phenothiazines

Last reviewed 07/2023

Phenothiazine itself is a veterinary anthelmintic, but the name is also used to denote a group of major tranquillisers resembling phenothiazine in molecular structure.

Phenothiazines were the first effective neuroleptics to be introduced and they are still commonly used. Over 20 clinically active preparations are available but only three broad types are required:

• a sedative neuroleptic, for example chlorpromazine
• a less sedating preparation, like trifluoperazine
• a long acting derivative for maintenance treatment, for example fluphenazine decanoate

Some authorities divide the phenothiazines into:

• Group 1 - generally characterised by pronounced sedative effects and moderate anti-muscarinic and extrapyramidal side effects. Includes chlorpromazine, methotrimepazine and promazine

• Group 2 - moderate sedative effects, marked antimuscarinic effects but fewer extrapyramidal side effects than groups 1 or 3. Includes pericyazine, pipothiazine and thioridazine

• Group 3 - fewer sedative effects, fewer antimuscarinic effects but more pronounced extrapyramidal side effects than groups 1 or 2. Includes fluphenazine, perphenazine, prochlorperazine and trifluoperazine

The phenothiazines, in particular, chlorpromazine, may cause photosensitivity characterised by burning, erythema, swelling and later, frank eczematous changes.