PACLITAXEL — paclitaxel injection, solution
Fresenius Kabi USA, LLC
Paclitaxel should be administered under the supervision of a physician experienced in the use of cancer chemotherapeutic agents. Appropriate management of complications is possible only when adequate diagnostic and treatment facilities are readily available.
Anaphylaxis and severe hypersensitivity reactions characterized by dyspnea and hypotension requiring treatment, angioedema, and generalized urticaria have occurred in 2 to 4% of patients receiving paclitaxel in clinical trials. Fatal reactions have occurred in patients despite premedication. All patients should be pretreated with corticosteroids, diphenhydramine, and H2 antagonists (see DOSAGE AND ADMINISTRATION). Patients who experience severe hypersensitivity reactions to paclitaxel should not be rechallenged with the drug.
Paclitaxel therapy should not be given to patients with solid tumors who have baseline neutrophil counts of less than 1,500 cells/mm3 and should not be given to patients with AIDS-related Kaposi’s sarcoma if the baseline neutrophil count is less than 1,000 cells/mm3. In order to monitor the occurrence of bone marrow suppression, primarily neutropenia, which may be severe and result in infection, it is recommended that frequent peripheral blood cell counts be performed on all patients receiving paclitaxel.
Paclitaxel Injection, USP is a clear, colorless to slightly yellow viscous solution. It is supplied as a nonaqueous solution intended for dilution with a suitable parenteral fluid prior to intravenous infusion. Paclitaxel Injection, USP is available in 30 mg (5 mL), 100 mg (16.7 mL), and 300 mg (50 mL) multidose vials. Each mL of sterile nonpyrogenic solution contains 6 mg paclitaxel, USP, 527 mg of polyoxyl 35 castor oil, NF, and 49.7% (v/v) dehydrated alcohol, USP.
Paclitaxel is a natural product with antitumor activity. Paclitaxel is obtained via a semi-synthetic process from Taxus baccata. The chemical name for paclitaxel is (2aR ,4S ,4aS ,6R ,9S ,11S ,12S ,12aR ,12bS)-1,2a,3,4,4a,6,9,10,11,12, 12a,12b-Dodecahydro-4,6,9,11,12,12b-hexahydroxy-4a,8,13, 13-tetramethyl-7,11-methano-5H -cyclodeca[3,4]-benz[1,2-b ] oxet-5-one 6,12b-diacetate, 12-benzoate, 9-ester with (2R ,3S)- N-benzoyl-3-phenylisoserine.
Paclitaxel has the following structural formula:
Paclitaxel, USP is a white to off-white powder with the empirical formula C47 H51 NO14 and a molecular weight of 853.9. It is insoluble in water, soluble in alcohol and melts at around 212°C to 217°C.
Paclitaxel is a novel antimicrotubule agent that promotes the assembly of microtubules from tubulin dimers and stabilizes microtubules by preventing depolymerization. This stability results in the inhibition of the normal dynamic reorganization of the microtubule network that is essential for vital interphase and mitotic cellular functions. In addition, paclitaxel induces abnormal arrays or “bundles” of microtubules throughout the cell cycle and multiple asters of microtubules during mitosis.
Following intravenous administration of paclitaxel, paclitaxel plasma concentrations declined in a biphasic manner. The initial rapid decline represents distribution to the peripheral compartment and elimination of the drug. The later phase is due, in part, to a relatively slow efflux of paclitaxel from the peripheral compartment.
