Drug allergies can involve many different compounds and types of reactions, but the two most common culprits are penicillin and sulfur drugs. Penicillin is the most common form of drug allergy over the last 65 years. The major antigen is the six carbon benzene ring that people react to. Patients usually develop a maculopapular rash, a diffuse red rash on the body or centripetal rash, which spreads out to the legs and arms.
Currently, there is no adequate test for penicillin allergy. One needs to test with both penicilloyl-polylysine or PPL to test the major determinants, and an MDM (minor determinant mixture) to check for fatal reactions. As the penicillin passes through the liver it is hydroxylated, sulfated and combines with albumin to produce different chemical compounds. The fatal reaction usually happens to the MDM. If necessary, one must do a graded penicillin challenge if the patient has a history of reacting to penicillin. However there has never been a fatal reaction to penicillin taken orally.
Sulfur is the second most common drug allergy in general medicine. Sulfur is present in water pills, celecoxib, Bactrim and Azulfidine anti-arthritic drugs. Because the liver is often a slow hydrolyzer, some patients digest sulfur slowly, resulting in the body being exposed to the chemical for longer periods of time. The most common manifestation of an IgE allergy to sulfur is a maculopapular rash. The patient can develop Stevens-Johnson Syndrome, or ulcers to mucosal surfaces such as the vagina, anus or mouth. This type of lesion can become a toxic epidermal necrolysis or a virtual burn. Patients can be desensitized to IgE sulfur reactions, but not Stevens-Johnson Syndrome. Sulfur drugs can also absorb sunlight and cause a photosensitive reaction on the sun exposed surfaces. These typically appear on the face, and the tops of the hands and feet.
Most drugs – even if they don’t cause IgE reactions – can be inured against when the need for a life saving therapy outweighs the patient’s history of an allergic reaction. A patient can be administered one hundredth to one thousandth of the dose, which is then doubled every half hour until the patient gets a therapeutic amount. A rush desensitization can be can be done in one day, and a slow one can be broken down to take one month.