Phenasen

Phenasen is indicated for induction of remission and consolidation in patients with acute promyelocytic leukemia (APL) who are refractory to, or have relapsed from, retinoid and anthracycline chemotherapy, and whose APL is characterized by the presence of the t(15;17) translocation or PML/RAR-alpha gene expression.

Recommended Dosage

Induction Treatment Schedule

Administer Phenasen intravenously at a dose of 0.15 mg/kg daily until Sections or subsections omitted from the full prescribing information are not listed. bone marrow remission. Do not exceed 60 doses for induction.

Consolidation Treatment Schedule

Begin consolidation treatment 3 to 6 weeks after completion of induction therapy. Administer Phenasen intravenously at a dose of 0.15 mg/kg daily for 25 doses over a period up to 5 weeks.

Dose Adjustment For Non-Hematologic Adverse Reactions

If a severe non-hematologic adverse reaction occurs (such as neurologic or dermatologic toxicity), consider delaying Phenasen infusion until the event has resolved (≤ Grade 1).

Instructions For Preparation And Intravenous Administration

Administration

Administer Phenasen intravenously over 1-2 hours. The infusion duration may be extended up to 4 hours if acute vasomotor reactions are observed. A central venous catheter is not required.

The Phenasen vial is single-dose and does not contain any preservatives. Unused portions of each vial should be discarded properly. Do not mix Phenasen with other medications.

Reconstitution

Dilute Phenasen with 100 to 250 mL 5% Dextrose Injection, USP or 0.9% Sodium Chloride Injection, USP, using proper aseptic technique, immediately after withdrawal from the vial. Do not save any unused portions for later administration.

Safe Handling Procedures

Phenasen is a cytotoxic drug. Follow applicable special handling and disposal procedures.

Stability

After dilution, Phenasen is chemically and physically stable when stored for 24 hours at room temperature and 48 hours when refrigerated.

Phenasen is contraindicated in patients who are hypersensitive to arsenic.

WARNINGS

Included as part of the PRECAUTIONS section.

PRECAUTIONS

APL Differentiation Syndrome

Nine of 40 patients with APL treated with Phenasen, at a dose of 0.15 mg/kg, experienced the APL differentiation syndrome. High-dose steroids have been administered at the first suspicion of the APL differentiation syndrome and appear to mitigate signs and symptoms. At the first signs that could suggest the syndrome (unexplained fever, dyspnea and/or weight gain, abnormal chest auscultatory findings or radiographic abnormalities), high-dose steroids (dexamethasone 10 mg intravenously BID) should be immediately initiated, irrespective of the leukocyte count, and continued for at least 3 days or longer until signs and symptoms have abated. The majority of patients do not require termination of Phenasen therapy during treatment of the APL differentiation syndrome.

Cardiac Conduction Abnormalities : Torsade de Pointes, Complete Heart Block, And QT Prolongation

Torsade de pointes and complete heart block have been reported. QT/QTc prolongation can occur. Sixteen of 40 patients (40%) had at least one ECG tracing with a QTc interval greater than 500 msec. Prolongation of the QTc was observed between 1 and 5 weeks after Phenasen infusion, and then returned towards baseline by the end of 8 weeks after Phenasen infusion.

Prior to initiating therapy with Phenasen, a 12-lead ECG should be performed and serum electrolytes (potassium, calcium, and magnesium) and creatinine should be assessed. Preexisting electrolyte abnormalities should be corrected and, if possible, drugs that are known to prolong the QT interval should be discontinued. If it is not possible to discontinue the interacting drug, perform cardiac monitoring frequently.

Monitor ECG weekly, and more frequently for clinically unstable patients.

For QTc greater than 500 msec, complete corrective measures and reassess the QTc with serial ECGs prior to initiating Phenasen. During Phenasen therapy, maintain potassium concentrations above 4 mEq/L and magnesium concentrations above 1.8 mg/dL. Reassess patients who reach an absolute QT interval value > 500 msec and immediately correct concomitant risk factors, if any, while the risk/benefit of continuing versus suspending Phenasen therapy should be considered. There are no data on the effect of Phenasen on the QTc interval during the infusion.

The risk may be increased when Phenasen is coadministered with medications that can lead to electrolyte abnormalities (such as diuretics or amphotericin B).

Carcinogenesis

The active ingredient of Phenasen, arsenic trioxide, is a human carcinogen. Monitor patients for the development of second primary malignancies.

