PGP and cleft palate: Studies in these animals have shown that treatment of heterozygous females with an isomer of avermectin, a known teratogenic substrate of P-gp, results in 100% cleft palate in fetuses deficient in P-gp(−/−), whereas the heterozygotes(+/−) are less susceptible and those expressing abundant P-gp(+/+) are protected from the effects of avermectin at the doses studied [18].