1. Friderichs E., Felgenhauer E., Jonschaap F., Osterloh G. (1978): Arznneim-Forsch 28, 122–134.
2. Osterloh G., Friderichs E., Fegenhauer E., Gumzier W.A., Henmii Z., Kitano T., Nakamura H., Ishii T. (1978): General Pharmacological studies on tramadol, a powerful analgesic agent, Arzneim.-Forsch, 28, 135–151.
3. Lagler F., Helm F., Etzel V., Kiel H. (1978): Toxicological investigation with tramadol, a new analgesic. Arzneim.-Forsch 28. 164–172.
4. Erlacin S., Frankus E., Lintz W. (1980): Metabolism of tramadol in man and animals, Naunyn-Schmiedeberg’s Arch. Pharmacol. 313 Suuppl. R 202.
5. Paxton J.W. (1981): Elementary pharmacokinetics in clinical practice 4. Genetic environmental and age influences on pharmacokinetics. The new Zealand Med. J., 697, 423–425.