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INTRODUCTION

Approximately 5% of all human exposures reported to poison control centers involve plants. The large number of exposures probably occur because plants are so accessible and attractive to youngsters. Approximately 80% of these cases involve individuals younger than 6 years. As indoor plants have become ever more popular, the incidence of plant exposures has increased. Data compiled by the American Association of Poison Control Centers (AAPCC) give some indication of which plants are more commonly involved (Chap. 130), but these plants typically have relatively limited toxicity. More than 80% of patients reported to the AAPCC as being exposed were asymptomatic, less than 20% had minor to moderate symptomatology, and less than 7% necessitated a health care visit. The benignity of these exposures in the United States, largely due to the unintentional nature of the event, is represented by a fatality rate of less than 0.001%. However, in other parts of the world, plant exposures, particularly those taken for self-harm and where health care is less accessible, carry a significant risk and public health burden.12 This chapter addresses the toxicologic principles associated with the most potentially dangerous plants.

HISTORY AND CLASSIFICATION OF PLANT XENOBIOTICS

Aconitine, from monkshood, exemplifies the rich history of plant toxicology. It was believed by the Greeks to be the first poison—“lycotonum”—created by the goddess Hecate from the foam of the river Cerebrus. Alkaloid constituents are responsible for its toxic (and therapeutic) effects. Alkaloids represent one of several classes of organic molecules found in plants as defined by the science of pharmacognosy, which is the science of medicines derived from natural sources. The pharmacognosy approach is consistent with the literature of plant efficacy and is applied here to their toxicity (Table 118–1). Unfortunately, the science of pharmacognosy is not always straightforward, and systems of classification may vary depending on the pharmacognosist. Hence, our approach borrows primarily from 2 groups of authors to keep the classification as consistent as possible.51,128 The major groups are as follows:

  1. Alkaloids: Molecules that react as bases and contain nitrogen, usually in a heterocyclic structure. Alkaloids typically have strong pharmacologic activity that defines many major toxidromes.

  2. Glycosides: Organic compounds that yield a sugar or sugar derivative (the glycone) and a nonsugar moiety (the aglycone) upon hydrolysis. The aglycone is the basis of subclassification into saponin or steroidal glycosides (including steroidal cardiac glycosides, cyanogenic glycosides, anthraquinone glycosides), and others such as atractyloside and salicin.

  3. Terpenes and resins: Assemblages of 5-carbon units (isoprene unit) with many types of functional groups (eg, alcohols, phenols, ketones, and esters) attached. This is the largest group of secondary metabolites; approximately 20,000 are identified. Most essential oils are mixtures of monoterpenes, and the terpene name depends on the number of isoprene assemblages. Monoterpenes have 2 units (C10H16), sesquiterpenes have 3 isoprene units (C15), diterpenes have 4 isoprene units (C...

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