Drug tolerance testing recommendations
Provocation tests (also called exposure tests or tolerance tests) consist of exposing a person to amounts of allergen that may cause the allergy under carefully controlled conditions. This type of testing is usually used in the study of allergy to food or drugs.
Administration of the substance may be by ingestion, inhalation or subcutaneous, intramuscular or intravenous injections; but usually the food or drug is given orally.
Challenge tests are always undertaken by trained and experienced medical staff. Normally, a full study lasts several hours.
During a challenge test usually no reactions occur but it is possible that minor problems can arise such as dizziness, which can occur in patients prone to it (such as after an analysis test, on seeing blood, pain, etc.). This can be accompanied by overheating, sweating and fainting.
Although the patient should report these symptoms, it is not about an allergic reaction but, in fact, a mild reaction which usually disappears even without medication. Furthermore, skin reactions may occur: itching or redness, or wheals that will disappear when testing is momentarily suspended and proper medication is administered.
More serious reactions are rare: Respiratory complications may occur such as hoarseness, whistling in the chest and feelings of suffocation, digestive or abdominal pain, nausea, vomiting or diarrhea. If they occur, the test is discontinued and treatment is administered. Very rarely dizziness accompanied by low blood pressure, tachycardia, seizures or severe cardiorespiratory complications can occur. In these cases, resuscitative measures will be taken. This is a severe reaction, but it is usually reversible.
Therefore, the decision to undertake a challenge test will depend largely on a conclusive medical history and that it is a commonly used drug.
In general, it should not be done when the suspect substance has caused severe symptoms which endanger the patient’s life.
As these tests cause severe allergic reactions, although rare, they should only be performed by a medical team led by an allergist with experience in this type of exploration.
Provocation test are carried out only on patients in good general health and always performed at hospital.
Any reaction that appears, even hours after finishing the test, should be assessed by medical staff, who will record the signs and symptoms present in the patient in order to be evaluated by the allergist who offered the test.
Challenge tests usually last several hours, so the place where they are carried out should be spacious and comfortable. The patient should be tranquil and seated, and have received all the information regarding the characteristics of the test and the possible alternatives. The patient would also have previously signed an informed consent form accepting its realization. The patient should always know the nature and purpose of the study, because their cooperation is essential to its success. Also, the patient may withdraw consent at any time, knowing that this refusal will not have a negative effect regarding the quality of the rest of the health care they will receive, but further provocation tests that are necessary for further diagnosis will not be followed. During testing, serial measurements of heart rate and blood pressure are usually carried out, which will be an objective measure to determine if any adverse reactions occur.
In addition, the necessary medical equipment for treatment of possible adverse reactions will be accessible: fluid therapy, intramuscular medications (epinephrine, corticosteroids, and antihistamines) and intravenous treatments.
Provocation tests should be done with the patient stable who has not taken drugs that may interfere with their results, such as antihistamines or corticosteroids or anti flu a week before.
In provocation with drugs there are no drawbacks with the patient having had breakfast. It should not be performed if the patient has flu or cold symptoms or other infectious conditions. Neither should it be performed during pregnancy.
It is important to be punctual, as it is not unusual that there are several patients who are treated in the same diagnostic test simultaneously, and it is advisable that all patients start at the same time, facilitating its implementation.
You should know that you will be under medical supervision at all times and any symptoms will be assessed and treated accordingly if necessary. Therefore, you must inform the medical staff of any symptoms. You should not leave the premises where testing is being performed unless you inform the appropriate medical staff.
Because the test can take several hours, it is recommended that the patient can engage in activities that make it more pleasant (reading, games, etc.), unless they interfere with medical observation or cause disturbance to the hospital staff or other patients.
In general, late reactions are less frequent and less severe than immediate responses. However, if after the study has been completed the patient has any symptoms, they should go to hospital to objectify their importance and request a written report of the health care provided, which will collect the constants and objective data (skin lesions, pulse, blood pressure, etc.) to identify the characteristics of the reaction. This report will then be delivered to the allergist responsible for the study.