Chemotherapy-induced nausea and vomiting
Chemotherapy-induced nausea and vomiting (CINV) is a common side-effect of many cancer treatments. Nausea and vomiting are two of the most feared cancer treatment-related side effects for cancer patients and their families. In 1983, Coates et al. found that patients receiving chemotherapy ranked nausea and vomiting as the first and second most severe side effects, respectively. Up to 20% of patients receiving highly emetogenic agents in this era postponed, or even refused, potentially curative treatments. Since the 1990s, several novel classes of antiemetics have been developed and commercialized, becoming a nearly universal standard in chemotherapy regimens, and helping to better manage these symptoms in a large portion of patients. Efficient mediation of these unpleasant and sometimes crippling symptoms results in increased quality of life for the patient, and better overall health of the patient, and, due to better patient tolerance, more effective treatment cycles.
There are several subtypes of CINV. The classifications of nausea and vomiting are:
- Acute: occurring within 24 hours of chemotherapy
- Delayed: occurring between 24 hours and 5 days after treatment
- Breakthrough: occurring despite prophylactic treatment
- Anticipatory: triggered by taste, odor, memories, visions, or anxiety related to chemotherapy
- Refractory: occurring during subsequent cycles when antiemetics have failed in earlier cycles
Emesis is a defense mechanism controlled by the area postrema of the medulla oblongata. There are various sources of input to the vomiting center. Receptors on the floor of the fourth ventricle of the brain represent the chemoreceptor trigger zone. The chemoreceptor trigger zone contains dopamine D2 receptors, serotonin 5-HT3 receptors, opioid receptors, acetylcholine receptors, and receptors for substance P. Stimulation of different receptors are involved in different pathways leading to emesis. In the final common pathway, substance P, which activates the Neurokinin-1 receptor, appears to be involved. Additionally, the vagal and enteric nervous system inputs transmit information regarding the state of the gastrointestinal system. Irritation of the GI mucosa by chemotherapy, radiation, distention, or acute infectious gastroenteritis activates the 5-HT3 receptors of these inputs. It is now widely known that cytotoxic chemotherapeutic agents cause a detectable increase in blood levels of serotonin (5-HT) and its major metabolite, 5-Hydroxyindoleacetic acid (5-HIAA). The presence of these chemicals in the blood activate 5-HT3 receptors in the chemoreceptor trigger zone, in turn releasing substance P, which activates NK1 receptors to cause an emetic response (vomiting).
Risk factors 
The risk of chemotherapy-induced nausea and vomiting varies based on the type of treatment received, as well as several outside factors. Some types of chemotherapy are more prone to causing nausea and vomiting than others. Some chemotheraputic agents may not cause nausea and vomiting on their own, but may when used in combination with other agents. Regimens that are linked to a high incidence (90% or higher) of nausea and vomiting are referred to as "highly emetogenic chemotherapy," and those causing a moderate incidence (30-90%) of nausea and vomiting are referred to as "moderately emetogenic chemotherapy."
- Cyclophosphamide (>1500 mg/m2)
- Carmustine (>250 mg/m2)
Some moderately emetogenic agents and regimens include:
- Cyclophosphamide (≤1500 mg/m2)
- Female sex
- Patient age (under 55 years old)
- History of light alcohol use
- History of previous CINV
- History of nausea and vomiting during pregnancy
- History of motion sickness
- Anxiety or depression
- Anticipation of CINV
Several treatment methods are available to help prevent CINV. Pharmaceutical treatment is generally separated into two types: prophylactic (preventative) treatment, given before the dose of chemotherapy agents, and rescue treatment, given to treat breakthrough nausea and vomiting.
5-HT3 inhibitors 
5-HT3 receptor antagonists are very effective antiemetics and constitute a great advance in the management of CINV. These drugs block one or more of the nerve signals that cause nausea and vomiting. During the first 24 hours after chemotherapy, the most effective approach appears to be blocking the 5-HT3 nerve signal. Approved 5-HT3 inhibitors include dolasetron (Anzemet), granisetron (Kytril, Sancuso), and ondansetron (Zofran). The newest 5-HT3 inhibitor, palonosetron (Aloxi), also prevents delayed nausea and vomiting, which can occur during the 2–5 days after treatment. Since some patients have trouble swallowing pills, these drugs are often available by injection, as orally disintegrating tablets, or as transdermal patches.
