Paraldehyde

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Paraldehyde is the cyclic form of three acetaldehyde molecules (a trimer). A colourless to pale yellow pungent liquid, it is sparingly soluble in water and highly soluble in alcohol. It has industrial and medical uses. It was first synthesized in 1829 by Wildenbusch. Paraldehyde decomposes in air, turning brown and producing an odour of acetic acid (and must then be disposed of). It quickly reacts with most plastics and rubber.

Contents

1 Medical applications

1.1 Administration

2 Industrial applications
3 References
4 External links

Medical applications

Toxicity	Oral rat LD50: 2711 mg/kg
Chemical Properties
Solubility in water	1 in 10
Melting point	12.5 C
Boiling point	124 C
Flash point	27.5 C
Specific gravity	0.995

Paraldehyde was introduced into clinical practice in the UK by the Italian physician Vincenzo Cervello in 1882. It is a CNS depressant and was soon found to be an effective anticonvulsant, hypnotic and sedative. It was included in some cough medicines as an expectorant (though this may have relied on the placebo effect: if it tastes horrible then it must be good for you). It was commonly used to induce sleep in sufferers from delirium tremens but has been replaced by other drugs in this regard. It is one of the safest hypnotics and was regularly given at bedtime in psychiatric hospitals and geriatric wards up to the 1960s. Up to 30% of the dose is excreted via the lungs (the rest via the liver). This contributes to a strong unpleasant odour on the breath.

Today, paraldehyde is used to treat status epilepticus. Unlike diazepam, it does not suppress breathing at therapeutic doses and so is safer when no resuscitation facilities exist or when the patient's breathing is already compromised. This makes it a useful emergency medication for parents and other carers of children with epilepsy. Since the dose margin between the anticonvulsant and hypnotic effect is small, paraldehyde treatment usually results in sleep.

Generic paraldehyde is available in 5ml sealed glass ampoules. The tradename in the US is Paral®.

Administration

Paraldehyde can be taken orally, rectally or by intravenous or intramuscular injection.

Injection. Paraldehyde is no longer given by injection since this can be very painful and lead to sterile abscesses, nerve damage, and tissue necrosis.

Oral. Used as a sedative. Paraldehyde has a hot burning taste and can upset the stomach. It is usually mixed with milk or fruit juice in a glass cup and stirred with a metal spoon.

Rectal. Used to treat status epilepticus. It is mixed 1 part paraldehyde with 9 parts saline or, alternatively, with an equal mixture of arachis or olive oil. This mixture cannot be made up in advance, which delays administration. Despite the reaction with plastic syringes and the rubber portion of the plunger, it is commonly given rectally via a plastic syringe and tube. The preparation and administration must therefore be done as quickly as possible.

Industrial applications

Paraldehyde has numerous alternate chemical names including paracetaldehyde, s-trimethyltrioxymethylene, and trimethyl-1,3,5-trioxane. Paraldehyde is used in resin manufacture, as a preservative, and in other processes as a solvent.

References

[Paraldehyde Injection B.P Data Sheet]
[Drugs.com: Paraldehyde]
A Practical Treatise on Materia Medica and Therapeutics by Robers Bartholow. 1887.
British National Formulary Edition 50.
[Paraldehyde Chemical Data]

External links

For a full list of external links to MSDSs, spectroscopic data, commercial chemicals suppliers etc. for this compound, see [Chemical sources].

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