Histamine-Induced Wheal and Flare: 10 mg/day. Pruritus: 10 mg/day. Severe Pruritus: 20 mg/day may be given initially. Reduce to 10 mg/day upon improvement of itching. Allergic Rhinitis or Chronic Idiopathic Urticaria: A daily single dose of 10 mg can be given. Seasonal Allergic Rhinitis (SAR): 20 mg/day.