The Pharmaceutical Journal Vol 267 No 7172 643-649
3 November 2001

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Letters to the Editor

Interactions (2 letters)

Lacidipine with terfenadine?

From Mr M. P. J. Hadley, MRPharmS

Further to my recent letter and the response from Dinesh Mehta (PJ, 20 October, p547), I would like to reply to the two points.

First, an even closer reading of the summary of product characteristics reveals that it does say that lacidipine prolongs the QT interval and in fact quantifies this. Surely when the SPC says that the drug should be used with caution that indicates an interaction or possible interaction. The drugs concerned are Class I and II antiarrhythmics, tricyclic antidepressants, antipsychotics, antibiotics and antihistaminic agents. Terfenadine was freely available as an over-the-counter medicine, but is now designated as a prescription only medicine because of concerns about its safety. It is infrequently prescribed because there are better and safer alternatives. Therefore on a risk/benefit basis I would suggest that pharmacists should consider suggesting a different antihistamine be taken with lacidipine.

Second, we are concerned here not with the choice of lacidipine but with the continuing use of terfenadine. Mr Mehta writes: "The BNF clearly states that terfenadine should be avoided in known or suspected prolongation of the QT interval. A careful prescriber would avoid the drug at the merest hint of cardiac conduction disorders including QT interval prolongation." In fact the SPC states that the QT interval is increased.This seems to be more than "the merest hint".

Finally, to accuse me of interpreting the SPC unwisely and providing spurious information is indeed a serious charge. My letter to The Journal was only sent after consulting the license holder of lacidipine (Boehringer Ingleheim) to see if our interpretation of the SPC was correct. License holders hold a lot more information than is published and are well placed to give advice on their own products.

Mike Hadley
Hadley Healthcare Solutions Ltd,
Malvern,
Worcestershire

TCM inhibition of drug metabolising enzyme?

From Mr M. H. Espley, MRPharmS

The reference to unlicensed traditional Chinese medicines (PJ, 1 September, p283) containing the Psoralea corylifolia fruit being involved with serious skin toxicity due to "variable levels of psoralen" made me wonder if this fruit could also be involved in drug interactions with certain calcium channel blockers and cyclosporin.

According to the PJ (May 3, 1997, p618), researchers at the Royal Postgraduate Medical School, London, found that a member of the psoralen family, ie, 6,7-dihydroxybergamottin inhibited the CYP3A4 type of cytochrome P450 drug metabolising enzyme, referring of course to the interactions involving grapefruit juice.

Malcolm Espley
Chester

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