Cowen Healthcare Royalty Partners, the specialist US investor in pharmaceutical royalties, has raised more than $250m for a top-up fund, becoming the latest private equity group to bolster the buying power of an existing fund.

Other private equity groups planning to raise top-up funds include KPS Capital, the US turnround investor that this year bought Waterford Wedgewood out of bankruptcy, and Graphite Capital, the UK-based owner of the Groucho Club.