Herbal Medicines and Anaesthesia (printer-friendly)

and Introduction Introduction The use of herbal remedies has been around for centuries and their use in both western and eastern societies are increasing. Patient surveys have reported that 12% of Americans, 12% of Australians, and 4.8% of patients in the UK use herbal remedies. The World Health Organization (WHO) estimates that up to 80% of the world's population still depend on herbal medicines. Although there has been concern in the medical community about the potential complications arising as a result of patient use of herbal medicines, the exact degree of concern remains unclear as very few of the huge number of remedies have been formally researched. The assumption by patients and healthcare professionals that these products are 'natural' and therefore safe is clearly dangerous. Many patients do not disclose their use and hence the anaesthetist may remain oblivious to potential side-effects and drug interactions. As pharmacokinetic and pharmacodynamic data are lacking, the American Society of Anaesthesiologists recommends that patients discontinue the use of herbal medications 2–3 weeks before surgery. However, patients are often unaware of this recommendation and, furthermore, may present for emergency surgery. There are no formal recommendations or guidelines governing their use for the perioperative period in the UK. Hence, all anaesthetists need to familiarize themselves with the potential perioperative complications that may occur. The aim of this article was to discuss the more commonly used herbal medicines, their side-effects and their effects on the conduct of anaesthesia. These include echinacea, ephedra, garlic, ginger, gingko biloba, ginseng, herbal diuretics, kava, St John's Wort, and valerian. The Scale of the Problem A significant proportion of conventional drugs today originate from compounds derived from plants. The increase in use of herbal medicines may be attributed to the belief that they are 'safer' although it may also be seen as a lack of confidence in conventional treatment options especially in more chronic illnesses. Examples of chronic illnesses believed to be cured by herbal remedies include diabetes mellitus, malignancies, arthritis, and even AIDS. Attributable side-effects of herbal medicines (Table 1) include cardiovascular instability, electrolyte disturbances, coagulation disorders, endocrine effects, hepatotoxicity, and renal failure. In the UK, the majority of herbal remedies are exempt from the licensing requirements set out in the Medicines Act 1968. This has come under close scrutiny as a recent report by the House of Commons Science and Technology Committee called for the NHS to cease funding homeopathy. Similarly, in the USA, herbal products are classified as dietary supplements by the Food and Drug Administration (FDA) and are not subjected to rigorous testing. Hence, herbal remedies available over-the-counter can be of variable quality and content. Heavy metals such as mercury, lead, thallium, cadmium, copper, iron, manganese, nickel, zinc, and arsenic have all been found in certain remedies. Herbal Medicines and Anaesthesia Adrian Wong BSc (Hons) MRCP (UK); Stephen ATownley MBBCh, BSc, MRCP, FRCA Posted: 03/01/2011; Cont Edu Anaesth Crit Care & Pain. 2011;11(1):14-17. © 2011 Oxford University Press Table 1. Commonly used herbal medicines, their uses, effects and perioperative considerations The lack of compulsory post-marketing surveillance means that the incidence and exact nature and scale of adverse effects in the UK are unknown. At an international level, more than 6000 suspected reactions were reported to the WHO before 1998 and 101 deaths were reported to the US FDA. Common Herbal Medicines Echinacea Echinacea is the most popular herbal remedy currently being used in the USA and UK. It is believed to improve the immune system through modulation of cytokine signalling and is used for the prevention and treatment of viral, bacterial, and fungal infections (especially upper respiratory tract infections). Current evidence suggests that echinacea may decrease the severity and duration of upper respiratory tract infections but is not useful as prophylaxis. Known side-effects include gastrointestinal disturbances, headache, and dizziness. Its effect on the immune system means that patients who may require perioperative immunosuppression, such as transplant candidates, should be advised to avoid them. This is because although immunostimulatory in the short-term, echinacea is a potent immunosuppressant in the long-term. Herbal medicine Uses Pharmacological effects Perioperative considerations Discontinuation recommendation Echinacea Improve immune system Modulates