Multicenter, randomized, double-blind, placebo-controlled study to evaluate the efficacy and safety of XC243 in patients with exacerbation of chronic cystitis. It is planned to include patients with chronic cystitis in 4 parallel groups, who will receive XC243 at a dose of 25 mg per day, 50 mg per day, 75 mg per day or placebo for 7-10 days. Efficacy will be assessed by time from first study treatment to resolution of the symptom "Pain, discomfort or burning when urination " assessed on a visual-analog scale (VAS).

The study will be conducted in 8 centers. The study will include the following periods: screening (1 day), treatment period (up to 10 days), follow-up period (7 days).

Upon completion of screening, patients will be randomized to 4 groups in the ratio 1:1:1:1: XC243 at a dose of 25 mg per day, 50 mg per day, 75 mg per day or placebo group.

Also, all patients will be prescribed furasidin daily at the same time, 2 capsules (total dose 100 mg) 3 times a day after meals. On day 8 the investigator will assess the symptoms of cystitis and decide whether to discontinue or prolong a course of therapy with XC243 and furasidin for up to 10 days.

Inclusion Criteria:

1. Availability of the Form signed and dated by the patient the Patient Information Leaflet informed consent (IMP).
2. Women aged 18 to 65 years inclusive at the time of signing the Informed IMP consent.
3. Established diagnosis of chronic bacterial cystitis (at least three relapses chronic cystitis within 12 months prior to screening or two cases within 6 months prior to screening, including relapse at study entry).
4. The presence of symptoms characteristic of exacerbation of chronic cystitis: pain syndrome (pain in lower abdomen, when urinating), dysuric symptoms (increased urination, pain or burning when urinating, urgency to urinate, feeling of incomplete emptying bladder).
5. The appearance of symptoms of exacerbation of chronic cystitis is not > 48 hours prior to screening visit.
6. Severity of the symptom "Pain, discomfort or burning with urination "from 4 to 8 VAS points.
7. No therapy for current cystitis exacerbation (including phosphomycin and/or furasidin for the treatment of current exacerbation).
8. The patient's consent to refrain from drinking alcoholic beverages during the period of participation in study.
9. Patient consent to use reliable methods contraception throughout the study and through 3 weeks after its end.

Exclusion Criteria:

1. Hypersensitivity to the active and/or any of excipients of the test drug.
2. Hypersensitivity to furasidine and/or any of the excipients concomitant medication.
3. Chronic recurrent cystitis due to infections, sexually transmitted diseases (STIs): gonorrhea, chlamydia, ureaplasmosis, mycoplasmosis, herpes, candidiasis, gardnerellosis, history of trichomoniasis.
4. Chronic recurrent cystitis of viral etiology (caused by adenovirus, cytomegalovirus, virus human papillomavirus herpes).
5. Axillary body temperature ≥ 38 ° C at the screening visit.
6. Presence of menstruation at randomization or estimated onset of menstruation during the period therapy.
7. Pain in the lumbar region.
8. Itching and abundant vaginal discharge and/or purulent discharge from the genitourinary tract.
9. History and/or findings of genitourinary anatomical disorders ultrasound examination (hydronephrosis, sclerosis of the bladder neck, cystocele, descent uterus, paraurethral cyst).
10. Presence of inflammatory diseases of the sexual system (vaginitis, colpitis, cervicitis).
11. Kidney and urinary tract diseases (including urolithiasis), with the exception of chronic cystitis, with a history that, in the opinion of study doctor, may affect the course and results of the clinical study.
12. Chronic renal failure.
13. Type 1 diabetes mellitus or uncontrolled type 2 diabetes mellitus.
14. History of pseudomembranous colitis.
15. Signs of macrohematuria (admixture of blood in the urine, discoloration of the urine).
16. Previous urinary tract surgery or radiation therapy.
17. History of malignancy, per excluding patients who have not had disease within the last 5 years, patients with completely cured basal cell carcinoma or completely cured carcinoma in situ.
18. Patients with HIV, syphilis, hepatitis B and C diseases, including a history.
19. Liver disease that the study doctor believes may affect course and outcomes clinical trial, history of hepatic failure.
20. Severe, decompensated or unstable somatic diseases (any diseases or conditions that threaten the patient's life or worsen the patient's prognosis, and also make it impossible to conduct clinical trial with this patient).
21. Use of analgesic drugs activity, including systemic NSAIDs, as well as antispasmodic drugs less than 24 hours before taking study drug/placebo.
22. No history of efficacy of furasidine and/or no data furasidin sensitivity based on a history of urine microbiology.
23. The need for the use of drugs from the list of prohibited therapy.
24. Use of systemic antibacterial drugs actions within 7 days prior to screening.
25. Administration of other medicinal products which, in the opinion of the study doctor, may affect progress and results clinical trial.
26. Participation in another clinical trial within 3 months prior to screening.
27. Pregnancy or breastfeeding.
28. Alcohol or drug dependence, history of mental illness.
29. Patient unwillingness or inability to comply with procedures protocol (in the opinion of the study physician).
30. Other conditions that prevent the patient from being included in the study.

Blinding was carried out by using placebo equivalent to XC243 tablets without active pharmaceutical ingredients (API) and the corresponding labeling of the ID.