Omeprazole dosage: the right dose for your condition

The BNF provides clear dosage recommendations for omeprazole based on the clinical indication.

In my prescribing practice, I always select the lowest effective dose for the shortest appropriate duration.

Gastro-oesophageal reflux disease (GORD):

• Mild symptoms: 10 mg once daily (available over the counter)
• Moderate to severe symptoms: 20 mg once daily for 4 to 8 weeks
• Maintenance in confirmed oesophagitis: 10 to 20 mg once daily

Gastric and duodenal ulcers:

• Duodenal ulcer: 20 mg once daily for 4 weeks
• Gastric ulcer: 20 mg once daily for 8 weeks
• NSAID-associated ulcer: 20 mg once daily for 4 to 8 weeks

Helicobacter pylori eradication:

• 20 mg twice daily as part of triple therapy for 7 days (with two antibiotics such as amoxicillin 1 g twice daily and clarithromycin 500 mg twice daily)

Zollinger-Ellison syndrome:

• Initial dose of 60 mg once daily, adjusted according to response. Doses up to 120 mg daily (in divided doses) may be required.

NSAID prophylaxis:

• 20 mg once daily for patients at risk of NSAID-related gastropathy

Omeprazole should be swallowed whole with water, ideally 30 minutes before breakfast. The capsule should not be chewed or crushed.

In older patients, I take particular care with omeprazole dosing. The BNF states that no dose adjustment is required solely on the basis of age, but there are important clinical considerations.

Elderly patients are more susceptible to the long-term side effects of PPIs, including:

• Bone fracture risk: the MHRA has highlighted increased fracture risk with long-term PPI use in elderly patients
• Hypomagnesaemia: older adults are more likely to be taking concomitant medications (such as diuretics) that compound magnesium depletion
• Drug interactions: polypharmacy is common in this age group, and omeprazole inhibits CYP2C19, which can affect the metabolism of drugs such as clopidogrel and phenytoin
• B12 deficiency: elderly patients already have higher rates of B12 deficiency, and PPI use may exacerbate this

In my practice, I routinely review PPI prescriptions in patients over 65 at annual medication reviews. If the original indication no longer applies, I recommend a gradual step-down:

1. Reduce from 40 mg to 20 mg for two weeks
2. Then from 20 mg to 10 mg for two weeks
3. Then trial withdrawal with antacids as needed

NICE guidance supports this approach, recommending the lowest effective dose and regular review for all long-term PPI users.

Omeprazole is licensed for use in children, and the BNF for Children provides weight-based dosing recommendations.

Paediatric prescribing should always be initiated by or in consultation with a specialist.

Children aged 1 to 11 years:

• Body weight 10 to 20 kg: 10 mg once daily, increased to 20 mg if necessary
• Body weight over 20 kg: 20 mg once daily, increased to 40 mg if necessary

Children aged 12 to 17 years:

• GORD: 20 mg once daily for 4 weeks
• Ulcer healing: 20 mg once daily for 4 to 8 weeks

Neonates and infants under 1 year:

• 700 micrograms per kg once daily, increased if necessary to 1.4 mg per kg (maximum 20 mg once daily in infants under 10 kg)

For children who cannot swallow capsules, omeprazole is available as a dispersible (MUPS) tablet that can be mixed with water or slightly acidic fruit juice.

Alternatively, the capsule contents can be mixed with yoghurt or fruit puree and taken immediately without chewing.

I always emphasise to parents that treatment duration should be as short as clinically appropriate, and that regular follow-up with the prescribing team is essential.

Getting the timing and method of administration right makes a significant difference to omeprazole's effectiveness. I routinely explain the following to my patients:

Timing:

• Take omeprazole 30 minutes before your first meal of the day
• Proton pump inhibitors work best when taken before eating because they target actively secreting proton pumps
• If prescribed twice daily (e.g. for H. pylori eradication), take the second dose 30 minutes before your evening meal

Method:

• Swallow the capsule whole with a glass of water
• Do not chew, crush or open the capsule (unless using MUPS tablets)
• If you have difficulty swallowing, speak to your pharmacist about the dispersible formulation

Missed doses:

• If you forget a dose, take it as soon as you remember unless it is nearly time for the next dose
• Do not take a double dose to make up for a missed one

Duration of treatment:

• Over-the-counter use for heartburn: up to 2 weeks
• Prescription for GORD: typically 4 to 8 weeks
• Ulcer healing: 4 to 8 weeks
• Long-term maintenance: only with regular medical review

Patients should not continue taking omeprazole indefinitely without a clear medical reason.

The NHS guidance recommends discussing ongoing need at each prescription review.

Omeprazole is metabolised by CYP2C19 and CYP3A4 in the liver, which creates several clinically important interactions that may influence dosing decisions.

Clopidogrel:

Omeprazole significantly reduces the antiplatelet effect of clopidogrel by inhibiting CYP2C19-mediated conversion to its active metabolite. The MHRA advises against concurrent use.

If a PPI is needed alongside clopidogrel, lansoprazole or pantoprazole are preferred alternatives.

Methotrexate:

PPIs can reduce renal clearance of methotrexate, leading to toxicity. The BNF recommends considering temporary PPI withdrawal in patients receiving high-dose methotrexate.

Phenytoin and warfarin:

Omeprazole can increase plasma concentrations of both drugs. INR monitoring should be intensified when starting or stopping omeprazole in patients on warfarin.

Antifungals:

Ketoconazole and itraconazole require gastric acid for absorption. Concurrent PPI use can substantially reduce their bioavailability.

HIV protease inhibitors:

Atazanavir and nelfinavir levels are significantly reduced by omeprazole. Co-administration is generally contraindicated.

I always check for interactions using the BNF interaction checker before prescribing omeprazole, particularly in patients taking multiple medications.

This is especially relevant in elderly patients where polypharmacy is common.