CLINICAL PHARMACOLOGY
Introduction
Wilson's disease (hepatolenticular degeneration) is an
autosomal inherited metabolic defect resulting in an inability to maintain a
near-zero balance of copper. Excess copper accumulates possibly because the
liver lacks the mechanism to excrete free copper into the bile. Hepatocytes
store excess copper but when their capacity is exceeded copper is released into
the blood and is taken up into extrahepatic sites. This condition is treated
with a low copper diet and the use of chelating agents that bind copper to
facilitate its excretion from the body.
Clinical Summary
Forty-one patients (18 male and 23 female) between the
ages of 6 and 54 with a diagnosis of Wilson's disease and who were intolerant
of d-penicillamine were treated in two separate studies with trientine
hydrochloride. The dosage varied from 450 to 2400 mg per day. The average
dosage required to achieve an optimal clinical response varied between 1000 mg
and 2000 mg per day. The mean duration of trientine hydrochloride therapy was
48.7 months (range 2-164 months). Thirty-four of the 41 patients improved, 4
had no change in clinical global response, 2 were lost to follow-up and one
showed deterioration in clinical condition. One of the patients who improved
while on therapy with trientine hydrochloride experienced a recurrence of the
symptoms of systemic lupus erythematosus which had appeared originally during
therapy with penicillamine. Therapy with trientine hydrochloride was discontinued.
No other adverse reactions, except iron deficiency, were noted among any of
these 41 patients.
One investigator treated 13 patients with trientine
hydrochloride following their development of intolerance to d-penicillamine.
Retrospectively, he compared these patients to an additional group of 12
patients with Wilson's disease who were both tolerant of and controlled with
d-penicillamine therapy, but who failed to continue any copper chelation
therapy. The mean age at onset of disease of the latter group was 12 years as
compared to 21 years for the former group. The trientine hydrochloride group
received d-penicillamine for an average of 4 years as compared to an average of
10 years for the non-treated group.
Various laboratory parameters showed changes in favor of
the patients treated with trientine hydrochloride. Free and total serum copper,
SG0T, and serum bilirubin all showed mean increases over baseline in the
untreated group which were significantly larger than with the patients treated
with trientine hydrochloride. In the 13 patients treated with trientine
hydrochloride, previous symptoms and signs relating to d-penicillamine
intolerance disappeared in 8 patients, improved in 4 patients, and remained
unchanged in one patient. The neurological status in the trientine
hydrochloride group was unchanged or improved over baseline, whereas in the
untreated group, 6 patients remained unchanged and 6 worsened. Kayser-Fleischer
rings improved significantly during trientine hydrochloride treatment.
The clinical outcome of the two groups also differed
markedly. Of the 13 patients on therapy with trientine hydrochloride (mean
duration of therapy 4.1 years; range 1 to 13 years), all were alive at the data
cutoff date, and in the non-treated group (mean years with no therapy 2.7
years; range 3 months to 9 years), 9 of the 12 died of hepatic disease.
Chelating Properties
Preclinical Studies
Studies in animals have shown that trientine
hydrochloride has cupriuretic activities in both normal and copper-loaded rats.
In general, the effects of trientine hydrochloride on urinary copper excretion
are similar to those of equimolar doses of penicillamine, although in one study
they were significantly smaller.
Human Studies
Renal clearance studies were carried out with
penicillamine and trientine hydrochloride on separate occasions in selected
patients treated with penicillamine for at least one year. Six-hour excretion
rates of copper were determined off treatment and after a single dose of 500 mg
of penicillamine or 1.2 g of trientine hydrochloride. The mean urinary
excretion rates of copper were as follows:
No. of Patients |
Single Dose Treatment |
Basal Excretion Rate (μCu + + /6hr) |
Test-dose Excretion Rate (μCu + + /6hr) |
6 |
Trientine, 1.2 g |
19 |
234 |
4 |
Penicillamine, 500 mg |
17 |
320 |
In patients not previously treated with chelating agents,
a similar comparison was made:
No. of Patients |
Single Dose Treatment |
Basal Excretion Rate (μCu + + /6hr) |
Test-dose Excretion Rate (μ Cu + + /6hr) |
8 |
Trientine, 1.2 g |
71 |
1326 |
7 |
Penicillamine, 500 mg |
68 |
1074 |
These results demonstrate that SYPRINE is effective as a
cupriuretic agent in patients with Wilson's disease although on a molar basis
it appears to be less potent or less effective than penicillamine. Evidence
from a radio-labelled copper study indicates that the different cupriuretic
effect between these two drugs could be due to a difference in selectivity of
the drugs for different copper pools within the body.
Pharmacokinetics
Data on the pharmacokinetics of trientine hydrochloride
are not available. Dosage adjustment recommendations are based upon clinical
use of the drug (see DOSAGE AND ADMINISTRATION).