Dr. Rahmat Awang
The Sun, July 25,1995
THE UNDESIRABLE AND DELETERIOUS consequence from consuming alcoholic beverages have been widely publicised and realised by both the medical profession and the general public. Despite this, the habit of drinking is still widespread. In almost all societies, many people still consider it as a normal practice.
The types of alcohol taken by man are not limited to ethanol only. Methanol, for example are taken as an inexpensive substitute for ethanol or used in adulterated beverages. In one instance in India in December 1991, about 70 patients were found to be intoxicated by methanol when a nightclub owner substituted methanol for ethanol to save money. Methanol may also be accidentally ingested as it makes up a component of a large variety of industrial and household chemicals. Besides being found in many household products and readily available at low cost, they have the general characteristics of being colourless, sweet smell and pleasant taste. This in a way attracts young children, and chronic alcoholic drinkers.
Methanol is a clear liquid obtained through the process of distillation of wood. It is also known as wood spirit or methyl alcohol. Unlike ethanol, methanol has no therapeutic use. It is mainly associated with household and industrial use such as antifreeze fluid, windshield washing fluids, paint remover, varnishes and shellacs.
Methanol itself is not toxic and depresses the brain to a lesser degree compared to ethanol. However, its metabolic by-products, formaldehyde and formic acid are the main cause of toxic manifestations seen in methanol poisoning. As much as 60 and 240ml of methanol can kill a person and as little as 10ml is considered toxic.
Generally, poisoned patient may develop vertigo (dizziness), vomiting, diarrhoea, severe abdominal pain, back pain, dyspnea, motor restlessness, cold and clammy extremities, blurring of vision, and redness of the optic disc with occasional blindness.
The effects on vision is thought to be most characteristic of methanol poisoning. Chronic exposure to methanol may become evident initially with a complaint of visual impairment. The patient experiences or complains of mild blurring of vision which later progresses to contraction of visual fields and ometimes complete blindness.
Formaldehyde in particular is believed to cause various degrees of visual disturbances associated with drinking methanol, ranging from blurred vision to frank blindness, photophobia or constricted visual fields. Formic acid on the other hand is believed to contribute to the visual disturbance by virtue of its direct toxic effect on the optic disc. It can change the blood pH to become acidic.
The symptoms of methanol intoxication are usually not seen until about 12 to 24 hours, though in some instances, it can be as early as one hour or as late as 72 hours. The latent period observed is believed to be due to the delayed formation of the two toxic methanol by-products. This delay in toxic manifestations can therefore be quite deceiving. It hampers the early detection of potential toxicity, and even the appropriateness or need for treatment.
As such methanol poisoning can be a "time bombs" with the potential to cause irreversible damage and death. In acute methanol poisoning, especially when it is unrecognised, between 25 to 50% of patients do not recover and visual impairment is not likely to show improvement after one week. In fact, the interval between ingestion and treatment is one of the most important factors in determining patient outcome.
Poisoning involving methanol usually occur as clusters of cases. Medical literature often describes it as "epidemics" of methanol poisoning. Such condition are often the result of drinking adulterated beverages. A number of methanol epidemics have been reported in Malaysia. One such incident in Negri Sembilan in January 1977. It involved 20 adults, and the final toll was 15 deaths, all within 24 hours.
Other substances frequently abused as ethanol substitutes are ethylene glycol and ispropyl alcohol. Ethylene glycol is a sweet-tasting solvent found in most antifreeze solutions, windshield cleaners, some transmission and brake fluids as well as in a variety of cosmetic preparations.
When ingested, patient may develop inebrination and central nervous system depression. Isopropyl alcohol on the other hand is a clear, bitter tasting liquid with a characteristic odour. It is commonly found in cosmetics, window cleaners, disinfectants and antifreeze. It is twice as toxic as ethanol with the principal effect seen being central nervous system depression.
Management of ethanol substitutes poisoning involves a number of approaches that are not without risk. The public needs to be informed about this and certain precautions should be planned and taken so as to reduce unnecessary exposure.
In an industrial site, all containers containing ethanol substitutes should be labelled properly, and the place where the containers are stored or where they are being handled should be adequately ventilated. Workers should be informed of the dangers of ethanol substitute ingestion.
