The absorption of CsA is highly variable in psoriasis patients which can be explained by the function and expression of the multidrug efflux transporter P-gp P-glycoprotein (MDR1 Multidrug Resistance Protein 1, ABCB1 ATP Binding Cassette Subfamily B Member 1) (Figure 1). The gene discussed is ABCB1; the disease is psoriasis.