Inhibitors continued mechanical effects

Where HjS is present, line failures due to penetration underneath pits can occur in a short time. The sulfide film formed may be anodic to the metal surface, and afford some degree of corrosion protection. In many cases, however, the layer of FeS is not continuous and if so, may be porous. The net result is pit formation and growth. Sulfide stress cracking and hydrogen embrittlement are also factors to consider in inhibition for HjS. In systems where H2S and CO2 are both present, the ratio of COj to HjS determines whether COj or H2S corrosion mechanisms will dominate. Inhibitors should be effective against both H2S and COj. 

Achieving steady-state operation in a continuous tank reactor system can be difficult. Particle nucleation phenomena and the decrease in termination rate caused by high viscosity within the particles (gel effect) can contribute to significant reactor instabilities. Variation in the level of inhibitors in the feed streams can also cause reactor control problems. Conversion oscillations have been observed with many different monomers. These oscillations often result from a limit cycle behavior of the particle nucleation mechanism. Such oscillations are difficult to tolerate in commercial systems. They can cause uneven heat loads and significant transients in free emulsifier concentration thus potentially causing flocculation and the formation of wall polymer. This problem may be one of the most difficult to handle in the development of commercial continuous processes. 

Ethambutol is a synthetic agent and not related to any of the other tuberculostatics. Its mechanism of action is not well understood but in actively dividing mycobacteria it appears to be an inhibitor of mycobacterial RNA synthesis. It also has effects on bacterial phosphate metabolism and on polyamine synthesis. It is an bacteriostatic agent and its main function in combination therapy is to delay the occurrence of resistance, mainly against isoniazid and rifampicin. It is well absorbed after oral administration. It is widely distributed, except to the CNS. Protein binding is about 20-30%. It is mainly excreted unchanged in the bile and urine with an elimination half-life of 3 h. Ethambutol is concentrated in erythrocytes and thus provides a depot for continuous release. 

As mentioned in the Introduction, bacterial resistance to currently used antibacterial agents poses a major threat to their continued effectiveness [2]. Interestingly, a number of enzymes are involved in the development of antibacterial resistance via several mechanisms. For example, there are enzymes that catalyze the inactivation of antibacterial agents [47], 3-Lactamases are the best-known examples of this class of enzymes and have been studied extensively as targets for new inhibitors that are used in combination with 3-lactams to prevent their inactivation [48], Several [3-lactamase inhibitors have been developed and are used in combination with [3-lactams (e.g., amoxicillin/clavulanic acid, piperacillin/tazo-bactam, and others) [49,50],... 

---