* 2018 revenue, net income to come in below expectations
* Shares sink 37 pct after drugmaker scraps guidance
* Best-seller's rapid market share loss to hit revenue by $25 mln
* Discounting of generic tablets to hit revenue by $50 mln
* Cuts revenue guidance on new potential blockbuster Sublocade (Adds shares, impact from market share loss, price changes)
July 11 (Reuters) - British drugmaker Indivior warned on Wednesday it would miss its full-year profit target as its best-selling opioid addiction drug faces new competitors in the United States, sending its shares down 37 percent.
The share slide wiped nearly 1 billion pounds ($1.3 billion)from the company's market valuation, sending the stock to its lowest in two years.
Indivior said its full-year guidance was no longer valid given an "accelerated" loss of market share for opioid treatment Suboxone Film as well as slower early uptake levels of its new opioid addiction drug Sublocade, launched in February.
In February the company had forecast 2018 net revenue of between $1.13 billion and $1.17 billion and adjusted net profit of $280 million to $320 million.
Suboxone Film generates 80 percent of Indivior's revenue but India's Dr.Reddy's Laboratories and U.S.-based Mylan NV received approval from the Food and Drug Administration (FDA) last month to launch generic versions of the blockbuster drug.
The film, which is placed under the tongue to suppress cravings, lost two-and-half percentage points of market share to 52 percent in the most recent weekly data, the company said. That fall alone would reduce 2018 net revenue by $25 million, it said.
Market prices have also fallen by 75 to 80 percent compared to list prices due to the level of discounting of the generic tablets, Indivior said, warning the impact of those price changes could also reduce annual net revenue by $50 million.
Indivior filed an injunction last month against the FDA's decision, and a U.S. court has issued a restraining order blocking Dr. Reddy's from selling its generic version of Suboxone until the end of June.
The UK drugmaker had previously warned that Dr. Reddy's launch could result in a rapid and material loss of U.S. market share for Suboxone.
On Wednesday, Indivior said it was also experiencing "some friction" in the new distribution and reimbursement model for Sublocade, making doctors less willing to prescribe the new drug at higher price levels.
As a result, Sublocade's 2018 net revenue is expected to range between $25 million and $50 million, about $50 million lower than its expectations, the company said.
Its shares were down 31 percent at 260 pence by 0900 GMT. ($1 = 0.7545 pounds) (Reporting by Justin George Varghese in Bengaluru; Editing by Amrutha Gayathri and Susan Fenton)