This is a within-participant comparison study to investigate the efficacy of a 28-day regimen of MK-0873 2% cream twice a day (b.i.d.) compared to MK-0873 vehicle (matching placebo) b.i.d. as well as to a positive control comparator calcitriol 0.0003% (3 µg/g) in participants with plaque psoriasis. In order to be enrolled in the study, patients need to have at least two pairs (lesions AB and CD) of approximately similar plaque lesions in severity and size of surface area involved and located in approximately symmetric regions such as the trunk or limbs of the body. Participants will be randomly assigned to apply either MK-0873 or MK-0873 vehicle to plaque A or B and will be randomly assigned to apply MK-0873 or calcitriol to plaque C or D. It is hypothesized that MK-0873 cream formulation administered to participants with psoriasis by the topical route will result in a statistically greater percent target lesion severity (TLS) reduction in plaque lesion than will MK-0873 Vehicle on Day 29.

Inclusion Criteria

• Is a male or female 18 to 65 years of age

• Female subjects of reproductive potential must have a negative serum pregnancy test at screening and agree to use and/or have their partner use two (2) acceptable methods of birth control

• Has a Body Mass Index (BMI) ≤36 kg/m^2 (up to 40 kg/m^2 may be enrolled, in consultation with Sponsor)

• Has diagnosis of plaque-type psoriasis at least 6 month prior to administration of study drug (participants with concurrent psoriatic arthritis may be enrolled)

• Has plaque-type psoriasis with at least two pairs of symmetrically located plaque lesions that exhibit similar baseline TLS values (TLS in each plaque ≥6 and

  ± 2 points difference between left and right plaque lesions)

• Has plaque-type psoriasis with lesion severity score ≥4 covering at least 1 to 20% of total body surface area at screening and at baseline.

• Is judged to be in good health based on medical history, physical examination, vital sign measurements, electrocardiogram assessment, and laboratory safety tests

Exclusion Criteria

• Has nonplaque forms of psoriasis (e.g., Erythrodermic, guttate, or pustular).
• Has current drug-induced psoriasis (e.g., a new onset of psoriasis or an exacerbation of psoriasis from beta blockers, calcium channel blockers or lithium).
• Has received phototherapy or any systemic medications/treatments that could affect psoriasis or TLS evaluation (including but not limited to oral or injectable corticosteroids, retinoids, 1, 25-dihydroxy vitamin D3 and analogues, psoralens, sulfsalazine, hydroxyurea, fumaric acid derivatives, or herbal treatments) within 4 weeks of study drug administration.
• Has used topical medications/treatments that could affect psoriasis or TLS evaluation (e.g., corticosteroids, coal tar, anthralin, calcipotriene, topical vitamin D derivatives, retinoids, tazarotene, methoxsalen, trimethyl psoralens) within 2 weeks of study drug administration.
• Has used any systemic immunosuppressants (e.g., Methotrexate, azathioprine, cyclosporine, 6-thioguanine, mercaptopurine, mycophenolate mofetil, hydroxyurea, or tacrolimus) within 4 weeks of study drug administration or biologics (e.g., anti-tumor necrosis factor [TNF], anti-interleukins) within 3 months of study drug administration.

http://engagezone.msd.com/doc/ProcedureAccessClinicalTrialData.pdf