Chemicals and Environmental Toxins 4 | | Alcohols, Glycols, and Aldehydes |
Ethanol
Mechanism of Toxicity
Toxicokinetics of Ingestion
Estimation of Blood Alcohol Concentration (BAC)
Characteristics of Acute Toxicity
Management of Acute Toxicity
Methanol
Toxicokinetics of Ingestion
Mechanism of Toxicity
Characteristics of Acute Toxicity
Management of Toxicity
Isopropanol
Ethylene Glycol
Mechanism of Toxicity
Characteristics of Toxicity
Management of Toxicity
Propylene Glycol
Formaldehyde
Mechanism of Toxicity
Characteristics of Toxicity
Management of Toxicity
Acetaldehyde
Acetone
Summary
Case Study: Ethanol Intoxication
History
Discussion
Case Study: Intoxication with Mouthwash
History
Discussion
Case Study: Poisoning by Wine in a Child
History
Discussion
Case Studies: Methanol Intoxication
History: Case 1
History: Case 2
Discussion
Case Studies: Ethylene Glycol Poisoning
History: Case 1
History: Case 2
History: Case 3
Discussion
Case Study: Formaldehyde Poisoning
History
Discussion
Review Questions
References
Alcohols are hydroxy derivatives of straight or branched chain aliphatic hydrocarbons. The more common alcohols may include up to three hydroxyl groups with no more than one on each carbon. Lesser common alcohols may contain more than one hydroxyl group per carbon atom. Those alcohols that are the most common causes of toxicity include ethanol (ethyl alcohol; alcohol), methanol (methyl alcohol), and isopropanol (isopropyl alcohol). In general, the longer the carbon chain, the greater the toxicity. The exception to this rule is methanol, which is more toxic than ethanol.
Dihydroxy alcohols are called glycols (glyc- or glyco-from the Greek stem word meaning sweet), referring to their sweet taste. Dihydroxyethane is better known as ethylene glycol, the simplest glycol. It is commonly referred to as permanent antifreeze and is a fairly frequent cause of poisoning. Another glycol is dihydroxypropane (propylene glycol), a constituent of numerous pharmaceutical products. For the most part, propylene glycol is not toxic.
Alcohols and glycols are discussed together in this chapter for several reasons. First, they are chemically similar. They also share many common characteristics of acute poisoning, and their acute toxicities are treated similarly. However, each of the compounds in this chapter has its own specific characteristics.
ETHANOL
Ethanol is the only alcohol that has widespread intentional internal human use. Ethanol is one of the oldest drugs and is the primary alcohol present in fermented and distilled beverages. It is also the most commonly used psychoactive drug in the world (1).
Ethanol is a clear, colorless liquid that imparts a burning sensation to the mouth and throat when swallowed. Pure ethanol has a slightly pleasant odor. Ethanol is a powerful CNS depressant that acts primarily on the reticular activating system in the brain. In fact, its actions are qualitatively similar to those of general anesthetics. It has a relatively low or der of toxicity compared to methanol or isopropanol.
Ethanol is discussed first because it is the most frequently reported cause of alcohol toxicity and because an understanding of certain aspects of its metabolic pathway and toxic actions is necessary to understand the mechanism of toxicity and management of overdoses involving methanol and ethylene glycol. As with all alcohols and glycols discussed in this chapter, only acute toxicologic considerations will be presented.
Mechanism of Toxicity
The exact mechanisms by which ethanol produces its pharmacologic and toxicologic actions are not completely understood and have been investigated for many years. The CNS is selectively affected. Ethanol is thought to act directly on neuronal membranes and not on synapses. At the membrane, it may involve ion transport and biogenic amines.
The effect of ethanol on the CNS is directly proportional to its blood concentration (47). The first region affected is the reticular activating system, resulting in disruption of the motor and thought processes. Suppressing the cerebral cortex causes a variety of behavioral changes. Which specific behaviors will be suppressed and which will be released from inhibition depend on the individual. In general, complex, abstract, and poorly learned behaviors are disrupted at low alcohol concentrations.
Ethanol depresses the CNS in a descending order from the cortex to the medulla. Table 4.1 illustrates the correlation between blood alcohol concentration (BAC) and the area of the brain affected. Also, subjective feelings are noted based on blood alcohol concentration and the area of the brain where ethanol produces its effect.
Toxicokinetics of Ingestion
Absorption
The physicochemical properties of ethanol are such that it is slightly polar and has a weak electronic charge and low molecular weight. Ethanol is miscible in water and lipid soluble. Therefore, it is easily absorbed and can pass through cell membranes by simple diffusion.
TABLE 4.1. Range of toxicity of ethanol
Clinical description/symptoms | Blood alcohol concentration (w/v) | Part of brain |
Mild Decreased inhibitions Slight visual impairment Slowing or reaction time Increased confidence | 0.05â0.10%(50â100 mg/dL) | Frontal lobe |
Moderate Ataxia Slurred speech Decreased motor skills | 0.15â0.30% (150â300 mg/dL) | Parietal lobe |
Decreased attention Diplopia | | Occipital lobe |
Altered perception Altered equilibrium | | Cerebellum |
Severe | 0.3â0.5%(300â500 mg/dL) | |
Vision impairment | | Occipital lobe |
Equilibrium | | Cerebellum |
Stupor | | Diencephalon |
Coma | | |
Respiratory failure | >0.5% (>500 mg/dL) | Medulla |
The most common route of exposure to ethanol is ingestion, but it also can be absorbed by inhalation of vaporized ethanol or through the skin. Ethanol absorption after ingestion begins in the stomach, but only a small percentage of the amount ingested is absorbed directly into the blood through the stomach wall. The rate of absorption is much greater in the small intestine. Since absorption through the stomach wall is minimal and rapid absorption occurs in the small intestine, any factor that delays or enhances gastric emptying will influence the rate of absorption of alcohol into the blood.
Several factors govern gas...