WASHINGTON — Excluding rare disease treatments from a Medicare pilot program to lower drug prices would wipe out much of the savings from retail drugs, according to a Harvard University researcher.

Biotech companies are lobbying the Trump administration to exclude treatments for rare, or “orphan,” diseases from two Medicare pilot programs: Global Benchmark for Efficient Drug Pricing (GLOBE) and Guarding U.S. Medicare Against Rising Drug Costs (GUARD). Those pilots are part of President Trump’s plan to get drugmakers to lower prices in the United States to the levels seen in other rich countries, an approach generally referred to as a “most-favored nation” policy.

The exact scope of those pilot programs has been in question. Some companies that struck most-favored nation pricing deals with the White House — including many of the largest drugmakers globally — have said they were exempted from the pilots, though details of those deals have not been made public.