Shares in Halozyme Therapeutics have plummeted further this week on the back of news that US regulators are seeking more information on the company’s immune system boosting drug.

The biopharmaceutical firm saw its shares plunge 19% on Monday morning, New York time – the greatest drop in almost eight years – to below $10 a share.

The setback followed the news that the US Food and Drug Administration had requested additional information in order to complete its review of the Biologics License Application for the drug HyQ, which is being developed with partner Baxter International.

The FDA’s request for more studies about the long-term use of HyQ will now delay approval of the drug, a combination product of Immune Globulin Infusion 10% (human) and recombinant human hyaluronidase, which is used to boost a weak immune system to help fight disease.   

However, this is not the first attack on Halozyme’s share price in recent weeks. Just last week, the company saw its stock drop as much as 14% after an analyst from Jefferies downgraded the stock from buy to hold and tagged it with a $10 target price. According to the analyst, the future potential of Halozyme has already been factored into the stock, meaning investors are unlikely to gain at the original price.  

Following the FDA news, shares in Baxter declined 5.2% at one point to $55.01.