Drug transporters in drug efficacy and toxicity.

Drug transporters are now widely acknowledged as important determinants governing drug absorption, excretion, and, in many cases, extent of drug entry into target organs. There is also a greater appreciation that altered drug transporter function, whether due to genetic polymorphisms, drug-drug interactions, or environmental factors such as dietary constituents, can result in unexpected toxicity. Such effects are in part due to the interplay between various uptake and efflux transporters with overlapping functional capabilities that can manifest as marked interindividual variability in drug disposition in vivo. Here we review transporters of the solute carrier (SLC) and ATP-binding cassette (ABC) superfamilies considered to be of major importance in drug therapy and outline how understanding the expression, function, and genetic variation in such drug transporters will result in better strategies for optimal drug design and tissue targeting as well as reduce the risk for drug-drug interactions and adverse drug responses.

The transfer of pravastatin in the dually perfused human placenta.

HMG-CoA reductase inhibitors (statins) are contraindicated during pregnancy. However, it has been suggested that the hydrophilic property of pravastatin prevents its placental transfer to the fetus, explaining neutral effects observed in controlled studies. Using the ex-vivo placental perfusion model, placental transfer of pravastatin (50 ng/ml) was determined. The mean maximum fetal concentration was 4.4 ng/ml. The transfer of pravastatin's across the placenta appears to be limited and slow. Combined with its rapid elimination half-life of 2 h and 50% protein binding, the transfer of pravastatin from maternal to fetal compartments is substantially more limited than observed in the perfusion experiments.

Disposition of atorvastatin, rosuvastatin, and simvastatin in oatp1b2-/- mice and intraindividual variability in human subjects.

Response to statin therapy is often unpredictable because of variability in metabolism and transport. In the recently created organic anion transporting-polypeptide 1b2 (Oatp1b2/Slco1b2)-null mice, the investigators found significantly lower liver-to-plasma ratios compared with controls for atorvastatin (16.0 ± 5.1 vs 43.5 ± 13.7, P = .002) and rosuvastatin (15.2 ± 3.3 vs 28.4 ± 9.3, P = .03), but not simvastatin (5.2 ± 1.1 vs 6.3 ± 2.9, P = .49), following tail vein injection of 1 mg/kg of each drug. In addition, the investigators examined intraindividual variation in atorvastatin, rosuvastatin, and simvastatin pharmacokinetics in healthy human subjects in a crossover study design. Areas under the plasma concentration-time curve of atorvastatin and simvastatin acid were significantly related (Spearman r = 0.68; P = .035), whereas rosuvastatin profile was not related to atorvastatin or simvastatin exposure. Together, these results in mice and humans demonstrate that predictability of exposure to one statin based on another is dependent on the specific statin pairs and the context in which they are compared.