdose: Domperidone: Agitation, seizures, altered consciousness, extrapyramidal reactions, QTc prolongation, arrhythmias, cardiac arrest. Omeprazole: Blurred vision, confusion, drowsiness, dry mouth, flushing, headache, nausea, tachycardia, diaphoresis.
Storage: Store below 25°C, in a cool, dry place. Protect from light and moisture. Keep out of reach of children. Do not use after the expiry date printed on the pack.