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.
 
Incidence
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.
 
Mechanisms
IgE-mediated hypersensitivity: positive skin tests + specific IgE ; especially in patients with anaphylactic shock or urticaria.
 
Intolerance: similar mechanisms to other NSAIDs.
 
Management
In patients with specific pyrazolone allergy, ascertain safe other NSAIDs.
 
Avoid all NSAIDs in cases of intolerance.
 

References

  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.