High school students in Sydney have shown a drug sold by "pharma bro" Martin Shkreli costs only US$2 to make - nowhere near the US$750 his company charges.
Mr Shkreli made headlines last year when he bought Turing Pharmaceuticals, which makes daraprim, and jacked up the price of a dose from US$13.50 to US$750.
Daraprim is on the World Health Organisation's list of essential medicines, and is used to combat infections like malaria and toxoplasmosis, as well as people with immunity problems, including HIV patients and pregnant women.
Students at Sydney Grammar School, with help from their chemistry teacher, have shown a drug equivalent to daraprim can be made from scratch for as little as US$2 a dose.
Mr Shkreli's posted reactions on both Twitter and YouTube. On the former, he appeared to mock the students' efforts, saying their "cook game" was nothing compared to his.
"Highest yield, best purity, most scale. I have the synthesis game on lock," he wrote. In another tweet, he said "no one schools the boss".
But on YouTube, he said he was "delighted" to hear about youngsters getting into medical science.
"We should congratulate these students for their interest in chemistry, and all be excited about what is to come."
While the students show how daraprim can be made cheaply, Mr Shkreli says it's an unfair comparison because he has to cover costs and turn a profit, while students in a high school lab don't. Nor do they have any way to make enough daraprim, or distribute it, at any scale, or the millions of dollars required to put their drug through testing before it can be brought to the market.
Mr Shkreli said on YouTube scientists at Turing Pharmaceuticals are working hard to replace daraprim with a safer, more effective drug.
The controversial millionaire made headlines a second time late last year when it emerged he'd bought the single copy of rap group Wu-Tang Clan's album Once Upon a Time in Shaolin for US $2 million.