Correlation of clinical pharmacokinetic parameters of cisplatin with efficacy and toxicity

Therapeutic drug monitoring for dose individualization of Cisplatin in testicular cancer patients based upon total platinum measurement in plasma

Cisplatin (CDDP) is an anticancer agent widely used in testicular cancer, for which pharmacokinetic (PK)/pharmacodynamic relationships have usually been based upon measurement of its unbound fraction in plasma. Because it has been shown that free CDDP clearance can be related to patient's body surface area (BSA), dosage is mostly adjusted a priori using only this single parameter, with mixed results for accurately predicting CDDP exposure and reducing toxicities. In contrast, the authors present here an original, 5-day continuous infusion schedule, coupled to a daily Bayesian adaptive dosing with feedback strategy, based upon the rapid assay of total, rather than free, CDDP in plasma. Nineteen patients (66 therapeutic courses) were treated with platinum-based combinational therapy. Plasma samples were analyzed to allow real-time Bayesian estimation of individual PK parameters with subsequent prospective dose adjustment in order to reach a target Cmax (Cend) of 1.95 mg/L of total platinum. Performance of the Bayesian dosing method was evaluated by comparing target Cmax with achieved Cmax. The mean+/-SD Cmax achieved was 1.93+/-0.16 mg/L. No statistically significant difference was observed between experimental and target values (P>0.05, t test), and Cend achievement was done with an overall 6.6% precision, a performance to be compared with the initial 54% interpatient variability observed in CDDP clearance. A nonlinear mixed effect model population PK analysis was subsequently performed to identify retrospectively the covariates associated with PK parameters of total CDDP. It showed a good correlation (r=0.84, P=0.004) between total platinum clearance and therapeutic course number. A weaker correlation (r=0.59) was found between BSA and total CDDP clearance and, importantly, no additional relationship was established with BSA when successive therapeutic courses, and not only the first one, were considered. This highlights the critical importance of total drug accumulation on CDDP pharmacokinetics when several infusions are to be administered in a row and, therefore, the need for real-time dose individualization that takes into account the course number, rather than BSA. Finally, doses of CDDP administered during each course were significantly higher (+20%, P<0.01) than the ones classically normalized with BSA, thus leading to an overall greater drug exposure in the patients. It is noteworthy that despite these markedly higher doses, little severe toxicity was reported, and all of the patients presented in this study were still alive and disease free after a follow-up of up to 15 years.

Body-surface area-based dosing does not increase accuracy of predicting cisplatin exposure

PURPOSE

Most anticancer drugs are dosed based on body-surface area (BSA) to reduce interindividual variability of drug effects. We evaluated the relevance of this concept for cisplatin by analyzing cisplatin pharmacokinetics obtained in prospective studies in a large patient population.

PATIENTS AND METHODS

Data were obtained from 268 adult patients (163 males/105 females; median age, 54 years [range, 21 to 74 years]) with advanced solid tumors treated in phase I/II trials with cisplatin monotherapy or combination chemotherapy with etoposide, irinotecan, topotecan, or docetaxel. Cisplatin was administered either weekly (n = 93) or once every 3 weeks (n = 175) at dose levels of 50 to 100 mg/m(2) (3-hour infusion). Analysis of 485 complete courses was based on measurement of total and non-protein-bound cisplatin in plasma by atomic absorption spectrometry.

RESULTS

No pharmacokinetic interaction was found between cisplatin and the anticancer drugs used in combination therapies. A linear correlation was observed between area under the curves of unbound and total cisplatin (r = 0.63). The mean plasma clearance of unbound cisplatin (CL(free)) was 57.1 +/- 14.7 L/h (range, 31.0 to 116 L/h), with an interpatient variability of 25.6%. BSA varied between 1.43 and 2.40 m(2) (mean, 1.86 +/- 0.19 m(2)), with an interpatient variability of 10.4%. When CL(free) was corrected for BSA, interindividual variability remained in the same order (23.6 v 25.6%). Only a weak correlation was found between CL(free) and BSA (r = 0.42). Intrapatient variability in CL(free), calculated from 90 patients was 12.1% +/- 7.8% (range, 0.30% to 32.7%).

CONCLUSION

In view of the high interpatient variability in CL(free) relative to variation in observed BSA, no rationale for continuing BSA-based dosing was found. We recommend fixed-dosing regimens for cisplatin.

Pharmacokinetics of cisplatin in combined cisplatin and 5-fluorouracil therapy: a comparative study of three different schedules of cisplatin administration

BACKGROUND

Cisplatin is widely used in combination chemotherapy against a variety of tumors; however, the optimal administration schedule of cisplatin is still controversial. To clarify the pharmacokinetic differences according to the administration schedules of cisplatin, we compared three different administration schedules of cisplatin such as single short-term infusion, daily short-term infusion and daily continuous infusion in combination with 5-fluorouracil. Preliminary clinical responses and toxicities were also investigated.

