Bisphosphonate-induced cutaneous adverse events: the difficulty of assessing imputability through patch testing.

BACKGROUND Cutaneous adverse drug reactions (CADRs) due to bisphosphonates (BPs) have been scarcely described in the literature. OBJECTIVE To discuss the diagnostic value and limitations of cutaneous provocation tests with BPs. METHODS A descriptive case series study with a control group of CADRs due to BPs studied using patch testing from 2005 to 2010 is presented. RESULTS Patient 1 showed a positive D4++ with alendronate at 1% in petrolatum and D4+++ with alendronate at 1 and 0.1% in water. Patient 2 showed a positive intradermal test D3++ with alendronate at 0.1% in water. Patient 3 showed a positive patch test D4+ with ibandronate at 1% in petrolatum and D4++ with ibandronate at 1% in water, and a positive intradermal test D3+++ with ibandronate at 0.1% in water. CONCLUSION Establishing a correct interpretation of a patch test reaction is difficult based just on cutaneous test results. Too high concentrations of the drug can cause irritation and too low concentrations can be responsible of false-negative test reactions.