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Aug 8 (Reuters) - Allergan Plc reported weaker-than-expected quarterly revenue after its Alzheimer's drug, Namenda IR, lost patent exclusivity and the company cut its full-year revenue forecast.

Allergan, known as Actavis until it bought Botox-maker Allergan last year and took on its name, cut its forecast for adjusted full-year net revenue to $14.65 billion to $14.90 billion, from its prior estimate of $17 billion.

The company's quarterly net revenue rose marginally, to $3.68 billion from $3.63 billion a year earlier, but this was far below the average Wall Street estimate of $4.08 billion.

Dublin-based Allergan's net loss attributable to ordinary shareholders increased to $571.3 million, or $1.44 per share, for the second quarter ended June 30, from $312.7 million, or 80 cents per share, a year earlier.

Excluding special items, the company earned $3.35 per share, beating the average analysts' estimate by 1 cent, according to Thomson Reuters I/B/E/S.

Allergan's shares were down 0.7 percent in light premarket trading on Monday. Up to Friday's close of $253.85, the stock had fallen nearly 19 percent this year.

Pfizer Inc dropped plans to buy Allergan for $160 billion in April after the U.S. government cracked down on so-called inversion deals, in which companies move their domicile to countries that have a lower tax rate.

The combination would have been the biggest deal ever in the pharmaceutical industry.

Allergan said last week it would sell its Anda distribution business for $500 million to Teva Pharmaceutical Industries Ltd , a day after the Israeli drugmaker completed the $40.5 billion acquisition of Allergan's generic-drug portfolio.

(Reporting by Natalie Grover in Bengaluru; Editing by Saumyadeb Chakrabarty and Ted Kerr)