Partners Group Private Equity (PEY) has written off its €20m (£17.3m) investment in Pharmathen, a Greek developer of advanced drug delivery technologies hit by an import alert from the US Food and Drug Administration (FDA) last year.

“Despite major operational turnaround initiatives over the last year,” PEY said restrictions to US exports meant “the implied enterprise value is unlikely to be sufficient to cover the company’s existing debt, and the investment was therefore written down to zero.”

There was also bad news from United States Infrastructure Corporation (USIC), a US-based provider of underground utility locating services, where a €24.4m stake at the end of last year was “also prudently adjusted down” to reflect lower earnings growth following “exceptional customer insourcing initiatives and operational headwinds”.

The two write-downs contributed to another negative month for PEY, a £562m London-listed private equity fund standing on a 32% discount to net asset value. NAV dropped 2.5% to €830.1m or €12,26 per share in April, the fourth month this year the portfolio has fallen after reporting an 8.7% fall last year. The company is the second worst performer in its sector over five years with a 13.6% loss for shareholders.

The completion of the sale of US health tech provider Clario, announced in November, saw PEY receive €23.9m in proceeds, enabling it to allocate a further €18.1m to share buybacks.

Stay a step ahead. Our daily newsletter brings you the latest on investment trusts and active ETFs. Subscribe here.