Alcohol

Abuse of alcohol (ethanol) is a major contributor to morbidity and mortality, far outstripping other drugs in its effects on the individual and on society. Alcohol is a drug with no receptor. The mechanisms by which it exerts its detrimental effect on cells and organs are not well understood, but the effects are summarized in Table 62.1.

Table 62.1

Effects of ethanol on organ systems

System	Condition	Effect
CNS	Acute	Disorientation → coma
	Chronic	Memory loss, psychoses
	Withdrawal	Seizures, delirium tremens
Cardiovascular	Chronic	Cardiomyopathy
Skeletal muscle	Chronic	Myopathies
Gastric mucosa	Acute	Irritation, gastritis
	Chronic	Ulceration
Liver	Chronic	Fatty liver → cirrhosis, decreased tolerance to xenobiotics
Kidney	Acute	Diuresis
Blood	Chronic	Anaemia, thrombocytopenia
Testes	Chronic	Impotence

For clinical purposes alcohol consumption is estimated in arbitrary ‘units’ – one unit representing 200–300 mmol of ethanol. The ethanol content of some common drinks is shown in Figure 62.1. The legal limit for driving in the UK is a blood alcohol level of 17.4 mmol/L (80 mg/dL).

Fig 62.1 Alcohol content of common drinks.

Metabolism of ethanol

Ethanol is metabolized to acetaldehyde by two main pathways (Fig 62.2). The alcohol dehydrogenase route is operational when the blood alcohol concentration is in the range 1–5 mmol/L. Above this most of the ethanol is metabolized via the microsomal P450 system. Although the end product in both cases is acetaldehyde, the side effects of induced P450 can be significant. Ethanol metabolism and excretion in a normal 70 kg man is summarized in Figure 62.3.