Special features

Nausea and vomiting — Pharmacological management

By Andrew Husband, MRPharmS, MSc, and Alan Worsley, MRPharmS, PhD

An understanding of the mechanisms of action of the drugs used to treat nausea and vomiting is important when selecting the best treatment for the patient. The drugs used vary in their efficacy depending on the cause of emesis, as described in this article

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Andrew Husband and Alan Worsley are senior lecturers in pharmacy practice at the University of Sunderland

Van Bucher/SPL

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Hyoscine, available as a transdermal patch, is used to prevent motion sickness

SUMMARY

Nausea and vomiting are complex mechanisms and the symptoms are influenced by the origin of the emetic response.

The pharmacist has a key role in providing information about the mechanism of action of antiemetic drugs, their pharmacokinetics and adverse effect profiles, in addition to monitoring antiemetic prescribing or prescribing the drugs themselves.

The pathogenesis of nausea and vomiting is complex, multifactorial and not entirely understood, as described in the first article in this special feature (p185). The development of one single treatment has not yet been possible, but the concept that the many parallel pathways involved in emesis may converge on a common output encourages the search for this target. The ultimate aim is to develop a universal or broad-spectrum antiemetic.1 Until, and if such developments occur, the clinical cause of emesis in each patient should be considered before prescribing. This could be an important point of input for pharmacists.

The drugs currently used in the treatment of nausea and vomiting vary in their efficacy depending on the primary cause of emesis. It is likely that a combination of anticholinergic, antihistaminergic and sedating effects contribute to the overall efficacy of an agent as an antiemetic. For the purposes of this article the drugs will be discussed based on their primary site of action.

In general, all drugs have a more pronounced effect on vomiting than on nausea. This is unfortunate because patients often report that they can cope with vomiting but the prolonged feeling of nausea is more difficult to manage. The control of nausea continues to be beyond modern medicine and to some extent is explained by our relatively poor knowledge of some of the physiological mechanisms involved.

Route of administration The route of administration of antiemetic therapy is particularly important in patients who are vomiting. Most preparations used for rescue treatment (ie, when a patient is actively vomiting) are available as intravenous or intramuscular injections. The rectal and buccal routes are also used to ensure adequate absorption of drugs administered to a vomiting patient. Scopaderm (hyoscine hydrobromide; Novartis) is the only transdermal antiemetic product licensed for use in the UK. It has a long duration of action but a delayed onset (of about four hours) so patients should be counselled in the use of this product to ensure adequate symptom control.

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