Mitoxantrone Hydrochloride Injection - Scientific Information
|Manufacture:||Fresenius Kabi USA, LLC|
|Condition:||Acute Nonlymphocytic Leukemia, Metastatic Breast Cancer (Breast Cancer, Metastatic), Multiple Sclerosis, Non-Hodgkin's Lymphoma, Prostate Cancer|
|Form:||Liquid solution, Intravenous (IV)|
|Proper Name:||mitoxantrone hydrochloride|
|Chemical Name:||1,4-dihydroxy-5,8-bis[[2-[(2-hydroxyethyl)amino]-ethyl]amino]anthraquione dihydrochloride|
|Molecular Formula:||C22H28N4O6 • 2HCl|
|Description:||Mitoxantrone hydrochloride, a synthetic anthracenedione is a potent antineoplastic agent. It is a hygroscopic dark blue solid that is moderately soluble in water.|
Clinical trials experience has established the dosage range, efficacy and safety profile of mitoxantrone hydrochloride.
A single dose can be given intermittently every three or four weeks. The recommended initial treatment dose in good risk patients is 14 mg/m2.
The following efficacy and safety results were generated from analyses of data.
Efficacy data are available on 349 patients with locally advanced or metastatic breast carcinoma. Results are dependent on many predisposing factors including prior chemotherapy and/or radiotherapy, the health of the patients, sites of metastases, and dose of the agent employed. In a European multicentre, first-line, single-agent trial using an initial dose of 14 mg/m2, the overall response rate was 39%, which compared favourably to doxorubicin therapy at a dose of 60 - 75 mg/m2, when given to patients with similar stage disease. In a study of a direct comparison with doxorubicin, given as second-line therapy to breast cancer patients who failed a standard first-line combination, response rates are 27% for mitoxantrone and 23% for doxorubicin. The mean duration of response observed after mitoxantrone was greater than those reported after doxorubicin. Responses have been seen in all major sites of metastases including lymph nodes, lung, bone, skin and viscera, in patients both with and without prior hormonal therapy. Available data suggest that mitoxantrone is comparable in efficacy with doxorubicin in the treatment of advanced breast cancer. Myelosuppression with 21-day treatment intervals is comparable with that observed with doxorubicin. Multiple courses of single-agent mitoxantrone therapy, in some cases for longer than twelve cycles, have been administered with excellent tolerance and good response. Mitoxantrone showed incomplete cross-resistance with doxorubicin since responses have been observed in patients in whom doxorubicin had failed or who relapsed after response to that drug. A continuing large-scale clinical trials program with combination therapy also demonstrated early positive results for efficacy and safety. In seven studies, over 100 cycles of combination therapy have been given to 77 patients.
A total of 966 patients have been treated with mitoxantrone for three other indications of which 259 patients had non-Hodgkin’s lymphoma (NHL), 546 had leukemia, and 161 had hepatocellular carcinoma (HCC). The following summarizes the accrual of these 966 patients:
|Indication||Lederle-Sponsored Studies (No. Treated)||Independent Studies Reported in the Literature (No. Treated)|
(including pediatric cases)
Non-Hodgkin’s Lymphoma (NHL)
Three key studies evaluated single-agent mitoxantrone in 148 patients with relapsed or refractory advanced NHL at a dose of 14 mg/m2, i.v., every 3 weeks. Of 127 patients evaluable for response in two trials, there were 10 complete responses (CR) and 42 partial responses (PR) producing an overall therapeutic response rate of 41%. The median duration of responses in the multicentre study (122 valuable patients) was 195 days. Many patients’ responses lasted in excess of one year. Responses were seen in all histological subtypes of NHL. Response to mitoxantrone was independent of prior chemotherapy and independent of whether the patient received prior doxorubicin. This demonstrated a lack of complete cross-resistance between mitoxantrone and other drugs including anthracyclines.
Mitoxantrone was evaluated in combination with other agents for the treatment of NHL. A total of 28 patients were treated with different regimens. A first-line comparative trial of the combination of intermediate dose methotrexate with leucovorin rescue + bleomycin + doxorubicin + cyclophosphamide + vincristine + dexamethasone (m-BACOD) versus the same combination with 10 mg/m2 mitoxantrone replacing doxorubicin (m-BNCOD) has shown activity: 4 PRs in 6 evaluable patients with m-BNCOD and 3 PRs in 6 with m-BACOD. The combination of mitoxantrone at 10 mg/m2, daily for 3 days, + vincristine + dexamethasone (NOD) produced 3 PRs in 5 evaluable patients. A first-line comparative trial of the combination of cyclophosphamide + vincristine + prednisone + doxorubicin (CHOP) versus the same combinations with 10 mg/m2 mitoxantrone replacing doxorubicin (CNOP) has only recently begun.