Embryo-Fetal Toxicity

Phenasen can cause fetal harm when administered to a pregnant woman. Arsenic trioxide was embryolethal and teratogenic in rats when administered on gestation day 9 at a dose approximately 10 times the recommended human daily dose on a mg/m² basis. A related trivalent arsenic, sodium arsenite, produced teratogenicity when administered during gestation in mice at a dose approximately 5 times the projected human dose on a mg/m² basis and in hamsters at an intravenous dose approximately equivalent to the projected human daily dose on a mg/m² basis. Advise pregnant women of the potential risk to a fetus. Advise females and males of reproductive potential to use effective contraception during and after treatment with Phenasen.

Laboratory Tests

The patient's electrolyte and glucose levels, as well as hepatic, renal, hematologic and coagulation profiles should be monitored at least twice weekly, and more frequently for clinically unstable patients during the induction phase and at least weekly during the consolidation phase.

Nonclinical Toxicology

Carcinogenesis, Mutagenesis, Impairment Of Fertility

Carcinogenicity studies have not been conducted with Phenasen by intravenous administration.

Arsenic trioxide and trivalent arsenite salts have not been demonstrated to be mutagenic to bacteria, yeast or mammalian cells. Arsenite salts are clastogenic in vitro (human fibroblast, human lymphocytes, Chinese hamster ovary cells, Chinese hamster V79 lung cells). Trivalent arsenic produced an increase in the incidence of chromosome aberrations and micronuclei in bone marrow cells of mice.

The effect of arsenic on fertility has not been adequately studied.

Use In Specific Populations

Pregnancy

Risk Summary

Phenasen can cause fetal harm when administered to a pregnant woman. Arsenic trioxide was embryolethal and teratogenic in rats when administered on gestation day 9 at a dose approximately 10 times the recommended human daily dose on a mg/m² basis. A related trivalent arsenic, sodium arsenite, produced teratogenicity when administered during gestation in mice at a dose approximately 5 times the projected human dose on a mg/m² basis and in hamsters at an intravenous dose approximately equivalent to the projected human daily dose on a mg/m² basis. There are no studies in pregnant women using Phenasen. Advise pregnant women of the potential risk to a fetus.

The background risk of major birth defects and miscarriage for the indicated population is unknown. However, the background risk in the U.S. general population of major birth defects is 2-4% and of miscarriage is 15-20% of clinically recognized pregnancies.

Data

Human Data

One patient who became pregnant while receiving arsenic trioxide had a miscarriage.

Animal Data

Studies in pregnant mice, rats, hamsters, and primates have shown that inorganic arsenicals cross the placental barrier when given orally or by injection. An increase in resorptions, neural-tube defects, anophthalmia and microphthalmia were observed in rats administered 10 mg/kg of arsenic trioxide on gestation day 9 (approximately 10 times the recommended human daily dose on a mg/m² basis). Similar findings occurred in mice administered a 10 mg/kg dose of a related trivalent arsenic, sodium arsenite (approximately 5 times the projected human dose on a mg/m² basis), on gestation days 6, 7, 8 or 9. Intravenous injection of 2 mg/kg sodium arsenite (approximately equivalent to the projected human daily dose on a mg/m² basis) on gestation day 7 (the lowest dose tested) resulted in neural-tube defects in hamsters.

Lactation

Arsenic is excreted in human milk. Because of the potential for serious adverse reactions in nursing infants from Phenasen, discontinue breastfeeding during treatment with Phenasen.

Females And Males Of Reproductive Potential

Contraception

Females

Phenasen can cause fetal harm when administered to a pregnant woman. Advise females of reproductive potential to use effective contraception during and after treatment with Phenasen.

Males

Males with female sexual partners of reproductive potential should use effective contraception during and after treatment with Phenasen.

Pediatric Use

There are limited clinical data on the pediatric use of Phenasen. Of 5 patients below the age of 18 years (age range: 5 to 16 years) treated with Phenasen, at the recommended dose of 0.15 mg/kg/day, 3 achieved a complete response.

In an additional study, the toxicity profile observed in 13 pediatric patients with APL between the ages of 4 and 20 receiving Phenasen at 0.15 mg/kg/day was similar to that observed in adult patients. No children less than 4 years of age were enrolled in the trial due to the rarity of APL in this age group.

Geriatric Use

Clinical trials of Phenasen (arsenic trioxide) did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Monitor elderly patients closely, reflecting the greater frequency of decreased hepatic and renal function, concomitant disease or other drug therapy in this population.

Patients With Renal Impairment

Exposure of arsenic trioxide may be higher in patients with severe renal impairment. Patients with severe renal impairment (creatinine clearance less than 30 mL/min) should be monitored for toxicity when these patients are treated with Phenasen, and a dose reduction may be warranted.

The use of Phenasen in patients on dialysis has not been studied.

Patients With Hepatic Impairment

Since limited data are available across all hepatic impairment groups, caution is advised in the use of Phenasen in patients with hepatic impairment. Monitor patients with severe hepatic impairment (Child-Pugh Class C) who are treated with Phenasen for toxicity.

