To characterize the efficacy, safety and tolerability of SNA-120 at 2 doses versus placebo when administered topically for the treatment of pruritus associated with psoriasis vulgaris (PV) and PV itself.

Inclusion Criteria:

• Informed consent/assent and Health Insurance Portability and Accountability Act (HIPAA) authorization
• Stable PV for at least 6 months prior to screening
• Chronic pruritus of the PV plaques to be present for at least 6 weeks prior to screening
• Mild to moderate PV at screening and baseline
• Has a target plaque at baseline on the trunk and/or limbs
• Subject's plaques are amenable to treatment with a topical ointment medication
• Willing and able to comply with the study instructions and attend all scheduled study visits.
• Willing to avoid prolonged exposure of the designated treatment plaques to ultraviolet radiation
• Females of childbearing potential must have a negative pregnancy test at baseline before randomization and must agree to use highly effective contraception during the study
• Men who are sexually active and can father children must agree to use highly effective forms of contraception during the study

Exclusion Criteria:

• Underlying conditions other than psoriasis that, in the opinion of the investigator, currently cause or influence pruritus of the overall skin
• Positive hepatitis serology
• Thyroid abnormalities that may impact itching
• Subjects with spontaneously improving or rapidly deteriorating PV and/or pruritus
• Current diagnosis of guttate, erythrodermic, exfoliative, or pustular psoriasis
• Active psoriasis or itch affecting the palmar/plantar regions
• Subjects with a clinical diagnosis of bacterial infection of the skin
• Any major medical illness or symptoms of a clinically significant illness that may influence the study outcome
• Any acute chronic medical or psychiatric condition or laboratory abnormality that would make them unsuitable for participation in this study
• Known hypersensitivity to the study treatment excipients and /or polyethylene glycol, that contraindicates participation
• Currently enrolled in an investigational drug or device study or has used an investigational drug or an investigational device treatment within 30 days of randomization/baseline (Note: Subjects who are enrolled in a long-term follow-up study and are not actively receiving an investigational drug or investigational device treatment may be eligible for participation in this study)
• Female who is pregnant or lactating, or is planning to become pregnant during the study
• Subjects participating in any previous SNA-120 (and/or CT327) clinical studies