UPDATE 1-Alder's migraine drug data disappoints, shares tumble

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June 27 (Reuters) - Alder BioPharmaceuticals Inc's late-stage study data on its experimental treatment to prevent episodic migraine fell short of investor expectation, sending its shares about 20 percent in premarket trading on Tuesday.

In the study, patients receiving a 300 mg dosage of the company's drug, eptinezumab, experienced a reduction of 4.3 days from baseline in monthly migraine days, 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.

The study data was statistically significant, the company 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 calcitonin gene-related peptide, or 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 looking to target 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 recouped some of their losses to trade down 14.4 percent at $16.

(Reporting by Ankur Banerjee in Bengaluru; Editing by Sriraj Kalluvila)