the inhibitory properties of and mode of action of plant essential oils ...

Similar findings occurred when testing the N’Dribala plant. A decoction of roots
given to human volunteers with uncomplicated P. falciparum infections caused no
significant side effects (Benoit-Vical et al. 2003) but, in vitro, the essential oil was
cytotoxic to K562 cells (a human erythroblastic cell line) IC50 = 860 – 950 µg ml -1
(Benoit-Vical et al. 2003). This was, however, far lower than the reported IC50 value
of the oil against the parasite (22 – 35 µg ml -1 ) (Benoit-Vical et al. 2003).
Eucalyptus oil, sometimes known as camphor oil and its major constituent eucalyptol
has been given “Generally Recognised as Safe” status by the Flavour and Extract
Manufacturer’s Association (FEMA) and is approved by the FDA for food additive
use (De Vincenzi et al. 2002). However, the oil is also widely regarded as being
extremely toxic if ingested, causing central nervous system (CNS) depression
(fatigue, loss of consciousness, headaches, decreased alertness) and tonic-clonic
seizures rapidly following its ingestion (Gouin & Patel 1996; Patel & Wiggins 1980).
Toxicological data for humans show a minimum lethal dose of 50 mg kg -1 which is
500 times greater than the proposed total daily intake limit of 0.1 mg kg -1 eucalyptol
(De Vincenzi et al. 2002). This oil may also be useful as an antiviral being 3 times
more toxic to herpes simplex virus (HSV) types 1 and 2 than to RC-37 cells (African
green monkey kidney cells) (Schnitzler, Schon and Reichling 2001).
Of the plant essential oils commonly used, TTO is probably the best known. It has
been tested extensively by scientists for its antibacterial and antifungal effects with
work now being carried out on its potential as an antiparasitic and antiviral agent.
This oil is considered to be non-poisonous and as such is freely available ‘over the
counter’ in chemists as an herbal remedy (Soderberg, Johansson and Gref 1996).
TTO has not been shown to be cytotoxic in vitro to human epithelial and fibroblast
cells (Soderberg, Johansson and Gref 1996). Only at concentrations greater than 100
µg ml -1 did cell viability rapidly decline, which was thought to be due to its lipophilic
character, with the oil interacting with cellular membranes, disrupting normal
membrane activity (Soderberg, Johansson and Gref 1996). Its use internally however,
should be avoided as the ingestion of less than 5 ml by children under the age of 24
months has caused severe poisoning with ataxia and a drowsiness with difficulty to
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