Rabeprazole

Rabeprazole belongs to the family of proton pump inhibitors, or PPIs. It is a substituted benzimidazole that blocks a specific enzyme, the H+/K+ ATPase known as the proton pump, located on the secretory surface of the parietal cells of the stomach. This pump carries out the final step of acid production: it expels hydrogen ions into the stomach in exchange for potassium ions. By neutralizing it, rabeprazole cuts off acid secretion at its source, without acting on the H2 histamine receptors and without any anticholinergic action.

Rabeprazole is a prodrug: it circulates in an inactive form and only becomes active on contact with acid, in the secretory canaliculi of the parietal cells. An acid-catalyzed cleavage then transforms it into a molecule able to bind to the pump and block it. These pumps are activated mainly during meals, which explains the recommended timing of the dose. The blood peak appears 2 to 5 hours after intake and the molecule leaves the blood quickly, with a half-life of 1 to 2 hours, while its effect on the pumps lasts much longer than its presence in the circulation.

The common thread across its indications is to reduce acidity so that a damaged mucosa can heal, or to prevent it from becoming damaged. Rabeprazole is prescribed for erosive or ulcerative gastro-oesophageal reflux, over a period of 4 to 8 weeks to achieve healing, then as maintenance to sustain it. It also treats symptomatic gastro-oesophageal reflux and duodenal ulcer, two situations where excess acid keeps the pain going and delays recovery.

It is also part of the eradication of Helicobacter pylori, the bacterium associated with many ulcers, in combination with two antibiotics, amoxicillin and clarithromycin. Finally, it is indicated for pathological hypersecretory conditions, including Zollinger-Ellison syndrome, where the stomach produces acid in abnormally high amounts. In all these cases, a lasting drop in acidity is the therapeutic lever being targeted.

The usual dose is 20 mg once a day. The tablet is taken whole: it should not be chewed, crushed or split, because its coating protects the molecule until it reaches its site of action. For most indications, it can be taken with or without food. Two exceptions: for duodenal ulcer, it is taken after a meal, and for H. pylori eradication, it is taken with food.

PPIs work better before a meal, because the proton pumps activate while we eat: they are then in full activity and the medication reaches them at the right moment. For a once-daily dose, the morning works well; for a second dose, it is placed about 30 minutes before the evening meal. Consistency matters, and stopping is not a decision to make alone: interrupting a PPI can trigger a rebound in acid secretion, with acidity temporarily stronger than before treatment. This point is discussed with the doctor, who adjusts the duration and the withdrawal.

In controlled trials in adults, the adverse effects occurring in at least 2% of patients are pain (3%), pharyngitis (3%), flatulence (3%), infection (2%) and constipation (2%). Headache is reported in fewer than 2% of treated adults, but at a frequency higher than with placebo. In adolescents aged 12 to 16, the profile differs: headache (9.9%), diarrhoea (4.5%), nausea (4.5%), vomiting (3.6%) and abdominal pain (3.6%).

Two effects deserve particular attention during prolonged treatment. Hypomagnesaemia, with or without symptoms, has been reported rarely in patients treated with PPIs for at least three months. And a treatment that reduces gastric acidity, continued for a long time, for example beyond three years, can lead to malabsorption of vitamin B12, because acid takes part in its release from food. The link sometimes raised between PPIs, fracture risk and calcium metabolism rests on conflicting data: this association is not established and the proposed mechanisms remain uncertain.

Rabeprazole alters the action or exposure of several medications. It reduces the area under the curve of the active metabolite of clopidogrel by about 12%. By lowering acidity, it decreases exposure to ketoconazole by about 31% and reduces the effectiveness of atazanavir and nelfinavir, whose absorption depends on gastric pH; combination with rilpivirine is contraindicated. It can also raise methotrexate levels, to the point that temporarily stopping the PPI may be considered with high doses. With warfarin, the INR is monitored, and with digoxin, blood concentrations.

Monitoring follows directly from these effects. In the case of prolonged treatment, monitoring of magnesium levels may be recommended, and vitamin B12 status deserves attention beyond three years. Rabeprazole is metabolized by the liver enzymes CYP3A and CYP2C19, a point that matters when another medication uses the same pathways. Any interruption is prepared with the doctor, to take account of the possible acid rebound.

By lowering acidity, rabeprazole affects two nutrients that the stomach specifically helps to absorb. Vitamin B12 is the best documented example: acid takes part in its release from food, and malabsorption can appear after several years of treatment. It is found only in products of animal origin: fish, meat, poultry, eggs, milk and dairy products. It is absent from plant foods, except those fortified with it, which makes intake more fragile in people who consume little of them.

Magnesium is the second point of vigilance, as hypomagnesaemia has been reported during prolonged treatment. It is drawn mainly from green leafy vegetables, but also from bananas, dried apricots, avocados, almonds, peas and beans, brown rice and milk. Iron, present in lean red meat, eggs, fish, beans, spinach, kale, broccoli and almonds, is absorbed less well when it comes from plants: pairing it with a little meat or with vitamin C improves its assimilation. When treatment reduces over time the ability to draw certain nutrients from food, a targeted intake makes sense, in addition to your treatment and never in its place.