The use of low dose levomepromazine (methotrimeprazine) in the management of nausea and vomiting

Summary

Levomepromazine (methotrimeprazine) is a phenothiazine closely related chemically to chlorpromazine but which, possibly because of its greater propensity to cause sedation and postural hypotension, has never enjoyed the popularity of the latter.

Its proven analgesic properties make it unique among the phenothiazines. It also has unique antiemetic properties. In chemotherapy-induced vomiting, levomepromazine appears to be as effective as monotherapy with a 5 HT, antagonist. In palliative care, it is often effective in controlling nausea and vomiting previously intractable to other anti-emetics. Historically, levomepromazine has often been given subcutaneously in doses of 50mg/24h or more (doses which commonly cause marked sedation). Recent experience has shown lower doses, e.g. 5-12.5mg/24h given orally or by continuous subcutaneous infusion, to be equally efficacious and generally non-sedating.

Receptor binding studies demonstrate that levomepromazine has negligible binding at 5HT, receptors. In contrast, it is a potent antagonist at 5HT, receptors which are found in abundance in the vomiting centre (‘emetic pattern generator’). Levomepromazine is also a potent histamine type 1 D₂- and a-receptor antagonist. 5HT, antagonism probably also explains its potent antipsychotic properties and its analgesic efficacy. Further anti-emetic studies are needed to elucidate optimum dosage and route of administration. Concurrent use with dexamethasone should also be explored.