Published: 5 September 2014

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Interaction Between Omeprazole and Citalopram/Escitalopram

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Prescriber Update 35(3):41-42
September 2014

Interactions between medicines can occur through pharmacokinetic and pharmacodynamic mechanisms.

Omeprazole and citalopram/escitalopram are metabolised by cytochrome P450 (CYP) 2C19. Co-administration of omeprazole and citalopram doubled exposure to the S-isomer of citalopram¹. Co-administration of omeprazole and escitalopram resulted in a 50% increase in plasma levels of escitalopram ¹.

The pharmacokinetic interaction between omeprazole and citalopram/escitalopram increases the risk of QT prolongation, as this effect is associated with higher doses of citalopram². The recommended maximum dose of citalopram is 20mg daily in patients who are also taking omeprazole³. Similarly a dose reduction of escitalopram may be needed in some patients also taking omeprazole ⁴.

Omeprazole and citalopram/escitalopram can each individually cause hyponatraemia. Therefore co-administration may increase the risk of hyponatraemia.

The Centre for Adverse Reactions Monitoring (CARM) has received six reports of hyponatremia in patients taking both omeprazole and citalopram/escitalopram. In four cases the patient's sodium level was close to the lower limit of normal on long term medicines including omeprazole, and experienced rapid falls within a week of adding citalopram/escitalopram. In one case severe hyponatraemia occurred within one week when omeprazole was added to long-term citalopram, with recovery when citalopram was discontinued. One patient experienced convulsions and two patients experienced confusion as a consequence of hyponatraemia. The majority of the patients were elderly, which is a known risk factor for developing hyponatraemia.

Caution is therefore advised when treating patients with omeprazole and citalopram/escitalopram concomitantly.

Please report any suspicions of drug interactions to CARM.

References

1. AstraZeneca Ltd. Losec Modified Release Capsule Data Sheet. 13 January 2014. URL: www.medsafe.govt.nz/profs/datasheet/l/Loseccap.pdf (accessed 28 July 2014)
2. Medsafe. 2012. Citalopram and Escitalopram - Similar Risk of QT Prolongation? Prescriber Update 33 (1): 3-4.
3. Healthcare Logistics. Cipramil Data Sheet. 29 July 2013. URL: www.medsafe.govt.nz/profs/datasheet/c/cipramiltab.pdf (accessed 28 July 2014)
4. Mylan New Zealand Ltd. Loxalate Data Sheet. 3 April 2014. URL:www.medsafe.govt.nz/profs/datasheet/l/loxalatetab.pdf (accessed 28 July 2014)