The following serious adverse reactions are described elsewhere in the labeling.

• APL Differentiation Syndrome
• Cardiac Conduction Abnormalities: Torsade de Pointes, Complete Heart Block, and QT Prolongation
• Carcinogenesis
• Embryo-Fetal Toxicity

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

Safety information was available for 52 patients with relapsed or refractory APL who participated in clinical trials of Phenasen. Forty patients in the Phase 2 study received the recommended dose of 0.15 mg/kg of which 28 completed both induction and consolidation treatment cycles. An additional 12 patients with relapsed or refractory APL received doses generally similar to the recommended dose. Most patients experienced some drug-related toxicity, most commonly leukocytosis, gastrointestinal (nausea, vomiting, diarrhea, and abdominal pain), fatigue, edema, hyperglycemia, dyspnea, cough, rash or itching, headaches, and dizziness. These adverse effects have not been observed to be permanent or irreversible nor do they usually require interruption of therapy.

Serious adverse events (SAEs), Grade 3/4 according to version 2 of the NCI Common Toxicity Criteria, were common. Those SAEs attributed to Phenasen in the Phase 2 study of 40 patients with refractory or relapsed APL included APL differentiation syndrome (n=3), hyperleukocytosis (n=3), QTc interval ≥ 500 msec (n=16, 1 with torsade de pointes), atrial dysrhythmias (n=2), and hyperglycemia (n=2).

Table 1 describes the adverse events that were observed in patients, between the ages of 5-73 years, treated for APL with Phenasen at the recommended dose at a rate of 5% or more. Similar adverse event profiles were seen in the other patient populations who received Phenasen.

Table 1 : Adverse Events (Any Grade) Occurring in ≥ 5% of 40 Patients with APL Who Received Phenasen (arsenic trioxide) Injection at a Dose of 0.15 mg/kg/day

The following additional adverse events were reported as related to Phenasen treatment in 13 pediatric patients (defined as ages 4 through 20): gastrointestinal (dysphagia, mucosal inflammation/stomatitis, oropharyngeal pain, caecitis), metabolic and nutrition disorders (hyponatremia, hypoalbuminemia, hypophosphatemia, and lipase increased), cardiac failure congestive, respiratory (acute respiratory distress syndrome, lung infiltration, pneumonitis, pulmonary edema, respiratory distress, capillary leak syndrome), neuralgia, and enuresis. Pulmonary edema (n=1) and caecitis (n=1) were considered serious reactions.

Postmarketing Experience

The following reactions have been reported from clinical trials and/or worldwide postmarketing surveillance. Because they are reported from a population of unknown size, precise estimates of frequency cannot be made.

Cardiacdis Orders : ventricular extrasystoles in association with QT prolongation, and ventricular tachycardia in association with QT prolongation.

Nervous System Disorders : peripheral neuropathy

Hematologic Disorders : pancytopenia

Investigations: gamma-glutamyltransferase increased

Respiratory, Thoracic, And Mediastinal Disorders : A differentiation syndrome, like retinoic acid syndrome, has been reported with the use of Phenasen for the treatment of malignancies other than APL.

Manifestations

Manifestations of Phenasen (arsenic trioxide) overdosage include convulsions, muscle weakness and confusion.

Management

If symptoms of Phenasen (arsenic trioxide) overdosage develop, the injection should be immediately discontinued and chelation therapy should be considered.

A conventional protocol for acute arsenic intoxication includes dimercaprol administered at a dose of 3 mg/kg intramuscularly every 4 hours until immediate life-threatening toxicity has subsided. Thereafter, penicillamine at a dose of 250 mg orally, up to a maximum frequency of four times per day (≤ 1 g per day), may be given.

Cardiac Electrophysiology

A dedicated QTc study was not performed with Phenasen. However, in a single arm trial of Phenasen (0.15 mg/kg daily), 16 of 40 patients (40%) had a QTc interval greater than 500 msec. Prolongation of the QTc was observed between 1 and 5 weeks after Phenasen infusion, and then returned towards baseline by the end of 8 weeks after Phenasen infusion.

