Antecedentes: Cualquier sustancia prescrita en el tratamiento de algún padecimiento es capaz de producir eventos dañinos o desagradables, y se denominan reacciones adversas a medicamentos. Estas reacciones se originan por mecanismos inmunológicos y no inmunológicos. Objetivos: Describir los mecanismos inmunológicos de las reacciones de hipersensibilidad a medicamentos, epidemiologia, factores de riesgo, clasificación, manifestaciones clínicas, diagnóstico, tratamiento y pronóstico. Métodos: Se revisó la bibliografía actualizada, en inglés y español, asociada con reacciones de hipersensibilidad a medicamentos en las principales bases de datos.  Resultados: Se describen los términos para definir las reacciones adversas y de hipersensibilidad a medicamentos, su clasificación y manifestaciones clínicas, métodos diagnósticos actuales y en estudio, algoritmos de tratamiento y pronóstico de los medicamentos más frecuentemente prescritos y con mayor prevalencia de eventos adversos reportados. Conclusión: Las reacciones adversas a medicamentos representan un reto, con una fisiopatología compleja y no del todo comprendida. Su abordaje requiere un enfoque cuidadoso, porque no todos los fármacos cuentan con pruebas validadas para establecer el diagnóstico y tratamiento específico. Antes de indicar cualquier medicamento debe considerarse la gravedad de la enfermedad, disponibilidad de otros tratamientos y riesgos potenciales de sufrir eventos adversos.

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Background Paclitaxel is a chemotherapeutic agent used in the treatment of multiple types of malignant tumors which was discovered from the Taxus brevofilia tree. In some patients, anaphylaxis develops during the first exposure to paclitaxel, suggesting that primary sensitization may have occurred through hidden or unidentified allergens that produce cross-reactivity. Skin testing may be useful in identifying sensitization to these allergens. Atopy has also been reported in patients with hypersensitivity reactions (HSR) to paclitaxel. The aim of this study is to evaluate the association between atopy and sensitization to allergens with the development of immediate HSR to paclitaxel. Methods Skin prick tests (SPT) for environmental and food allergens were applied to 76 patients recently diagnosed with cancer. A SPT to paclitaxel was applied and if negative, an intradermal test was performed. After paclitaxel's infusion, the development of immediate HSR was observed. Results Of 76 skin tests, 43% of patients had allergen sensitization and 57% did not. HSR occurred in 12.1% and 11.6% of each group, respectively. Five percent of patients tested positive to paclitaxel and only one had an immediate HSR. Eighty-nine percent of patients who developed an HSR had a family or personal history of atopy. Conclusions Sensitization to environmental or food allergens does not appear to be a risk factor for the development of immediate HSR to paclitaxel, suggesting that there are other non-IgE-mediated immunologic mechanisms responsible for their development, however, a personal and family history of atopy increases 8x the risk of developing anaphylaxis.