Cladribine is a prodrug that becomes active upon phosphorylation to its 2-chlorodeoxyadenosine triphosphate (Cd-ATP) metabolite.
The pharmacokinetic parameters presented below were assessed following oral administration of cladribine 10 mg, unless otherwise specified. The cladribine mean maximum concentration (Cmax) was in the range of 22 to 29 ng/ mL and corresponding mean AUC was in the range of 80 to 101 ng∙h/mL.
The Cmax and AUC of cladribine increased proportionally across a dose range from 3 to 20 mg.
No accumulation of cladribine concentration in plasma was observed after repeated dosing.
Absorption
The bioavailability of cladribine was approximately 40%. Following fasted administration of cladribine, the median time to maximum concentration (Tmax) was 0.5 h (range 0.5 to 1.5 hours).
Effect of Food
Following administration of cladribine with a high fat meal, the geometric mean Cmax decreased by 29% and AUC was unchanged. The Tmax was prolonged to 1.5 hours (range 1 to 3 hours). This difference is not expected to be clinically significant.
Distribution
Cladribine mean apparent volume of distribution ranges from 480 to 490 liters. The plasma protein binding of cladribine is 20% and is independent of concentration, in vitro.
Intracellular concentrations of cladribine and/or its metabolites in human lymphocytes were approximately 30 to 40 times extracellular, in vitro.
Cladribine has the potential to penetrate the blood brain barrier. A cerebrospinal fluid/plasma concentration ratio of approximately 0.25 was observed in cancer patients.
Elimination
Cladribine estimated terminal half-life is approximately 1 day. The intracellular half-life of the cladribine phosphorylated metabolites cladribine monophosphate (Cd-AMP) is 15 hours and Cd- ATP is 10 hours. Cladribine estimated median apparent renal clearance is 22.2 liter per hour and non-renal clearance is 23.4 liter per hour.
Metabolism
Cladribine is a prodrug that is phosphorylated to Cd-AMP by deoxycytidine kinase (and also by deoxyguanosine kinase in the mitochondria) in lymphocytes. Cd-AMP is further phosphorylated to cladribine diphosphate (Cd-ADP) and the active moiety Cd-ATP. The dephosphorylation and deactivation of Cd-AMP is catalyzed by cytoplasmic 5'-nucleotidase (5'-Ntase).
The metabolism of cladribine in whole blood has not been fully characterized. However, extensive whole blood and negligible hepatic enzyme metabolism was observed, in vitro.
Excretion
After administration of 10 mg oral cladribine in MS patients, 28.5 [20] (mean [SD]) percent of the dose was excreted unchanged via the renal route. Renal clearance exceeded the glomerular filtration rate, indicating active renal secretion of cladribine.
Specific Populations
No studies have been conducted to evaluate the pharmacokinetics of cladribine in elderly or in patients with renal or hepatic impairment.
There were no clinically significant differences in the pharmacokinetics of cladribine based on age (range 18 to 65 years) or gender. The effect of hepatic impairment on the pharmacokinetics of cladribine is unknown.
Patients with Renal Impairment
Renal clearance of cladribine was shown to be dependent on creatinine clearance (CLCR). No dedicated studies have been conducted in patients with renal impairment, however patients with mild renal impairment (CLCR of 60 mL to below 90 mL per minute) were included in Study 1. A pooled pharmacokinetic analysis estimated a decrease of 18% in total clearance in a typical subject with a CLCR of 65 mL per minute leading to an increase in cladribine exposure of 25%.
Clinical experience in patients with moderate to severe renal impairment (i.e., CLCR below 60 mL per minute) is limited [see Use in Specific Populations (8.6)].
Drug Interaction Studies
Clinical Studies
No clinically significant differences in cladribine pharmacokinetics were observed when used concomitantly with pantoprazole or interferon beta-1a.
No clinically significant differences in ethinyl estradiol and levonorgestrel pharmacokinetics were observed when a combined oral hormonal contraceptive (containing 150 µg levonorgestrel and 30 µg ethinyl estradiol) was used concomitantly with cladribine.
In Vitro Studies
It has been reported that lamivudine can inhibit the phosphorylation of cladribine intracellularly. Potential competition for intracellular phosphorylation exists between cladribine and compounds that require intracellular phosphorylation to become active (e.g., lamivudine, zalcitabine, ribavirin, stavudine, and zidovudine).
Cytochrome P450 (CYP) Enzymes: Cladribine is not a substrate of cytochrome P450 enzymes and does not show significant potential to act as inhibitor of CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A4. Cladribine has no clinically meaningful inductive effect on CYP1A2, CYP2B6 and CYP3A4 enzymes.
Transporter Systems: Cladribine is a substrate of P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), equilibrative nucleoside transporter 1 (ENT1) and concentrative nucleoside transporter 3 (CNT3). Inhibition of BCRP in the gastrointestinal tract may increase the oral bioavailability and systemic exposure of cladribine. Intracellular distribution and renal elimination of cladribine may be altered by potent ENT1, CNT3 transporter inhibitors.