METHODS

A total of 12 courses in combination of cisplatin and 5-fluorouracil therapy was studied. The schedules of cisplatin tested were as follows: single short-term infusion (80 mg/m2, day 1,2 h div., n = 4), daily short-term infusion (20 mg/m2, days 1 to 5, 2 h div., n = 4), daily continuous infusion (100 mg/m2, 120 h, n = 4). In all schedules, 5-fluorouracil was continuously administered at a dose of 800 mg/m2/day on days 1 to 5. The area under the time-concentration curve (AUC) and the maximum concentration (Cmax) of total and free Pt were investigated.

RESULTS

The highest AUC of total and free Pt and the lowest Cmax of free Pt were observed in the daily continuous infusion (total AUC; 162.53 +/- 18.39 micrograms h/ml, free AUC; 5.50 +/- 0.9 micrograms h/ml, free Cmax; 0.07 +/- 0.01 microgram/ml, mean +/- SEM). Two patients in the single short-term infusion and one patient in the daily continuous infusion indicated partial responses clinically. No nephrotoxicity or ototoxicity was observed. All toxicities were mild and tolerable in all regimens; however, the incidence of GI toxicity in daily continuous infusion seemed to be relatively higher.

CONCLUSIONS

Daily continuous infusion of cisplatin gave the best pharmacokinetic results and to evaluate the clinical advantage of this schedule a prospective randomized trial should be conducted with sufficient numbers of patients.

Benefits of pharmacological knowledge in the design and monitoring of cancer chemotherapy

Prescribing chemotherapy is a difficult task, because of drug resistance, which prevents all tumors to respond to a given protocol and because of drug toxicity, which is generally unavoidable but which must be limited to acceptable levels. The therapeutic window of anticancer drugs is very narrow and clinicians have to try to optimize the individual doses and schedules of the drugs to be administered. They can rely upon simple anthropometric features, such as body weight or surface area; they can also take into account the physiological status of the patient: age, liver and kidney function, genetic characteristics of drug metabolism, etc. The best way for dose adaptation lies in the establishment of pharmacokinetic/pharmacodynamic relationships, i.e., between the behavior of a drug in the body and its efficacy and toxicity. When it is established that the optimal effect of a drug is related to a given parameter, such as the area under the curve plotting plasma concentration vs. time (AUC), it becomes possible to administer the drug with the dose allowing to obtain the target parameter value. Individual dose adaptation can be achieved thanks to the study of the pharmacokinetics of a test dose preceding that of the therapeutic dose, or by the measure of drug plasma levels, either at steady state during a protracted infusion, or from cycle to cycle during repetitive protocols. Population analysis now allows the adaptation of anticancer drug dosing from a minimum knowledge of individual pharmacokinetic features, together with other characteristics of the patients such as age, gender or physiological functions.

Evaluation of a prediction model of cisplatin dose based on total platinum plasma concentration

The aim of this study was to validate prospectively a model of cisplatin dose adjustment. 27 patients (63 courses) with lung cancer were treated by a 5 day continuous infusion of cisplatin and etoposide. The dose of cisplatin was adjusted in order to reach a target plasma concentration of total platinum (TP) of 2000 mu/l at the end of the infusion. The target concentration was reached with a mean bias of 2.7% and a precision of 7.8%. The results were compared with those of a population of 38 patients (97 courses) with lung cancer and treated with the same protocol of chemotherapy, but without dose adjustment. The average dose adjustment was an increase of cisplatin dose of 20.2%. This augmentation was most important during the first course, decreasing during the following courses. There was also an increase in the etoposide AUC, although its dose was not modified. Toxicity to polymorphonuclear cells was significantly increased and was linked to etoposide AUC.

Pharmacokinetics and tissue distribution of cisplatin in nude mice: platinum levels and cisplatin-DNA adducts

The pharmacokinetics of platinum (Pt) and cisplatin (CDDP)-DNA adducts were studied in nude mice after single-dose CDDP treatments. Whole blood, serum, kidney, lever, testis, brain, and tumor were collected at different intervals after injection of CDP at different dose levels. Pt was measured with flameless atomic absorption spectrometry (FAAS) or adsorptive voltammetry (AdV) and CDDP-DNA adducts with quantitative immunohistochemistry. The drug was immediately absorbed into the blood circulation (peak serum Pt levels were reached within 5 min) after i.p. CDDP administration, and distribution into most tissues also occurred rapidly (tissue Pt levels peaked at 15 min). With a sampling period of 7 days there was a biphasic elimination of Pt from blood, serum, and tissues. In the brain the pharmacokinetics differed with a gradual accumulation of Pt occurring during the 1st week. Formation of CDDP-DNA adducts in tissues was a slower process, with maximal levels being achieved at between 30 min and 4 h after drug administration, followed by a steady state lasting for at least 24 h. Each tissue type had its specific immunohistochemical staining pattern of adducts. With escalating CDDP doses there was a linear, or almost linear, increase in Pt concentrations and CDDP-DNA adduct levels in all sample types examined. These results suggest that a fair estimation of the amount of drug in tumor and normal tissues can be made from analysis of serum Pt at a fixed time point after a single dose of CDDP.

