The present invention is directed to the intramuscular use of ropivacaine for the manufacture of a medicament for use in the treatment of muskuloskeletal pain, in particular myofascial pain and tendinitis. 
The most common diagnosis in most pain clinics is a disorder of skeletal muscle and connective tissue origin, which may stem from previous trauma, muscle tension or postural abnormalities.  The two dominating muscle pain disorders are the generalized condition fibromyalgia and the mainly localized myofascial pain.  Myofascial pain conditions are characterized by discrete tender loci known as trigger points or tender points.  These points are located by several methods including digital palpation or pressure pain threshold algometer testing and sometimes detection of skin loci with lowest electrical independence.  The pathophysiology of human myofascial pain remains unknown.  However, it has been suggested that myofascial tenderness may be the result of a lowered pressure pain threshold, a stronger response to presuures in the noxious range (Jensen K, Quantification of tenderness by palpation and use of pressure algometers; In: friction Jr, Awad E., Advances in pain Research and Therapy, Vol.  17, Raven press, New York, 199, 1990, pp.  165-181).  The nociceptive processes are also qualitatively altered in patients with chronic myofascial pain indicating that myofascial pain may be mediated by low-threshold mechanosensitive afferents projecting to sensitized dorsal horn neurons (Bendsten L., Jensen R, Oleson J. Qualitatively altered nociception in Chronic Myofascial pain, Pain 1996; 65: pp.  259-264 ). 
A wide range of therapeutic methods have been used over the years in order to cure long lasting myofascial pain.  The mostly used methods have been massage, TENS, acupuncture, heat or cold packs, relaxation, unloading aching structures, traction and manipulation.  Various analgesics, anti-inflammatory drugs and injected corticosteroids have also been used.  The various treatments often give initial relief of pain but the pain often recurs thereby necessitating repeated treatments. 
In a double-blind study of myofascial pain syndrome (MPS), the effect on pain has been compared between bupivacaine (0.25%), lignocaine (1%), and saline (Tschopp K P, Gysin C. Local Injection therapy in 107 patients with myofascial pain syndrome of the head and neck; J. Oto-Rhino-Laryng and Rel.  Spec.  1996; 58: 306-310).  No significant difference between these compounds has, however, been reported. 
Outline of the Invention
The problem underlying the present invention was to find a new way of therapy for muskuloskeletal pain, in particular myofascial pain and tendinitis.  The inventors of the present invention have found that the local anaesthetic ropivacaine is useful for the just mentioned therapy. 
Ropivacaine refers to (S)-(xe2x88x92)-i-propyl-2xe2x80x2,6xe2x80x2-pipecoloxylidide hydrochloride known to be useful for injection.  It is described, including its long lasting local anesthetic effects, in EP 151 110 B1.  In particular ropivacaine can be used in the form of its monohydrate in high enantiomeric purity, disclosed in EP 239 710 B1. 
However, the routes of administration previously disclosed for ropivacaine, are epidural administration, nerve block and peripheral infiltration.  Hitherto ropivacaine has not been disclosed for the therapeutic use in accordance with the present invention. 
The present invention is thus directed to a new use of ropivacaine for the manufacture of a medicament for use in the treatment of muskuloskeletal pain, in particular myofascial pain. 
The medical indication xe2x80x9cmuskuloskeletal painxe2x80x9d is a well established condition, and will be appreciated by a person skilled in the art. 
The medical indication xe2x80x9cmyofascial painxe2x80x9d is defined as a regional pain complaint; pain complaint or alterred sensation in the expected distrubution of referred pain from a myofascial trigger point; taut band palpable in an accessible muscle; exquisite spot tenderness at one point along the length of the taut band; some degree of restricted range of motion, when measurable.  A person skilled in the art will however appreciate the medical pain conditions belonging to this specific pain indication. 
A further specific medical condition which is within the scope of the definition muskuloskeletal pain, is xe2x80x9ctendinitisxe2x80x9d.  A person skilled in the art will appreciate what patients belong to this group, but the following can however be mentioned as characterizing symptoms: regional pain complaint; localized tenderness; increased pain on movement; and limited range of motion. 
xe2x80x9cTrigger pointxe2x80x9d (TP) is a focus of hyperirritability in a muscle or its fascia that causes the patient pain.  It causes referred pain and tenderness at rest, or with motion.  The trigger point is always tender, and is located in a palpable band of muscle fibers.  It prevents full lengthening of the muscle.  It usually weakens the muscle, refers pain on direct compression, and mediates a local twitch response of the palpable band of muscle fibres when mechanically stimulated.  Myofascial TPs can initiate referred autonomic phenomena, which generally appear in the pain reference zone. 