Pharmacokinetic parameters of paclitaxel following 3- and 24-hour infusions of paclitaxel at dose levels of 135 and 175 mg/m2 were determined in a Phase 3 randomized study in ovarian cancer patients and are summarized in the following table:
TABLE 1. SUMMARY OF PHARMACOKINETIC PARAMETERS – MEAN VALUES
|Dose (mg/m2)||Infusion Duration (h)||N (patients)||Cmax (ng/mL)||AUC(0-∞) (ng•h/mL)||T-HALF (h)||CLT (L/h/m2)|
|Cmax = Maximum plasma concentrationAUC (0-∞) = Area under the plasma concentration-time curve from time 0 to infinityCLT = Total body clearance|
It appeared that with the 24-hour infusion of paclitaxel, a 30% increase in dose (135 mg/m2 vs 175 mg/m2) increased the Cmax by 87%, whereas the AUC (0-∞) remained proportional. However, with a 3-hour infusion, for a 30% increase in dose, the Cmax and AUC (0-∞) were increased by 68% and 89%, respectively. The mean apparent volume of distribution at steady state, with the 24-hour infusion of paclitaxel, ranged from 227 to 688 L/m2 , indicating extensive extravascular distribution and/or tissue binding of paclitaxel.
The pharmacokinetics of paclitaxel were also evaluated in adult cancer patients who received single doses of 15 to 135 mg/m2 given by 1-hour infusions (n=15), 30 to 275 mg/m2 given by 6-hour infusions (n=36), and 200 to 275 mg/m2 given by 24-hour infusions (n=54) in Phase 1 and 2 studies. Values for CLT and volume of distribution were consistent with the findings in the Phase 3 study. The pharmacokinetics of paclitaxel in patients with AIDS-related Kaposi’s sarcoma have not been studied.
In vitro studies of binding to human serum proteins, using paclitaxel concentrations ranging from 0.1 to 50 mcg/mL, indicate that between 89 to 98% of drug is bound; the presence of cimetidine, ranitidine, dexamethasone, or diphenhydramine did not affect protein binding of paclitaxel.
After intravenous administration of 15 to 275 mg/m2 doses of paclitaxel as 1-, 6-, or 24-hour infusions, mean values for cumulative urinary recovery of unchanged drug ranged from 1.3% to 12.6% of the dose, indicating extensive non-renal clearance. In 5 patients administered a 225 or 250 mg/m2 dose of radiolabeled paclitaxel as a 3-hour infusion, a mean of 71% of the radioactivity was excreted in the feces in 120 hours, and 14% was recovered in the urine. Total recovery of radioactivity ranged from 56% to 101% of the dose. Paclitaxel represented a mean of 5% of the administered radioactivity recovered in the feces, while metabolites, primarily 6α-hydroxypaclitaxel, accounted for the balance. In vitro studies with human liver microsomes and tissue slices showed that paclitaxel was metabolized primarily to 6α-hydroxypaclitaxel by the cytochrome P450 isozyme CYP2C8; and to 2 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 PRECAUTIONS, Drug Interactions).
The disposition and toxicity of paclitaxel 3-hour infusion were evaluated in 35 patients with varying degrees of hepatic function. Relative to patients with normal bilirubin, plasma paclitaxel exposure in patients with abnormal serum bilirubin ≤2 times upper limit of normal (ULN) administered 175 mg/m2 was increased, but with no apparent increase in the frequency or severity of toxicity. In 5 patients with serum total bilirubin >2 times ULN, there was a statistically nonsignificant higher incidence of severe myelosuppression, even at a reduced dose (110 mg/m2), but no observed increase in plasma exposure (see PRECAUTIONS, Hepatic and DOSAGE AND ADMINISTRATION). The effect of renal or hepatic dysfunction on the disposition of paclitaxel has not been investigated.
Possible interactions of paclitaxel with concomitantly administered medications have not been formally investigated.
The safety and efficacy of paclitaxel followed by cisplatin in patients with advanced ovarian cancer and no prior chemotherapy were evaluated in 2, Phase 3 multicenter, randomized, controlled trials. In an Intergroup study led by the European Organization for Research and Treatment of Cancer involving the Scandinavian Group NOCOVA, the National Cancer Institute of Canada, and the Scottish Group, 680 patients with Stage IIB–C , III, or IV disease (optimally or non-optimally debulked) received either paclitaxel 175 mg/m2 infused over 3 hours followed by cisplatin 75 mg/m2 (Tc) or cyclophosphamide 750 mg/m2 followed by cisplatin 75 mg/m2 (Cc) for a median of 6 courses. Although the protocol allowed further therapy, only 15% received both drugs for 9 or more courses. In a study conducted by the Gynecological Oncology Group (GOG), 410 patients with Stage III or IV disease (>1 cm residual disease after staging laparotomy or distant metastases) received either paclitaxel 135 mg/m2 infused over 24 hours followed by cisplatin 75 mg/m2 or cyclophosphamide 750 mg/m2 followed by cisplatin 75 mg/m2 for 6 courses.
