The spelling of "tenifuge" may seem confusing at first glance. However, it is derived from the Latin word "tenia" which means tapeworm, and "fugare" which means to repel or drive away. The pronunciation is /ˈtɛnɪfjuːdʒ/, with the stress on the first syllable. The "fuge" ending is also used in words like "insectifuge" which means insect repellent. Therefore, the spelling of "tenifuge" is logical once you understand its etymology and the use of the "fuge" ending.
Teniafuge.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.