A Simple Dilution Analog Computer for Simulation of Drug Distribution Processes

A simple technique is described which provides plots of simulated tandem first-order processes much like the analog computer. The exponential change in concentration of a solution under-going dilution at constant volume provides the basis for simulation of first-order processes. A UV-absorbing indicator is introduced into the first of a series of connected containers and the solution is rapidly pumped through the system. The continuously changing indicator concentration in any container can be measured and continuously monitored by a spectrophotometer equipped with a flow cell and recorder. Several pharmacokinetic models, as in delayed-release formulation and in molecular modification, were studied with this device and the resulting plots were found to be accurate and reproducible. The validity of dilution analog simulation of first-order processes is shown mathematically. One of the uses of the dilution analog simulator is in teaching and visualizing tandem first-order reactions such as pharmacokinetic models.