Chemical Properties
Misoprostol is a yellow, viscous liquid with a musty odour. Miscible with ethanol, ether or chloroform, extremely insoluble in water or n-hexane. Very unstable at room temperature and undergoes thermal epimerization to the 8-isomer. It is also extremely sensitive to the Ph value. It removes the hydroxyl group at the 11α position in acidity and alkalinity, converts it into A-type prostaglandins, and isomerizes into B-type prostaglandins. However, it is relatively stable in the dispersion system of hydroxypropyl methylcellulose and can be stored at room temperature.
Definition
ChEBI: 7-[(1R,2R,3R)-3-hydroxy-2-(4-hydroxy-4-methyloct-1-enyl)-5-oxocyclopentyl]heptanoic acid methyl ester is a prostanoid.
Indications
Misoprostol (Cytotec), which is an analogue of
prostaglandin E1, has been approved for use in the prevention
of nonsteroidal antiinflammatory drug–induced
ulceration. It also is approved in other countries for the
treatment of peptic ulcer disease.
Preparation
synthesis of Misoprostol
To a 1000 ml dried flask under a nitrogen atmosphere was added 74.6 g of(E)-trimethyl-[[1-methyl-1-[3-(tributylstannyl)-2-propenyl]pentyl]oxy]silane,125 ml anhydrous THF and 24.2 g of copper (I) iodide. The mixture wasstirred at room temperature for 30 minutes and then it was cooled to -25 to -30°C. 98.8 ml of methyllithium (2.86 M) in DEM was added dropwise and theresultant solution was stirred at -15°C for 2 hours. Then the reaction mixturewas cooled to -78°C and 25 g of methyl-5-oxo-3-[(triethylsilyl)oxy]-1-cyclopentene-1-heptanoate in 100 ml of THF was added rapidly. After stirringthe mixture for 5 min at -78°C, it was quenched into a mixture of 750 ml ofaqueous ammonium chloride solution and 200 ml of ammonium hydroxide.The resulting mixture was warmed to room temperature and stirred until adeep blue aqueous layer was obtained. Ethyl acetate (250 ml) was used forextraction. Then the combined organic layers were washed with brine andsubsequently dried over magnesium sulfate. After a filtration andconcentration under reduced pressure, an oil (105 g) was obtained. This oilcontaining the protected prostaglandin was subjected to acidic deprotection(cat. PPTS, acetone and water) and purification (chromatography on silica gel)to provide 15.8 g (60%) of misoprostol was identical.
Brand name
Cytotec (Searle);Cyprostol;Oxaprost;Prostalgin.
Therapeutic Function
Antiulcer
General Description
Misoprostol, (16-(R,S)-methyl-16-hydroxy)-PGE1, methyl ester (Cytotec), is a modified prostaglandinanalog that shows potent gastric antisecretory and gastroprotectiveeffects when administered orally. Misoprostol isadministered orally in tablet form in a dose of 100 to 200 μg4 times a day to prevent gastric ulceration in susceptibleindividuals who are taking NSAIDs. Misoprostol is combinedwith the NSAID diclofenac (Voltaren) in an analgesic product(Arthrotec by Pharmacia), which is potentially safe for longtermantiarthritic therapy. This prostaglandin derivative absolutelyshould be avoided by pregnant women because of itspotential to induce abortion. In fact, the combined use of intramuscularmethotrexate and intravaginal misoprostol has beenclaimed to be a safe and effective, noninvasive method for thetermination of early pregnancy.
Biological Activity
Cytoprotective prostaglandin E 1 analog that displays agonist activity at EP receptors. K i values are 120, 250, 67 and 67 nM at cloned mouse EP 1 , EP 2 , EP 3 and EP 4 receptors respectively. Prevents NSAID-induced gastric ulceration.
Pharmacology
Misoprostol is absorbed
rapidly after oral administration and is hydrolyzed
to the active compound. It is metabolized by
the liver and excreted mainly in the urine. Adverse effects
include crampy abdominal pain, dose-related diarrhea,
and uterine contractions. The last-named effect
has led to its use in the control of postpartum bleeding.
Clinical Use
Benign gastric and duodenal ulceration and NSAID
associated ulceration
Prophylaxis of NSAID induced ulceration
Veterinary Drugs and Treatments
Misoprostol may be useful as primary or adjunctive therapy in
treating or preventing
gastric ulceration, especially when caused
or aggravated by non-steroidal antiinflammatory drugs (NSAIDs).
Misoprostol is most useful to prevent GI ulceration or GI adverse
effects (anorexia, vomiting) associated with NSAID therapy. While
it can be used for treating gastric ulcers, other drugs are probably
just as effective and less expensive. It does not appear to be very
effective in reducing gastric ulceration secondary to high dose corticosteroid
therapy
Misoprostol may be efficacious in reducing or reversing cyclosporine-
induced nephrotoxicity. More data is needed to confirm
this effect.
One study demonstrated that misoprostol can reduce the clinical
signs associated with atopy somewhat in dogs.
Misoprostol’s effects on uterine contractibility and cervical softening/
opening make it effective as an adjunctive treatment in pregnancy
termination.
Metabolism
Rapidly metabolised to its active form (misoprostol acid)
after oral doses. Misoprostol acid is further metabolised
by oxidation in several body organs and is excreted mainly
in the urine.
storage
Desiccate at -20°C
Mode of action
Misoprostol is a synthetic prostaglandin E1 analogue which has ulcer healing, gastric acid antisecretory and mucosal protective properties. The antisecretory activity is mediated by direct action on specific prostaglandin receptors on the surface of gastric parietal cells. In dogs with innervated Pavlov pouches, inhibition of secretion is achieved at a lower dosage by intrapouch injection than by intravenous or intragastric administration, suggesting that the local effect may predominate. The mucosal protective effect against various damaging agents has been demonstrated in humans with doses that inhibit and doses which minimally affect acid secretion.
