Losec

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Losec on Prescriptsy

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Losec is the original brand name for omeprazole, a proton pump inhibitor (PPI) developed and manufactured by AstraZeneca.

It was the first PPI to reach the global market and has been in clinical use since 1988, becoming one of the most widely prescribed medicines in history.

Losec is licensed in the United Kingdom for the treatment of gastro-oesophageal reflux disease (GORD), gastric and duodenal ulcers, Zollinger-Ellison syndrome, NSAID-associated ulceration, and as part of Helicobacter pylori eradication therapy.

It is available as hard capsules in strengths of 10 mg, 20 mg, and 40 mg.

Acid-related disorders of the upper gastrointestinal tract are extremely common in the UK.

GORD affects an estimated 10 to 30% of the adult population, while peptic ulcer disease (gastric and duodenal ulcers) remains a significant cause of morbidity and healthcare utilisation.

Proton pump inhibitors such as Losec have transformed the management of these conditions by providing profound and sustained suppression of gastric acid secretion.

This page provides a comprehensive clinical overview of Losec, including how it works, dosing guidance, side effects, safety warnings, drug interactions, and how to obtain a prescription in the UK.

Important safety information about Losec

Before reading further, note the following key safety points about Losec (omeprazole).

• Do not start Losec if you have alarm symptoms such as unintentional weight loss, difficulty swallowing, vomiting blood, or black tarry stools without first seeking medical evaluation. These may indicate a serious condition that requires investigation before PPI therapy is started.
• Long-term PPI use should be reviewed regularly. Your prescriber should periodically assess whether continued treatment is necessary and whether the dose can be reduced.
• Omeprazole may interact with clopidogrel (a blood-thinning medicine). If you take clopidogrel, inform your prescriber so an alternative PPI can be considered.
• Prolonged use may be associated with low magnesium levels, vitamin B12 deficiency, and a small increase in the risk of bone fractures.

What is gastro-oesophageal reflux disease

Gastro-oesophageal reflux disease (GORD) is a chronic condition in which stomach acid and, in some cases, bile flows back (refluxes) into the oesophagus, causing symptoms and potentially damaging the oesophageal lining.

The most common symptoms are heartburn (a burning sensation rising from the stomach or lower chest towards the neck) and acid regurgitation (the sensation of acid or food rising into the throat or mouth).

Other symptoms may include chest pain, difficulty swallowing (dysphagia), an acidic or bitter taste, chronic cough, hoarseness, and dental erosion.

The lower oesophageal sphincter (LOS) normally acts as a one-way valve, allowing food into the stomach while preventing stomach contents from refluxing upwards.

In GORD, the LOS may be weakened or may relax inappropriately, allowing acid to escape into the oesophagus.

Risk factors include obesity, pregnancy, hiatus hernia, smoking, alcohol consumption, certain foods (fatty, spicy, or acidic), and medications that relax smooth muscle (such as calcium channel blockers and nitrates).

GORD is classified as non-erosive reflux disease (NERD) when the oesophageal lining appears normal on endoscopy despite troublesome symptoms, or erosive oesophagitis when visible mucosal damage is present.

The Los Angeles classification system grades erosive oesophagitis from A (minor mucosal breaks) to D (severe circumferential erosion).

Prolonged untreated GORD can lead to complications including oesophageal stricture (narrowing), Barrett oesophagus (replacement of normal squamous epithelium with intestinal-type columnar epithelium), and, in rare cases, oesophageal adenocarcinoma.

How Losec works: mechanism of action

Omeprazole, the active ingredient in Losec, belongs to the substituted benzimidazole class of proton pump inhibitors.

It acts by irreversibly inhibiting the hydrogen-potassium adenosine triphosphatase (H+/K+ ATPase) enzyme, commonly referred to as the gastric proton pump.

This enzyme is located on the apical (luminal) membrane of the parietal cells in the gastric mucosa and is responsible for the final step of hydrochloric acid secretion into the stomach lumen.

