UK drugmaker Shire has reported promising data on two new drugs for attention-deficit hyperactivity disorder, providing further evidence that concerns about the threat to the business of flagship ADHD drug Adderall XR are receding.

Data from a Phase III trial of its once-daily SPD503 (guanfacine) for attention-deficit hyperactivity disorder provide strong evidence of its efficacy. This is great news for Shire, as guanfacine is a novel ADHD product that could have a strong differentiation in the marketplace because it is non-stimulant.

SPD503, when given as a monotherapy, significantly improved ADHD symptoms in children aged six to 17, according to the results, which were presented at the US Psychiatric and Mental Health Congress.

In the Phase III study, 345 subjects were randomised to receive 2mg, 3mg or 4mg daily doses of the drug for a period of 11 weeks (a two-week screening section, followed by a seven-day washout period to allow for discontinuation of current medication and an eight-week treatment phase). Efficacy was assessed using the standard 18 point ADHD rating scale, which measures hyperactivity, impulsivity and inattention.

The results showed that treatment produced an average 16.7 point symptom reduction, compared with 8.9 in the placebo group. An improvement was seen as early as two weeks into the study, with significant benefit in all the dosage groups occurring at week three.

Meanwhile, Shire also reported that its SPD465 an extended version of Adderall XR (which shows bio-equivalence to Adderall XR over 16 hours and better control) stood up in a comparative study against Adderall XR plus a dose of immediate release Adderall.

The trial enrolled 20 subjects who were randomized to receive either a once-daily 37.5mg administration of SPD465, or 25mg Adderall XR followed eight hours later by 12.5mg of Adderall. Participants initially underwent a seven-day washout period, before receiving either regimen for two and half days. Blood samples were collected from subjects during this phase of the programme, with each treatment cohort being switched to receive the alternate therapy once the two and a half day period had elapsed.

The results showed that plasma concentrations of both D-amphetamine and L-amphetamine were similar in the two groups , and there were no clinically meaningful differences between the groups in terms of adverse events.

Shire submitted an New Drug Application for SPD465 to the US Food and Drug Administration earlier this year.

Shire's ADHD franchise grew by 28% to $224 million, with Adderall XR sales up 25% to $208 million, and threat of generic competition postponed after Shire cut a deal with patent challenger Barr. The company now claims a 29% share of the US prescription market for ADHD drugs, helped by the launch of ADHD patch product Daytrana (methylphenidate) which added $10 million in sales in its first quarter on the market.

Meanwhile, future growth for the franchise seems assured with three new products due for launch in 2007, including NRP104, partnered with New River Pharmaceuticals, which is awaiting labelling and scheduling approval before it can be launched in the USA.