Mylan is leaning on Pfizer to do more to relieve shortages of the EpiPen Auto-Injector. Although the drugmaker based in the US and the UK owns the rights to the EpiPen, which is recommended to prevent anaphylactic shock, it subcontracts manufacturing to Pfizer’s Meridian Medical arm.

Pfizer has struggled to meet demand recently, so that some US patients cannot find it in their local pharmacies. The US Food and Drug Administration (FDA) put the medicine on its official shortages list in May, and the prospect of a severe shortfall in August and September, when children return to school, is worrying authorities.

Reports say Pfizer has failed to fix manufacturing issues that have persisted for decades, and new issues continue to crop up. The plant in in St Louis, Missouri, which produces all the EpiPens sold in the US, is said to have struggled to maintain production levels following an inspection and a warning letter about quality control sent by the FDA last September.

The New York pharmaceutical giant is also facing shortfalls of several other products because of issues at other US plants. According to US pharmaceutical journals, this is due to a number of underperforming manufacturing facilities it acquired with the purchase of Hospira for $17 billion in 2015.

In a joint statement, Pfizer and Mylan said both companies “are fully aware of the life-saving importance of EpiPen and we are working together, as we have throughout our long collaboration, to increase production and expedite shipments as rapidly as possible.”

The EpiPen shortage is embarrassing to Mylan, especially as it is hoping to put behind it negative fallout encountered when it priced a two-pack of the injectors at roughly $600 – a rise of 50% against the 2005 level.

In 2016, the drugmaker with headquarters in both the US and the UK, paid $465 million to the US government to settle claims it improperly classified the EpiPen as a generic product to gain rebates from the public health insurer Medicaid, while at the same time billing it as a brand-name drug for other purposes. The classification as a generic meant it could grant lower rebates to the insurer.

Mylan’s pricing practices were also investigated by the state of New York.  The company neither admitted nor denied liability. It later corrected its pricing and classification.