A further aspect of the present invention is a method for the treatment of muskuloskeletal pain, in particular myofascial pain and tendinitis, whereby ropivacaine is administered intramuscularly to a patient suffering from said pain condition. 
The active substance ropivacaine which is used in accordance with the present invention, is administered intramuscularly by injection in muscular xe2x80x9ctender and/or trigger pointsxe2x80x9d.  A xe2x80x9ctender pointxe2x80x9d is defined as a point over a muscle/tendon which is tender and elicits palpabral reflex on digital palpation.  Although the definition of tender points and trigger points differ slightly, the two words are used interchangeably. 
Ropivacaine is administered as a formulation suitable for intramuscular administration and in an amount effective to ameliorate pain. 
Accordingly, 0.1-10 ml ropivacaine is injected intramuscularly, preferably directly into each tender or trigger point.  The concentration of ropivacaine for administration intramuscularly is preferably 1-20 mg/ml, more preferably 2-10 mg/ml.  A concentration as low as 2-5 mg/ml may advantageously be used. 
Biological Evaluation
Ropivacaine hydrochloride 7.5 mg/ml solution for injection was used (Naropin(copyright), Astra AB, Sweden).  Ropivacaine was administered as a single dose intramuscular tender point (TP) injection.  Injection by means of one needle insertion per tender point was preceded by aspiration before infiltrating the study drug over the entire tender area.  A standard disposable syringe with a 0.4 mm diameter needle was used.  Injection rate was about 1 ml/30 sec.  Injections were made at one occassion at a visit to the clinic.  Follow-up data were obtained at a study end visit to the clinic 1 week after the injection. 
(I) Patient Characteristics
Prior to the treatment the following information was recorded. 
Demographic data: Date of birth, gender, race, body weight and height. 
Past and current diagnoses: allergy and information related to significant past or present medical and surgical diagnoses excluding minor self-healing conditions with no obvious importance for the purpose of this study. 
Current medication. 
Active alcohol or drug abuse (yes/no). 
A case history information including the duration of the present orofacial muscle pain was collected.  A clinical examination of the orofacial region including digital palpation of the temporomandibular joints and masticatory muscles. 
10 patients (5 men and 5 women) whose age varied from 19 years up to 69 years (mean 42.9 years of age) were included in this test.  The duration of complaints ranged from 1 month and up to 10 years (mean 26.5 months). 
All patients were subjected to unilateral injections of ropivacaine into tender points of the masseter muscle.  Three patients received 1 ml, 5 patients received 2 ml, 1 patient received 3 ml and 1 patient received 4 ml of the study drug. 
(II) Clinical Measurements
(i) Pain on Maximal Mouth Opening
The patient rated their pain on a 100 mm visual analogue scale (VAS).  On the VAS, 0 represents xe2x80x9cno painxe2x80x9d and 100 represents xe2x80x9cworst pain imaginablexe2x80x9d.  The primary efficacy variable was VAS pain score at maximal mouth opening.  The patient was asked to open the mouth as much as possible and then they rated the experienced pain. 
(ii) Pain at Rest
The non-functional pain (aw at rest) was also assessed by the patient on the VAS scale.  This parameter was rated before the rating of pain on maximal mouth opening. 
(iii) Tender Muscular Points
A tender point was defined as point over a muscle/tendon which was tender and elicited a palpabral reflex on digital palpation.  Bilateral digital palpation of the temporalis muscle, the masseter muscle, the lateral pterygoid muscle and the temporalis tendon was used for the registration of tender points.  The number and site of injected tender points and the total amount of the study drug used were recorded.  The assessment of tender muscle points was made prior to the assessment of range of movement. 
(iv) Range of Movement
The distance between the edges of the right upper and the corresponding lower medial incisor was used for the measurements of maximum mouth opening.  Both maximum opening with and without pain was registered. 
Results
The primary efficacy parameter, VAS rated pain at maximal mouth opening, showed a dramatic reduction as a result of the treatment.  The median VAS value at baseline was 59.5 mm compared to 6 mm at the follow-up.  The data is shown in Table 1 below.