Pharmaceutical company Indivior reported a drop in first-quarter net revenue but impressed with results of trials for its new treatment for schizophrenia.The company - which was spun off by Reckitt Benckiser late last year - posted operating profit of $115m, down 30% from $165m in the same period last year, on net revenue down 10% to $251m.The decline in the numbers reflected higher rebates in the US, in connection with offering discounts to gain access to lists of approved drugs, or formularies, for its heroin-addition drug Suboxone, continuing a trend from the second half of 2014.Indivior was also hit by expected higher operating costs as a standalone public company, including $2m exceptional costs arising from the demerger and establishment of Indivior Plc."We have enjoyed a good start to the year with 1Q numbers modestly exceeding our plan which anticipated no rapid deterioration in the quarter's trading environment," said chief executive officer Shaun Thaxter, who in February had warned of a "very uncertain" market as to the timing, extent and impact of price erosion."In the US, generic tablet pricing has not yet disrupted our market share while branded competitors had very limited impact although as in the second half of last year we continued to offer tactical rebates in connection with formulary access for Suboxone Film."He added that in Europe, government austerity measures and price constraints continued to be no worse than expected, meaning if the situation continues, management "may have room to reassess our full-year guidance at the half year".The company also said on Tuesday that its RBP-7000 product has met the primary and secondary endpoints in its phase 3 trial for the treatment of schizophrenia.This helped to push the shares up and by 14:00 they were 8% higher at 219.30p.