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An SR on drugs to treat diabetic neuropathic pain searched for studies where
they were compared with placebo as well as comparative studies (the search was
carried out up to December 2004), and only five comparative RCTs were found
(228). These studies had a reduced number of patients and they lasted between
two and six weeks, therefore any possible conclusion is quite limited in terms of
validity. The drugs compared were tricyclic antidepressants in contrast to gabapentin,
carbamazepine and SSRI antidepressants. No differences were found as
regards pain intensity nor in the percentage of patients who gave up the treatment
due to adverse effects, with the exception of a study which compared paroxetine
with imipramine (plus discontinuance with imipramine).
Another three further comparative RCTs have been found. A trial done in
India compared amitriptyline with lamotrigin on a cross-over study which lasted
two weeks (234). No differences were found as regards effectiveness; the adverse
effects were more frequent and predictable with amitriptyline (somnolence, anticholinergic
effects), while lamotrigin created an increase in the serum creatinine
which lead to four patients interrupting the treatment.
An extension study (235) compared duloxetine 60 mg to the common treatment
(mainly gabapentin, amitriptyline and venlafaxine) for 52 weeks, after a
double blind period of 13 weeks. No differences in effectiveness or quality of life
were observed; duloxetine was well tolerated.
An RCT (236) compared the combination of morphine with gabapentin to
each of the drugs. Pain relief was higher with the association of drugs; the most
frequent adverse effects of the combination were constipation, sedation and dry
mouth.
Appendix 7 includes the dosage and most frequent adverse effects of common
drugs for neuropathic pain (237).
SR of RCT
1+
RCT
1+
RCT
1-
RCT
1+
Summary of evidence
1++ In painful diabetic neuropathy, tricyclic antidepressants (amitriptyline, desimipramin,
imipramine) and traditional anticonvulsants (carbamazepine, lamotrigin, sodium valproic
acid) have proved to be more effective in contrast to placebo than SSRI antidepressants
(citalopram) or duloxetine and that new anticonvulsants (oxcarbazepine, gabapentin,
pregabalin), with a moderate risk of interrupting the treatment due to adverse effects.
Opioids (oxycodone, tramadol) have proved to be moderately effective, although their
adverse effects profile can limit their use in the long-term. Capsaicin proved to be effective
in a study (229).
1+ There are few comparative trials between the different drugs and moreover, they contain
methodological flaws (low statistical power, short duration, cross-over design). In the
comparisons carried out (tricyclic antidepressants vs. gabapentin, carbamazepine, SSRI
(228) and lamotrigin (234) or duloxetine in contrast to the common treatment (235)) no
differences were observed as regards effectiveness, and, in general, the adverse effects
of tricyclic antidepressants were frequent and predictable.
1+ There is limited evidence that the treatment of combined drugs with different action
mechanisms can improve its response though it also increases adverse effects (236).
94 CLINICAL PRACTICE GUIDELINES IN THE NHS