Long-term pharmacokinetic behavior of platinum after cisplatin administration

PURPOSE

The platinum concentration in plasma was studied in 19 patients treated by 3 or 4 successive courses of chemotherapy including cisplatin for head and neck cancers.

METHODS

Cisplatin was given i.v. daily at 25 mg/m2 by 1-h infusions for 4 days every 3 weeks. Total and ultrafiltrable platinum were measured in plasma using an inductively coupled plasma mass spectrometry (ICPMS) technique.

RESULTS

A progressive accumulation of total platinum in plasma was observed with consecutive infusions. The mean (+/- SD) total plasma platinum level detected at the end of cisplatin infusion was 1134 +/- 234, 1407 +/- 268, and 1618 +/- 282 micrograms/l at the end of the first, second, and third courses, respectively. The minimal platinum concentration measured before the second and third courses also increased to 221 +/- 59 and 309 +/- 76 micrograms/l, respectively. The steady state was not reached before the third course. However, differences in the evolution of platinum plasma levels were found among the 19 patients. In 14 patients the pharmacokinetics of platinum was characterized by low initial levels, a progressive accumulation, and a long terminal half-life with a very late steady state. In 5 patients, the pharmacokinetic behavior of platinum was different: platinum levels were directly high, without progressive accumulation, the steady state being reached as early as the first course. Significant levels of ultrafiltrable platinum were found throughout the treatment, even during the intervals between courses with this very sensitive analytical method. A close equilibrium between ultrafiltrable and total platinum (ratio, 6%) persisted for as long as 3 weeks after cisplatin administration.

DISCUSSION

These results underline the importance of individual differences in platinum metabolism. The relationship between total and ultrafiltrable platinum are discussed.

Individual dose adaptation of anticancer drugs

The dose of anticancer drugs is currently adjusted to the patient body surface area, although patients have different abilities to clear anticancer drugs. The dose adjustment to physiological functions permits major toxic accidents to be avoided. The adjustment to tumour drug content is considered, but for ethical or technical reasons, it cannot be used routinely The best criterion for the dose adjustment seems to be drug plasma concentration. The relationship between plasma concentration and efficacy may not be excellent, since it depends on the presence of resistant cells and on the blood flow through the tumour. A relationship between plasma concentration and/or the area under the curve (AUC) with toxicity has been reported with all major anticancer drugs. Different methods of dose adjustment to the drug plasma concentration are reported. In conclusion, dose adjustment to the drug plasma concentration or to the AUC can improve the chemotherapy efficacy, while reducing toxicity.

Pharmacokinetic and biotransformation studies of ormaplatin in conjunction with a phase I clinical trial

Ormaplatin is a second-generation platinum (Pt) analogue with in vitro activity against some cisplatin-resistant malignant cell lines. We have evaluated the pharmacokinetics and biotransformations of ormaplatin during a phase I trial in which ormaplatin was administered by daily 30-min infusions on 5 consecutive days every 28 days. Sixteen patients received 25 courses at doses ranging from 5.0 to 11.6 mg/m2 per day. Pharmacokinetic parameters determined for ultrafilterable Pt measured by atomic absorption spectrophotometry revealed a short half-life (t1/2 16 min), moderate volume of distribution (Vd 12 l/m2), and relatively fast systemic clearance (Cls 544 ml/min per m2). Cls and percentage of drug unbound decreased during the 5-day administration period. Average systemic exposure increased with dose; however, inter-individual variability in Cls produced overlap in systemic exposure between the dose levels. The major active biotransformation product [PtCl2(dach)] was evaluated at the highest dose level by HPLC. This product decayed monoexponentially with a mean t1/2 of 13 min and a higher degree of pharmacokinetic variability than that of ultrafilterable Pt at this dose. No unreacted ormaplatin was detected; however, several inactive biotransformation products persisted for at least 120 min. Approximately 32% of the dose was excreted in the urine during the first day, one-third of this during the initial 1.5 h. The human pharmacokinetic characteristics of ormaplatin resemble those of cisplatin; however, additional study will be required to discern which analyte of ormaplatin correlates best with clinical effects.