Funding will be used to expand services such as potable water, sanitation and electricity, according to a bank release.
The Amazonas state government will also contribute US$120mn to the works, bringing total phase III investments to US$400mn.
"With this new stage, our goal is to expand the benefits from the first phases in order to guarantee that, by 2015, an additional 75,960 residents will be enjoying the programs' benefits," said IDB team leader Yvon Mellinger.
The 25-year loan has a five-year grace period and Libor-based variable interest rate, the release said.
Since Prosamim was first launched in 2006, US$404mn has been invested, with US$313mn coming from IDB loans. Work has so far included the installation of 58,226 sewerage system connections, 22.4km of drainage pipeline and paving of 30km of roads.