Clinical pharmacokinetics in organ transplant patients

Diseases of the liver, kidney and heart influence the pharmacokinetics of several drugs. Organ transplantation is an accepted therapeutic option for the treatment of several disease states associated with these organs. Recently, there has been an increase in both graft and patient survival after transplantation of the liver, heart, kidney and bone marrow. Such patients normally receive a wide range of drugs, and optimisation of drug therapy requires a thorough understanding of the pharmacokinetics and pharmacodynamics of these drugs in transplant patients. However, only limited studies have been carried out to characterise drug kinetics in these situations. Available information indicates that drug kinetics cannot be considered normal in transplant patients. Drug absorption generally appears to be similar to that in healthy subjects. The plasma protein binding of drugs that primarily bind to albumin increases after transplantation, but remains lower than that observed in healthy subjects. While the binding of certain basic drugs may increase after transplantation due to an increase in the concentration of alpha 1-acid glycoprotein, a lower albumin concentration may mask this effect. Oxidative and conjugative metabolism as measured by the kinetics of antipyrine (phenazone) and paracetamol (acetaminophen) is normal, while the metabolism of steroids may be impaired. Serum creatinine does not appear to be a good indicator of the functional status of the kidney in transplant patients. It is also important to realise that there will be time-dependent changes in several kinetic parameters of drugs due to improvement in the physiological function from that associated with the disease state to that of the normal state. Individualisation and close monitoring of drug therapy is necessary in transplant patients.