Inhibitory concentration, half

Another important kinetic parameter usually determined is the value of IC50, defined as the half maximal inhibitory concentration that provides an indication of the potency of an inhibitor under certain the specific conditions of an evaluation. This parameter is typically determined from dose-response plots in which the percentage conversation or inhibition is plotted against the logarithmic concentration of inhibitor employed in each evaluation. The parallel nature of the /.tPLC system described in this chapter is ideal for the evaluation of this parameter. 

ICso half maximal inhibitory concentration of a substance... 

The absorption and excretion of carbenicillin in man has been reported [396]. The antibiotic is not absorbed intact from the gut intramuscular injection (which is painful) often provides adequate serum levels (approximately 20 Mg/ntl) but infections with Pseudomonas strains having minimum inhibitory concentrations up to, or higher than, 100 Mg/ml require intravenous thbrapy to achieve such levels. No evidence of active metabolite formation has been obtained. Marked reductions in the half-life (and serum levels) of carbenicillin follow extracorporeal dialysis or peritoneal dialysis, the former producing the most striking effect [397]. These results were, of course, obtained in patients with severe renal failure. Patients with normal renal function rapidly eliminate the drug but, as with all penicillins, renal tubular secretion can be retarded by concurrent administration of probenecid. 

If enzymes are described under tbe aspect of reaction mechanisms, the maximal rate of turnover Vmax. the Michaelis and Menten constant Km, the half maximal inhibitory concentration ICso, and tbe specific enzyme activity are keys of characterization of the biocatalyst. Even though enzymes are not catalysts in a strong chemical sense, because they often undergo an alteration of structure or chemical composition during a reaction cycle, theory of enzyme kinetics follows the theory of chemical catalysis. 

The rate of clearance of chlorhexidine from the mouth after one mouth rinse with 10 mL of a 0.2% aqueous solution follows approximately first-order kinetics, with a half-life of 60 minutes. This means that following application of a single rinse with a 0.2% chlorhexidine solution, the concentration of the compound exceeds the minimum inhibitory concentration (MIC) for oral streptococci (5 mg/mL) for almost 5 hours. The pronounced substantivity, along with the relative susceptibility of oral streptococci, may account for the great effectiveness of chlorhexidine in inhibiting supragingival plaque formation. 

Zanamivir is delivered directly to the respiratory tract via inhalation. Ten to twenty percent of the active compound reaches the lungs, and the remainder is deposited in the oropharynx. The concentration of the drug in the respiratory tract is estimated to be more than 1000 times the 50% inhibitory concentration for neuraminidase, and the pulmonary half-life is 2.8 hours. Five to fifteen percent of the total dose (10 mg twice daily for 5 days for treatment and 10 mg once daily for prevention) is absorbed and excreted in the urine with minimal metabolism. Potential adverse effects include cough, bronchospasm (occasionally severe), reversible decrease in pulmonary function, and transient nasal and throat discomfort. 

IC50 or half-maximal inhibitory concentration Concentration required to inhibit a given bioiogioai prooess by haif. 

Cytotoxicity is denoted by inhibition of human epidermal carcinoma (KB-16), human lung adenocarcinoma (A549), human colon carcinoma (HT-29), and murine lymphocytic leukemia (P-388) cells at half maximal inhibitory concentration (IC50) values of pg/mL. bFor the cell lines tested, an IC50 value of <4 pg/mL is regarded as active. 

Platelets were preincubated with DMSO (0.5%, control) or each compound at 37 °C for 3 minutes, and the inducer [arachidonic acid (AA), collagen, platelet-activating factor (PAF), or thrombin] was added. bActivity denoted by antiplatelet aggregation at IC50 (half maximal inhibitory concentration) values of <300 pM. 

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