NK1 inhibitors 
A newer class of drugs known as the NK1 antagonists are a recently developed class of very efficacious drugs for controlling CINV. These drugs are often used alongside 5HT3 inhibitors and corticosteroids to form a very potent cocktail of antiemetics that verge on achieving a nearly complete patient response (that is, completely stopping CINV). The substance P inhibitor aprepitant (Emend), which became available in 2005, is highly effective in controlling nausea and vomiting associated with cancer chemotherapy. Aprepitant has been shown to inhibit both the acute and delayed emesis induced by cytotoxic chemotherapeutic drugs by blocking substance P landing on receptors in the brains neurons. This has been proven by Positron Emission Tomography (PET) studies, which have demonstrated that aprepitant can penetrate the brain and NK1 receptors in the brain. It has also been shown to increase the activity of the 5-HT3 receptor antagonists ondansetron and the corticosteroid dexamethasone, which are also used to prevent nausea and vomiting caused by chemotherapy.
Other drugs 
Olanzapine, as well as several other neuroleptic drugs, have also has been investigated for the control of CINV. A 2007 study demonstrated Olanzapine's successful potential for this use, achieving a complete response in the acute prevention of nausea and vomiting in 100% of patients treated with moderately and highly-emetogenic chemotherapy, when used in combination with palonosetron and dexamethasone. Neuroleptic agents are now indicated for rescue treatment and the control of breakthrough nausea and vomiting.
Some studies and patient groups say that the use of cannabinoids derived from marijuana during chemotherapy greatly reduces the associated nausea and vomiting, and enables the patient to eat. Synthesized Tetrahydrocannabinol (also one of the main active substances in marijuana) is marketed as Marinol and may be practical for this application. Natural marijuana, known as medical cannabis is also used and recommended by some oncologists, though its use is regulated and it is not legal in all jurisdictions. However, Marinol was less effective than megestrol in helping cancer patients regain lost appetites. A phase III study found no difference in effects of an oral cannabis extract or THC on appetite and quality of life (QOL) in patients with cancer-related anorexia-cachexia syndrome (CACS) to placebo.
Dexamethasone, a corticosteroid, is often used alongside other antiemetic drugs, as it has synergistic action with many of them, although its specific antiemetic mechanism of action is not fully understood. Metoclopramide, a 5HT4 receptor agonist, is an older drug that is sometimes used, either on its own or in combination with others. Histamine blockers such as diphenhydramine or meclozine may be used in rescue treatment. Lorazepam and Diazepam may sometimes be used to relieve anxiety associated with CINV before administration of chemotherapy, and are also often used in the case of rescue treatment.
Alternative treatments 
Ginger (Zingiber Officinale) There are several compounds that have been identified within ginger that have been shown to possess properties that are likely to be beneficial in the treatment of CINV. This includes 5-HT3 and Substance P antagonism, modulation of gastrointestinal motility, and antioxidant properties.   There have been multiple clinical trials that have investigated the use of ginger supplementation as a treatment for CINV. However, due to conflicting results and methodological issues, a recent review summarized the results of these trials as stating that "Despite the widespread use of ginger in the treatment of nausea in other contexts such as gestational nausea, the current literature provides mixed support for the use of ginger as a standard part of anti-CINV control for patients undergoing chemotherapy."
Other alternative treatments Non-pharmacological approaches to remedy CINV typically involve small lifestyle alterations, such as using unscented deodorants and soaps, avoiding strong scents altogether, and dietary modifications such as eating several small meals throughout the day, eating high-protein, high-calorie food, drinking lots of clear liquids, and removing spicy, fatty, fried, or acidic foods from the diet. Patients may also participate in alternative practices such as self-hypnosis, relaxation and imagery therapy, distraction, music therapy, biofeedback, desensitization, or accupressure.
See also 
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