Express Scripts Holding, the biggest pharmacy benefits manager in the US, said it plans to list Imprimis Pharmaceuticals’ cheaper alternative to the toxoplasmosis treatment Daraprim (pyrimethamine) for $1 per pill.

Daraprim is being offered for $750 per pill by Turing Pharmaceuticals, which in August acquired marketing rights to the 62-year-old drug sold only in the US. The previous rights owner, Impax Laboratories, had sold it for $13.50 per pill.

After provoking outrage among doctors, patients and politicians – most prominently US presidential candidate Hillary Clinton – over the 50-fold hike, Turing later said it would reduce the price but did not disclose by how much or when this would take place.

Several other drugmakers have made headlines recently by purchased rights to old and cheap medicines that represent the only treatment for serious diseases and subsequently engaging in what is perceived by many as price gouging. Turing’s hike was especially controversial as toxoplasmosis mainly threatens people with weak immune systems, such as HIV and organ transplant patients, along with pregnant women.

The capsules provided by Imprimis, a young drug compounder based in San Diego, contain pyrimethamine and leucovorin. They will not require approval by the US Food and Drug Administration as the ingredients are already approved. Like the sulfonamide used with Daraprim, the California firm will use leucovorin to limit pyrimethamine's side effects.

Leaders of the US HIV Medicine Association and The Infectious Diseases Society of America have urged other pharmacy benefits managers and health insurers to make the Imprimis option available, saying care providers have faced "significant challenges" in obtaining the treatment for patients since Turing raised the price.

Express Scripts, which manages prescription drug benefits for about 85 million people, has repeatedly criticized price gouging. Last year, it waded into the debate over the high cost of hepatitis C treatments by choosing AbbVie's Viekira Pak over more expensive drugs produced by Sovaldi and Harvoni. Subsequently it won a hefty price reduction from the latter two companies.