Express Scripts Holding Co. has included a new class of migraine drugs from Eli Lilly and Co. and Amgen Inc. in its 2019 national preferred formulary.

However, the pharmacy benefit manager excluded Teva Pharmaceutical Industries Ltd.'s migraine therapy Ajovy — which works similarly to Eli Lilly's Emgality and Amgen's Aimovig — from its list. According to research firm GlobalData, the exclusion may have something to do with certain manufacturing problems at Celltrion Inc.'s Incheon plant in South Korea which produces an active pharmaceutical ingredient needed for the drug.

All three medicines were approved by the U.S. Food and Drug Administration earlier this year and target a protein in the body called calcitonin gene-related peptide receptor, or CGRP, that is believed to be responsible for causing migraines.

Teva said it was disappointed by the pharmacy benefit manager's decision, which provides insurance coverage to 25 million Americans. The debt-laden Israeli drugmaker also said it was running programs to ensure patient access to Ajovy which is seeing "strong demand" since its launch.

The setback to Teva's so-called CGRP antagonist means Amgen and Eli Lilly's medicines will be vying for the top spot, leaving Ajovy with a more conservative estimate from its previously considered status as a potential blockbuster drug that could reel in at least $1 billion in annual sales, research firm GlobalData said in a report.

GlobalData expects the migraine market to experience a period of significant growth over the next decade thanks to the three medicines plus a fourth CGRP antagonist called eptinezumab that is being developed by Alder Biopharmaceuticals Inc.