L Carnitine MCCM Medical Cosmetics Injectable L Carnitine How It Works & What to Expect? L Carnitine injection is recommended at 1 ampule every 2 3 days for best results. The L Carnitine is taken intravenously either by normal injection or using a butterfly needle. After taking this L Carnitine, you American Regent Introduces Levocarnitine Injection, USP; FDA Approved, "AP" Rated, and Therapeutically Equivalent to Carnitor