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	The Pharmaceutical Journal Vol 270 No 7240 p366-367 15 March 2003	This page Reprint Photocopy
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Adverse reactions

Report all drug reactions with warfarin

From Mr A. R. Cox, MRPharmS, and Mr C. Anton

Coleman and colleagues’ quality standards for community pharmacist-led anticoagulant clinics (PDF 65K) will be helpful to all pharmacists who wish to set up such a scheme (PJ, 1 March, p308). Several of the competencies they list as necessary relate to the adverse effects and interactions of warfarin with drugs, food and herbal remedies. We would like to emphasise the importance of reporting any serious adverse effects, and any interactions, to the Committee on Safety of Medicines via the yellow card scheme.

We have found previously that only one in 12 doctors would report warfarin-induced haemorrhage.¹ In a recent study of elderly patients in the community in New England, 121 of 27,617 experienced an adverse reaction to anticoagulants in 12 months. It was the fifth highest cause of adverse drug events.²

Serious adverse events to warfarin should always be reported via the yellow card scheme, even though well-known. In addition, any interaction with warfarin should be reported, whether it is a known interaction or not. Valuable clinical and demographic information is lost every time such a report is not submitted. One study found 73 per cent of patients with an admission related to warfarin took medication with the potential to interact with warfarin, as indicated by the 42nd edition of the British National Formulary. There was a mean of 1.8 (range 1–3) interacting drugs per patient. Interacting drugs included antibiotics, anti-arrhythmics, non-steroidal anti-inflammatory drugs and H2-receptor antagonists.³

Pharmacists involved in the monitoring of anticoagulation are in an ideal place to identify adverse effects and interactions.⁴ We would encourage all pharmacists in anticoagulant clinics to incorporate the reporting of adverse reactions and interactions associated with warfarin as part of the quality standards of their clinic, and other pharmacists to incorporate this activity into their routine clinical practice.

References

1. Cox A, Anton C, Goh CHF, Easter M, Langford NJ, Ferner RE. Adverse drug reactions in patients admitted to hospital identified by discharge ICD-10 codes and by spontaneous reports. Br J Clin Pharmacol 2001; 52:337–9.

2. Gurwitz JH, Field TS, Harrold LR et al. Incidence and preventability of adverse drug events among older persons in the ambulatory setting. JAMA 2003;289: 1107–16.

3. Dent SN, Cox AR, Marriott JF, Langley CA, Wilson KA. Warfarin toxicity: do discharge ICD-codes and yellow cards accurately identify serious adverse drug reactions? Int J Pharm Pract 2002;10(Suppl):R40 (PDF 45K)

4. Bradley MJ, Cox A. Suspected interaction between celecoxib and warfarin. Pharm Pract 2001;11: 243–5.

Anthony Cox
Christopher Anton
West Midlands Centre for Adverse Drug Reaction Reporting

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