The potential for interactions between medical drugs and herbal remedies is just about �flavour of the month� in the literature and discussion groups lately. This raised consciousness, while appropriate, is causing some anxiety among some colleagues.
The purpose of this article is not to try to provide a definitive list of potential interactions,
but rather to give some guidelines so we know when alarm bells should start ringing.
The first thing to recognise about this topic is that no-one has many answers. Even with conventional drugs standard texts generally only discuss interactions between pairs of drugs. How 3, 4 or more drugs may all interact together is not really known, and many patients are on multiple drug combinations. The situation is somewhat similar, but more-so, with herbs with their multiplicity of active constituents, but exacerbated because few people have really looked at the possibilities of interactions until recently.
How then do we deal with this problem if we can�t easily get definitive answers to which herbs interact with which drugs? Here are some common sense guidelines, which if followed should keep you from causing any serious trouble for your patients.
Firstly, keep up with the current thought on interactions (for example, through the NHAA website discussion list, and our various professional journals, as well as the lay press). It is most often these examples which your patients or their medical Doctor�s will rightly expect you to be aware of. Interactions discussed at these levels are usually still speculative or theoretical, but still give us some areas to be cautious.
Secondly, be aware of the pharmacology of drugs and herbs. Those that have similar effects or mechanisms of action warrant caution, as there may be synergistic or additive effects leading to toxicity, or even negating effects (e.g. by �false transmitter� actions). Examples might be; diuretics and Tarax fol. (similar effects), SSRI anti-depressants (i.e. Prozac type) and St Johns Wort (similar mechanism) and HRT or the OCP, and phyto-oestrogens (possible false transmitter effect).
Thirdly and perhaps most importantly, by being aware of those medical drugs which have a low therapeutic index. That is drugs where the therapeutic dose is quite close to the toxic dose. These drugs warrant caution when any-thing else is added to the patient�s regime, especially alternative remedies where information on interactions is so sparse. St Johns Wort is the latest to cause concern in this area, as it can induce liver cytochrome P450 enzymes which metabolise many drugs. However, it is not unreasonable to think that many of our �detox� herbs may have similar effects. Fortunately, patients on these types of drugs are usually closely monitored to assess blood levels of the drugs. If treating such patients it is prudent to inform the doctor managing this aspect of the patient�s treatment of any new remedies. A statement along the lines;- "Patient �X� has consulted me for treatment of �Y� condition. I propose to use �Z� in his/her treatment. While I know of no interactions with his/her medical treatment, this has not been extensively studied. You may wish to monitor him/her more closely while the treatment is introduced".
I have listed some of the drugs you are more likely to encounter (as opposed to those likely to be used within hospitals) which have a low therapeutic index. This is not to suggest that herbs cannot be used in any patients on these drugs, but you need to ensure that they understand that there may be some risk, and that appropriate medical monitoring occurs.
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COMMONLY USED LOW THERAPEUTIC INDEX DRUGS.
(not an exhaustive list)
-
Digoxin (Lanoxin)
- Warfarin (Coumadin, Marevan)
- Theophylline (Neulin, TheoDur)
- Thyroxine (Oroxine)
- Cisapride (Prepulsid)
- Quinine (many brands)
- Cyclosporin (Sandimmune, Neoral)
- Gentamicin injection
- Most anti-convulsants
- Most anti-viral drugs (especially for HIV)
- Most anti-cancer drugs
- Long acting anti-rheumatic drugs, especially Methotrexate. (not NSAID�s)
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Useful Resources;
'Herb/Drug Interactions� lecture by Berris Burgoyne. (Notes should be available through MediHerb). This covers most (?all) recent reports of interactions where there is laboratory or clinical evidence (not necessarily conclusive) rather than just a theoretical basis. There are actually not that many given the widespread useage of herbs.
�Herb/Drug Interactions� lecture by Gerald Quigley (another Pharmacist and Herbalist)
(Notes should be available through Nutrition Care). Gerald had a good perspective on how to interact with medical doctors on this issue, but I�m not sure how much of that would be in the notes. You may have to wait for a repeat presentation.
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NHAA Email chat group
www.nhaa.org.au for the TGA recommendations on St John�s Wort;-
www.health.gov.au/
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