Lamisil Once (terbinafine film-forming solution) is an over-the-counter antifungal medication. It's sold only in certain countries, such as Britain and Australia. You apply it once. It starts working right away. Then you wait a few weeks for it to finish working.
The maker, Novartis, advertises it as a treatment for athlete's foot. But the company writes that it "is only recommended for the treatment of athlete's foot (tinea between the toes)". For jock itch (tinea cruris) or ringworm (tinea corporis / tinea capitis / tinea manuum), Novartis recommends that you choose a different product (such as ordinary Lamisil cream) instead.
Why does Novartis recommend that sufferers of jock itch and ringworm choose a less-convenient product?