Pyrazoline drugs or pyrazolones

Clinical use of this family of analgesics was sharply curtailed due to its potentially fatal bone marrow toxicity (agranulocytosis).
Metamizol. Propylphenazone. Amidophenazone. Phenazone.
Metamizol: from 0.13% to 2.4% of cutaneous reactions.
Clinical manifestations
Anaphylactic shock.
Urticaria, angioedema (allergy).
Allergic vasculitis.
Fixed drug eruption.
Erythema multiforme.
Toxic epidermal necrolysis.
Maculopapular eruption.
Allergy contact dermatitis.
Bronchospasm (intolerance).
Diagnostic methods
Cutaneous testing
Intradermal skin-tests: positive at 0.001 to 0.01% in most patients with allergic symptoms (anaphylactic shock, urticaria).
Specific IgE (RAST) for 1 - phenyl - 2.3 - dimethyl - 3 - pyrazoline - 5 - one found in 17/19 pyrazolone sensitive patients.
Oral challenge
Contraindicated if anaphylactic shock.
Sometimes useful in patients with asthma or urticaria.
IgE-mediated hypersensitivity: positive skin tests + specific IgE ; especially in patients with anaphylactic shock or urticaria.
Intolerance: similar mechanisms to other NSAIDs.
In patients with specific pyrazolone allergy, ascertain safe other NSAIDs.
Avoid all NSAIDs in cases of intolerance.


  1. Zhu D, Becker W.M, Schulz K.H, Schubeler K, Schlaak M, "Detection of IgE antibodies specific for 1 - phenyl - 2,3 - dimethyl - 3 - pyrazoline - 5 - one by RAST*: a serological diagnostic method for sensitivity to pyrazoline drugs", Asian. Pac. J. Allergy. Immunol., 1992 ; 10 (2): 95-101
  2. Voigtlander V, "Adverse dermatological reaction to pyrazolones", Agents. Actions. Suppl., 1986 ; 19: 303-11
  3. Szczeklik A, "Analgesics, allergy and asthma", Drugs. 1986 ; 32 (s4): 148-63

As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.