CLINICAL PHARMACOLOGY
About 90% of a therapeutic dose of Actigall is absorbed
in the small bowel after oral administration. After absorption, ursodiol enters
the portal vein and undergoes efficient extraction from portal blood by the
liver (i.e., there is a large “first-pass” effect) where it is conjugated with
either glycine or taurine and is then secreted into the hepatic bile ducts.
Ursodiol in bile is concentrated in the gallbladder and expelled into the
duodenum in gallbladder bile via the cystic and common ducts by gallbladder contractions
provoked by physiologic responses to eating. Only small quantities of ursodiol
appear in the systemic circulation and very small amounts are excreted into
urine. The sites of the drug's therapeutic actions are in the liver, bile, and
gut lumen.
Beyond conjugation, ursodiol is not altered or
catabolized appreciably by the liver or intestinal mucosa. A small proportion
of orally administered drug undergoes bacterial degradation with each cycle of enterohepatic
circulation. Ursodiol can be both oxidized and reduced at the 7-carbon,
yielding either 7- keto-lithocholic acid or lithocholic acid, respectively.
Further, there is some bacterially catalyzed deconjugation of glyco- and
tauro-ursodeoxycholic acid in the small bowel. Free ursodiol, 7-ketolithocholic
acid, and lithocholic acid are relatively insoluble in aqueous media and larger
proportions of these compounds are lost from the distal gut into the feces.
Reabsorbed free ursodiol is reconjugated by the liver. Eighty percent of
lithocholic acid formed in the small bowel is excreted in the feces, but the
20% that is absorbed is sulfated at the 3-hydroxyl group in the liver to
relatively insoluble lithocholyl conjugates which are excreted into bile and
lost in feces. Absorbed 7-ketolithocholic acid is stereospecifically reduced in
the liver to chenodiol.
Lithocholic acid causes cholestatic liver injury and can
cause death from liver failure in certain species unable to form sulfate
conjugates. Lithocholic acid is formed by 7-dehydroxylation of the dihydroxy bile
acids (ursodiol and chenodiol) in the gut lumen. The 7-dehydroxylation reaction
appears to be alpha-specific, i.e., chenodiol is more efficiently
7-dehydroxylated than ursodiol and, for equimolar doses of ursodiol and
chenodiol, levels of lithocholic acid appearing in bile are lower with the
former. Man has the capacity to sulfate lithocholic acid. Although liver injury
has not been associated withursodiol therapy, a reduced capacity to sulfate may
exist in some individuals, but such a deficiency has not yet been clearly
demonstrated.
Pharmacodynamics
Ursodiol suppresses hepatic synthesis and secretion of
cholesterol, and also inhibits intestinal absorption of cholesterol. It appears
to have little inhibitory effect on synthesis and secretion into bile of
endogenous bile acids, and does not appear to affect secretion of phospholipids
into bile.
With repeated dosing, bile ursodeoxycholic acid
concentrations reach a steady-state in about 3 weeks. Although insoluble in
aqueous media, cholesterol can be solubilized in at least two different ways in
the presence of dihydroxy bile acids. In addition to solubilizing cholesterol
in micelles, ursodiol acts by an apparently unique mechanism to cause
dispersion of cholesterol as liquid crystals in aqueous media. Thus, even
though administration of high doses (e.g., 15 - 18 mg/kg/day) does not result
in a concentration of ursodiol higher than 60% of the total bile acid pool,
ursodiol-rich bile effectively solubilizes cholesterol. The overall effect of
ursodiol is to increase the concentration level at which saturation of
cholesterol occurs.
The various actions of ursodiol combine to change the
bile of patients with gallstones from cholesterol-precipitating to
cholesterol-solubilizing, thus resulting in bile conducive to cholesterol stone
dissolution.
After ursodiol dosing is stopped, the concentration of
the bile acid in bile falls exponentially, declining to about 5 to 10% of its
steady-state level in about 1 week.
Clinical Results
Gallstone Dissolution
On the basis of clinical trial results in a total of 868
patients with radiolucent gallstones treated in 8 studies (three in the U.S.
involving 282 patients, one in the U.K. involving 130 patients, and four in
Italy involving 456 patients) for periods ranging from 6 to 78 months with
Actigall doses ranging from about 5 - 20 mg/kg/day, an Actigall dose of about 8
- 10 mg/kg/day appeared to be the best dose. With an Actigall dose of about 10
mg/kg/day, complete stone dissolution can be anticipated in about 30% of unselected
patients with uncalcified gallstones < 20 mm in maximal diameter treated for
up to 2 years. Patients with calcified gallstones prior to treatment, or
patients who develop stone calcification or gallbladder nonvisualization on
treatment, and patients with stones > 20 mm in maximal diameter rarely dissolve
their stones. The chance of gallstone dissolution is increased up to 50% in
patients with floating or floatable stones (i.e., those with high cholesterol
content), and is inversely related to stone size for those < 20 mm in
maximal diameter. Complete dissolution was observed in 81% of patients with stones
up to 5 mm in diameter. Age, sex, weight, degree of obesity, and serum
cholesterol level are not related to the chance of stone dissolution with
Actigall.
