UPDATE 2-Alder's migraine drug data disappoints, shares tumble

(Adds analyst comment, shares)

June 27 (Reuters) - Alder BioPharmaceuticals Inc's late-stage study data on its experimental treatment to prevent episodic migraine fell short of investors' expectation, sending its shares down about 23 percent in premarket trading on Tuesday.

Patients receiving a 300 mg quarterly dose of the company's drug, eptinezumab, through infusion, experienced a reduction of 4.3 days from baseline in monthly migraine attacks, while those on the 100 mg saw a reduction of 3.9 days.

This compared with the average 3.2-day reduction for patients on placebo.

Leerink Partners analyst Paul Matteis said the mean reduction looked slightly numerically lower than other late-stage calcitonin gene-related peptide (CGRP) trials, highlighting the larger placebo rate for the intravenous.

The study data was statistically significant and met the main goal, Alder said.

Alder is among a clutch of companies racing to develop a new, more effective migraine treatment.

Amgen Inc, Eli Lilly Co and Teva Pharmaceutical Industries Ltd are the other drugmakers looking to develop treatments that target CGRP, a protein involved in pain-signaling during migraine.

Earlier this month, Teva's experimental drug to prevent migraines cleared another late-stage study, setting it on course for U.S regulatory approval and launch in the second half of 2018. Lilly's treatment also cleared key studies last month.

The companies are aiming at the about 36 million Americans who suffer migraines, which are characterized by recurrent episodes of moderate-to-severe headaches accompanied by nausea, vomiting, and sensitivities to light and sound.

The lack of effective medicines and the sheer number of patients guarantee that each company's drug, if approved, will eventually generate at least $1 billion in sales, analysts have forecast.

Alder said it expects to complete enrollment later this year in another late-stage trial testing patients with chronic migraine.

The company's shares were down at $14.40 in premarket trading. (Reporting by Ankur Banerjee in Bengaluru; Editing by Sriraj Kalluvila)