Omeprazole is a weak base that is acid-labile and is therefore formulated as enteric-coated granules within a gelatin capsule (or as a MUPS formulation, covered separately).

After oral administration, the enteric coating protects the drug from degradation in the acidic stomach environment, allowing it to pass intact to the alkaline environment of the small intestine, where it is absorbed.

Once absorbed into the systemic circulation, omeprazole accumulates in the acidic secretory canaliculi of the parietal cells (pH approximately 1.0), where it undergoes acid-catalysed conversion to its active form, a sulphenamide derivative.

This active metabolite binds covalently and irreversibly to cysteine residues on the alpha subunit of the H+/K+ ATPase, permanently inactivating the enzyme.

Because the inhibition is irreversible, acid secretion resumes only when new proton pump molecules are synthesised by the parietal cell, a process that takes approximately 3 to 5 days.

This accounts for the sustained acid-suppressing effect of omeprazole even though the drug itself has a short plasma half-life of approximately 0.5 to 1 hour.

A single dose of omeprazole 20 mg inhibits approximately 70% of gastric acid output, and with repeated once-daily dosing, steady-state inhibition of approximately 95% is achieved by day 5 of treatment.

Clinical evidence and national guidelines

Omeprazole has been the subject of extensive clinical research, with thousands of published studies supporting its efficacy and safety across multiple acid-related conditions. Key evidence and guideline recommendations are summarised below.

For GORD, randomised controlled trials have consistently demonstrated that omeprazole is superior to histamine H2-receptor antagonists (such as ranitidine) for both symptom relief and healing of erosive oesophagitis.

Healing rates of 80 to 90% at 8 weeks have been reported with omeprazole 20 to 40 mg daily, compared with approximately 50% with H2-receptor antagonists.

NICE Guideline NG184 (Gastro-oesophageal reflux disease and dyspepsia in adults: investigation and management) recommends a full-dose PPI for 4 to 8 weeks as first-line pharmacological treatment for GORD, followed by stepping down to the lowest effective dose for maintenance, or on-demand therapy where appropriate.

For peptic ulcer disease, omeprazole dramatically accelerates ulcer healing compared with H2-receptor antagonists.

Duodenal ulcer healing rates of approximately 95% at 4 weeks and gastric ulcer healing rates of approximately 90% at 8 weeks are achieved with omeprazole 20 mg daily.

In NSAID-associated ulceration, omeprazole has been shown to be effective for both healing and prophylaxis in patients who require continued NSAID therapy.

For Helicobacter pylori eradication, omeprazole-based triple therapy (omeprazole plus two antibiotics for 7 days) achieves eradication rates of approximately 80 to 90% in treatment-naive patients.

NICE recommends testing for H. pylori in patients with dyspepsia or peptic ulcer disease and prescribing appropriate eradication therapy if the test is positive.

Dosage and administration

Losec capsules should be swallowed whole with a glass of water.

They should not be chewed or crushed, as the enteric coating protects the drug from degradation in stomach acid.

Losec should preferably be taken in the morning, 30 to 60 minutes before the first meal of the day, to coincide with the time when the maximum number of proton pumps are active.

Gastro-oesophageal reflux disease

For symptomatic GORD without oesophagitis, the usual dose is 20 mg once daily for 4 weeks.

If symptoms have not resolved, treatment may be extended for a further 4 weeks.

For erosive oesophagitis, the dose is 20 mg once daily for 4 to 8 weeks, with 40 mg daily used for severe cases (Los Angeles grade C or D).

For maintenance therapy to prevent relapse, the dose is 10 to 20 mg once daily, or on-demand treatment (taking a dose only when symptoms recur) may be appropriate for some patients.

Gastric and duodenal ulcers

The usual dose for duodenal ulcer healing is 20 mg once daily for 4 weeks.

For gastric ulcers, the usual dose is 20 mg once daily for 8 weeks.

