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Table 4 Calculated comparative Michaelis – Menten parameters of some enzyme inducing and inhibiting drugs

From: Application of modified Michaelis – Menten equations for determination of enzyme inducing and inhibiting drugs

Drug Vmax Km Cs R CMR Vo CLimt % Saturation % Unsaturation S/Km
Theophylline* 17.4 ± 8.7 8.5 ± 3.5 1.4 ± 0.3 0.9 ± 0.8 7.6 ± 3.8 3.0 ± 1.0 2.1 ± 0.3 22.6 ± 0.6 77.4 ± 13.7 0.4 ± 0.3
Mibefradil** 6.8 ± 0.0b 70.2 ± 0.0a 1.0 ± 0.0b 0.0 ± 0.0b 30.0 ± 0.0b 0.0 ± 0.0b 0.1 ± 0.0b 1.4 ± 0.0b 98.6 ± 0.0a 0.01 ± 0.0b
Voriconazile* 114.0 ± 0.0a 1.2 ± 0.0b 7.7 ± 0.0a 661.2 ± 0.0a 49.5 ± 0.0a 160 ± 0.0a 99.1 ± 0.0a 87.0 ± 0.0a 13.0 ± 0.0b 6.7 ± 0.0a
Metronidazole** 0.45 ± 0.1b 0.6 ± 0.3b 0.7 ± 0.3b −1.1 ± 1.1b 0.2 ± 0.0b 2.1 ± 1.9 3.1 ± 0.9a 54.6 ± 2.3a 45.4 ± 1.9b 1.2 ± 0.1a
Isoniazid** 30.9 ± 0.0a 1.70 ± 0.0b 2.5 ± 0.0a 27.8 ± 0.0a 13.4 ± 0.0a 46.3 ± 0.0a 18.5 ± 0.0b 60.0 ± 0.0a 40.0 ± 0.0b 1.5 ± 0.0a
Puromicin** 193.9 ± 0.0a 0.04 ± 0.0b 0.0 ± 0.0b 0.0 ± 0.0b 84.2 ± 0.0a 0.0 ± 0.0b 0.9 ± 0.0b 0.0 ± 0.0b 100 ± 0.0a 0.0 ± 0.0b
Phenytoin* 18.1 ± 9.9a 50.2 ± 40.8a 0.5 ± 0.5b 0.1 ± 0.1b 7.9 ± 4.3 0.2 ± 0.0b 0.2 ± 0.1b 0.8 ± 0.3b 99.2 ± 0.3a 0.01 ± 0.0b
Thiopental* 0.9 ± 0.1b 22.0 ± 2.0a 1.0 ± 0.0b 0.0 ± 0.0b 0.4 ± 0.0b 0.01 ± 0.0b 0.04 ± 0.0b 4.5 ± 0.4b 95.5 ± 0.4a 0.05 ± 0.0b
Thymidine* 2.5 ± 0.0b 45.5 ± 0.0a 1.0 ± 0.0b 0.0 ± 0.0b 1.1 ± 0.0b 0.1 ± 0.0b 0.1 ± 0.0b 2.1 ± 0.0b 97.9 ± 0.0a 0.02 ± 0.0b
Thymine* 2.6 ± 0.0b 82.5 ± 0.0a 1.0 ± 0.0b 0.0 ± 0.0b 1.1 ± 0.0b 0.03 ± 0.0b 0.03 ± 0.0b 1.2 ± 0.0b 98.8 ± 0.0a 0.01 ± 0.0b
Fluorouracil* 2.2 ± 0.0b 39.8 ± 0.0a 1.0 ± 0.0b 0.0 ± 0.0b 0.9 ± 0.0b 0.1 ± 0.0b 0.1 ± 0.0b 2.5 ± 0.0b 97.5 ± 0.0a 0.03 ± 0.0b
Tylosin* 0.02 ± 0.0b 0.4 ± 0.0b 0.6 ± 0.0b 0.01 ± 0.0b 0.01 ± 0.0 0.03 ± 0.0 0.05 ± 0.0 61.1 ± 0.0 39.0 ± 0.0b 1.6 ± 0.0a
  1. Keys: * = Enzyme inducer; ** = Enzyme inhibitor; a = significantly higher (P < 0.05); b = significantly lower (p < 0.05); Vmax Maximal velocity (mg/h), Km Metabolism constant (mg/L), Cs Concentration of substrate (μg; ng; μm; mg), R Rate of endogenous substrate production (h), CMR Cellular metabolic rate (/h), Vo Initial velocity (mg/h), Clint Proportionality constant between rate of metabolism and the drug substrate concentration at the enzyme site Cs, % saturation Extent of enzyme saturation and unsaturation