Unichem Laboratories on Friday entered into a pact to acquire 19.99 per cent stake each in Optimus Drugs Pvt Ltd and Optrix Laboratories Pvt Ltd by way of primary issuance and secondary transfer of shares. These Hyderabad-based firms, owned by the same management, are engaged in research, development, manufacturing, marketing and distribution of APIs and intermediates. However, the deal size was not disclosed. Investors will closely track the development.