For NSAID-associated ulcers, 20 mg once daily is recommended for healing, with the same dose used for prophylaxis in patients at high risk of ulcer complications who require continued NSAID therapy.

Helicobacter pylori eradication

Omeprazole 20 mg twice daily is given for 7 days as part of triple therapy with two antibiotics.

Common regimens include omeprazole, amoxicillin 1 g twice daily, and clarithromycin 500 mg twice daily (OAC), or omeprazole, metronidazole 400 mg twice daily, and clarithromycin 500 mg twice daily (OMC).

The choice of regimen depends on local antibiotic resistance patterns and any drug allergies.

Zollinger-Ellison syndrome

The initial dose is 60 mg once daily, adjusted according to clinical response and gastric acid output measurements.

Some patients require doses up to 120 mg daily, given in divided doses. Doses above 80 mg daily should be divided into two daily doses.

Side effects of Losec

Common side effects

The most frequently reported side effects of omeprazole include headache, abdominal pain, nausea, diarrhoea, constipation, and flatulence. These are generally mild and self-limiting.

In clinical trials, the overall incidence of adverse events with omeprazole was similar to placebo for short-term courses of treatment.

Uncommon and rare side effects

Uncommon side effects include dizziness, paraesthesia (tingling or numbness), dry mouth, altered taste, sleep disturbance, raised liver enzymes, and skin rash.

Peripheral oedema, malaise, and blurred vision have been reported rarely.

Interstitial nephritis is a rare but clinically important adverse reaction that may present with fever, rash, eosinophilia, and deteriorating renal function.

If suspected, omeprazole should be stopped immediately and renal function monitored.

Risks of long-term use

Prolonged PPI therapy has been associated with several potential risks.

Hypomagnesaemia may develop after at least 3 months of use, potentially causing serious symptoms including tetany, seizures, and cardiac arrhythmias.

Magnesium levels should be measured before starting long-term therapy and periodically thereafter.

Vitamin B12 deficiency may occur due to reduced acid-dependent absorption, particularly in elderly patients or those with inadequate dietary intake.

Observational studies have reported a small but statistically significant increase in the risk of osteoporotic fractures (hip, spine, wrist) with long-term PPI use, possibly related to impaired calcium absorption.

Patients at risk of osteoporosis should ensure adequate calcium and vitamin D intake.

An increased risk of Clostridium difficile and other enteric infections has been reported, as gastric acid provides a natural barrier against ingested pathogens.

Reporting side effects

If you experience any side effect, whether listed here or not, contact your prescriber. You can also report suspected adverse reactions directly via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk.

Warnings and precautions

Exclusion of malignancy

Before starting PPI therapy, serious underlying conditions must be excluded in patients with alarm symptoms.

Alarm symptoms include unintentional weight loss, progressive difficulty swallowing, persistent vomiting, haematemesis (vomiting blood), melaena (black tarry stools), and anaemia.

PPI therapy can provide symptomatic relief that masks the presentation of gastric or oesophageal cancer, potentially delaying diagnosis.

Patients over 55 years presenting with new unexplained dyspepsia, or any patient with alarm symptoms, should be referred for urgent upper gastrointestinal endoscopy as per NICE Guideline NG12 (Suspected cancer: recognition and referral).

Drug interactions

Omeprazole is metabolised primarily by CYP2C19 and CYP3A4, and it also inhibits CYP2C19.

Clinically significant interactions include clopidogrel (reduced antiplatelet efficacy due to CYP2C19 inhibition; consider lansoprazole or pantoprazole as alternatives), methotrexate (increased plasma levels with potential for toxicity; consider temporary PPI discontinuation during high-dose methotrexate therapy), and certain antiretroviral agents (such as atazanavir and rilpivirine, which require gastric acidity for absorption).

Ketoconazole and itraconazole absorption may be reduced. Always provide a complete medication list to your prescriber and pharmacist.