In both studies, patients treated with paclitaxel in combination with cisplatin had significantly higher response rate, longer time to progression, and longer survival time compared with standard therapy. These differences were also significant for the subset of patients in the Intergroup study with non-optimally debulked disease, although the study was not fully powered for subset analyses (TABLES 2A and 2B). Kaplan- Meier survival curves for each study are shown in FIGURES 1 and 2.
TABLE 2A. EFFICACY IN THE PHASE 3 FIRST-LINE OVARIAN CARCINOMA STUDIES
|Intergroup (non-optimally debulked subset)||GOG-111|
|T175/3a c75 (n=218)||C750a c75 (n=227)||T135/24a c75 (n=196)||C750a c75 (n=214)|
|• Clinical Responseb – rate (percent) — p-valuec||(n=153) 58||0.016||(n=153) 43||(n=113) 62||0.04||(n=127) 48|
|• Time to Progression — median (months) — p-valuec — hazard ratio (HR)c — 95% CIc||13.2||0.0060 0.76 0.62 to 0.92||9.9||16.6||0.0008 0.70 0.56 to 0.86||13.0|
|• Survival — median (months) — p-valuec — hazard ratio (HR)c — 95% CIc||29.5||0.0057 73 0.58 to 0.91||21.9||35.5||0.0002 0.64 0.50 to 0.81||24.2|
|a Paclitaxel dose in mg/m2 /infusion duration in hours; cyclophosphamide and cisplatin doses in mg/m2.b Among patients with measurable disease only.c Unstratified for the Intergroup Study, Stratified for Study GOG-111.|
TABLE 2B. EFFICACY IN THE PHASE 3 FIRST-LINE OVARIAN CARCINOMA INTERGROUP STUDY
|T175/3a c75 (n=342)||C750a c75 (n=338)|
|• Clinical Responseb – rate (percent) — p-valuec||(n=162) 59||0.014||(n=161) 45|
|• Time to Progression — median (months) — p-valuec — hazard ratio (HR)c — 95% CIc||15.3||0.0005 0.74 0.63 to 0.88||11.5|
|• Survival — median (months) — p-valuec — hazard ratio (HR)c — 95% CIc||35.6||0.0016 0.73 0.60 to 0.89||25.9|
|a Paclitaxel dose in mg/m2 /infusion duration in hours; cyclophosphamide and cisplatin doses in mg/m2.b Among patients with measurable disease only.c Unstratified.|
Figure 1. Survival: Cc Versus Tc (Intergroup)
Figure 2. Survival: Cc Versus Tc (GOG-111)
The adverse event profile for patients receiving paclitaxel in combination with cisplatin in these studies was qualitatively consistent with that seen for the pooled analysis of data from 812 patients treated with single-agent paclitaxel in 10 clinical studies. These adverse events and adverse events from the Phase 3 first-line ovarian carcinoma studies are described in the ADVERSE REACTIONSsection in tabular (TABLES 10 and 11) and narrative form.
Data from 5, Phase 1 and 2 clinical studies (189 patients), a multicenter randomized Phase 3 study (407 patients), as well as an interim analysis of data from more than 300 patients enrolled in a treatment referral center program were used in support of the use of paclitaxel in patients who have failed initial or subsequent chemotherapy for metastatic carcinoma of the ovary. Two of the Phase 2 studies (92 patients) utilized an initial dose of 135 to 170 mg/m2 in most patients (>90%) administered over 24 hours by continuous infusion. Response rates in these 2 studies were 22% (95% CI, 11 to 37%) and 30% (95% CI, 18 to 46%) with a total of 6 complete and 18 partial responses in 92 patients. The median duration of overall response in these 2 studies measured from the first day of treatment was 7.2 months (range, 3.5 to 15.8 months) and 7.5 months (range, 5.3 to 17.4 months), respectively. The median survival was 8.1 months (range, 0.2 to 36.7 months) and 15.9 months (range, 1.8 to 34.5+ months).
