Furthermore, people who had initially received ondansetron were more likely to be admitted on the return visit than people who had not received the drug. However, this effect may simply be due to the agent being used more frequently in people who present with more severe illness.
Its use was not found to mask serious diagnoses. As such, little data are available to guide dosage recommendations. The use of ondansetron has not been studied in people older than 75 years of age, and it is not known if dosage should be adjusted for this group.
In these people, ondansetron is cleared from the body at half to one-third the rate as in healthy people. In all instances, the adverse reactions resolved completely. Pediatric cases consistent with serotonin syndrome have been reported after inadvertent oral overdoses of ondansetron exceeding estimated ingestion of 5 mg per kg in young children.
Reported symptoms included somnolence , agitation, tachycardia , tachypnea , hypertension , flushing, mydriasis , diaphoresis, myoclonic movements, horizontal nystagmus , hyperreflexia, and seizure. Patients required supportive care , including intubation in some cases, with complete recovery without sequelae within 1 to 2 days. While its mechanism of action has not been fully characterized, ondansetron is not a dopamine -receptor antagonist.
Serotonin receptors of the 5- HT 3 type are present both peripherally on vagal nerve terminals and centrally in the chemoreceptor trigger zone of the area postrema. However, cytotoxic chemotherapy appears to be associated with release of serotonin from the enterochromaffin cells of the small intestine.
In humans, urinary 5-hydroxyindoleacetic acid 5-HIAA excretion increases after cisplatin administration in parallel with the onset of emesis. The released serotonin may stimulate the vagal afferents through the 5-HT3 receptors and initiate the vomiting reflex. Pharmacodynamics In healthy subjects, single intravenous doses of 0.
Multiday administration of ondansetron has been shown to slow colonic transit in healthy subjects. Ondansetron has no effect on plasmaprolactin concentrations. Cardiac Electrophysiology QTc interval prolongation was studied in a double-blind, single-intravenous dose, placebo-and positive-controlled, crossover trial in 58 healthy subjects. In this study, the 8-mg dose infused over 15 minutes did not prolong the QT interval to any clinically relevant extent.
Pharmacokinetics Absorption Ondansetron is absorbed from the gastrointestinal tract and undergoes some first-pass metabolism. Ondansetron systemic exposure does not increase proportionately to dose. This may reflect some reduction of first-pass metabolism at higher oral doses. Food Effects Bioavailability is also slightly enhanced by the presence of food. Circulating drug also distributes into erythrocytes. The metabolites are observed in the urine. The new information on QT prolongation does not change any of the recommended oral dosing regimens for ondansetron.
It also does not change the recommended lower dose intravenous dosing of ondansetron to prevent post-operative nausea and vomiting. As part of the ongoing safety review of ondansetron, FDA continues to assess data about the risk of QT prolongation and will update the public when more information becomes available. The first dose is infused over 15 minutes beginning 30 minutes before the start of emetogenic chemotherapy.
In particular, this applies to alkaline solutions as a precipitate may form. Seek emergency medical attention or call the Poison Help line at Overdose symptoms may include sudden loss of vision, severe constipation, feeling light-headed, or fainting. What should I avoid while taking Zofran? Zofran may impair your thinking or reactions. Zofran side effects Get emergency medical help if you have signs of an allergic reaction to Zofran: Call your doctor at once if you have: Common Zofran side effects may include: This is not a complete list of side effects and others may occur.
Call your doctor for medical advice about side effects. Side effects in more detail What other drugs will affect Zofran? Zofran can cause a serious heart problem, especially if you use certain medicines at the same time, including antibiotics, antidepressants, heart rhythm medicine, antipsychotic medicines, and medicines to treat cancer, malaria, HIV or AIDS.
Tell your doctor about all medicines you use, and those you start or stop using during your treatment. Taking ondansetron while you are using certain other medicines can cause high levels of serotonin to build up in your body, a condition called "serotonin syndrome," which can be fatal.
Tell your doctor if you also use: This list is not complete and many other drugs can interact with ondansetron.
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