• To objectively establish the probability that a specific medication caused Stevens-Johnson Syndrome (SJS) or Toxic Epidermal Necrolysis (TEN).
• Superior to general adverse drug reaction scales (like Naranjo) due to strict timeline parameters specific to epidermal necrolysis.

• Delay to onset: (Time from initial drug intake to onset of index day). Peak causality is 5 to 28 days.
• Probability of drug presence in the body on the index day.
• Prechallenge & Rechallenge: Prior exposure to the drug with or without a reaction.
• Dechallenge: Drug stopped and disease progression stops (less heavily weighted due to natural SJS/TEN progression).
• Drug Notoriety: How often the drug is known to cause SJS/TEN (e.g., allopurinol, anti-epileptics).
• Exclude other causes: Presence of infections or other highly notorious drugs.

• < 0: Very unlikely
• 0 - 1: Unlikely
• 2 - 3: Possible
• 4 - 5: Probable
• ≥ 6: Very probable

• A medication started > 8 weeks prior to onset or < 4 days prior to onset is extremely unlikely to be the cause of SJS/TEN.
• Always calculate an ALDEN score for every medication the patient is taking before discontinuing everything blindly, though stopping all non-essential medications immediately is standard.

Permanently add any drug scoring ≥ 4 to the patient’s severe allergy list and notify family members, as there is a strong genetic HLA linkage for some SJS/TEN drugs (e.g., HLA-B*1502 and carbamazepine).