Mitoxantrone at 5 mg/m2, daily for 3 days every 3 weeks, produced one CR and 2 PRs in 8 evaluable patients with NHL; ten patients enrolled. Several other studies, reported in the literature and not sponsored by Lederle, support the activity of mitoxantrone in the treatment of NHL.
Four key studies sponsored by Lederle evaluated single-agent mitoxantrone in 181 adult patients with refractory or relapsed acute nonlymphocytic leukemia (ANLL) or chronic myelogenous leukemia in blast crisis (B-CML) at doses ranging from 8 to 12 mg/m2, i.v., daily for 5 days, every 3 weeks. A dose-response effect was evident. Optimal activity was seen at a dose of 12 mg/m2, daily for 5 days. At this dose level, there were 19 CRs in 49 evaluable adult patients with ANLL in relapse producing an overall response rate of 39%. The median duration of complete response in the largest (121 patients) single-agent study was 98 days. Several patients had remissions lasting in excess of one year.
There were four studies comprising 63 patients in which mitoxantrone was evaluated in combination with other agents in the treatment of leukemia. The highest complete remission rate of 49% (11 CRs in 23 evaluable patients with ANLL) was obtained when mitoxantrone at 10 to 12 mg/m2, daily for 3 days, was combined with cytosine arabinoside at 100 mg/m2 daily for 7 days. When mitoxantrone at 10 mg/m2, daily for 5 days, was combined with the same dose of cytosine arabinoside, it produced 2 CRs in 8 evaluable patients. Treatment of patients with acute lymphoblastic leukemia using 10 mg/m2 mitoxantrone, daily for 3 days, + vincristine + prednisone produced 10 responses in 16 evaluable patients, for a response rate of 62.5%.
Activity was also seen in B-CML. Since no standard therapy exists for this disease and bone marrow is never truly normal in this disorder, both CRs and PRs were considered evidence of efficacy. The optimal dose of mitoxantrone was 12 mg/m2, daily for 5 days, producing 6 responses in 17 evaluable patients.
Experience in pediatric leukemia patients is limited. Twenty-four patients were treated with 6 to 8 mg/m2 mitoxantrone daily for 5 days. There were 3 responses in 24 evaluable children.
Fourteen adult leukemia patients received 20 to 37 mg/m2 mitoxantrone once every two weeks. No therapeutic responses were observed using this schedule.
Several other studies reported in the literature and not sponsored by Lederle support the activity of mitoxantrone in the treatment of ANLL and B-CML.
Hepatocellular Carcinoma (HCC)
Three clinical trials sponsored by Lederle have been conducted using mitoxantrone in the therapy of HCC. Mitoxantrone was administered to 65 patients intravenously at 12 mg/m2 every 3 weeks in two studies, and in one study with 10 patients at 6 to 10 mg/m2/day by continuous hepatic artery infusion for three consecutive days, every 3 weeks. Considering the short life span of patients presenting with HCC, a response of stable disease was included along with PRs and CRs in assessing efficacy. In these three studies, the overall therapeutic response rate was 46.7% (11 CRs and PRs + 10 stable disease in 45 evaluable patients). Activity was confirmed in other studies not sponsored by Lederle. Duration of response was variable among these studies and ranged between 3 and 52 weeks.
Data on the overall safety profile of mitoxantrone (based on 989 patients) demonstrated advantages of mitoxantrone compared to the anthracyclines with respect to both the quality of life and the long-term safety of patients. The majority of side effects with mitoxantrone are mild in nature. Removal of patients from mitoxantrone treatment for reasons of toxicity has been rare in clinical studies. A number of patients have reported no side effects at all. In addition, the relatively low risk of serious side effects has permitted treatment of patients on an out- patient basis. The most common acute effects were nausea and/or vomiting (only 3.5% severe or very severe with mitoxantrone, compared to 10 - 15% reported with doxorubicin), stomatitis/mucositis (only 0.3% severe or very severe with mitoxantrone) and alopecia (only 0.9% severe or very severe, and 15% overall with mitoxantrone compared with 85% severe or very severe and 100% overall reported with doxorubicin). Serious local reactions have been reported rarely following extravasation of mitoxantrone at the infusion site.
