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Abstract
Coevaporates of paracetamol and rifampicin with Eudragit polymers of different natures (anionic, cationic, and zwitterionic) were prepared. Determination of dissolution rate of these coevaporates in dissolution media simulating those of the gastrointestinal tract (GIT) revealed that the release rate of paracetamol is retarded from all the coevaporates studied. In this respect, Eudragit L100-SS shows the highest sustainment of drug release, while Eudragit E100 shows the lowest. Conversely, the release of rifampicin from its coevaporates with the anionic Eudragit S100 polymer is more retarded than the corresponding coevaporate with the zwitterionic Eudragit RL100 or from coevaporates with equal mixtures of the two polymers.
Increasing the polymer weight fraction in rifampicin coevaporates with Eudragit S100 up to 0.5 resulted in a corresponding decrease in the dissolution rate. However, beyond this weight fraction, the polymer effect on the dissolution rate of the drug becomes minimized. The results confirmed that the process of dissolution of the two drugs from their coevaporates is a diffusion-controlled release process.
The biological performance of paracetamol coevaporates was monitored in rabbits; paracetamol level in plasma was found to follow first-order kinetics. for all the investigated paracetamol coevaporates, the peak plasma level was less than 50 μg/ml compared to a value of 60, μg/ml for the drug per se. The coevaporates of the drug with Eudragit L100-55 showed slowest rates of absorption and elimination as well as greatest half-peak and half-life times. Biological peformance of rifampicin coevaporates was assessed in human subjects receiving a single oral dose equivalent to 300 mg of the drug. The results depicted sustainment of drug release as a function of polymer weight fraction. A strict correlation was shown to exist between the total amount of drug excreted during 24 hr post dosing of the coevaporates and its in vitro dissolution rate.
The results depicted that paracetamol can be formulated in the form of a coevaporate with Eudragit L100-55 to prepare a more safe sustained-release formulation with minimal side effects, and also revealed the advantages of administration of rifampicin in the form of a coevaporate with Eudragit S100 (4:1) at a single oral dose equivalent to 600 mg of drug.