Commonly used to manage nausea and vomiting post-operatively. They may also be beneficial in chemotherapy and in opioid related nausea and vomiting. Prochlorperazine may also be beneficial in vestibular disorders.
Levomepromazine is often used in palliative care.
Caution:
- Children (risk of dystonia)
- Elderly
- Renal impairment
- Hepatic impairment
- Cardiovascular disease and risk of prolonged QT interval
- Parkinson's disease
- Epilepsy (may reduce seizure threshold)
- Prostatic hypertrophy
- Glaucoma
Contra-indicated in coma. Best avoided in pregnancy and breast feeding.
Two sites in the brainstem are involved in vomiting: the chemoreceptor trigger zone (CTZ) and the vomiting centre. The CTZ responds to substances in the systemic circulation and the vomiting centre to neural input from the vestibular system, gut and other parts of the brain.
Phenothiazines are dopamine antagonists. Dopamine receptors are found in the CTZ and this is the location of phenothiazine action.
Available in oral, buccal and intramuscular forms.
Phenothiazines are divided into 3 groups, with slightly differing side effects. The common side effect issues are sedation, extra-pyramidal and anti-muscarinic effects. Other issues to be aware of are:
- Hypotension
- Neuroleptic malignant syndrome
- Gastro-intestinal effects
- Respiratory depression
Extra-pyramidal side effects can be divided into:
- Parkinsonian symptoms
- Dystonia (abnormal face and body movements)
- Tardive dyskinesia (rhythmic involuntary movements of the tongue, jaw and face)
- Akathisia (restlessness)
These are caused by blocking dopamine pathways.
Anti-muscarinic effects are:
- Dilated pupils
- Blurred vision
- Dry mouth
- Nausea
- Constipation
- Headache
- Urinary retention / difficulty micturating
- Hypotension
- Psychomotor impairment
Levomepromazine is a group 1 drug with sedative, extra-pyramidal and anti-muscarinic effects. Prochlorperazine belongs to group 3, and has particular issues with extra-pyramidal side effects. It has less sedative and antimuscarinic effects than other types of phenothiazine.
Phenothiazines are involved in a number of drug-drug interactions, particularly with drugs that can cause long QT syndrome (leading to an increased risk of arrhythmia) or those which have similar side effects (sedation, anti-muscarinic, hypotensive).
Alcohol may potentiate CNS effects of phenothiazines.
Nil of note.
