federal officials and major drugmakers are scrambling to prevent national shortages of critical drugs for treating cancer, diabetes and heart disease, as well as medical devices and supplies, that are manufactured at 80 plants in hurricane-ravaged Puerto Rico.Pharmaceuticals and medical devices are the island’s leading exports, and Puerto Rico has become one of the world’s biggest centers for pharmaceutical manufacturing. Its factories make 13 of the world’s top-selling brand-name drugs, from Humira, the rheumatoid arthritis treatment, to Xarelto, a blood thinner used to prevent stroke, according to a report released last year.With business of nearly $15 billion a year at stake in Puerto Rico, drug companies and device makers are confronting a range of obstacles on the island: locating enough diesel fuel for generators to run their factories; helping their employees get to work from areas where roads are damaged and blocked, electricity is down and phones don’t work. Companies have taken out radio ads pleading with workers to check in. The pharmaceutical and device industries contribute to the employment of nearly 100,000 people on the island, according to trade groups.