Mechanism of action
Ursodeoxycholic acid has a complex mechanism aimed at reducing cholesterol levels in bile. The action is implemented at three levels:
- In the intestine: The drug disrupts cholesterol absorption, reducing its entry into the bloodstream.
- In the liver: Cholesterol synthesis is suppressed. This is achieved by inhibiting the key enzyme — 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CoA reductase).
- In the gallbladder: Directly in the bile, the acid interacts with cholesterol, forming liquid crystals with it (unlike chenodeoxycholic acid, which forms a micellar solution).
Pharmacological effects
Due to the described mechanism, the following clinically significant effects are achieved:
- Reduced entry of cholesterol into bile.
- Prevention of new gallstone formation.
- Dissolution of existing cholesterol stones (litholytic effect).
Note: Compared to chenodeoxycholic acid, Ursodesoxycholic acid has higher efficacy and a better safety profile.
Indications and prescribing features
The main indication for use is medical dissolution of gallstones (litholytic therapy).
Dosing regimen: The drug is prescribed orally at a rate of 0.01 g/kg of body weight. The entire dose is taken once daily at bedtime. This regimen is strictly justified: it is at night that the physiological peak of elevated cholesterol content in bile is observed.
Course duration: Treatment is always prolonged. The course ranges from 3 months to 2 years.
Side effects
Although the drug has a favorable safety profile and side effects are less pronounced than those of analogues, typical reactions for litholytics are possible:
- Gastrointestinal: diarrhea, nausea, epigastric pain.
- Laboratory parameters: temporary increase in blood levels of hepatic transaminases.
Dynamics: Adverse reactions usually do not require discontinuation of the drug and resolve spontaneously 2–3 weeks after the start of therapy.
Contraindications to litholysis
Medical stone dissolution is strictly contraindicated in a number of conditions:
- Gallbladder and duct pathologies: acute inflammatory processes, "excluded" (non-functioning) gallbladder, large stones (diameter greater than 2 cm).
- Concomitant gastrointestinal diseases: liver diseases, gastric and duodenal ulcer, chronic pancreatitis, acute intestinal inflammation.
- Systemic conditions: diabetes mellitus, pregnancy.
Prescription writing rules
The drug is available in 0.25 g capsules. The dosage is calculated individually depending on the patient's body weight.
Rp.: Caps. Acidi ursodesoxycholici 0.25 D.t.d. N. 50 S. Oral at 0.01 g/kg of body weight once daily at night.
Briefly: answers to topical questions
In which hepatobiliary system diseases, besides cholelithiasis, is ursodeoxycholic acid used?
In addition to cholelithiasis, ursodeoxycholic acid is used in the following hepatobiliary pathologies:
- Primary sclerosing cholangitis — prescribed as lifelong therapy upon the development of this specific complication of inflammatory bowel diseases.
- Acute viral hepatitis — used in cholestatic forms with a confirmed leading cholestasis syndrome and a prolonged jaundice period.
- Non-alcoholic fatty liver disease — used as part of complex therapy together with essential phospholipids, hypoglycemic, and lipid-lowering drugs.
"URSO" works while you sleep: taken strictly at night, as the peak release of cholesterol into bile occurs in the dark.
Class and exam questions
Why is the drug prescribed specifically at bedtime?
This is due to circadian rhythms: at night, a physiological peak of elevated cholesterol content in bile is observed. Bedtime administration ensures the maximum concentration of the drug at the right time.
How does ursodeoxycholic acid differ from chenodeoxycholic acid?
Ursodeoxycholic acid forms liquid crystals with cholesterol (rather than a micellar solution), has higher efficacy and a better safety profile (fewer side effects).
Can any gallstones be dissolved?
No, litholytic therapy is effective only for cholesterol stones up to 2 cm in diameter and provided the gallbladder is functioning ("not excluded").
What else to study on this topic
- Cholesterol biosynthesis and the role of the enzyme HMG-CoA reductase.
- Differences between cholesterol stones and pigment/mixed stones.
- Physiology of bile formation and enterohepatic circulation of bile acids.
- Comparative pharmacology of chenodeoxycholic and ursodeoxycholic acids.
- The concept of an "excluded" gallbladder in surgery and therapy.
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