Rebound acid hypersecretion

Abrupt discontinuation of PPIs after prolonged use may result in rebound acid hypersecretion, characterised by a temporary increase in gastric acid production above pre-treatment levels.

This can cause a recurrence of reflux symptoms that is sometimes interpreted as evidence of ongoing disease.

To minimise rebound symptoms, your prescriber may recommend tapering the dose gradually over 2 to 4 weeks rather than stopping abruptly.

Pregnancy and breastfeeding

Omeprazole has been extensively used during pregnancy, and available epidemiological data from large cohort studies and meta-analyses have not demonstrated an increased risk of major congenital malformations.

Nevertheless, as with all medications during pregnancy, it should be used only when the expected benefit justifies the potential risk to the fetus.

Omeprazole is excreted in breast milk in small amounts. The clinical significance to the nursing infant is not well established, and a risk-benefit assessment should be made.

Discuss your situation with your prescriber or midwife.

How to get a Losec prescription in the UK

Losec at prescription strengths (20 mg and 40 mg) is classified as a prescription-only medicine (POM) in the UK.

Your GP can prescribe it following a clinical assessment that may include symptom evaluation, H. pylori testing, and, where indicated, referral for endoscopy.

If you are already taking omeprazole and require a repeat prescription, this can be arranged through your GP surgery, an authorised online prescriber registered with the GPhC, or through the NHS repeat prescription service.

Omeprazole 10 mg capsules and tablets are available without prescription from pharmacies as a pharmacy-only medicine (P) for the short-term relief of reflux symptoms in adults aged 18 years and over.

This over-the-counter product is intended for a maximum of 4 weeks of self-treatment. If symptoms persist beyond this period, a medical consultation is advised.

The standard NHS prescription charge in England is currently 9.90 pounds per item; prescriptions are free in Scotland, Wales, and Northern Ireland.

Generic omeprazole capsules are therapeutically equivalent to Losec and are more commonly dispensed due to lower cost, unless the prescriber specifies the brand.

Living with GORD: practical management

While Losec provides effective acid suppression, lifestyle modifications can significantly complement pharmacological treatment and, in some cases, allow dose reduction or discontinuation. The following measures are recommended by NICE and supported by clinical evidence.

• Raise the head of the bed by 10 to 20 centimetres using blocks or a wedge pillow. This reduces nocturnal reflux by using gravity to prevent acid from travelling up the oesophagus.
• Avoid eating large meals within 3 hours of lying down or going to bed.
• Identify and avoid foods and drinks that trigger your symptoms, which may include fatty or spicy foods, chocolate, citrus fruits, tomato-based sauces, peppermint, carbonated drinks, alcohol, and caffeine.
• Lose weight if you are overweight or obese. Excess abdominal fat increases intra-abdominal pressure and promotes reflux. Even modest weight loss can improve symptoms significantly.
• Stop smoking. Smoking reduces lower oesophageal sphincter pressure and increases reflux episodes.
• Avoid tight-fitting clothing around the waist, which can increase abdominal pressure.
• Review your current medications with your prescriber, as some drugs (including NSAIDs, calcium channel blockers, nitrates, and bisphosphonates) can worsen reflux.

When to seek urgent medical advice

Contact your GP or NHS 111 if your symptoms do not improve after completing the prescribed course of Losec, if you notice a change in the character of your symptoms, or if you develop new symptoms such as difficulty swallowing or unintentional weight loss.

Seek emergency care (call 999 or attend A&E) if you vomit blood or material that resembles coffee grounds, pass black tarry stools, experience severe abdominal pain, or develop signs of a severe allergic reaction such as swelling of the face, lips, tongue, or throat, or difficulty breathing.

Report any suspected adverse reactions via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk .

Sources

• Losec capsules 20 mg, Summary of Product Characteristics (EMC)
• Omeprazole, British National Formulary (BNF)
• NICE NG184: Gastro-oesophageal reflux disease and dyspepsia in adults
• Omeprazole, NHS
• MHRA Yellow Card Scheme