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Adelaide-based pharmaceutical manufacturer Mayne Pharma (ASX: MYX) has been awarded $13.27 million in legal costs by the Supreme Court of NSW against Cosette Pharmaceuticals, the latest salvo in a protracted dispute stemming from a $672 million takeover deal that collapsed after the Australian Treasurer blocked it on national interest grounds.
The costs order follows Mayne Pharma's successful defence of proceedings brought by US-based Cosette, which had sought to validate its purported termination of a scheme implementation deed (SID) signed by the two companies in February 2025.
The court found in Mayne Pharma's favour in October 2025, ruling that Cosette had no right to terminate the agreement.
The news comes on the heels of a separate and broader damages claim Mayne Pharma filed against Cosette in February 2026 in the same court.
That claim targets Cosette Pharmaceuticals, its parent Cosette Pharmaceuticals Holdings, private equity backer Avista Capital Holdings - trading as Avista Healthcare Partners - and Avista's managing partner and CEO David Burgstahler.
Mayne Pharma is seeking substantial damages for alleged breach of the SID and for inducing that breach, though the quantum has not been publicly disclosed.
The saga traces back to February 2025, when Mayne Pharma entered into the SID with Cosette under which Cosette would acquire all Mayne Pharma shares at $7.40 per share, valuing the company at $672 million.
The deal required approval from Australia's Foreign Investment Review Board (FIRB).
In November 2025, Federal Treasurer Jim Chalmers issued an order blocking the proposed acquisition on national interest grounds.
Mayne Pharma has alleged the FIRB rejection was the direct result of conduct by Cosette and its affiliates that was "wilful and intentional" and effectively defeated the FIRB condition required for the scheme to proceed.
Cosette moved to terminate the SID, but the Supreme Court of NSW found in October 2025 that the termination was invalid.
Cosette has strongly rejected Mayne Pharma's characterisation of events, stating that Mayne Pharma's public announcements on the matter contain material inaccuracies, and asserting that it complied with its legal obligations in all respects and was at all times fully transparent with FIRB.
Mayne Pharma had itself moved to terminate the SID in December 2025, citing Cosette's alleged breaches and failure to satisfy the FIRB condition.
The company also noted it was entitled to a $6.7 million break fee under the terms of the agreement.
Shares in Mayne Pharma were trading at $2.44 this afternoon, or about a third of the $7.40 per share Cosette had agreed to pay under the scheme.
The court is yet to determine the payment timeframe for the $13.27 million costs award or the interest amount, while the separate substantial damages claim remains before the court.
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