A nonvisualizing gallbladder by oral cholecystogram prior
to the initiation of therapy is not a contraindication to Actigall therapy (the
group of patients with nonvisualizing gallbladders in the Actigall studies had
complete stone dissolution rates similar to the group of patients with
visualizing gallbladders). However, gallbladder nonvisualization developing
during ursodiol treatment predicts failure of complete stone dissolution and in
such cases therapy should be discontinued. Partial stone dissolution occurring
within 6 months of beginning therapy with Actigall appears to be associated
with a > 70% chance of eventual complete stone dissolution with further
treatment; partial dissolution observed within 1 year of starting therapy
indicates a 40% probability of complete dissolution.
Stone recurrence after dissolution with Actigall therapy
was seen within 2 years in 8/27 (30%) of patients in the U.K. studies. Of 16
patients in the U.K. study whose stones had previously dissolved on chenodiol
but later recurred, 11 had complete dissolution on Actigall. Stone recurrence
has been observed in up to 50% of patients within 5 years of complete stone
dissolution on ursodiol therapy. Serial ultrasonographic examinations should be
obtained to monitor for recurrence of stones, bearing in mind that radiolucency
of the stones should be established before another course of Actigall is instituted.
A prophylactic dose of Actigall has not been established.
Gallstone Prevention
Two placebo-controlled, multicenter, double-blind,
randomized, parallel group trials in a total of 1,316 obese patients were
undertaken to evaluate Actigall in the prevention of gallstone formation in
obese patients undergoing rapid weight loss. The first trial consisted of 1,004
obese patients with a body mass index (BMI) ≥ 38 who underwent weight
loss induced by means of a very low calorie diet for a period of 16 weeks. An
intent-to-treat analysis of this trial showed that gallstone formation occurred
in 23% of the placebo group, while those patients on 300, 600, or 1200 mg/day
of Actigall experienced a 6%, 3%, and 2% incidence of gallstone formation,
respectively. The mean weight loss for this 16-week trial was 47 lb for the
placebo group, and 47, 48, and 50 lb for the 300, 600, and 1200 mg/day Actigall
groups, respectively.
The second trial consisted of 312 obese patients (BMI
≥ 40) who underwent rapid weight loss through gastric bypass surgery. The
trial drug treatment period was for 6 months following this surgery. Results of
this trial showed that gallstone formation occurred in 23% of the placebo
group, while those patients on 300, 600, or 1200 mg/day of Actigall experienced
a 9%, 1%, and 5% incidence of gallstone formation, respectively. The mean
weight loss for this 6-month trial was 64 lb for the placebo group, and 67, 74,
and 72 lb for the 300, 600, and 1200 mg/day Actigall groups, respectively.
Alternative Therapies
Watchful Waiting
Watchful waiting has the advantage that no therapy may
ever be required. For patients with silent or minimally symptomatic stones, the
rate of development of moderate-to-severe symptoms or gallstone complications
is estimated to be between 2% and 6% per year, leading to a cumulative rate of
7 to 27% in 5 years. Presumably the rate is higher for patients already having
symptoms.
Cholecystectomy
For patients with symptomatic gallstones, surgery offers
the advantage of immediate and permanent stone removal, but carries a high risk
in some patients. About 5% of cholecystectomized patients have residual
symptoms or retained common duct stones. The spectrum of surgical risk varies
as a function of age and the presence of disease other than cholelithiasis.
Mortality Rates for Cholecystectomy in the U.S.
(National Halothane Study, JAMA 1966;197:775-8) 27,600 Cholecystectomies
(Smoothed Rates ) Deaths /1000 Operations ***
|
Age (Yrs) |
Cholecystectomy |
Cholecystectomy + Common Duct Exploration |
Low Risk Patients* |
Women |
0 - 49 |
.54 |
2.13
|
50 - 69 |
2.80 |
10.10 |
Men |
0 - 49 |
1.04 |
4.12 |
50 - 69 |
5.41 |
19.23 |
High Risk Patients** |
Women |
0 - 49 |
12.66 |
47.62 |
50 - 69 |
17.24 |
58.82 |
Men |
0 - 49 |
24.39 |
90.91 |
50 - 69 |
33.33 |
111.11 |
* In good health or with moderate systemic disease.
** With severe or extreme systemic disease.
*** Includes both elective and emergency surgery. |
Women in good health or who have only moderate systemic
disease and are under 49 years of age have the lowest surgical mortality rate
(0.054); men in all categories have a surgical mortality rate twice that of
women. Common duct exploration quadruples the rates in all categories. The
rates rise with each decade of life and increase tenfold or more in all
categories with severe or extreme systemic disease.