With respect to myelosuppression, initial mitoxantrone doses of 14 mg/m2 every three weeks are well tolerated in good-risk patients. Severe degrees of myelosuppression have been rare. The median white cell nadir in a European second-line study was 2.5 x 103; in a European first-line study, only 4.8% (2/42) of patients experienced a nadir of less than 1,000. The nadir usually occurs around day 10 or 11 and returns to normal baseline value by day 21, in time for the next course of treatment. After multiple courses of mitoxantrone, white blood cell and platelet nadirs show no further decrease beyond those observed in the first few cycles, indicating no cumulative or permanent effects of mitoxantrone on marrow reserves.
Mitoxantrone had an exceptional safety profile and was well tolerated by patients treated for NHL, leukemia and hepatoma, as well as for breast cancer. However, due to the pathophysiology of leukemia and the higher doses of mitoxantrone employed, the safety profile differed from that seen in NHL and in hepatoma (see Adverse Reactions). The most severe and life-threatening events, i.e., bleeding and infection, are well described morbid complications of acute leukemia. Many of the episodes of hepatic dysfunction were probably related to the increased bilirubin load and increased exposure to hepatic viruses as a result of the multiple transfusions of blood products necessary in the proper treatment of this disorder.
In investigational trials of intermittent single doses, patients who received up to the cumulative dose of 140 mg/m2 had a cumulative 2.6% probability of clinical congestive heart failure. The overall cumulative probability rate of moderate or serious decreases in LVEF at this dose was 13% in comparative trials. In contrast, doxorubicin has been reported to produce chronic cardiomyopathy and irreversible congestive heart failure in up to 11% of patients given nine or more courses of that drug at the usual dose schedule (60 mg/m2 every three weeks).
Mitoxantrone clearance is reduced by hepatic impairment. Patients with severe hepatic dysfunction (bilirubin greater than 3.4 mg/dL) have an AUC more than 3 times greater than that of patients with normal hepatic function receiving the same dose. Patients with hepatic impairment should be treated with caution and dosage adjustment may be required. Mitoxantrone should not be used in patients with severe hepatic dysfunction (see Contraindications).
Mitoxantrone, a synthetic anthracenedione, is a potent antineoplastic agent. It has a cytocidal effect on both proliferating and nonproliferating cultured human cells. It is four to seven times more potent than doxorubicin in inhibiting nucleic acid synthesis. In experimental tumour systems in mice, the therapeutic index of mitoxantrone is eight to fifteen times that of doxorubicin.
Mitoxantrone increases life span and numbers of long-term survivors among mice with leukemia P388 and L1210 leukemias or with B16 melanoma and colon 26 carcinoma solid neoplasms. It is active by the intraperitoneal, subcutaneous, and intravenous routes in mice, but oral activity has not been demonstrated. In conventional mouse test systems, mitoxantrone shows improved antineoplastic activity over that of doxorubicin, cyclophosphamide, 5-fluorouracil, methotrexate, cytosine arabinoside, and vincristine against intraperitoneally implanted tumours; data are presented in the table below:
|Drugs||Increase in Life Span (%)a in Mice With:|
|P388 Leukemia||L1210 Leukemia||B16 Melanoma||Colon 26 Carcinoma|
|Mitoxantrone||> 200||> 226||> 300||> 224|
|Doxorubicin||159||> 118||> 224||> 155|
|Methotrexate||149||96||> 25||> 25|
|Cytosine arabinoside||≥ 90||85||--||--|
a Percent increase in life span over untreated controls on day 30
Similar results have been reported by other investigators in comparative studies with antitumour antibiotics in mice with P388 or L1210 leukemias, or B16 melanoma implanted intraperitoneally, or with subcutaneously implanted Lewis Lung carcinoma; data are presented in the following table:
a Modified from Fujimoto and Ogawa, 1982
* Criteria is equivalent to “curable” rating
The therapeutic index of mitoxantrone was shown to be eight to fifteen times greater than that of doxorubicin against intraperitoneally implanted leukemias.