The inorganic, lyophilized form of arsenic trioxide, when placed into solution, immediately forms the hydrolysis product arsenious acid (As^III). As^III is the pharmacologically active species of arsenic trioxide. Monomethylarsonic acid (MMA^V), and dimethylarsinic acid (DMA^V) are the main pentavalent metabolites formed during metabolism, in addition to arsenic acid (As^V) a product of As oxidation. The pharmacokinetics of arsenical species ([As^III], [As^V], [MMA^V], [DMA^V]) were determined in 6 APL patients following once daily doses of 0.15 mg/kg for 5 days per week. Over the total single dose range of 7 to 32 mg (administered as 0.15 mg/kg), systemic exposure (AUC) appears to be linear. Peak plasma concentrations of arsenious acid (As^III), the primary active arsenical species were reached at the end of infusion (2 hours). Plasma concentration of As declined in a biphasic manner with a mean elimination half-life of 10 to 14 hours and is characterized by an initial rapid distribution phase followed by a slower terminal elimination phase. The daily exposure to As^III (mean AUC0-24) was 194 ng·hr/mL (n=5) on Day 1 of Cycle 1 and 332 ng·hr/mL (n=6) on Day 25 of Cycle 1, which represents an approximate 2-fold accumulation. The primary pentavalent metabolites, MMA^V and DMA^V, are slow to appear in plasma (approximately 10-24 hours after first administration of arsenic trioxide), but, due to their longer half-life, accumulate more upon multiple dosing than does As^III. The mean estimated terminal elimination half-lives of the metabolites MMA^V and DMA^V are 32 hours and 72 hours, respectively. Approximate accumulation ranged from 1.4- to 8-fold following multiple dosing as compared to single dose administration. As^V is present in plasma only at relatively low levels.

Distribution

The volume of distribution (Vss ) for As^III is large (mean 562 L, N=10) indicating that As^III is widely distributed throughout body tissues. Vss is also dependent on body weight and increases as body weight increases.

Metabolism

Much of the As^III is distributed to the tissues where it is methylated to the less cytotoxic metabolites, monomethylarsonic acid (MMA^V) and dimethylarsinic acid (DMA^V) by methyltransferases primarily in the liver. The metabolism of arsenic trioxide also involves oxidation of As^III to As^V, which may occur in numerous tissues via enzymatic or nonenzymatic processes. As^V is present in plasma only at relatively low levels following administration of arsenic trioxide.

Excretion

Approximately 15% of the administered Phenasen dose is excreted in the urine as unchanged As^III. The methylated metabolites of As^III (MMA^V, DMA^V) are primarily excreted in the urine. The total clearance of As^III is 49 L/h and the renal clearance is 9 L/h. Clearance is not dependent on body weight or dose administered over the range of 7-32 mg.

Renal Impairment

The effect of renal impairment on the pharmacokinetics of As^III, As^V, and the pentavalent metabolites MMA^V and DMA^V was evaluated in 20 patients with advanced malignancies. Patients were classified as having normal renal function (creatinine clearance [CrCl] > 80 mL/min, n=6), mild renal impairment (CrCl 50-80 mL/min, n=5), moderate renal impairment (CrCl 30-49 mL/min, n=6), or severe renal impairment (CrCl < 30 mL/min, n=3). Following twice weekly administration of 0.15 mg/kg over a 2- hour infusion, the mean AUC0-∞ for As^III was comparable among the normal, mild and moderate renal impairment groups. However, in the severe renal impairment group, the mean AUC0-∞ for As^III was approximately 48% higher than that in the normal group.

Systemic exposure to MMA^V and DMA^V tended to be larger in patients with renal impairment; however, the clinical consequences of this increased exposure are not known. As^V plasma levels were generally below the limit of assay quantitation in patients with impaired renal function. The use of arsenic trioxide in patients on dialysis has not been studied.

Hepatic Impairment

The effect of pharmacokinetics of As^III, As^V, and the pentavalent metabolites MMA^V and DMA^V was evaluated following administration of 0.25-0.50 mg/kg of arsenic trioxide in patients with hepatocellular carcinoma. Patients were classified as having normal hepatic function (n=4), mild hepatic impairment (Child-Pugh class A, n=12), moderate hepatic impairment (Child-Pugh class B, n=3), or severe hepatic impairment (Child-Pugh class C, n=1). No clear trend toward an increase in systemic exposure to As^III, As^V, MMA^V or DMA^V was observed with decreasing level of hepatic function as assessed by dose-normalized (per mg dose) AUC in the mild and moderate hepatic impairment groups. However, the one patient with severe hepatic impairment had mean dose-normalized AUC0-24 and Cmax values 40% and 70% higher, respectively, than those patients with normal hepatic function. The mean dose-normalized trough plasma levels for both MMA^V and DMA^V in this severely hepatically impaired patient were 2.2-fold and 4.7-fold higher, respectively, than those in the patients with normal hepatic function.

Pediatric Patients

Following IV administration of 0.15 mg/kg/day of arsenic trioxide in 10 APL patients (median age = 13.5 years, range 4-20 years), the daily exposure to As^III (mean AUC0-24h) was 317 ng·hr/mL on Day 1 of Cycle 1.