C6H12N2O4Pt M.W. 371.25
Carboplatin, USP is a crystalline powder. It is soluble in water at a rate of approximately 14 mg/mL, and the pH of a 1% solution is 5 to 7. It is virtually insoluble in ethanol, acetone, and dimethylacetamide.
Carboplatin, like cisplatin, produces predominantly inter strand DNA cross-links rather than DNA-protein cross-links. This effect is apparently cell-cycle nonspecific. The aquation of carboplatin, whichis thought to produce the active species, occurs at a slower rate than in the case of cisplatin. Despite this difference, it appears that both carboplatin and cisplatin induce equal numbers of drug-DNA cross-links, causing equivalent lesions and biological effects. The differences in potencies for carboplatin and cisplatin appear to be directly related to the difference in aquation rates.
In patients with creatinine clearances of about 60 mL/min or greater, plasma levels of intact carboplatin decay in a biphasic manner after a 30-minute intravenous infusion of 300 mg/m2 to 500 mg/m2 of carboplatin. The initial plasma half-life (alpha) was found to be 1.1 to 2 hours (n = 6), and the postdistribution plasma half-life (beta) was found to be 2.6 to 5.9 hours (n = 6). The total body clearance, apparent volume of distribution and mean residence time for carboplatin are 4.4 L/hour, 16 L and 3.5 hours, respectively. The C maxvalues and areas under the plasma concentration versus time curves from 0 to infinity (AUC inf) increase linearly with dose, although the increase was slightly more than dose proportional. Carboplatin, therefore, exhibits linear pharmacokinetics over the dosing range studied (300 mg/m2 to 500 mg/m2).
Carboplatin is not bound to plasma proteins. No significant quantities of protein-free, ultrafilterable platinum-containing species other than carboplatin are present in plasma. However, platinum from carboplatin becomes irreversibly bound to plasma proteins and is slowly eliminated with a minimum half-life of 5 days.
The major route of elimination of carboplatin is renal excretion. Patients with creatinine clearances of approximately 60 mL/min or greater excrete 65% of the dose in the urine within 12 hours and 71% of the dose within 24 hours. All of the platinum in the 24-hour urine is present as carboplatin. Only 3% to 5% of the administered platinum is excreted in the urine between 24 and 96 hours. There are insufficient data to determine whether biliary excretion occurs.
In patients with creatinine clearances below 60 mL/min, the total body and renal clearances of carboplatin decrease as the creatinine clearance decreases. Carboplatin dosages should therefore be reduced in these patients (see DOSAGE AND ADMINISTRATION).
The primary determinant of carboplatin injection clearance is glomerular filtration rate (GFR) and this parameter of renal function is often decreased in elderly patients. Dosing formulas incorporating estimates of GFR (see DOSAGE AND ADMINISTRATION) to provide predictable carboplatin injection plasma AUCs should be used in elderly patients to minimize the risk of toxicity.
CLINICAL STUDIES
Use with Cyclophosphamide for Initial Treatment of Ovarian Cancer
In two prospectively randomized, controlled studies conducted by the National Cancer Institute of Canada, Clinical Trials Group (NCIC) and the Southwest Oncology Group (SWOG), 789 chemotherapy naive patients with advanced ovarian cancer were treated with carboplatin or cisplatin, both in combination with cyclophosphamide every 28 days for 6 courses before surgical reevaluation. The following results were obtained from both studies:
Comparative Efficacy
Overview of Pivotal Trials
Clinical Response in Measurable Disease Patients
Pathologic Complete Response*
*114 Carboplatin and 109 Cisplatin patients did not undergo second look surgery in NCIC study.
90 Carboplatin and 106 Cisplatin patients did not undergo second look surgery in SWOG study.
Progression-Free Survival (PFS)
*Kaplan-Meier Estimates
Unrelated deaths occurring in the absence of progression were counted as events (progression) in this analysis.
**Analysis adjusted for factors found to be of prognostic significance were consistent with unadjusted analysis.
Survival
*Kaplan-Meier Estimates
**Analysis adjusted for factors found to be of prognostic significance were consistent with unadjusted analysis.
Comparative Toxicity
The pattern of toxicity exerted by the carboplatin-containing regimen was significantly different from that of the cisplatin-containing combinations. Differences between the two studies may be explained by different cisplatin dosages and by different supportive care.
The carboplatin-containing regimen induced significantly more thrombocytopenia and, in one study, significantly more leukopenia and more need for transfusional support. The cisplatin-containing regimen produced significantly more anemia in one study. However, no significant differences occurred in incidences of infections and hemorrhagic episodes.
Non-hematologic toxicities (emesis, neurotoxicity, ototoxicity, renal toxicity, hypomagnesemia, and alopecia) were significantly more frequent in the cisplatin-containing arms.
ADVERSE EXPERIENCES IN PATIENTS WITH OVARIAN CANCER NCIC STUDY
† May have been affected by cyclophosphamide dosage delivered
ADVERSE EXPERIENCES IN PATIENTS WITH OVARIAN CANCER SWOG STUDY
† May have been affected by cyclophosphamide dosage delivered
Use as a Single Agent for Secondary Treatment of Advanced Ovarian Cancer
In two prospective, randomized controlled studies in patients with advanced ovarian cancer previously treated with chemotherapy, carboplatin achieved 6 clinical complete responses in 47 patients. The duration of these responses ranged from 45 to 71+ weeks.