ALden Algorithm: Determines the probability that Allopurinol is the culprit drug in SJS/TEN.
Time from Drug Intake to Reaction
Daily Dosage
Other Suspect Drugs
Guidelines & Evidence
Clinical Details
Section 1
When to Use
When to Use
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.
Section 2
Formula & Logic
Scoring Parameters
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.
Interpretation
< 0: Very unlikely
0 - 1: Unlikely
2 - 3: Possible
4 - 5: Probable
≥ 6: Very probable
Section 3
Pearls/Pitfalls
Clinical Pearls
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.
Section 4
Next Steps
Next Steps
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).
