Biochemistry of Gallstone Formation

Gallstone dissolution

Many methods are available for gallstone dissolution, including oral bile salts; cholesterol solvents such as mono-octanoin or methyl tert-butyl either; and calcium or pigment solvents such as EDTA and polysorbate. Which of these approaches will be appropriate for an individual patient depends on the type of stones; whether they are in the gallbladder or the bile ducts; whether access to the biliary tree is available; the patient's age and general medical condition; and the availability of necessary expertise. In the US, both chenodeoxycholate and ursodeoxycholate are now available. Ursodeoxycholate is more expensive but appears to produce fewer side effects and may be more efficacious. These agents are most effective in thin women with small floating, radiolucent cholesterol stones in a functioning gallbladder. Only about half of the small subset of patients will experience partial or complete dissolution of stones within a year. Stone recurrence and the potential toxicity of long-term therapy are problems with this approach. Therefore, for most patients, cholecystectomy, either in the traditional fashion or using a laparoscopic approach (see article later in this issue by Gadacz et al), is the most cost-effective and perhaps the safest option. Intragallbladder instillation of methyl tert-butyl ether probably will be applicable only to a small subset of patients, and treatment is likely to be followed by a high recurrence rate. In patients with retained common duct cholesterol stones and access to the biliary tree, mono-octanoin therapy is advantageous in that it can be initiated as soon as cholangiography demonstrates no extravasation. In properly selected patients, a 90% success rate with this technique can be expected within 7 days.

Agents for gallstone dissolution

Numerous methods are presently available for gallstone dissolution, including oral bile salts; cholesterol solvents such as mono-octanoin and methyl tert-butyl ether; calcium or pigment solvents such as EDTA and polysorbate; mechanical extraction techniques through a T-tube tract or after endoscopic sphincterotomy; or fragmentation methods such as ultrasonography or electrohydraulic lithotripsy, lasers, and extracorporeal shock waves. Which, if any, of these methods will be appropriate for an individual patient depends on the type of stones, whether they are in the gallbladder or bile ducts, whether access to the biliary tree is available, the patient's age and general medical condition, and the availability of expert radiologists, endoscopists, and newer equipment. In the United States, the only available oral bile salt for cholesterol gallstone dissolution is chenodeoxycholate. Ursodeoxycholate, which is more rapid and less toxic, has not been approved by the Federal Drug Administration. These agents are most effective in thin women with small, floating, radiolucent cholesterol gallstones in a functioning gallbladder. Only about half of this small subset of patients, however, will experience partial or complete dissolution of stones in 6 to 12 months. Moreover, recurrence is very likely, and the potential toxicity of long-term therapy is unknown. Thus, for most patients, cholecystectomy remains the most cost-effective and, perhaps, safest option. Intragallbladder instillation of methyl tert-butyl ether and extracorporeal shock wave therapy are also likely to be applicable to only small subsets of patients and to be associated with high recurrence rates. In patients with retained ductal cholesterol stones and access to the biliary tree, mono-octanoin therapy is advantageous in that it can be begun as soon as cholangiography demonstrates no extravasation. In properly selected patients, a 90 percent success rate with mono-octanoin infusion can be expected within a week. Radiologic or endoscopic extraction techniques require maturation of a relatively straight T-tube tract but are not dependent on the type of stone. In the hands of experts, these techniques are highly successful. In postcholecystectomy patients without access to the biliary tree, endoscopic sphincterotomy has become the preferred method of management and can be expected to succeed in more than 90 percent of patients. At this point, the exact role for ultrasonic or electrohydraulic lithotripsy and lasers is unknown. However, these techniques may be applicable in the future in patients with retained bile duct stones in whom extraction and infusion techniques have failed.