The purpose of this study was to assess the effect of cyclobenzaprine hydrochloride (HCl) extended release (CER) 15 mg capsule once daily in participants with muscle spasms associated with acute painful musculoskeletal conditions.

The drug being tested in this study was cyclobenzaprine hydrochloride (HCl) extended-release (CER). CER was being tested to treat participants who had muscle spasms associated with acute painful musculoskeletal conditions. This study looked at medication helpfulness, relief from muscle spasms and pain, and improvement in range of motion and daily living activities.

The study enrolled 180 participants. Participants were randomly assigned (by chance, like flipping a coin) to one of the two treatment groups which remained undisclosed to the participant and study doctor during the study:

• CER 15 mg
• Placebo (dummy inactive pill) - this was a capsule that looks like the study drug but had no active ingredient

All participants were asked to take one capsule at the same time each day throughout the study.

This multi-center trial was conducted in the Russian Federation. The overall time to participate in this study was up to 45 days. Participants made multiple visits to the clinic, and were contacted by telephone after the last dose of study drug for a follow-up assessment.

Inclusion Criteria:

1. In the opinion of the investigator, the participant is capable of understanding and complying with protocol requirements.
2. Signs and dates a written, informed consent form and any required privacy authorization prior to the initiation of any study procedures.
3. Is experiencing for no more than 14 days cervical or lower back pain (as assessed by the participant) due to muscle spasms (confirmed by the physician) associated with acute, painful musculoskeletal conditions.
4. Is male or female and aged 18 to 50 years, inclusive.
5. Female participants require to be either 2 years postmenopausal or surgically sterile by bilateral tubal ligation, hysterectomy, or bilateral oophorectomy, or, if premenopausal, had to be using an approved contraceptive method.
6. Female participants of child-bearing potential must have a negative urine human chorionic gonadotropin (hCG) test result for pregnancy at study entry.
7. After signing the informed consent form, the participant agrees not to make changes to dietary, exercise, or smoking habits and not to enter a weight loss program during his/her participation in the study.

Exclusion Criteria:

1. Has muscular pain secondary to acute trauma or fractures (e.g., due to osteoporosis). Such conditions could have been ruled out based on medical history, x-ray, or physical examination.

2. Has received any investigational compound within 30 days prior to Screening.

3. If female, the participant is pregnant or lactating or intending to become pregnant before, during, or within 1 month after participating in this study; or intending to donate ova during such time period.

4. Has a history of drug abuse or recent (within the last 12 months) history of excessive alcohol consumption defined as >2 drinks/day (>90 ml of 80 proof alcohol or equivalent).

5. Has mild, moderate, severe liver impairment.

6. Is an immediate family member, study site employee, or is in a dependent relationship with a study site employee who is involved in conduct of this study (eg, spouse, parent, child, sibling) or may consent under duress.

7. Takes any concomitant medication including over-the-counter and herbal products for muscle spasms. If a participant is taking such medications, the medications has to be discontinued before starting the study.

8. Takes or took within last 14 days medications, such as:

   1. selective serotonin reuptake inhibitors (SSRIs);
   2. serotonin norepinephrine reuptake inhibitors (SNRIs);
   3. tricyclic antidepressants (TCAs);
   4. monoamine oxidase (MAO) inhibitors;
   5. tramadol;
   6. bupropion;
   7. meperidine;
   8. verapamil;
   9. non-steroid anti-inflammatory drugs (NSAIDs);
   10. topical anti-inflammatory medications

9. Has a history or clinical manifestations of significant medical condition, such as:

   1. hyperthyroidism;
   2. acute recovery phase of myocardial infarction;
   3. arrhythmias, heart block or conduction disturbances;
   4. congestive heart failure;
   5. angle-closure glaucoma;
   6. urinary retention;
   7. increased intraocular pressure.

10. Has abnormal physical findings or a medical condition that might have placed the participant at risk or interfered with the participant's ability to participate in the study.

11. Has any known condition or disorder that might have affected absorption of the study drug.

12. Has a history of hypersensitivity or allergies to cyclobenzaprine and/or tricyclic antidepressants or any of their components.

13. Has a history of hypersensitivity to any NSAIDs including salicylate sensitivity.

14. Has a history of thrombocytopenia.

15. Has a history of gastro-intestinal bleeding, cerebrovascular bleeding or other bleeding disorders.

16. Had active or history of recurrent peptic ulcer/haemorrhage (two or more distinct episodes of proven ulceration or bleeding)

17. Has a history of severe renal impairment

18. Had a major surgery during the 6 months preceding study entry.

19. Has a language barrier or any other problems precluding good communication or cooperation.

20. Has any reason to believe that he/she would not be able to complete the evaluations needed in this study.

21. Has a known history of positive screen for hepatitis B surface antigen, hepatitis C antibody, or human immunodeficiency virus (HIV) antibody.

22. Drug abuse in anamnesis.