cytokines; stimulate macrophages and NK cells Avoid known hepatotoxic drugs No data available; discontinue 2 weeks before surgery Ephedra CNS stimulant; weight loss; asthma treatment Sympathomimetic Caution with other sympathomimetic; arrhythmias with halothane Discontinue 24 h before surgery Garlic Treatment of hypertension, hyperlipidaemia, atherosclerosis Anti-platelet effects Risk of bleeding Discontinue 7 days before surgery Ginger Anti-inflammatory; Anti-emetic Inhibit serotonergic pathways; stimulate GI tract Risk of bleeding No data available. Discontinue 2 weeks before surgery. Gingko biloba Neuroprotective; Improve blood flow Free radical scavenger; anti-platelet effects Risk of bleeding Discontinue 36 h before surgery Ginseng Mood enhancer; aphrodisiac Sympathomimetic Risk of bleeding; hypoglycaemic effect; caution with other sympathomimetic Discontinue 7 days before surgery Kava Sedative; anxiolytic Potentiate GABA mediated system Reduce anaesthetic requirements Discontinue 24 h before surgery St John's Wort Antidepressant Inhibit MAOIs; induces cytochrome p450 Serotonergic crisis; sedative effect Discontinue 5 days before surgery Valerian Anxiolytic; hypnotic Potentiate GABA-ergic system Reduce anaesthetic requirements No data available; discontinue 2 weeks before surgery. Chronic use of echinacea can result in hepatic failure, which can then enhance the hepatotoxic effects of drugs such as amiodarone, methotrexate and halothane. Pharmacokinetic data on echinacea are lacking and there are no available recommendations regarding their use in the perioperative period. Ephedra Originating from China, ephedra (also known as Ma Huang) contains the alkaloids ephedrine, pseudoephedrine, methylephedrine, and nor-pseudo-ephedrine. Of these, ephedrine is the predominant compound. It has direct agonist effect on αand β-adrenergic receptors and can also indirectly increase the release of norepinephrine from presynaptic neurones. Its sympathomimetic effects mean that it is marketed as a central nervous system (CNS) stimulant, weight loss supplement and in the treatment of asthma. Perhaps more worryingly, it has become a drug of abuse with street names such as 'Herbal Ecstasy' and 'Cloud 9'. Side-effects are predictable and include palpitations, hypertension, tachycardia, stroke, and seizures. Chronic use has been associated with cardiomyopathy. Other adverse effects reported include myocardial infarction, fatal arrhythmias, acute hepatitis, and psychosis. Its sale has thus been restricted in both Australia and the USA. The effects of ephedra on anaesthesia are partly predictable. In combination with other sympathomimetic drugs, it can result in life-threatening arrhythmias, hypertension, and hyperthermia. Long-term use of ephedra may deplete endogenous catecholamine stores leading to further cardiovascular instability intra-operatively and tachyphylaxis to other sympathomimetic drugs. In such a situation, direct-acting sympathomimetic agents may be preferred. Fatal arrhythmias have also been reported in patients taking ephedra exposed to halothane anaesthesia. Pharmacokinetic studies of ephedra suggest that the herb should be discontinued for at least 24 h before surgery. Garlic Perhaps, better known as a cooking ingredient, garlic (Allium sativum) has also been used for centuries for its medicinal properties. It claims to be beneficial in cardiovascular disease, diabetes, infection, and even tumours. These actions are believed to be because of the cysteine contained in garlic, which decreases thromboxane formation and alters arachidonic acid metabolism. It inhibits platelet aggregation in a dose-dependent fashion, although this has not been demonstrated consistently in volunteers. Adverse effects of garlic include nausea, hypotension, and allergy. In addition, there have been several case reports of garlic causing bleeding problems. It can potentiate the anti-platelet effects of aspirin and non steroidal anti-inflammatory drugs (NSAIDs). This effect may be irreversible and hence patients should be advised to discontinue their use for at least 7 days before surgery. Ginger Ginger (Zingiber officinale) is marketed as an anti-inflammatory and an anti-emetic. In addition to direct stimulation of the gastrointestinal (GI) tract, it is postulated to inhibit peripheral and central serotonergic pathways. A systematic review of randomized controlled trials showed no significant difference in the incidence of postoperative nausea and vomiting between the ginger and placebo groups. It is a potent inhibitor of thromboxane synthetase enzyme that can prolong bleeding time. Risk assessment for bleeding is prudent especially when used in combination with NSAIDs and warfarin.