Inclusion Criteria:

- Male and female patients ages 18 to 70 years.

- Established diagnosis of PBC based on at least three of the following criteria:

- Detectable anti-mitochondrial antibodies (AMA)

- Cholestatic biochemical pattern

- Liver biopsy compatible with PBC

- Appropriate exclusion of other liver diseases.

- Therapy with UDCA at adequate dose (13-15mg/kg/d) for at least six months and
evidence of suboptimal response defined by alkaline phosphatase levels that did not
normalize and remain elevated by at least 1.5 times the upper limit of normal.

- No history or present hepatic decompensation (e.g. variceal hemorrhage,
encephalopathy, or poorly controlled ascites).

Exclusion Criteria:

- Findings highly suggestive of liver disease of other etiology.

- A score >=10 points on the Revised Scoring System for autoimmune hepatitis (AIH),
supporting a diagnosis of PBC/AIH overlap.

- Patients on steroids (systemic), immunosuppressants, or immunomodulatory agents
within the previous 6 months.

- Patients with clinical or laboratory evidence suggestive of decompensated cirrhosis.

- Hypersensitivity to PTX or the methylxanthines (caffeine, theophylline, theobromine).

- History of cerebral or retinal hemorrhage.

- Other medical comorbidities (such as cardiac, renal, cancer) that would interfere
with completion of the study.

- Patients taking Theophylline or Coumadin because of potential drug-drug interactions
with PTX. In addition, patients taking low molecular weight heparin preparations.

- Pregnant or nursing women.