Skin tests with drugs can be of value in investigating patients who have de
veloped cutaneous adverse drug reactions (CADR), but their specificity and
relevance remain to be determined. A false-positive result on skin testing
can happen if it is not compared to results in control subjects. When perfo
rming intradermal tests (IDT), we have determined the lowest concentrations
that induce false-positive results for many drugs, including betalactam an
tibiotics, cephalosporins, other antibiotics or non-steroidal anti-inflamma
tory drugs. Some drugs in their commercialized form contain sodium lauryl s
ulfate and can induce irritation when patch tested as such. When patch test
ed with colchicine at 10% in pet. or with a Cytotec((R)) pill (containing m
isoprostol) at 30% in pet., respectively, 80% of the 29 and 9 of the 10 neg
ative controls developed false-positive results. Lastly, positive results o
f patch tests with drugs can be related to contact allergy to one of the co
mponents of the commercialized form of the drug, without any relevance to t
he investigation of a CADR, as observed in 2 cases with iodine or avocado o
il.