Study to Evaluate the Effect of the Coadministration of SCH 497079 (a Histamine 3 [H3] Receptor Antagonist) Plus Desloratadine on Nasal Congestion in Subjects With Seasonal Allergic Rhinitis Who Have Been Exposed to Pollen in the Vienna Challenge Chamber (VCC)

INTERVENTION: Product Name: SCH 497079 100 mg capsule Pharmaceutical Form: Capsule* Current Sponsor code: SCH 497079 Other descriptive name: H3 Antagonist Concentration unit: mg milligram(s) Concentration type: equal Concentration number: 100 mg‐ Pharmaceutical form of the placebo: Capsule* Route of administration of the placebo: Oral use Trade Name: Aerius 5 mg Product Name: desloratadine Product Code: SCH 34117 Pharmaceutical Form: Tablet Current Sponsor code: desloratadine Other descriptive name: SCH 34117 Concentration unit: mg milligram(s) Concentration type: equal Concentration number: 5 mg‐ Pharmaceutical form of the placebo: Tablet Route of administration of the placebo: Oral use Product Name: pseudoephedrine 240 mg Product Code: SCH 4855 Pharmaceutical Form: Tablet Current Sponsor code: Pseudoephedrin Other descriptive name: SCH 4855 Concentration unit: mg milligram(s) Concentration type: equal Concentration number: 240 mg‐ Pharmaceutical form of the placebo: Tablet Route of administration of the placebo: Oral use Product Name: SCH 497079 10 mg capsule Pharmaceutical Form: Capsule* Current Sponsor code: SCH 497079 Other descriptive name: H3 Antagonist Concentration unit: mg milligram(s) Concentration type: equal Concentration number: 10 mg‐ Pharmaceutical form of the placebo: Capsule* Route of administration of the placebo: Oral use CONDITION: Seasonal Allergic Rhinitis ; MedDRA version: 7.0 Level: LLT Classification code 10039776 INCLUSION CRITERIA: 1. Subjects must be willing to give written informed consent and adhere to dose and visit schedules. 2. Subjects must have the appropriate washout times from the prohibited medications (see Section 7.4.2.1.1). 3. Clinical laboratory tests (CBC, blood chemistries, urinalysis) at screening must be within normal limits or clinically acceptable to the investigator. 4. Subjects must skin test positive confirming hypersensitivity to Dactylis glomerata grass allergen extract which is cross reactive with pollen mixture used in the chamber, unless a positive test was obtained within the previous 12 months. IgE‐mediated hypersensitivity must be documented by a positive response to the skin prick test with wheal diameter ?3 mm larger than diluent control. 5. Female subjects of childbearing potential must have a negative serum pregnancy test prior to treatment with study medication; a negative urine pregnancy test must be obtained at least every 28 days during PRIMARY OUTCOME: Main Objective: The primary objective of this study is to evaluate the effect on nasal congestion of a maximally tolerated dose of SCH 497079, when taken in combination with DL 5 mg (identified in Phase 1 studies), in subjects with seasonal allergic rhinitis (SAR) who have been exposed to pollen in the VCC. This objective will be accomplished by comparison of the effect on nasal congestion, over the 7.5 hour observation period, of the coadministration of DL 5 mg and SCH 497079 100 mg with that of DL 5 mg taken alone. Primary end point(s): The primary efficacy variable is the subjectively evaluated symptom of nasal congestion. The nasal decongestant effect is expressed as an average change from Baseline over the 7.5‐hour evaluation period. The primary comparison for this variable is SCH 497079 100 mg plus DL 5 mg taken in combination vs DL 5 mg taken alone.; Pairwise comparisons will be made using linear contrasts of the treatment means obtained from an analysis of variance model that extracts sources of variation due to treatment, subject, and phase.; Summary statistics for the primary variable will be provided for the subject subgroups of sex and race (Caucasian and non‐Caucasian).; Secondary Objective: Key secondary objectives include calculation of the estimates of the following treatment differences over the 7.5‐hour observation period and at each time point:; The comparison of the effect on nasal congestion of the coadministration of DL 5 mg and SCH 497079, at a 20 mg dose, with that of DL 5 mg taken alone.The comparison of the effect on nasal congestion of DL 5 mg, taken in combination with each of two dose levels of SCH 497079, 100 mg and 20 mg, versus concurrent administration of DL plus PSE 240 mg. Evaluation of the safety profiles among the five treatments of postdose vital signs and adverse events compared with predose evaluations. Single dose plasma SCH 497079, DL 3‐OH DL, and pseudoephedrine concentrations and pharmacokinetic parameters will be listed and summarized using means, and percent coefficients of variation. In addition, an association between plasma concentrations and observed decongestant activity will be explored if the data allow.;