A method for treating pulmonary hypertension and other diseases involving a
defect in collagen metabolism, by administration of an effective amount of
a liposome encapsulated copolymer conjugate antifibrotic composition, is
disclosed. The antifibrotic agent is preferably a proline analog, such as
cis-4-hydroxy-L-proline (cHyp). Consistent, high loadings (>98%) of the
antifibrotic agent are achieved by first forming a dipeptide with
L-lysine, after which the dipeptide is copolymerized with the polymer
component to form the copolymer conjugate. The polymer is preferably
poly(ethylene glycol) having a weight average molecular weight of from
about 500 to about 15,000. There is thus provided the efficient delivery
and rateable release of the antifibrotic agent to inhibit collagen
accumulation and thereby treat the diseases involved. Accordingly, there
is a substantial reduction in the quantity of antifibrotic agent
necessary, and thus a corresponding reduction in the potential for
toxicity that would otherwise result from its prolonged administration.