Table 1 –

ALDEN algorithm for the assessment of drug causality in Stevens-Johnson Syndrome and toxic epidermal necrolysis.

Criterion	Rule	Interpretation	Point value
1. Delay from initial drug component intake to onset of reaction (Index Day) [−3 to 3]	5–28 Days or If previous rxn to same drug: 1–4 days	Suggestive	+3
	29–56 Days	Compatible	+2
	1–4 Days or If previous rxn to same drug: 5–56 Days	Likely	+1
	>56 Days	Unlikely	−1
	Started on or after the index day	Excluded	−3
2. Drug present in the body on index day [−3 to 0]	Drug continued up to index day or stopped at a time point less than 5× the elimination half-life before the index day	Definite	0
	Drug stopped at a time point prior to the index day by more than five times the elimination half-life but liver to kidney function alterations or suspected drug interactions are present	Doubtful	−1
	Drug stopped at a time point prior to the index day by more than five times the elimination half-life without liver or kidney function alterations or suspected drug interactions.	Excluded	−3
3. Prechallenge/rechallenge [−2 to 4]	SJS/TEN after use of the same drug	Positive specific for disease and drug	+4
	SJS/TEN after use of similar drug or other reaction with same drug	Positive specific for disease or drug	+2
	Other reaction after use of similar drug	Positive unspecific	+1
	No known previous exposure to this drug	Not done/unknown	0
	Exposure to this drug without any reaction (before or after reaction)	Negative	−2
4. Dechallenge [−2 or 0]	Drug stopped (or unknown)	Neutral	0
	Drug continued without harm	Negative	−2
5. Type of drug (notoriety) [−1 to 3]	Drug of the high-risk list according to previous case-control studies	Strongly associated	+3
	Drug with definite but lower risk according to previous case-control studies	Associated	+2
	Several previous reports, ambiguous epidemiology results (drug “under surveillance”)	Suspected	+1
	All other drugs including newly released ones	Unknown	0
	No evidence of association from previous epidemiology study with sufficient number of exposed controls	Not Suspected	−1
Intermediate score: total of all previous criteria [−11 to 10]
6. Other cause	Rank all drugs from highest to lowest intermediate score–if at least one has an intermediate score >3, subtract 1 point from the score of each of the other drugs taken by the patient (another cause more likely).	Possible	−1
Final score: [−12 to 10]

Table adapted from: Sassolas, B., et al. ALDEN, an algorithm for assessment of drug causality in Stevens-Johnson Syndrome and toxic epidermal necrolysis: comparison with case-control analysis. Clin Pharmacol Ther 88, 60–68 (2010).