"[clinical] investigation" and "clinical trial":
clinical investigations concern
medical devicesWhat is a clinical investigation?
A
clinical investigation is defined as “any systematic investigation or study in or on one or more human subjects, undertaken to assess the safety and/or performance of a
medical device.” (SG5/N1:2007).
http://ec.europa.eu/health/medical-devices/files/meddev/2_7_...clinical trials concern pharmaceutical products/new
medecinesThe development of new and better
medicines is vital for public health. A key step in taking potential new medicines from the laboratory to humans is the phase 1
clinical trial, when they are given to humans for the first time. ...
http://www.abpi.org.uk/our-work/library/guidelines/Documents...You have given almost no context, but it's very possible that this is the difference between investigation/clinical trial in your text. As for the official translation of these terms, you can take a look at the database of EU legislation.