The present invention relates to crystalline R-guanidines of (2S)-2-Ethoxy-3-{4-[2-(10H-phenoxazin-10-yl)ethoxy]phenyl}propanoate, its preparations and its use as therapeutic agents. More specifically the present invention relates to crystalline Arginine (2S)-2-Ethoxy-3-{4-[2-(10H-phenoxazin-10-yl)ethoxy]phenyl}propanoate, preferably (L)-Arginine (2S)-2-Ethoxy-3-{4-[2-(10H-phenoxazin-10-yl)ethoxy]phenyl}propanoate, its preparation and its use as therapeutic agent.