What is known about aloe remedies and drug interactions, in particular with warfarin?/nThe question

Fråga: What is known about aloe remedies and drug interactions, in particular with warfarin? The question concerns a patient treated with ordinary doses of warfarin and who is considering self-medication with aloe vera.

Sammanfattning: There is no data on interactions between warfarin and aloe remedies. Theoretically, aloe remedies might either potentiate anticoagulant therapy by reducing absorption of vitamin K from the gut or reduce the anticoagulant effect through diminished warfarin absorption.

Svar: Aloe species are succulents that mainly grow in South Africa and West Indies (2). Aloe remedies are often synonymously called aloe vera, although different preparations have somewhat different constituents and exert different pharmacological actions.

Aloe remedies often refer to two different products, aloe and aloe vera, which are obtained from aloe species but various parts of the plant´s leaf (1,2). Aloe is obtained from dried leaf juice and mainly contains anthranoids (Aloins A,B), chromones (aloerin) and phenyl pyrones (1). It is mainly used as a laxative agent and the pharmacological actions can be attributed to the anthranoid glucoside content. The glycosides are metabolised by glycosidase in the intestinal flora to form active anthrones. Anthrones increase the motility of the large intestine by inhibition of the Na+/K+ pump and Cl- channels, resulting in increased chloride and fluid secretion. Another suggested indication for use is for treatment of suppressed menstruation, but no documented pharmacological effect has been found in the literature. Aloe vera is obtained from leaf gel, the mucilaginous tissue located in the leaf parenchyma, and is reported to contain mono- and polysaccharides, tannins, sterols, organic acids, enzymes (including Cyclooxygenase), saponins, vitamins and minerals (1). Traditionally it has been used in ointments and creams to assist the healing of wounds, burns, eczemas and psoriasis. Today it is used mainly in cosmetic preparation. However, depending on how the leafs are prepared both the juice and the mucilaginous tissue from the leafs can be found in some products and consequently exert pharmacological effects.

A thorough literature search did not reveal any published reports of interaction between aloe remedies and warfarin. The cathartic action of aloes may result in decreased absorption of drugs, vitamins or other nutritive substances. Theoretically this may potentate anticoagulant therapy by reducing absorption of vitamin K from the gut. However, loss of anticoagulant effect due to reduced gastrointestinal absorption of warfarin is also possible.

Two studies, comprising of a total of 41 patients, suggest that aloe vera juice can lower blood-glucose in patients with non-insulin dependent diabetes (3,4). Although, none of the patients suffered from hypoglycaemia, patients treated with glucose-lowering agents who wants to self medicate with aloe remedies should be informed about this potential adverse effect.

Long-term use of aloe-containing anthranoids might also result in electrolyte imbalance with potassium deficiency and hypokalemia. This might lead to toxicity from drugs such as cardiac glycosides and intensify the potassium depleting effect of diuretics. In two references it is mentioned that aloe can interact with antiarrhytmics, cardiac glycosides, loop diuretics, other potassium wasting drugs such as steroids and thiazides (5,6). However, this is based on theoretical considerations rather than clinical data. It is therefore difficult to evaluate whether these interactions will be of clinical importance.