Increasing the amounts of mitoxantrone produces a progressive reduction in mouse bone marrow cellularity. A cytocidal effect in both actively proliferating and nonproliferating human cell cultures has been shown. These results indicate that mitoxantrone is not cell cycle phase-specific.
Mitoxantrone demonstrates rapid plasma clearance, a long elimination half-life, and extensive tissue distribution in both animals and humans. It is excreted primarily in the bile. There is little uptake by the brain, spinal cord and cerebrospinal fluid, indicating that mitoxantrone does not cross the blood-brain barrier to any appreciable extent.
Plasma and Whole Body Elimination
In rats, dogs, and monkeys given intravenous doses at 0.25 to 0.75, 0.37, and 1.0 mg/kg of 14C-mitoxantrone respectively, radioactivity concentrations disappear rapidly from both plasma and whole blood during the first 2 hours after dosing; thereafter, concentrations decreased slowly. In all three species, mitoxantrone is concentrated in red cells during early sampling times. Prolonged, though low (< 5 ng/mL), plasma levels were seen in dogs and monkeys through at least 58 and 35 days, respectively.
Total radioactivity has linear, sex-independent, and dose-independent characteristics. Pharmacokinetic parameters of mitoxantrone, studied most extensively in the rat, reveal an elimination half- life of 12 days, a final volume of distribution of 392 L/kg, and clearance values for total plasma, renal, and nonrenal compartments of 15.8, 1.7, and 14.1 mL/min/kg, respectively.
In rats, dogs, and monkeys, 10 days after a single i.v. dose of 14 C-mitoxantrone, 65 to 85% of the administered radioactivity is accounted for in the excreta; 80 to 90% of the recovered radioactivity being excreted in the feces and 10 to 20% excreted in the urine. While excretion is prolonged, only slightly detectable amounts are still being excreted daily 2 to 4 months after dosing.
Bile is the major excretory route in rats; within 6 hours of dosing, 22% of the radioactivity was excreted in the bile of bile-cannulated rats given 0.5 mg/kg radiolabelled mitoxantrone intravenously. Little radioactivity was found in the bile of the rats given radiolabelled mitoxantrone orally, confirming the poor absorption of the drug.
Tissue Distribution and Metabolism
Mitoxantrone is rapidly and extensively distributed into the organs of rats, dogs, and monkeys; distribution is independent of dose. One or two days after dosing, radioactivity was highest in bile, gallbladder (except rats), liver, spleen, and kidney. In all three species, tissue concentrations are greater than respective plasma levels; radioactivity levels decrease with time. Little or no radioactivity is detected in brain, spinal cord, and cerebrospinal fluid indicating poor penetration of mitoxantrone through the blood-brain barrier. Amounts found in testes are also relatively low.
In pregnant rats, fetal uptake is negligible and amniotic fluid contains no appreciable amount of drug; these findings along with results showing appreciable uptake of radioactivity by the placenta indicate that the placenta is an effective barrier.
In all pharmacokinetic studies, the evidence suggests that rats, dogs, and monkeys are similar to humans relative to absorption, elimination, and tissue distribution. In clinical trials, studies in patients following i.v. administration of 12 mg/m2 (0.35 mg/kg)a of 14C-mitoxantrone also demonstrate a rapid plasma clearance, a long elimination half-life and persistent tissue concentrations. Published clinical results also indicate that mitoxantrone is taken up rapidly by tissue and released slowly.
Studies to determine the extent of metabolism and identity of metabolites of mitoxantrone are ongoing.
Mitoxantrone has an exceptionally favourable toxicity profile relative to other antineoplastic agents, including doxorubicin. Most importantly, the chronic toxicity of mitoxantrone does not include the dose-limiting progressive cardiomyopathy that is characteristic of chronic i.v. administration of anthracyclines in animals and humans. Moreover, compared to other antineoplastic agents, the severity of gastrointestinal effects of mitoxantrone is less, atrophy of hair follicles is not produced, and no irritation occurs when accidentally extravasated. Mitoxantrone is also not teratogenic in rats or rabbits, a finding which is probably attributable to an effective placental barrier in these species. The reversibility of clastogenic effects of mitoxantrone in rats given tolerated doses every 3 weeks and the absence of a dominant lethal effect may suggest that with clinical use dosing, there may be little mutagenic risk to humans receiving mitoxantrone.
