Long acting, synthetic opioid analgesic. Prepn: P. A. J. Janssen, G. H. P. Van Daele, DE 2610228; eidem, US 3998834 (both 1976 to Janssen). Receptor affinity and pharmacological potency: K. D. Stahl et al., Eur. J. Pharmacol. 46, 199 (1977). Structural study: C. De Ranter et al., Arch. Int. Physiol. Biochim. 87, 1031 (1979). Antinociceptive effects in cats: A. S. Tung, T. L. Yaksh, Pain 12, 343 (1982). Opiate receptor binding studies of 3H-lofentanil: W. Gommeren, J. E. Leysen, Arch. Int. Pharmacodyn. Ther. 258, 171 (1982); B. Ilien et al., ibid. 313; P. M. Laduron, P. Janssen, Life Sci. 31, 457 (1982).