The Editorial Executive Committee welcomes letters, which should be less than 250 words. Before a decision to publish is made, letters which refer to a published article may be sent to the author for a response. Any letter may be sent to an expert for comment. When letters are published, they are usually accompanied in the same issue by their responses or comments. The Committee screens out discourteous, inaccurate or libellous statements. The letters are sub-edited before publication. Authors are required to declare any conflicts of interest. The Committee's decision on publication is final.

Letter to the Editor

In regards to the article on the management of warfarin therapy,1 the statement on page 46 ‘drugs that may increase INR – macrolide antibiotics, imidazole antifungals, sulfamethoxazole/trimethoprim, amiodarone, statins, some non-steroidal anti-inflammatory drugs and some complementary medicines such as St John’s wort’ may not be correct.

In the literature, St John’s wort decreases the INR through induction of cytochrome P450 (CYP)-mediated metabolism of warfarin and increases warfarin clearance.2-9

Angela Cattanach
Siboniso Sibindi
Clinical pharmacists
Lismore Base Hospital
Lismore, NSW

Author's comments

Gregory Roberts, one of the authors of the article, comments:

Thank you for pointing out the error in the article.1 St John’s wort induces CYP enzymes with a resultant increase in warfarin clearance and decrease in INR, not a possible increase in INR as described in the article. Decreases of 20% in AUC (area under the curve) have been noted in single warfarin dose studies,2 so while prudent INR monitoring should be undertaken, the interaction is likely to be of clinically minor importance.