Indications
Ondansetron (Zofran) is potent antagonists of 5-HT3 receptors,which is found peripherally
on vagal nerve terminals and centrally in the
CTZ. During chemotherapy that induces vomiting, mucosal
enterochromaffin cells in the GI tract release serotonin,
which stimulates 5-HT3 receptors.
Manufacturing Process
Preparation of 3-ethoxalyl-9-methyl-1,2,3,9-tetrahydro-4H-carbozol-4-one
3.0 g (0.13 mole) of sodium metal are portionwise added to a stirred mixture containing 19.93 g (0.1 mole) of 9-methyl-1,2,3,9-tetrahydro-4H-carbazol-4one, 19.0 g (0.13 mole) of diethyl oxalate, 2 g of ethanol and 200 ml of dioxane. The slightly warming reaction mixture is stirred at 40° to 50°C for 4 hours, then 16 g of glacial acetic acid and finally 200 ml of water are added thereto at room temperature. After filtering off the yellow crystalline suspension, the precipitate is washed with water and dried to give the title compound in a yield of 24 g (80.2%), m.p. 118°-120°C
Preparation of 3-hydroxymethyl-9-methyl-1,2,3,9-tetrahydro-4H-carbazol-4one-3-glyoxylic acid lacton
After adding 0.1 g of triethylamine to a stirred suspension containing 3.00 g (0.01 mole) of the 3-ethoxalyl-9-methyl-1,2,3,9-tetrahydro-4H-carbazol-4
2512 one, in 20 ml of acetone, 1.13 g (0.015 mole) of formol solution are dropwise added to the mixture. The suspension becomes clear within 1 to 2 minutes and crystals begin to precipitate. After further stirring at 35° to 40°C for one hour, the reaction mixture is cooled down to room temperature, filtered off, the precipitate is washed with 50% acetone and dried to give 2.10 g (74.2%) of the title compound, m.p. 242°-244°C.
Preparation of ondansetron base (chemically 9-methyl-3-[(2-methyl-1-Himidazol-1-yl)methyl]-1,2,3,9-tetrahidro-4-H-carbazol-4-one)
A mixture containing 2.83 g (0.01 mole) of 3-hydroxymethyl-9-methyl-2,3,9tetrahydro-4H-carbazol-4-one-3-glyoxylic acid lactone, 15 ml of dioxane, 1.32 g of triethylamine, 1.0 g of ethanol and 1.64 g (0.02 mole) of 2methylimidazole is boiled under reflux while stirring for 5 hours. Thereafter, the reaction mixture is diluted with 45 ml of water and cooled down. The precipitate is filtered off, washed with aqueous dioxane and dried to obtain 2.56 g (87.3%) of the title compound, m.p. 220°-223°C.
Preparation of 9-methyl-3-[(2-methyl-1-H-imidazol-1-yl)methyl]-1,2,3,9tetrahydro-4H-carbazol-4-one hydrochloride dihydrate The process above described is followed, except that after cooling down the reaction mixture to room temperature after boiling, 20 ml of 37% aqueous hydrochloric acid are added thereto. Then, the precipitate is filtered off, washed with isopropanol and dried to obtain 2.40 g (65.6%) of the title salt, m.p. 178°-180°C. The active agent content of the product was found to be 100.3% based on potentiometric titration with sodium hydroxide solution. The theoretical water content is 9.85% (calculated for C18H19N3OHCl2H2O).The water content measured is 10.03%.
Side effects
This causes vagal
afferent discharge, inducing vomiting. In binding to
5-HT3 receptors, ondansetron blocks
serotonin stimulation, hence vomiting, after emetogenic
stimuli such as cisplatin. Headache is the most frequently
reported adverse effect of these medications.
Veterinary Drugs and Treatments
Used as an antiemetic when conventional antiemetics are ineffective,
such as when administering cisplatin or for other causes of
intractable vomiting. The use of ondansetron in cats is somewhat
controversial and some state it should not be used in this species.
Metabolism
Ondansetron is metabolised in the liver through multiple
enzymatic pathways; it is a substrate for cytochrome
P450 isoenzymes, primarily CYP3A4, but also CYP1A2
and CYP2D6. The metabolites do not contribute to the
pharmacological activity of ondansetron. Less than 5% of
a dose is excreted unchanged in the urine
