(New throughout, adds background and details from lawsuit)

By Deena Beasley

Nov 13 Specialty pharmacy Park Irmat Drug Corpis suing OptumRx, saying the pharmacy benefit unit ofUnitedHealth Group plans to remove Irmat from itsnetwork as of the end of the month.

In the suit, filed late on Thursday in New York SupremeCourt, Irmat said it received notice that it will be cut offfrom reimbursement by OptumRx, which operates a mail-orderpharmacy that competes with Irmat, particularly for medicinesthat treat dermatological ailments.

Irmat is the latest specialty, mail-order pharmacy to bedropped by a payer after drugmaker Valeant PharmaceuticalsInternational Inc was accused of using its close tieswith Philidor Rx Services to improperly inflate revenue. Valeanthas denied the allegations and cut ties with Philidor, promptingother payers to follow suit.

OptumRx did not have an immediate comment on the lawsuit.

Several pharmacy benefit managers, including OptumRx, haveremoved Philidor from their networks and said they areevaluating other specialty pharmacies.

Express Scripts Holding Co, the largest U.S.pharmacy benefit manager, has cut Linden Care pharmacy from itsnetwork, citing close ties with drugmaker Horizon Pharma LLC.

Irmat is seeking an injunction barring Optum fromterminating or excluding it. Irmat said it was in danger ofgoing out of business as the result of Optum's action.

Irmat's mail-order business has been an unmitigated success.From 2012 to 2015, the pharmacy's business grew exponentially,both in revenue and geographic scope.

By way of example, Irmat's revenue from Optum membersincreased from approximately $1.99 million in 2012, to $3.8million in 2013, to $15.3 million in 2014, and was projected togrow to $33 million in 2015.

In its lawsuit, Irmat says it began in 2013 to participatein programs sponsored by drugmakers Galderma SA and AquaPharmaceuticals under which the manufacturers covered patient co-payments on leading dermatological drugs.

Galderma is owned by Nestle SA. Aqua is owned byAlmirall SA. (Reporting by Michele Gershberg and Deena Beasley; Editing byDavid Gregorio)