Dược Động Học :
▧ Absorption :
The absorption of cyclosporine from the gastrointestinal tract is incomplete and variable. The extent of absorption is dependent on the individual patient, the patient population, and the formulation. The absolute bioavailability of cyclosproine administered as Sandimmune® is dependent on the patient population, estimated to be less than 10% in liver transplant patients and as great as 89% in some renal transplant patients. Compared to an intravenous infusion, the absolute bioavailability of the oral solution is approximately 30% based upon the results in 2 patients. The cyclosporine capsules and oral solution are bioequivalent. The time of peak blood concentrations (Tmax) following oral administration of cyclosporine [modified] ranged from 1.5 - 2.0 hours.
▧ Volume of Distribution :
The steady state volume of distribution during intravenous dosing has been reported as 3 to 5 L/kg in solid organ transplant recipients. Cyclosporine is excreted in human milk.
▧ Protein binding :
In the plasma, approximately 90% is bound to proteins, primarily lipoproteins. In blood, the distribution is concentration dependent. Approximately 33% to 47% is in plasma, 4% to 9% in lymphocytes, 5% to 12% in granulocytes, and 41% to 58% in erythrocytes.
▧ Metabolism :
Hepatic, extensively metabolized by the cytochrome P450 3A enzyme system in the liver. It is also metabolized in the gastrointestinal tract and kidney to a lesser degree. The metabolites are significantly less potent than the parent compound. The major metabolites (M1, M9, and M4N) result from oxidation at the 1-beta, 9-gamma, and 4-N-demethylated positions, respectively.
▧ Route of Elimination :
Elimination is primarily biliary with only 6% of the dose (parent drug and metabolites) excreted in the urine. Only 0.1% of the dose is excreted in the urine as unchanged drug.
▧ Half Life :
Biphasic and variable, approximately 7 hours (range 7 to 19 hours) in children and approximately 19 hours (range 10 to 27 hours) in adults.
▧ Clearance :
Following intravenous administration, the blood clearance of cyclosporine (assay: HPLC) is approximately 5 to 7 mL/min/kg in adult recipients of renal or liver allografts. Blood cyclosporine clearance appears to be slightly slower in cardiac transplant patients. The following are clearance parameters (CL/F) for select patient populations:
* 593 ± 204 mL/min [De novo renal transplant patients, 597±174 mg/day]
* 492 ± 140 mL/min [Stable renal transplant patients, 344±122 mg/day]
* 577 ± 309 mL/min [De novo liver transplant, 458±190 mg/day]
* 613 ± 196 mL/min [De novo rheumatoid arthritis, 182±55.6 mg/day]
* 723 ± 186 mL/min [De novo psoriasis, 189±69.8 mg/day]
* 285 ± 94 mL/min [Stable Liver Transplant, Age 2 - 8, Dosed T.I.D 101±25 mg/day]
* 378 ± 80 mL/min [Stable Liver Transplant, Age 8 - 15, Dosed B.I.D 188±55 mg/day]
* 171 mL/min [Stable liver transplant, Age 3, Dosed B.I.D 120 mg/day]
* 328 ± 121 mL/min [Stable liver transplant, Age 8 - 15, Dosed B.I.D 158±55 mg/day]
* 418 ± 143 mL/min [Stable renal transplant, Age 7 - 15, Dosed B.I.D 328±83 mg/day]