Topotecan Hydrochloride (Page 4 of 6)
12.3 Pharmacokinetics
Following administration of topotecan hydrochloride for injection at doses of 0.5 to 1.5 mg/m2 (0.1 to 0.3 times the recommended single agent dose) administered as a 30-minute infusion, area under the curve (AUC) increases proportionally with dose.
Distribution
Protein binding of topotecan is approximately 35%.
Elimination
The terminal half-life of topotecan is 2 to 3 hours following intravenous administration.
Metabolism
Topotecan undergoes a reversible pH-dependent hydrolysis of its pharmacologically active lactone moiety. At pH less than or equal to 4, the lactone is exclusively present, whereas the ring-opened hydroxyl-acid form predominates at physiologic pH. Topotecan is metabolized to an N-demethylated metabolite in vitro. The mean metabolite: parent AUC ratio was about 3% for total topotecan and topotecan lactone following intravenous administration.
Excretion
The overall recovery of total topotecan and its N-desmethyl metabolite in urine and feces over 9 days averaged 73% ± 2% following an intravenous dose. Mean values of 51% ± 3% as total topotecan and 3% ± 1% as N desmethyl topotecan were excreted in the urine. Fecal elimination of total topotecan accounted for 18% ± 4% while fecal elimination of N-desmethyl topotecan was 1.7% ± 0.6%. An O-glucuronidation metabolite of topotecan and N-desmethyl topotecan has been identified in the urine.
Specific Populations
No clinically significant differences in the pharmacokinetics of topotecan were observed based on age, sex, or hepatic impairment following intravenous administration.
Patients with Renal Impairment
Compared to patients with CLcr (calculated by the Cockcroft-Gault method using ideal body weight) greater than 60 mL/min, plasma clearance of topotecan lactone decreased by 33% in patients with CLcr 40 to 60 mL/min and decreased 65% in patients with CLcr 20 to 39 mL/min. The effect on topotecan pharmacokinetics in patients with CLcr less than 20 mL/min is unknown [see Dosage and Administration (2.6)].
Drug Interaction Studies
Clinical Studies
No clinically significant changes in topotecan pharmacokinetics were observed when coadministered cisplatin. No clinically significant changes in the pharmacokinetics of free platinum were observed in patients coadministered cisplatin with topotecan.
In Vitro Studies
Topotecan does not inhibit CYP1A2, CYP2A6, CYP2C8/9, CYP2C19, CYP2D6, CYP2E, CYP3A, or CYP4A or dihydropyrimidine dehydrogenase.
13 NONCLINICAL TOXICOLOGY
13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility
Carcinogenicity testing of topotecan has not been performed. Topotecan is known to be genotoxic to mammalian cells and is a probable carcinogen. Topotecan was mutagenic to L5178Y mouse lymphoma cells and clastogenic to cultured human lymphocytes with and without metabolic activation. It was also clastogenic to mouse bone marrow. Topotecan did not cause mutations in bacterial cells.
Topotecan given to female rats prior to mating at an intravenous dose of 1.4 mg/m2 [about equal to the clinical dose based on body surface area (BSA)] caused superovulation possibly related to inhibition of follicular atresia. This dose given to pregnant female rats also caused increased pre-implantation loss. Studies in dogs given at an intravenous dose of 0.4 mg/m2 (about 0.25 times the clinical dose based on BSA) of topotecan daily for a month suggest that treatment may cause an increase in the incidence of multinucleated spermatogonial giant cells in the testes.
14 CLINICAL STUDIES
14.1 Ovarian Cancer
The efficacy of topotecan hydrochloride for injection was evaluated in two clinical trials of 223 patients with metastatic ovarian cancer. All patients had disease that had recurred on, or was unresponsive to, a platinum-containing regimen. Patients in these trials received an initial dose of 1.5 mg/m2 as an intravenous infusion for 5 consecutive days, starting on Day 1 of a 21-day cycle.
One trial (Study 039) was a randomized trial of 112 patients who received topotecan hydrochloride for injection and of 114 patients who received paclitaxel (175 mg/m2 intravenously over 3 hours on Day 1 of a 21-day cycle). All patients had recurrent ovarian cancer after a platinum-containing regimen or had not responded to at least 1 prior platinum-containing regimen. Patients who did not respond to the trial therapy, or who progressed, could be given the alternative treatment. The efficacy outcome measures were overall response rate, response duration, time to progression, and overall survival (OS).
The results of the trial did not show statistically significant improvements in response rates, response duration, time to progression, and OS as shown in Table 4.
Table 4. Efficacy Results in Ovarian Cancer in Study 039
| P arameter | Topotecan Hydrochloride for Injectio n ( n = 112) | P aclitaxel (n = 114) |
| Overall response rate (95% CI) | 21% (13%, 28%) | 14% (8%, 20%) |
| Complete response rate | 5% | 3% |
| Partial response rate | 16% | 11% |
| Response durationa (months) Median (95% CI) | 6 (5.1, 7.6) | 5 (3.7, 7.8) |
| Time to progression (months) Median (95% CI) Hazard ratio (95% CI) | 4.4 (2.8, 5.4) 3.4 (2.7, 4.2) 0.76 (0.57, 1.02) | |
| Overall survival (months) | 14.5 (10.7, 16.5) 12.2 (9.7, 15.8) | |
| Median (95% CI) | ||
| Hazard ratio (95% CI) | 0.97 (0.71, 1.34) | |
Abbreviation: CI, confidence interval.
a The calculation for response duration was based on the interval between first response and time to progression.
The median time to response was 7.6 weeks (3.1 weeks to 5 months) with topotecan hydrochloride for injection compared with 6 weeks (2.4 weeks to 4.1 months) with paclitaxel. In the cross-over phase, 13% of 61 patients who received topotecan hydrochloride after paclitaxel had a partial response and 10% of 49 patients who received paclitaxel after topotecan hydrochloride had a response (2 complete responses).
Topotecan hydrochloride for injection was active in ovarian cancer patients who had developed resistance to platinum-containing therapy, defined as tumor progression while on, or tumor relapse within 6 months after completion of, a platinum-containing regimen. One complete and 6 partial responses were seen in 60 patients, for a response rate of 12%. In the same trial, there were no complete responders and 4 partial responders on the paclitaxel arm, for a response rate of 7%.
Topotecan hydrochloride for injection was also studied in an open-label, non-comparative trial in 111 patients with recurrent ovarian cancer after treatment with a platinum-containing regimen, or who had not responded to 1 prior platinum-containing regimen. The response rate was 14% (95% CI: 7%, 20%). The median duration of response was 5 months (4.6 weeks to 9.6 months). The time to progression was 2.6 months (5 days to 1.4 years). The median survival was 1.3 years (1.4 weeks, to 2.2 years).
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