Increased Systemic Exposure and Stronger Cardiovascular and Metabolic Adverse Reactions to Fenoterol in Individuals with Heritable OCT1 Deficiency

Fenoterol is a widely used anti‐asthmatic and tocolytic agent, but high plasma concentrations of fenoterol may lead to severe and even fatal adverse reactions. We studied whether heritable deficiency of the liver organic cation transporter 1 (OCT1), a trait observed in 3% of Europeans and white Americans, affects fenoterol plasma concentrations and toxicity. OCT1 transported fenoterol with high affinity, and OCT1 inhibition in human hepatocytes reduced fenoterol uptake threefold. After administration of 180 µg of fenoterol to 39 healthy individuals, the OCT1‐deficient individuals (zero active OCT1 alleles; n = 5) showed 1.9‐fold greater systemic fenoterol exposure (P = 4.0 × 10−5) and 1.7‐fold lower volume of distribution (P = 8.0 × 10−5). Correspondingly, the OCT1‐deficient individuals had a 1.5‐fold stronger increase in heart rate (P = 0.002), a 3.4‐fold greater increase in blood glucose (P = 3.0 × 10−5), and significantly lower serum potassium levels. In conclusion, heritable OCT1 deficiency significantly increases plasma concentrations of fenoterol and may be an important factor underlying the excess mortality associated with fenoterol.