The Phase 3 study had a bifactorial design and compared the efficacy and safety of paclitaxel, administered at 2 different doses (135 or 175 mg/m2) and schedules (3- or 24-hour infusion). The overall response rate for the 407 patients was 16.2% (95% CI, 12.8 to 20.2%), with 6 complete and 60 partial responses. Duration of response, measured from the first day of treatment was 8.3 months (range, 3.2 to 21.6 months). Median time to progression was 3.7 months (range, 0.1+ to 25.1+ months). Median survival was 11.5 months (range, 0.2 to 26.3+ months).
Response rates, median survival, and median time to progression for the 4 arms are given in the following table.
TABLE 3. EFFICACY IN THE PHASE 3 SECOND-LINE OVARIAN CARCINOMA STUDY
|175/3 (n=96)||175/24 (n=106)||135/3 (n=99)||135/24 (n=106)|
|• Response — rate (percent) — 95% Confidence Interval||14.6 (8.5 to 23.6)||21.7 (14.5 to 31)||15.2(9 to 24.1)||13.2(7.7 to 21.5)|
|• Time to Progression — median (months) — 95% Confidence Interval||4.4(3 to 5.6)||4.2(3.5 to 5.1)||3.4(2.8 to 4.2)||2.8(1.9 to 4)|
|• Survival — median (months) — 95% Confidence Interval||11.5(8.4 to 14.4)||11.8(8.9 to 14.6)||13.1(9.1 to 14.6)||10.7(8.1 to 13.6)|
Analyses were performed as planned by the bifactorial study design described in the protocol, by comparing the 2 doses (135 or 175 mg/m2) irrespective of the schedule (3 or 24 hours) and the 2 schedules irrespective of dose. Patients receiving the 175 mg/m2 dose had a response rate similar to that for those receiving the 135 mg/m2 dose: 18% versus 14% (p=0.28). No difference in response rate was detected when comparing the 3-hour with the 24-hour infusion: 15% versus 17% (p=0.50). Patients receiving the 175 mg/m2 dose of paclitaxel had a longer time to progression than those receiving the 135 mg/m2 dose: median 4.2 versus 3.1 months (p=0.03). The median time to progression for patients receiving the 3-hour versus the 24-hour infusion was 4 months versus 3.7 months, respectively. Median survival was 11.6 months in patients receiving the 175 mg/m2 dose of paclitaxel and 11 months in patients receiving the 135 mg/m2 dose (p=0.92). Median survival was 11.7 months for patients receiving the 3-hour infusion of paclitaxel and 11.2 months for patients receiving the 24-hour infusion (p=0.91). These statistical analyses should be viewed with caution because of the multiple comparisons made.
Paclitaxel remained active in patients who had developed resistance to platinum-containing therapy (defined as tumor progression while on, or tumor relapse within 6 months from completion of, a platinum-containing regimen) with response rates of 14% in the Phase 3 study and 31% in the Phase 1 and 2 clinical studies.
The adverse event profile in this Phase 3 study was consistent with that seen for the pooled analysis of data from 812 patients treated in 10 clinical studies. These adverse events and adverse events from the Phase 3 second-line ovarian carcinoma study are described in the ADVERSE REACTIONSsection in tabular (TABLES 10 and 12) and narrative form.
The results of this randomized study support the use of paclitaxel at doses of 135 to 175 mg/m2 , administered by a 3-hour intravenous infusion. The same doses administered by 24-hour infusion were more toxic. However, the study had insufficient power to determine whether a particular dose and schedule produced superior efficacy.
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