- Rush/Cluster Immunotherapy - An allergen is given in increasing doses over 2 to 5 weeks. During rush therapy, the dose is increased rapidly over 1 to 2 days until a moderate level dose is reached. To reduce the chance of an allergic reaction, patients take prednisone, cetirizine (Zyrtec® (Registered Trademark)), ranitidine (Zantac® (Registered Trademark)) and montelukast (Singular® (Registered Trademark)) starting 24 hours before treatment begins until rush therapy ends. After discharge on the third day, patients return to the clinic once a week for the next 2 to 5 weeks for cluster therapy, in which the dose is increased more gradually to a maintenance level.