• Five proton pump inhibitors (PPIs) are currently available in the UK: esomeprazole (an isomer of omeprazole), lansoprazole, omeprazole, pantoprazole, and rabeprazole:
• Differences among the PPIs in terms of clinical efficacy and safety are minimal [Aronson, 2006b; MeReC, 2006].
• Of the five PPIs available, lansoprazole and omeprazole are preferred because they are both available generically and are considerably less expensive than other PPIs.
• When prescribing a PPI for people on low-dose aspirin who are at high risk of gastrointestinal adverse effects or who continue to have dyspepsia:
• Offer a dose licensed for gastroprotection, for example:
• For lansoprazole: 15 mg once daily (if necessary, increasing to 30 mg daily).
• For omeprazole: 20 mg once daily.
• 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 similar. The most common adverse effects include headache, diarrhoea, nausea, abdominal pain, constipation, dizziness, and rash.
• 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].

[Aronson, 2006b; ABPI Medicines Compendium, 2008a]