Q: How many days usually it takes for Clopidogrel (Plavix) hypersensitivity to manifest?

Answer:  About one week

Interestingly, it takes few days before Clopidogrel manifests its hypersensitivity. Usually, it presents as an erythematous, macular, morbilliform rash which usually begins on the face, chest, or abdomen, and slowly spreads to the proximal and then distal extremities. It may even involve palms and soles. It is rarely but can be pruritic. The median time from drug introduction to appearance of symptoms is between 5 and 10 days.

Hypersensitivity can be managed without discontinuation of drug. (see references). 

References:

1. Cheema AN, Mohammad A, Hong T, et al. Characterization of clopidogrel hypersensitivity reactions and management with oral steroids without clopidogrel discontinuation. J Am Coll Cardiol 2011; 58:1445.

2. von Tiehl KF, Price MJ, Valencia R, et al. Clopidogrel desensitization after drug-eluting stent placement. J Am Coll Cardiol 2007; 50:2039.

3. Campbell KL, Cohn JR, Fischman DL, et al. Management of clopidogrel hypersensitivity without drug interruption. Am J Cardiol 2011; 107:812.