A eutectic mixture of prilocaine/lidocaine spray (Fortacin™, Recordati, Milan, Italy) has been approved for the management of patients affected by life-long premature ejaculation (PE), but to date, there is a lack of dose- or time-finding studies in the literature that indicate the best method of intake to optimize treatment outcomes. In this multicentre, randomized, two-phase study, we aimed to compare, in terms of treatment effectiveness (primary objective) and safety (secondary objective), different treatment regimens (various doses and times of drug delivery) of Fortacin™ in 91 patients affected with lifelong PE who were recruited at four different centres and randomized (1:1:1 ratio) into three different groups. The study included two phases: during the first phase (focused on time-finding), the same drug dose (three sprays) was taken at different intervals before intercourse (5, 15, 30 min). In the second phase (focused on dose finding), different drug doses (1, 3, 5 sprays) were taken at the same interval before intercourse (5 min). The main outcome measure instruments were self-measured intravaginal ejaculation latency time (sm-IELT), the premature ejaculation diagnostic tool (PEDT), and the International Index of Erectile Function-5 (IIEF-5). Furthermore, patients were asked to report any side effects that appeared during the study period. Our main study findings showed that the treatment regimen with three sprays of Fortacin™ administered 5 min before sexual intercourse showed the best results in terms of ejaculation time and control (Phase I, IELT 221 ± 3.4, PEDT 7.7 ± 0.3; Phase II, IELT 213 ± 4.9, PEDT 7.8 ± 0.4) with a safety profile that was identical to other treatment regimens. Based on these data, patients who are prescribed Fortacin™ should stick to this regimen to optimize treatment results.