Adverse drug reactions & debrisoquine/sparteine (P450IID6) polymorphism in patients with fibromyalgia (FM)

OBJECTIVE: To assess the frequency of adverse drug reaction in
patients with fibromyalgia in relation to medications
prescribed for this condition. To evaluate the potential role
of the P450IID6 phenotype in the pathogenesis of these adverse
drug reactions.

METHODS: Thirty-five patients with
fibromyalgia were assessed using a structured questionnaire
with demographic and clinical data and perceived adverse drug
reactions. A sample of 60 patients with rheumatoid arthritis
and 62 patients with localized back pain served as controls.
The P450IID6 phenotype was determined for each of the
fibromyalgia patients.

RESULTS: Overall, 141 patients had used
NSAID and 79 (56%) of them reported adverse effects.
Antidepressant drugs were used by 68 patients and 35 (51%)
patients had adverse effects. Muscle relaxant drugs were used
by 48 patients and 15 (31%) of them reported side effects.
Analgesics were used by 122 patients and 22 (18%) had
experienced adverse effects. Statistical differences in the
frequency of adverse effects were found with antidepressant
drugs in the fibromyalgia group, compared with rheumatoid
arthritis (p=0.01) and back pain (p=0.02). Four of the 35
patients (11.4%) had a metabolic ratio (M.R.) greater than
0.30 (log M.R.= -0.52) indicative of the poor metabolizers
(PM) phenotype. M.R. varied from 0.005 (log M.R. = -2.30) to
4.99 (log M.R. = 0.70).

CONCLUSIONS: The problem of adverse
drug reactions in fibromyalgia patients does not appear to
correlate with the PM phenotype of the P450IID6 oxidative
enzyme. It also is unlikely that altered xenobiotic
detoxification attributable to this PM phenotype would have a
significant role in the development of fibromyalgia.

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