Duloxetine is a drug used to treat depression and incontinence and it can be also be useful in treating certain types of pain. Pain can be produced spontaneously from damaged parts of the nervous system used to transmit pain information to the brain (neuropathic pain). When this damage is to nerves outside the spinal cord it is called a neuropathy. Pain is also produced when the nerves sense damage to another tissue (for example a pin being pressed into the skin) and this is called nociceptive pain. Some pain is of unclear origin, as no damage to the nervous system or to the tissues to which the nerves connect can be identified. This sort of pain happens, for example, in fibromyalgia. Duloxetine is also used to treat depression and problems with bladder function but the objective of this review was to consider all the evidence from double-blind randomised controlled trials relating to the use of duloxetine to treat painful neuropathy and chronic pains of all sorts.
We looked at all the published scientific literature and identified six drug trials involving a total of 2220 participants that were of sufficient quality and reliability to include. Three tested the effect of duloxetine on painful diabetic neuropathy and three on the pain of fibromyalgia.
The usual dose of duloxetine is 60 mg. At this dose, there was moderately strong evidence that duloxetine reduced pain in both painful diabetic peripheral neuropathy and fibromyalgia. In diabetic peripheral neuropathic pain the relative rate of 50% improvement with duloxetine 60 mg per day was just over one and a half times more than with placebo. This equates to needing to treat 6 people with diabetic peripheral neuropathic pain with duloxetine to achieve a 50% response in one person. The effect on fibromyalgia was similar. A dose of 20 mg was not effective and a higher dose of 120 mg was no more effective than 60 mg.
Most people taking duloxetine will have at least one side effect. These are mostly minor and are commonly feeling sick, being too awake or too sleepy, developing a headache, having a dry mouth or becoming constipated or dizzy. About one in six people stop duloxetine because of side effects but serious problems caused by duloxetine are very rare.
Duloxetine may be about as good at reducing these sorts of pain as some of the other antidepressant drugs on the market but the evidence supporting this comparison is not strong.
We have concluded that duloxetine is useful for treating pain caused by fibromyalgia and diabetic neuropathy and it seems to be about as effective as other similar drugs already on the market. No direct comparison has been performed between duloxetine and any of these other drugs. As yet it is not clear whether the use of duloxetine is cost effective when compared to the other drugs already in use.