Stirling Products (ASX:STI) will extend its proof-of-concept studies to include a more direct delivery method after analysis of levels of its beta agonist ST810, a single enantiomer form of salbutamol, in the bloodstream of merino lambs showed that the growth promoter was not getting into the bloodstream.

Significantly, the positive control, a mixed enantiomer form of salbutamol, also failed to get into the bloodstream.

Managing director Calvin London said that as a result, sufficient plasma levels of the drug were not achieved, and no significant physical effects such as reduction in fat or increase in muscle were observed.

Now, the company plans to look at using a more precise controlled release delivery directly into the tissue. The follow-on study is expected to begin in April.