Fibromyalgia (FM) is a chronic rheumatic disease of high prevalence and great clinical impact. However, the treatment for FM has limited efficacy, with an effect size of about 0.5. Recent studies have found raised levels of glutamate in the insula, hippocampus and posterior cingulate cortex regions of the brain. This has led a number of authors to suggest the usefulness of glutamate blocking drugs in the treatment of FM.

Aims: To evaluate the efficacy of memantine in the treatment of pain and other symptoms of FM and to assess its efficacy in reducing brain glutamate levels in patients with FM. Material and methods: Randomized controlled trial, of six months duration (including a dose adjustment period of one month). 60 patients with FM will be recruited for inclusion in the study upon fulfillment of selection criteria, and they will be randomized in two groups: A) Treatment group (n=30), will receive 20 mg of memantine o.d ; B) Control group (n=30) will receive placebo. The main objective is to assess the efficacy of memantine in the treatment of pain (pain threshold, pain perception) and other symptoms in fibromyalgia (cognitive state, health status, state of anxiety and depression, quality of life and perceived improvement. Discussion: There is a need for the development of innovative and more effective alternatives for the treatment of FM. This clinical trial will determine whether memantine can be considered as an option in the treatment of FM patients.

Inclusion Criteria:

1. Male or female aged between 18 and 65 years.
2. Ability to understand Spanish.
3. Diagnosis of fibromyalgia carried out by a rheumatologist according to the American College of rheumatology criteria (ACR1990).
4. Ability to read and understand the Patient Information Sheet
5. Signature of Informed Consent Form.

6 .In the case of women of childbearing age, commitment not to become pregnant during the entire duration of the study.

Exclusion Criteria:

1. Undergoing drug treatment for fibromyalgia. Patients undergoing treatment for fibromyalgia will stop treatment and perform a washout period of one week. During that week the patient may take, if necessary, analgesic such as paracetamol, ibuprofen and other NSAIDS to minimize the influence of medication on brain imaging.

2. Currently taking memantine or having taken memantine during the 2 months prior to recruitment.

3. Another Axis I psychiatric disorder using SCID-I that might hinder adherence to the protocol (e.g.: dementia, alcohol and/or substance abuse/dependence, schizophrenia, chronic delirium, acute depression).

4. Pregnancy or breast-feeding.

5. Hypersensitivity to the active ingredient, memantine, or to the excipients.

6. Medical conditions that require special precautions when administering memantine according to the summary of product characteristics:

   • Epilepsy.
   • Circumstances that may cause high urine pH owing to Proteus urinary infection, renal tubular acidosis or vegetarian diet, recent myocardial infarction, congestive heart disease and uncontrolled arterial hypertension.

7. Clinically significant and active evidence of liver or kidney disease, haematological, respiratory, endocrine or cardiovascular disease or disorders (patients with controlled diabetes and patients with controlled hypertension and complete or incomplete right bundle branch block can be included in the study).

8. Use of prescription drugs that may cause relevant drug interactions with memantine according to the summary of product characteristics: NMDAR antagonists (amantadine, ketamine, dextromethorphan), L-Dopa, dopamine agonists and cholinergic agonists.

9. Use of non-permitted concomitant medication during the week prior to the first evaluation visit or when the patient is expected to require treatment (with at least one of the drugs not permitted during the study): antidepressants (duloxetine, venlafaxine, mirtazapine, bupropion, SSRI, etc.), analgesics (pregabalin, gabapentin, opiates, etc.)