Turing Pharmaceuticals has announced it will lower the price of Daraprim after faced a backlash following raising the price of the drug used by AIDS patients by over 5,000%.

Turing CEO Martin Shkreli told reporters he would drop the price following the outcry, but did not say by how much.

Turing Pharmaceuticals acquired the rights to Daraprim in August 2015.

The company then raised the cost of the drug, which treats a parasitic infection, from $13.50 to $750.

Amid criticism from medical groups – one called the cost “unjustifiable” – Martin Shkreli on September 21 defended the increase, saying the profits would help research new treatments.

Martin Shkreli accused critics of not understanding the pharmaceutical industry.

He has now told ABC News: “We’ve agreed to lower the price on Daraprim to a point that is more affordable and is able to allow the company to make a profit, but a very small profit.”

Earlier in the day, PhRMA, the pharmaceutical industry’s main lobbying group, tweeted that Turing “does not represent the values of PhRMA member companies”.

Agreeing a price for any drug is a tricky business.

In the US, the buyers are private insurance companies as well as the government through the Medicare and Medicaid system. It’s a market and prices can go up and down, depending on what people are willing to pay.

In recent years, pharmaceutical research and development has slowed and companies have to think carefully about what they invest in. Blockbusters such as Viagra pull in money, but orphan drugs for rare diseases can be less attractive. Not many patients use them, and so turning a profit may be difficult.