The primary objective of this Phase IIa trial is to determine the effective doses and treatment period for an upcoming RX-10100 Phase IIb trial in subjects with erectile dysfunction (ED). The secondary objectives of this trial are to evaluate the safety and the quality of life in subjects with ED receiving RX-10100 treatment.

Inclusion Criteria:

• Have had ED for at least six months
• Stable, heterosexual relationship for at least 3 months
• Make at least one attempt of sexual intercourse per week during the untreated, 2-week screening period
• At least 50% of attempts of sexual intercourse during the untreated baseline period must be unsuccessful
• 'Moderate' or 'mild to moderate' ED, defined as an IIEF-EF domain score between 11 and 21 measured

Exclusion Criteria:

• Following previous or current medical conditions

  • Any unstable medical, psychiatric, or substance abuse disorder
  • Penile anatomical abnormalities
  • Primary hypoactive sexual desire
  • Spinal cord injury
  • Hypogonadism
  • Surgical prostatectomy
  • Stable or unstable angina pectoris
  • Myocardial infarction, stroke, or life-threatening arrhythmia
  • Uncontrolled atrial fibrillation/flutter at screening
  • Severe chronic or acute liver disease
  • Moderate or severe hepatic impairment
  • Clinically significant chronic hematological disease
  • Bleeding disorder
  • Significant active peptic ulcer disease
  • Resting hypotension or hypertension
  • Malignancy (cancers)
  • NYHA Class II to IV heart failures
  • Positive test for Hepatitis B surface antigen (HBsAg) or Hepatitis C
  • Symptomatic postural hypotension

• Following concomitant medication

  • Androgens or estrogens
  • Anti-androgens
  • Potent inhibitors of cytochrome P450 3A4
  • Any other investigational drug within 30 days before Visit 1
  • Any treatment for ED within 7 days before Visit 1 or during the study
  • Antibiotics in the penicillin class

• Following abnormal laboratory values

  • Serum total testosterone level (at least 25% lower)
  • Serum creatinine (> 3.0 mg/dl)
  • Elevation of AST and/or ALT (> 3 times the upper limit of normal)
  • Diabetic subjects with an HbAlc (> 6.5%)

• Subjects with known hypersensitivity to amoxicillin

• Subjects with a history of unresponsiveness to any PDE5 Inhibitor treatment or a history of significant side effects leading to its treatment discontinuation