A study involving 271 children with asthma showed that the group of children with poor metabolism of the specific cytochrome P450 2C19 haplotypes had higher rates of upper respiratory tract infections after administration of lansoprazole when compared to the placebo group, OR 2.46 (95% CI: 1.02–5.96) [23]. Here, CYP2C19 is linked to Recurrent upper respiratory tract infections.