SLCO1B1 and myopathy: The rs4149056 polymorphism has been shown to influence statin pharmacokinetics in all of these haplotypes: in studies on simvastatin, CC homozygotes (0%-6% of patients), with the lowest OATP1B1 activity, had higher plasma exposure to active simvastatin acid than TT homozygotes (55%-88% of patients); TC heterozygotes (11%-36% of patients) had intermediate exposure.38,40 It is thought that the higher plasma exposure to simvastatin acid in those with the C allele is responsible for myopathy, but the mechanism for the effect is not clear.