Hello, it is Week 2 of NURS615. We are going to talk about adverse drug reactions.
Adverse drug reactions are harmful or unintended responses. They are fairly common ranging from mild to life-threatening. Some adverse drug reactions can occur in anyone. They can occur because of overdose, a patient can intentionally overdose on drugs, or they can unintentionally take too many of them. They can have excessive effects from the medication, or they can have drug interactions by taking the medication with another medication that it interacts with. Some of the adverse drug reactions occur in individuals who are susceptible due to intolerance to the medication, an idiosyncratic reaction or an actual allergy.
Idiosyncratic drug reactions are adverse effects that appear unpredictably. These are the ones that basically didn’t see coming. Allergic reactions are hypersensitivity responses. Small drugs, small in terms of the size of the molecule, are not direct immunogens. These drugs act as what are called haptens. They bind chemically or covalently with a protein to trigger an immune response. There are actually four types of hypersensitivity responses that you want to be aware of.
Type I hypersensitivity response results from production of IgE after exposure to an antigen. When you have the Type I hypersensitivity response, this is the most severe response that you can have to a drug, and it will result in anything from urticaria (rash) to wheezing all of the way up to anaphylaxis. Remember that a Type I hypersensitivity response is the most severe. Type II hypersensitivity responses occur when the drug actually binds to red blood cells and is recognized by an antibody that the body has produced, usually IgG. This is a complement and cytotoxic T cells are activated. This response is rare. This does not occur very often.
A third type of response occurs when IgG and IgM (antibodies) are formed against actual soluble antigens. These form complexes, and they are deposited in tissues such as joint and lungs. It causes serum sickness. This was the type of response that occurred with the antibiotic called Ceclor. You will often see patients who say that they were allergic to Ceclor. They can still take penicillins. They can still take cephalosporins because this was a very rare type of hypersensitivity allergic drug reaction, adverse drug response. It was not anaphylaxis. This was an idiosyncratic type of allergic response that happened with Ceclor.
Them the Type IV type of hypersensitivity response is a delayed response. It is a cytotoxic one in which cytotoxic T cells are activated. Well-known Type IV responses are poison ivy and latex, so it causes a contact dermatitis. With repeated exposures to drugs, you can get sort of a cytokine storm, but the best example of Type IV is poison ivy.
Here is a chart. It’s a little small so it might be hard to see, but it gives you examples of what is happening when you have each of the types of responses (adverse drug responses) going on at a cellular level.