By Manas Mishra and Michael Erman (Reuters) – Pfizer Inc said on Tuesday it will pay $11.6 billion to buy Biohaven Pharmaceutical Holding Co, making a big bet on its ability to boost sales of the top-selling pill in a new class of migraine drugs. The boards of both companies have approved the deal, they said. Biohaven shares jumped 70% to $141.31, while Pfizer was up slightly at $48.83. Pfizer is flush with cash from a once-in-a-lifetime surge in revenue from COVID-19 vaccines and therapeutics and has said it is looking to buy companies or drugs that could add at least $25 billion in annual sa…