Immunotherapy in general practice
Immunotherapy should be administered in a setting that permits the prompt recognition and management of adverse reactions. The preferred setting is the prescribing physician’s office, especially for high-risk patients. However, patients may receive immunotherapy injections at another health care facility if the physician and staff at that location are equipped to recognize and manage systemic reactions, in particular anaphylaxis. Because of the potential for anaphylaxis, immunotherapy should not be administered at home. Informed consent should be obtained prior to administering immunotherapy. A full, clear, and detailed documentation of the patient’s immunotherapy schedule must accompany the patient when receiving injections at another health care facility. Use of a constant uniform labeling system for dilutions may reduce errors in administration. The maintenance concentration and serial dilutions should be prepared and labeled for each individual patient.
A brief review of a patient’s current health status is recommended prior to dosing. It is important to assess any current asthma symptoms, increased allergic symptoms, any new medications, or any delayed reactions to the previous injection. In patients with asthma, peak expiratory flow rate measurements should be obtained prior to each injection. In general, immunotherapy injections should be withheld if the patient presents with an acute asthma exacerbation or if peak flow measurements are below 20% of the patient’s baseline values. Immunotherapy may need to be decreased or held if significant allergic symptoms are present prior to an injection.
Table. Immunotherapy vaccine labeling.
| Dilution
from Maintenance |
Dilution
Designation in Volume per Volume (V/V) |
Color | Number |
| Maintenance | 1:1 | Red | 1 |
| 10-fold | 1:10 | Yellow | 2 |
| 100-fold | 1:100 | Blue | 3 |
| 1000-fold | 1:1000 | Green | 4 |
| 10,000 fold | 1:10,000 | Silver | 5 |
Most severe reactions develop within 20 to 30 minutes after the immunotherapy injection, but reactions can occur after this time. Patients need to wait at the physician’s office for at least 20 to 30 minutes after the immunotherapy injection. In some cases, the wait may need to be longer depending on the patient’s history of previous reactions.
It is usual practice to reduce the dose of vaccine when the interval between injections is longer than prescribed. This reduction in dose should be clearly stated on the patient’s immunotherapy schedule. Because of the potential of extract degradation over time, when new vials are started the initial dose is decreased and then built back up to maintenance. When a systemic reaction occurs, the physician needs to decide if immunotherapy should be continued. This should be done in consultation with the allergist/immunologist who prescribed the immunotherapy. If the decision is to continue, the dose of the vaccine needs to be appropriately reduced to lessen the risk of a subsequent systemic reaction.
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