Nexus Pharmaceuticals will have to wait until patent expiry in 2031 to launch its proposed generic version of CorMedix Therapeutics’ intravenous antibiotic Minocin (minocycline), after the US Court of Appeals for the Federal Circuit affirmed that the generics firm’s product infringes a valid patent.
The Federal Circuit has affirmed a judgment of the US District Court for the Northern District of Illinois that Nexus’s generic minocycline product infringes claims of US patent 9,084,802, and that Nexus had failed to prove those claims invalid.
The dispute arose from Nexus’s abbreviated new drug application, filed in October 2020, seeking US Food and Drug Administration approval to market a generic version of Minocin, a reformulated injectable form of the tetracycline antibiotic minocycline.
CorMedix’s wholly owned subsidiary Melinta Therapeutics had sued Nexus for infringement of the ‘802 patent and a second US patent, 9,278,105.
After a four-day bench trial in 2023, the district court found that Nexus’s generic infringed all the asserted claims and rejected its invalidity defenses, which spanned obviousness, indefiniteness, inadequate written description and lack of enablement.
As a result, the court permanently enjoined Nexus from manufacturing, using, offering for sale or selling its ANDA product until the two patents expire.
According to the FDA’s Orange Book, the reformulated Minocin – approved by the agency in 2015 – is protected by the ‘802 and ‘105 patents, both of which expire on May 12, 2031.
The FDA granted tentative approval to Nexus’s generic in 2025, but the injunction keeps it off the market until that expiry.
An additional Orange Book-listed patent also expires in May 2031, while a further patent runs its course in October 2032.
Nexus’s Position Ruled Internally Inconsistent
Minocin is an intravenous formulation of minocycline, a tetracycline-derived antibiotic used largely in hospital and acute-care settings against serious and drug-resistant infections, including multidrug-resistant Acinetobacter baumannii.
The original formulation of intravenous minocycline was first approved in the US in the early 1970s. Melinta’s Rempex Pharmaceuticals subsidiary later reformulated it, adding magnesium and raising the pH to improve the drug’s solubility and stability and to allow it to be given in a smaller volume of fluid.
According to court documents, the patents-in-suit turn on that reformulation. Both are directed to methods in which adding magnesium to the injectable antibiotic reduces hemolysis – the destruction of red blood cells – at the injection site.
The ‘802 patent claims a method of treating bacterial infection by intravenously administering a composition of minocycline, a magnesium salt and a base, at a magnesium-to-minocycline molar ratio greater than about 4:1 and a pH between 4 and 6, whereby injection-site hemolysis is reduced relative to a composition that does not include magnesium.
Before the Federal Circuit, Nexus raised two issues concerning the ‘802 patent. The first was a claim-construction argument over the terms “composition” and “administering.”
Nexus contended that, because claim 1 uses the closed-ended term “consists of” and the listed ingredients do not include a diluent, the claimed composition cannot contain one. Its own generic product, it argued, requires a diluent to be added before injection, and so could not infringe.
The Federal Circuit disagreed, agreeing with the district court that “composition” refers to the minocycline, magnesium and base mixed into solution before the diluent required for intravenous administration is added, and that “administering” means giving the diluted composition to a patient intravenously.
Both the patent specification and external evidence supported that reading, the court said, pointing to the specification’s instructions for preparing the admixture; testimony from three expert witnesses that a skilled person would know to dilute the composition before administering it; and the prescribing information for both 1973 and 2010 versions of Minocin, which call for reconstitution and then further dilution.
The court also found Nexus’s position internally inconsistent. Quoting the district court, it noted that to hold “composition” includes a diluent while “consists of” does not “is inconsistent at best, because both terms describe the same list of ingredients.”
Taken to its conclusion, the court observed, it would place Melinta’s own product outside the claims too, since both the branded drug and the generic require a diluent.
Because it upheld the construction, the Federal Circuit rejected Nexus’s challenge to the finding of infringement, which had rested on that construction.
District Court Had Not Clearly Erred In Finding The Patent Adequately Described
Nexus’s second argument went to validity. The ‘802 patent requires that hemolysis be “reduced relative to intravenous administration of a composition that does not include magnesium,” and the parties disagreed over what that comparator formulation was.
Nexus contended the comparison had to be against any formulation without magnesium, including one containing a different metal cation such as calcium.
On that reading, it argued, the patent was invalid for lack of written description, because the inventors had never shown they possessed a magnesium formulation that reduced hemolysis compared with a calcium-containing one.
Melinta argued that Nexus had waived the point by confining it to a single sentence of its post-trial brief. The Federal Circuit rejected that, finding Nexus had said enough to preserve the issue under the applicable Seventh Circuit standard, citing precedent that an argument is not waived even when “woefully underdeveloped.”
On the merits, however, the court held that the district court had not clearly erred in finding the patent adequately described.
The most natural comparator for a formulation “that does not include magnesium,” it said, was the same formulation without magnesium – here the prior-art minocycline product, which contained no magnesium or any other metal cation.
The specification’s focus throughout was on the advantage of adding magnesium to a formulation lacking divalent cations, not on any benefit of magnesium over calcium, the court found.
It noted that a 1973 Minocin product had warned against using a calcium-containing diluent because “a precipitate may form,” which suggested the limitation was never meant to set up a magnesium-versus-calcium comparison.
Inventor testimony and the patent’s prosecution history pointed the same way. The closest prior art was commercial intravenous minocycline without a multivalent cation, and the experiments compared the magnesium formulation against that.
The inventors, the court concluded, possessed an invention showing that a minocycline solution with magnesium reduced hemolysis relative to one without.
Having upheld the ‘802 patent as infringed and not invalid, the Federal Circuit declined to take up the validity of the ‘105 patent.
“Because both the ‘802 patent and the ‘105 patent have the same expiration date, and because counsel agreed that if either patent is held not invalid, the district court’s finding of infringement must be upheld, it is unnecessary for us to address the question of the validity of the ‘105 patent,” the Federal Circuit concluded.
Minocin is a core part of the antibiotics franchise of CorMedix, which acquired Melinta in a $300m deal – that closed in 2025 – and has since rebranded as CorMedix Therapeutics.
“We are pleased that the Federal Circuit has affirmed the district court’s thorough and well-reasoned decision,” commented Joseph Todisco, CorMedix’s chairman and CEO.
“This ruling validates the strength of the Minocin intellectual property portfolio and recognizes the innovative work that led to important improvements in intravenous minocycline therapy for patients.”
“The decision reinforces the importance of protecting pharmaceutical innovation and the substantial investments required to develop improved therapies. We
