The pharmacokinetics of total paclitaxel following 30- and 180-minute infusions of paclitaxel protein-bound particles for injectable suspension (albumin-bound) at dose levels of 80 to 375 mg/m2 (0.31 to 1.15 times the maximum approved recommended dosage) were determined in clinical studies. Dose levels of mg/m2 refer to mg of paclitaxel in paclitaxel protein-bound particles for injectable suspension (albumin-bound). Following intravenous administration of paclitaxel protein-bound particles for injectable suspension (albumin-bound) to patients with solid tumors, paclitaxel plasma concentrations declined in a biphasic manner, the initial rapid decline representing distribution to the peripheral compartment and the slower second phase representing drug elimination.

Following paclitaxel protein-bound particles for injectable suspension (albumin-bound) infusion, paclitaxel exhibited linear drug exposure (AUC) across clinical doses ranging from 80 to 300 mg/m2 (0.31 to 1.15 times the maximum approved recommended dosage). The pharmacokinetics of paclitaxel in paclitaxel protein-bound particles for injectable suspension (albumin-bound) were independent of the duration of intravenous administration.

The pharmacokinetic data of 260 mg/m2 paclitaxel protein-bound particles for injectable suspension (albumin-bound) administered over a 30-minute infusion was compared to the pharmacokinetics of 175 mg/m2 paclitaxel injection over a 3-hour infusion. Clearance was larger (43%) and the volume of distribution was higher (53%) for paclitaxel protein-bound particles for injectable suspension (albumin-bound) than for paclitaxel injection. There were no differences in terminal half-lives.

Distribution

Following paclitaxel protein-bound particles for injectable suspension (albumin-bound) administration to patients with solid tumors, paclitaxel is evenly distributed into blood cells and plasma and is highly bound to plasma proteins (94%). The total volume of distribution is approximately 1741 L; the large volume of distribution indicates extensive extravascular distribution and/or tissue binding of paclitaxel.

In a within-patient comparison study, the fraction of unbound paclitaxel in plasma was significantly higher with paclitaxel protein-bound particles for injectable suspension (albumin-bound) (6.2%) than with solvent-based paclitaxel (2.3%). This contributes to significantly higher exposure to unbound paclitaxel with paclitaxel protein-bound particles for injectable suspension (albumin-bound) compared with solvent-based paclitaxel, when the total exposure is comparable. In vitro studies of binding to human serum proteins, using paclitaxel concentrations ranging from 0.1 to 50 µg/mL, indicated that the presence of cimetidine, ranitidine, dexamethasone, or diphenhydramine did not affect protein binding of paclitaxel.

Elimination

At the clinical dose range of 80 to 300 mg/m2 (0.31 to 1.15 times the maximum approved recommended dosage), the mean total clearance of paclitaxel ranges from 13 to 30 L/h/m2 and the mean terminal half-life ranges from 13 to 27 hours.

Metabolism

In vitro studies with human liver microsomes and tissue slices showed that paclitaxel in paclitaxel protein-bound particles for injectable suspension (albumin-bound) was metabolized primarily to 6α-hydroxypaclitaxel by CYP2C8; and to two minor metabolites, 3'-p-hydroxypaclitaxel and 6α, 3'-p-dihydroxypaclitaxel, by CYP3A4. In vitro, the metabolism of paclitaxel to 6α-hydroxypaclitaxel was inhibited by a number of agents (ketoconazole, verapamil, diazepam, quinidine, dexamethasone, cyclosporin, teniposide, etoposide, and vincristine), but the concentrations used exceeded those found in vivo following normal therapeutic doses. Testosterone, 17α-ethinyl estradiol, retinoic acid, and quercetin, a specific inhibitor of CYP2C8, also inhibited the formation of 6α-hydroxypaclitaxel in vitro. The pharmacokinetics of paclitaxel may also be altered in vivo as a result of interactions with compounds that are substrates, inducers, or inhibitors of CYP2C8 and/or CYP3A4 [see Drug Interactions (7)].

Excretion

After a 30-minute infusion of 260 mg/m2 doses of paclitaxel protein-bound particles for injectable suspension (albumin-bound), the mean values for cumulative urinary recovery of unchanged drug (4%) indicated extensive non-renal clearance. Less than 1% of the total administered dose was excreted in urine as the metabolites 6α-hydroxypaclitaxel and 3'-p-hydroxypaclitaxel. Fecal excretion was approximately 20% of the total dose administered.

Specific Populations

No clinically meaningful differences in the pharmacokinetics of paclitaxel in paclitaxel protein-bound particles for injectable suspension (albumin-bound) were observed based on body weight (40 to 143 kg), body surface area (1.3 to 2.4 m2), sex, race (Asian vs. White), age (24 to 85 years), type of solid tumors, mild to moderate renal impairment (creatinine clearance 30 to <90 mL/min), and mild hepatic impairment (total bilirubin >1 to ≤1.5 x ULN and AST ≤10 x ULN).

Patients with moderate (total bilirubin >1.5 to 3 x ULN and AST ≤10 x ULN) or severe (total bilirubin >3 to 5 x ULN) hepatic impairment had a 22% to 26% decrease in the maximum elimination rate of paclitaxel and approximately 20% increase in mean paclitaxel AUC compared with patients with normal hepatic function (total bilirubin ≤ULN and AST ≤ULN) [see Dosage and Administration (2.5) and Use in Specific Populations (8.7)].

The effect of severe renal impairment or end stage renal disease (creatinine clearance < 30 mL/min) on the pharmacokinetics of paclitaxel in paclitaxel protein-bound particles for injectable suspension (albumin-bound) is unknown.

Drug Interaction Studies

Carboplatin: Administration of carboplatin immediately after the completion of the paclitaxel protein-bound particles for injectable suspension (albumin-bound) infusion to patients with NSCLC did not cause clinically meaningful changes in paclitaxel exposure. The observed mean AUCinf of free carboplatin was approximately 23% higher than the targeted value (6 min*mg/mL), but its mean half-life and clearance were consistent with those reported in the absence of paclitaxel.