title: Photostability studies on (±)-tramadol in a liquid formulation.
abstract: BACKGROUND
  Tramadol ((±)-TRA) is recommended for the treatment of mild to moderate cancer pain by the World Health Organization. An oral liquid formulation of (±)-TRA is preferable for patients with a compromised swallowing function. However, the stability of (±)-TRA in aqueous solution has yet to be determined in a clinical setting. The aim of this study was to evaluate the photostability of (±)-TRA in aqueous solution in a clinical setting.
  
  
  METHODS
  We improved high performance liquid chromatography (HPLC) method for the enantiomeric separation of (±)-TRA, and then the (±)-TRA concentration was determined using HPLC method. We investigated the photodegradation of (±)-TRA in an aqueous solution irradiated with ultraviolet (UV) light: UV-A, UV-B, and UV-C. We also evaluated the stability of liquid formulations of (±)-TRA in a clinical setting by keeping (±)-TRA aqueous solution in normal dispensing bottles and in light-shading dispensing bottles under conditions of both sunlight and diffused light in a room. Samples were collected sequentially over time.
  
  
  RESULTS
  (±)-TRA in aqueous solution was degraded the most rapidly when irradiated with UV-C, but was not affected by irradiation with UV-A. No significant difference was observed in the photodegradation behavior of (+)-TRA and (-)-TRA with UV-A, UV-B, and UV-C irradiation. The residual percentages of (±)-TRA were 94.6-104.3% after 14 days in the presence of either sunlight or diffused light in a room, with or without protection from light.
  
  
  CONCLUSIONS
  These results demonstrated the stability of (±)-TRA in aqueous solution to both sunlight and diffused light in a room. Therefore, liquid formulations of TRA are preserved at room temperature for up to 2 weeks, with or without protection from light. Our results provide additional treatment options with tramadol for pain control.
authors.affiliation: Department of Oncology Pharmaceutical Care & Sciences, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, 2-5-1, Shikata-cho, Kita-ku, Okayama, 700-8558 Japan.
authors.forename: Manabu
authors.initials: M
authors.lastname: Suno
authors.affiliation: Department of Oncology Pharmaceutical Care & Sciences, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, 2-5-1, Shikata-cho, Kita-ku, Okayama, 700-8558 Japan.
authors.forename: Hidenori
authors.initials: H
authors.lastname: Ichihara
authors.affiliation: Department of Oncology Pharmaceutical Care & Sciences, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, 2-5-1, Shikata-cho, Kita-ku, Okayama, 700-8558 Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Ishino
authors.affiliation: Department of Oncology Pharmaceutical Care & Sciences, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, 2-5-1, Shikata-cho, Kita-ku, Okayama, 700-8558 Japan.
authors.forename: Kento
authors.initials: K
authors.lastname: Yamamoto
authors.affiliation: Department of Oncology Pharmaceutical Care & Sciences, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, 2-5-1, Shikata-cho, Kita-ku, Okayama, 700-8558 Japan.
authors.forename: Yuta
authors.initials: Y
authors.lastname: Yoshizaki
keywords: Liquid formulation; Photodegradation; Photostability; Tramadol
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