PKB171 Against Placebo in Couples With Mild Male Factor Infertility

Inclusion Criteria: * Subjects eligible for inclusion in this study must meet all the following criteria: 1. Written informed consent form signed before any study test or procedure. 2. Unable to conceive for more than 6 months and less than 24 months, despite regular and adequate unprotected sexual intercourse. 3. Willing and able to comply with the protocol. 4. Female subjects with the following criteria: * Age ≥ 18 and ≤ 38 years. * Regular spontaneous menstrual cycles with a 25- to 35-day length (intercycle variation less than 5 days) within the last six cycles before the first visit. * Normal uterine cavity shown on transvaginal sonography. * Normal ovarian reserve, demonstrated by AMH ≥ 1 ng/ml at day 2-5 of the cycle. * Antral follicle count (sum of both ovaries) ≥ 6 5. Male subjects with the following criteria: * Age ≥ 18 and ≤ 50 years. * Spermiogram with semen volume ≥ 1mL, concentration \> 11 M/mL, \< 42% total mobility and normal forms ≥ 2% Exclusion Criteria: Subjects eligible for this study, both women and men, must not meet any of the following criteria: 1. Body mass Index (BMI) \< 18 and ≥ 32 kg/m². 2. Any sexual intercourse with another partner (other than corresponding trial subject) within 12 weeks entry in the study and during it. 3. Couples who had any previous assisted reproductive technology (ART) cycle (in vitro fertilization, IVF, or intracytoplasmic sperm injection, ICSI) before inclusion into the trial. 4. Active hepatitis B, C, HIV, genital herpes, Chlamydia, Gonorrhea or Syphilis infection. 5. History of malignant disease (cancer). Previous or planned chemotherapy or radiotherapy. 6. History of cerebral or retinal hemorrhage, acute myocardial infarction. 7. In females: Prohibited concomitant intravaginal products or procedures. 8. Hypersensitivity or intolerance to pentoxifylline, xanthine derivatives or any of the excipients of the IMP. 9. Employees of the investigator or trial center, with direct involvement in the proposed trial or other studies under the direction of that investigator or trial center, as well as family members of the employees or the principal investigator. 10. People committed to an institution by virtue of an order issued either by the judicial or other authorities. 11. Reasonable expectation that the subject will not be able to satisfactorily complete the study: * History of current psychiatric illness that would interfere with the subject's ability to comply with protocol requirements or give informed consent. * History of alcohol or drug abuse that would interfere with the subject's ability to comply with protocol requirements. * Receipt of any investigational drug within three months of screening visit. * Previous enrolment in this trial. * Documented noncompliance. * Any other condition of the subject that in the opinion of the investigator may compromise evaluation of the trial treatment or may jeopardize subject's safety or compliance to protocol requirements. 12. Patients with peptic ulcers or recent history thereof. 13. Patients with haemorrhage (e.g. extensive retinal bleeding) or at risk of increased bleeding 14. Patients with severe coronary artery disease, when in the physician's judgement myocardial stimulation might prove harmful. 15. Patients with severe hepatic and renal impairment. 16. Patients without adequate laboratory parameters according to the normal ranges of local laboratory. 17. Female risk factors of infertility defined by any of the following: * Absence of any or both ovaries. * Abnormal uterine cavity assessed by transvaginal sonography. Specially, submucosal fibroids, intramural fibroids affecting the uterine cavity (any size), more than 5 intramural fibroids ≥ 4 cm in diameter, or more than 6 intramural fibroids of any size. Women with any subserosal fibroid ≥ 8cm will also be excluded. * Risk factors for fallopian tube obstruction as abdominal surgery, diseases such as endometriosis, tuberculosis, ruptured appendix or peritonitis, Pelvic Inflammatory Disease (PID), Chlamydia and gonorrhea. * Antecedents of long-term amenorrhea, polycystic ovarian syndrome, type III or IV endometriosis, or fallopian tube obstruction. * Previous gynecological surgery, excluding caesarean section or myomectomy within predefined limits. * For women, prohibited concomitant therapies within 28 days before enrolled into the study until last treatment visit: sex hormones, selective estrogen receptor modulators, aromatase inhibitors or oral pentoxifylline. * Two or more clinical or preclinical spontaneous miscarriages. * Lactation or pregnancy. * Known abnormal karyotype 18. Male risk factors of infertility defined by any of the following: * Vasectomy * Known genetic abnormalities related to infertility: i.Endocrine or systemic disorders causing hypergonadotropic hypogonadism (either, congenital or acquired). ii.Known abnormal karyotype * Previously diagnosed varicocele * The use of certain drugs (e.g., anabolic steroids, antineoplastic agents, erythromycin, tetracycline, gentamycin). * Viral process with fever ≥ 38ºC in the past 70 days