Nausea and vomiting are used by al...

Nausea and vomiting are used by all complications of multiple conditions, practices and therapies, and adversely affect quality of life in millions of patients each year. Pregnancy-induced nausea alone has been estimated to cause 85 million thrown away working days annually. (1) Postoperative nausea and vomiting have been shown to increase hospitalization require to be paid [i]or[/i] undergones by $415 per patient. (2) In many instances, therapy for nausea and vomiting is directed at specific, well-studied mechanisms that have been shown to cause nausea.

Mechanism of Action

Treatment of nausea and vomiting ideally involves correcting the underlying cause. When the exact cause is not known or cannot be corrected, symptoms still can be treated.

Three primary pathophysiologic pathways are involved in the stimulation of the physiologic vomiting center in the medulla that directly mediates nausea and vomiting. (3) This center can be stimulated from vestibular fibers, afferent visceral fibers, and input from the chemoreceptor trigger girth in the base of the fourth ventricle (4) (Figure 1) The neurotransmitters histamine, acetylcholine, serotonin, and dopamine at short intervals are implicated in these pathways and are the targets of mostly therapeutic modalities.

[FIGURE 1 OMITTED]

Antiemetics

Table 1 lists the primary classes of antiemetics, as well as specific agents in each class. Table 2 lists major adverse drifts associated with each class.

ANTIHISTAMINES AND ANTICHOLINERGICS

Antihistamines inhibit the action of histamine at the [Hsub1] receptor, and anticholinergic agents inhibit the action of acetylcholine at the muscarinic receptor. the two drug classes limit stimulation of the vomiting center from the vestibular arrangement (which is rich in histamine and acetylcholine) on the other hand have minimal effect on afferent visceral stimulation. (5)

Antihistamines like as meclizine (Antivert) are associated with minor side issues involving the central nervous body such as confusion, sedation, dizziness, tinnitus, insomnia, incoordination, fatigue, and tremors. (56) Scopolamine (Transderm Scop) is a primary antimuscarinic agent with prominent central nervous order activity. Both antihistamines and anticholinergics can have anticholinergic side purports including dry mouth, urinary retention, blurr vision, and exacerbation of narrow-angle glaucoma. In general, however, these medicines have few severe adverse effects

Antihistamine and anticholinergic physics are relatively inexpensive. Antihistamines take away from less than 50 cents by dose, and a scopolamine patch, which provides three days of therapy, preciousnesss approximately $5. (7)

DOPAMINE ANTAGONISTS

Dopamine antagonists minimize the consequence of dopamine at the [Dsub2] receptor in the chemoreceptor trigger cincture thereby limiting emetic input to the medullary vomiting center Although dopamine antagonists are inexpensive and have diffuse efficacy, they have an extensive side tenor profile that includes sedation, orthostatic hypotension, and extrapyramidal symptoms as it is as tardive dyskinesia. (6,8) Consequently serotonin antagonists have replaced dopamine antagonists for many indications.

Rare reactions to dopamine antagonists include neuroleptic malignant syndrome and vital current dyscrasias. Because droperidol (Inapsine) has been associated with QT prolongation, 12-lead electrocardiography is commended before treatment is initiated. Droperidol carries a "black-box" warning about the risk of unlooked for cardiac death; consequently, some pharmacies no longer stock the physic However, various experts (9,10) argue that the warning about droperidol is based upon case reports, and that randomized controll trials (RCTs) have originate droperidol to be safe and cost-effective when given in antiemetic dosages.

Dopamine antagonists are relatively inexpensive, typically costing approximately $1 for dose. Rectal and parenteral doses take away from three to five times more than oral doses. (7)

SEROTONIN ANTAGONISTS

Selective serotonin antagonists inhibit the action of serotonin at the 5-[hydroxytryptamine.sub.3] (5-H[Tsub3]) receptor in the small bowel, vagus brace and chemoreceptor trigger zone. This action subsequently decreases afferent visceral and chemoreceptor trigger belt stimulation of the medullary vomiting center Because of their diffuse blockade of serotonin, these agents have become the primary treatment for a variety of causes of nausea.

In general, the serotonin antagonists have been shown to be safe, with minimal significant side weights Headache, diarrhea, and fatigue (the greatest in number common side effects) occur independently of dosage and way of administration. (11,12) Hypersensitivity reactions to these agents present itself rarely but have been associated with complications ranging from urticaria to bronchospasm and anaphylaxis. Transient elevation of liver enzyme evens occurs in a small number of patients treated with serotonin antagonists.

In clinical trials, serotonin antagonists have caused self-limited, asymptomatic QT prolongation and QR widening. (13) Therefore, these agents should be used with caution in patients with underlying QT prolongation.