In rats, dogs, and monkeys, mitoxantrone produces myelosuppression typical of other antineoplastic agents. Since myelosuppression is the sole dose-limiting effect of mitoxantrone, the degree of leukopenia is indicative of the maximum tolerated dose (MTD) in both animals and humans. In all three animal species, doses above the single or multiple MTD produce life-threatening myelosuppression. For this reason, the degree of leukopenia should be carefully monitored in the clinical use of mitoxantrone.
Single Dose (Acute) Toxicity Studies
The acute lethality of mitoxantrone following single intravenous doses in mice and rats is shown below:
|Species||Sex||LD10 (mg/kg)||LD50 (mg/kg)|
Similar LD50s were determined for mice and rats dosed intraperitoneally. Signs of toxicity for mice and rats via i.v. or i.p. routes included salivation, paleness, rough fur, decreased body weight gain and weight loss, abdominal distension, diarrhea, epistaxis, chromodacryorrhea, swelling of the nasal region, lacrimation, and hematuria.
In dogs and monkeys, the lethal single i.v. dose of mitoxantrone was 0.5 mg/kg for dogs and ≥ 1 mg/kg for monkeys. In contrast, the single lethal i.v. dose of doxorubicin has been reported to be 2.5 mg/kg for dogs and 4.2 mg/kg for monkeys. For mitoxantrone, signs of acute toxicity are related primarily to effects on the gastrointestinal tract and include emesis and diarrhea (dogs) and decreased food consumption and body weight (both species). Erythropenia and leukopenia are accompanied by bone marrow hypocellularity and lymphocytic depletion of lymphoid organs.
Multiple Dose Studies
Multiple dose i.v. studies in rats, dogs, and monkeys were designed to investigate the chronic toxicity of mitoxantrone with careful attention being paid to the presence or absence of cardiomyopathy characteristic of anthracyclines. Repeated administration of doxorubicin in animals or man is associated with progressive cardiomyopathy leading to congestive heart failure.
In rats, both daily and intermittent (once every 3 weeks) multiple dose studies were conducted. In the daily study, rats were given doses ranging from 0.003 to 0.3 mg/kg once daily for 1 month. In the intermittent study, rats were given doses of 0.03, 0.3, 0.6, and 0.9 mg/kg i.v. once every 3 weeks for 18 dosing cycles. In both studies, sublethal and lethal doses of mitoxantrone did not produce progressive anthracycline-like cardiomyopathy. Subchronic and chronic toxicity was limited to effects on the kidneys and the hematopoietic system, effects similar to those reported for doxorubicin in rats. Ongoing studies in rats to investigate carcinogenicity of mitoxantrone have also revealed no evidence of progressive anthracycline-like cardiomyopathy after 21 dosing cycles (once/3 weeks) at i.v. doses of 0.01, 0.03, and 0.10 mg/kg.
In dog and monkey studies, doxorubicin was studied simultaneously as a model for anthracycline-induced cardiomyopathy. Mitoxantrone was given intravenously to dogs and monkeys once every 3 weeks at dose levels of 0.125 and 0.25 mg/kg; doxorubicin was administered at a single dose level of 1.64 mg/kg similarly. Doses selected for these studies approximated one-half the single lethal i.v. dose of each compound in dogs and monkeys. From range-finding studies, these doses were also those which would produce degrees of leukopenia generally tolerated without producing life-threatening myelosuppression in either species and were therefore considered to be maximum tolerated doses (MTDs) in dogs and monkeys.
The results of these dog and monkey multiple dose studies revealed that mitoxantrone produced a generally comparable (at the low dose) or greater (at the high dose) degree of leukopenia than doxorubicin. Therefore, mitoxantrone was evaluated for chronic toxicity under conditions more severe than doxorubicin. Only doxorubicin displayed treatment-limiting toxicity, i.e., progressive cardiomyopathy in both dogs and monkeys necessitating sacrifice of animals before the intended completion of the studies. Mitoxantrone animals received 10 (dog) or 12 (monkey) dosing cycles while doxorubicin animals received 8 - 9 (dog) or 9 - 10 (monkey) dosing cycles.
