To assess the exact cause and extent of transdermal glyceryl trinitrat
e (GTN)-induced allergic reactions, a study of continuous and intermit
tent use of GTN patches was conducted in 320 patients with New York He
art Association (NYHA) class II and III angina pectoris. Three commerc
ially available GTN patch systems were used. Twenty-one patients (6.5%
) developed cutaneous reactions. In 17 patients (5.3%), the reactions
were confined to the area of application and were characterised as irr
itant reactions. Four patients (1.2%) developed both localised and rem
ote from the area of application lesions and one patient developed a g
eneralised anaphylactic reaction. The rate of discontinuation of thera
py was 3.4%. The irritant skin reactions were mainly due to contaminan
ts and additives. Changing to a different transdermal system reduced t
he incidence of local reactions - a particularly desirable effect in p
atients who respond well to GTN therapy.