Drug safety pharmacodynamic interactions

Furthermore, as more information is wrung from the human genome, it is likely that many drug interactions that we currently view as idiosyncratic will acquire mechanistic explanations. This form of personalized medicine, with the capability to predict a pharmacokinetic or pharmacodynamic interaction by knowing the patient s phenotype in advance, will be a powerful therapeutic tactic in the interests of patient safety and optimization of therapy. 

Hatorp V, Hansen KT, Thomsen MS. Influence of drugs interacting with CYP3 A4 on the pharmacokinetics, pharmacodynamics, and safety of the prandial glucose regulator repaglinide. J Clin Pharmacol 2003 43(6) 649-60. 

While formulation interactions often are subject to in vitro investigations, the section below presents a particular example of an in vivo formulation interaction study (CPMP/EWP/QWP/1401/98 2002) a potential interaction of a drug in medical practice frequently given concomitantly with another drug (i.e. both mixed in a syringe) was subject to a clinical study which is illustrated below. For the purposes of simplicity, the description is limited to the collection, handling, and interpretation of pharmacokinetic data although clearly safety and pharmacodynamic parameters were also studied. 

Consider the difference in response to drugs between older and younger people. Treatment should reflect biological age (rather than chronological). Pharmacokinetics, pharmacodynamics, tolerability, adverse reactions, economy and patient choice will all influence therapy chosen. Most commonly, car-bamazepine or sodium valproate are chosen for older people as their effects in older people are well documented. Both show a favourable balance of safety, efficacy and economy. Phenytoin is less preferable because of drug interactions, adverse effects and potential for toxicity (zero order kinetics). 

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