Findings relative to effects on the heart of dogs and monkeys receiving mitoxantrone i.v. were not representative of anthracycline toxicity. Neither irreversible cellular damage nor functional signs of cardiotoxicity were seen in dogs or monkeys receiving mitoxantrone. In contrast, dogs given doxorubicin showed evidence of progressive cardiomyopathy following the fourth dose. The myocyte changes progressed in severity with time and cumulative dose to irreversible cardiomyopathy characteristic of anthracyclines. Clinical signs of congestive heart failure in doxorubicin-treated dogs were also evident. In monkeys given doxorubicin, similar irreversible cardiac changes and clinical signs of cardiotoxicity, the latter characterized by progressive decreases in mean blood pressure and ECG changes, were also detected. Therefore, these chronic studies in dogs and monkeys clearly show that, in spite of myelosuppression which was at least as great with mitoxantrone as with doxorubicin, chronic progressive cardiomyopathy was not present for mitoxantrone. However, typical anthracycline-induced cardiomyopathy was present for doxorubicin.
Additional studies in dogs and rabbits have been sponsored by the National Cancer Institute. From these studies, descriptions of acute toxic response to mitoxantrone include effects on the heart. Because doses in these particular studies were lethal doses in which death resulted from renal, hepatic, and hematopoietic failure, the cardiac effects (thrombosis, myocarditis, necrosis and fibrosis) were secondary to generalized organ toxicity involving the kidney, liver, and bone marrow. The cardiac effects from these studies are neither predictive nor typical of progressive anthracycline-like cardiomyopathy.
Mutagenicity and Cytogenetic Studies
In microbial mutagenicity tests, mitoxantrone causes frame-shift mutations. In primary rat hepatocyte cultures assayed for unscheduled DNA synthesis (DNA repair), mitoxantrone causes DNA damage. Mitoxantrone does not cause a dominant lethal effect in rats. The spectrum of genetic activity seen with mitoxantrone is similar to other antineoplastic drugs and is consistent with its activity as a DNA-reactive agent.
When an in vivo cytogenetic study was conducted using intraperitoneal doses of 0.5 to 2.0 mg/kg once daily for 5 consecutive days, mitoxantrone caused chromosomal aberrations. However, when the study was repeated using a dosing regimen that more closely resembled a clinically used regime (single 0.3 mg/kg intravenous doses at 21-day intervals), chromosomal damage, noted one day after the first dose, did not accumulate or persist. The incidence of chromosome damage, 21 days after one or two doses, resembled that noted in controls. Thus, at a dose approximating clinical use levels, the clastogenic effect is reversible.
Reproductive Toxicology and Teratology
In these studies at the highest tolerated daily doses allowing evaluation of reproduction and teratology, mitoxantrone had no effect on reproductive performance, fertility, or gestation in rats. Slight dose-related decreases in epididymal weights were noted in the F0 generation. However, F1 and F2 generations were not affected by dosing of the F0 generation.
Mitoxantrone, given i.v. to pregnant rats and rabbits, was not teratogenic in either species. Decreased fetal body weight in high-dose rats was attributed to maternal toxicity although an increased incidence of premature delivery was noted in rabbits. In contrast, doxorubicin is known to be embryotoxic and teratogenic in rats and embryotoxic and abortifacient in rabbits.
Rationale for Expression of Mitoxantrone Doses in mg/kg
Throughout our studies with mitoxantrone, doses have been expressed on a body weight basis rather than on a body surface area basis. Although clinical oncologists generally use body surface area as the basis for determining doses in man, the use of body weight in comparing doses between animals and man is considered more appropriate in the case of mitoxantrone and doxorubicin.
Based on the use of body surface area, an apparently wide discrepancy between MTDs in animals and man exists for both compounds. For example, when body surface area is used to compare doses for mitoxantrone in dogs, monkeys, and man, the MTDs are 5, 3, and 12 - 14 mg/m2, respectively; for doxorubicin, the values for dogs, monkeys, and man are 34, 19.7, and 65 mg/m2, respectively. However, on a body weight basis, the MTDs for dogs, monkeys, and man for mitoxantrone are 0.25, 0.25, and 0.35 - 0.41 mg/kg, respectively; likewise, the MTDs for doxorubicin are respectively 1.6, 1.6, and 1.9 mg/kg. Essentially no difference exists between animals and man relative to the MTDs when doses are expressed on a mg/kg basis. Therefore, the use of body weight is a more direct and accurate way to compare mitoxantrone doses between animals and humans.