Comparison of the Efficacy of Duloxetine With Placebo in Patients With Chronic Low Back Pain With a Radicular Component

Objective:

The objective of this study is to compare the efficacy of duloxetine in the treatment of patients with chronic low back pain with a radicular component to placebo.

Study hypothesis:

Duloxetine is a new substance now in use for the treatment of neuropathic pain. It has proven its efficacy in diabetic peripheral neuropathy and fibromyalgia in several trials. The investigators therefore hypothesize that duloxetine will be efficacious in patients with chronic low back pain and a radicular component.

Study Rationale:

Chronic low back pain is an extremely common diagnosis. However, therapeutic options for the condition are limited and therapy remains difficult. Duloxetine has proven its efficacy in patients with neuropathic pain and may also be useful in chronic low back pain. If the investigators are able to show a benefit for patients in the duloxetine arm, the substance may constitute a further treatment alternative in chronic low back pain.

Study Design:

Prospective, randomized, double-blind placebo-controlled cross over study. Patients will be administered duloxetine for 4 weeks followed by a 2 week wash-out phase after which they will be medicated with placebo for 4 weeks. A second group of patients will receive the medication in reversed order. The primary study endpoint is constituted the weekly mean of VAS-Score in the last week of each treatment period. Secondary endpoints are defined as use of rescue medication, Beck Depression Inventory score, Health related Quality of Life SF-36 score and side effects/adverse events.


Eligibility Criteria:
Inclusion Criteria:

* Low back pain ( below L1)
* Chronic pain, \>6 months
* Visual Analogue Scale (VAS) ≥ 5
* Back pain with radicular component defined as pain with a burning, tingling sensation within the anatomic distribution of the nerve root and diagnosed by painDETECT questionnaire
* Failed back surgery

Exclusion Criteria:

* Current mood disorder (dysthymia, bipolar mood disorder)
* Major Depression \> 12 months (Beck Depression Inventory Score ≥ 18)
* History of a psychoactive substance use disorder within the preceding 12 months
* Major coexisting medical illness (e.g. severe heart failure, pulmonary hypertension, renal insufficiency)
* Glaucoma
* Acute myocardial infarction
* uncontrolled hypertension
* Prostate hyperplasia
* History of convulsion
* Pregnancy; women of childbearing age will be required to use contraceptives during the duration of the study. Furthermore a pregnancy test will be performed prior to the beginning of the study and once a month during the study period.
* Participation in a clinical trial in the 3 weeks preceding the study
* Allergy to study medication
* Use of the following medication:

  * opioids except for tramadol,
  * benzodiazepines other than indicated at low doses for sleep disorders
  * antineuropathic medication including except for that specified in the study protocol
  * muscle relaxants
  * antidepressants other than indicated at low doses for sleep disorders
  * NSAID, Paracetamol
  * non-selective MAO-Inhibitors
  * Fluvoxamine, Ciprofloxacin, Enoxacin
  * Selective Serotonin-reuptake Inhibitors (SSRI)

if tapering of these drugs is impossible before inclusion.

* Impaired kidney function (Creatinine \> 1.5mg/dl)
* Impaired hepatic function (GOT, GPT \>2 fold standard levels)
* Patients who are not able to understand the study measures and are not able to complete pain assessment forms.