A drug company has resigned from the biggest pharmaceutical lobbying group in Washington a few months after the manufacturer got into hot water over high drug prices.

The resignation of Marathon Pharmaceuticals from the Pharmaceutical Research and Manufacturers of America, the industry's top lobbying group, comes amid a high-profile ad campaign from the group to change the industry's image.

PhRMA confirmed Friday that Marathon left the group but did not comment on the reason for the departure.

A source familiar with the matter said that PhRMA is doing a review of its membership criteria to be out later this year, but didn't elaborate on what the new criteria will be.

The Illinois-based Marathon drew public and congressional ire in February for charging $89,000 a year for a drug that treats a rare pediatric disease. The same drug is sold overseas for about $1,000 a year.

Marathon sold the drug, called Emflaza, on Thursday to PTC Therapeutics.

In a note obtained by the Washington Examiner, the company informed PhRMA of the sale and said it was "discontinuing its membership in all relevant trade associations."

The departure comes one week after another drugmaker, Mallinkrodt Pharmaceuticals, also left the group.

The Irish drug maker had to pay a $100 million fine in January to the federal government to settle charges that it slowly raised the price of a pediatric drug. Mallinkrodt raised the price of a drug to treat seizures in infants from $40 a vial in 2001 to more than $34,000 a vial today, according to the Federal Trade Commission.

PhRMA is trying to rehab the drug industry's image after years of criticism from the public and Congress over high drug prices. It started an ad campaign called "Go Boldly" that seeks to highlight scientists working on new treatments and patients undergoing treatment.

The ad campaign coincides with more sharp rhetoric from President Trump on the industry and targeting high drug prices. However, Trump has yet to back any legislation focusing on the issue.