[Fluoxetine versus fluvoxamine for treatment of chronic pain]

This study aimed: 1) to compare the analgesic efficacy and profile of two antidepressants with the same mechanism of action (SSRI: selective serotonine reuptake inhibitors): fluoxetine vs fluvoxamine; 2) to investigate the relationship between analgesic efficacy and antidepressant effects in both drugs; 3) to evaluate the relationship between the analgesic profile and the quality (global or neuropathic) of pain.

Fifty-three depressed patients were randomly treated with 20 mg/die of fluoxetine and 100 mg/die of fluvoxamine for chronic pain. Forty subjects (20 with fluoxetine and 20 with fluvoxamine) completed the 2-month study and were followed up on day 14, 28 and 56 of treatment. The intensity and quality of pain was assessed using Quid and depression-anxiety symptoms with the Hamilton Rating Scale (HAMD).

The intensity and overall quality of pain deteriorated at day 14 in the fluvoxamine group and improved in those treated with fluoxetine. However, a comparable level of analgesia was achieved with both drugs at 2 months. After 2 weeks the neuropathic component of pain improved in patients treated with fluvoxamine. The improvement in pain observed in patients treated with fluoxetine depended on an improvement in depressive symptoms, whereas this relationship was not observed in the fluvoxamine group.

Although a comparable level of analgesia was observed after two months of treatment, the two drugs show different analgesic profiles. Their analgesic action appears to depend on different mechanisms.