• When gastric ulcer is suspected, exclude the possibility of malignancy before treatment with a proton pump inhibitor (PPI) is instituted, as treatment may alleviate symptoms and delay diagnosis.
• Stop or do not initiate PPIs at least 14 days before endoscopy, as they may mask gastric cancer.
• Check if the individual is taking omeprazole which has been brought over the counter. The 10 mg tablet is licensed for the relief of reflux-like symptoms (e.g. heartburn) in those aged 18 and over [ABPI Medicines Compendium, 2004].
• PPIs are generally well tolerated and adverse reactions have generally been mild and reversible.
• The type and frequency of adverse effects reported with lansoprazole, omeprazole, pantoprazole, and rabeprazole are comparable. The most common adverse effects include headache, diarrhoea, nausea, abdominal pain, constipation, dizziness, and skin rashes.
• Drug interactions:
• PPIs undergo extensive hepatic metabolism. In people with liver disease, do not exceed 20 mg daily for omeprazole, pantoprazole, and esomeprazole and 30 mg daily for lansoprazole. There are no data on the use of rabeprazole in people with severe hepatic impairment, and the manufacturer advises caution.
• Occasional and unpredictable bleeding have been reported with warfarin and certain proton pump inhibitors (esomeprazole, omeprazole and lansoprazole). The interaction is not thought to occur with rabeprazole or pantoprazole [Baxter, 2006].
• There are case reports of omeprazole, esomeprazole and lansoprazole interacting with phenytoin (causing an increase in phenytoin level). The mechanism is not well understood and information is very limited. No special precautions would normally seem necessary if lansoprazole or omeprazole is given with phenytoin but prescribers should be aware of this possible interaction if concurrent use is necessary. Pantoprazole and rabeprazole appear not to interact with warfarin [Baxter, 2006].
• Because of decreased intragastric acidity, the absorption of ketoconazole or itraconazole may be reduced during PPI treatment.
• PPIs can significantly reduce the efficacy of clopidogrel by inhibition of the CYP2C19 isoenzyme. The Medicines and Healthcare products Regulatory Agency (MHRA) has advised that concomitant use of clopidogrel and any PPI should be avoided unless considered essential [MHRA, 2009].

[NICE, 2005; Aronson, 2006; ABPI Medicines Compendium, 2008]