Dangerous Allergic Reaction
Even though penicillin and its relatives are beneficial medications, killing bacterial infections, some people are severely allergic and develop a condition known as anaphylactic shock. This is the most dangerous penicillin allergy and it can be life-threatening.
If you are highly sensitive to penicillin, your reaction is immediate, with dizziness, difficulty breathing, wheezing, swelling of the tongue or throat, a drop in your blood pressure, rapid or weak pulse and a loss of consciousness. You may also develop diarrhea, nausea and vomiting, and your skin may develop a bluish color.
You are more likely to develop a severe allergic reaction if you suddenly develop hives after taking a dosage; if you have a positive skin test for penicillin or if you have had a previous anaphylactic reaction after taking penicillin, according to WebMD. This site points out that severe allergic reactions develop within an hour of taking the medication.
If you have had a dangerous, anaphylactic reaction to penicillin, your doctor can prescribe another antibiotic for your infection. You can also undergo desensitization therapy (an allergist gives you tiny amounts of the drug in injections and begins to gradually increase each dose until you no longer develop a severe reaction. You may need to undergo another desensitization session in the future because the effects are not permanent.