Drug Interactions in Organ Transplantation

Drug-drug interactions may have potentially life-threatening consequences in transplant recipients, who have several risk factors for interactions including multiple concomitant diseases and the use of narrow therapeutic index drugs. The purpose of this chapter is to describe potentially adverse drug interactions and explore the influence of pharmacogenomics on their occurence. Pharmacokinetic interactions are those in which one drug affects the absorption, distribution, metabolism or excretion of another drug. Pharmacodynamic interactions are those in which concurrently administered drugs have similar or opposing pharmacologic effects. These interactions may increase or decrease efficacy or toxicity of the drug combination. Complete avoidance of drug interactions is not possible in transplant patients. Therefore, when drug combinations of potentially interacting agents are administered, patients must be more closely monitored for loss of efficacy and/or enhanced toxicity. Many drug interactions can be safely managed with appropriate dose changes, addition of drugs or an increase in the dose of drugs that minimize or treat the toxicity.