Arsenic Trioxide Injection

Arsenic trioxide is used to treat acute promyelocytic leukemia (APL; a type of cancer in which there are too many immature blood cells in the blood and bone marrow) in people who have not been helped by other types of chemotherapy or whose condition has improved but then worsened following treatment with other types of chemotherapy. Arsenic trioxide is in a class of medications called anti-neoplastics. It works by slowing or stopping the growth of cancer cells.

Arsenic trioxide comes as a solution (liquid) to be injected into a vein by a doctor or nurse in a medical office or clinic. Arsenic trioxide is usually injected over 1 to 2 hours, but it may be injected over as long as 4 hours if side effects are experienced during the infusion. It is usually given once a day for a specific period of time.

Before receiving arsenic trioxide injection,

• tell your doctor and pharmacist if you are allergic to arsenic trioxide or any other medications.
• tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention the medications listed in the IMPORTANT WARNING section. Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
• tell your doctor if you have or have ever had kidney disease.
• tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. Talk to your doctor about using birth control to prevent pregnancy during your treatment with arsenic trioxide. If you become pregnant while receiving arsenic trioxide, call your doctor. Arsenic trioxide may harm the fetus.
• if you are having surgery, including dental surgery, tell the doctor or dentist that you are receiving arsenic trioxide.

The following serious adverse reactions have been associated with TRISENOX in clinical trials and are discussed in greater detail in other sections of the label.

• APL Differentiation Syndrome [see WARNINGS AND PRECAUTIONS]
• Cardiac Conduction Abnormalities: Torsade de Pointes, Complete Heart Block, and QT Prolongation [see WARNINGS AND PRECAUTIONS]
• Carcinogenesis [see WARNINGS AND PRECAUTIONS]
• Embryo-Fetal Toxicity [see WARNINGS AND PRECAUTIONS]
• Laboratory Tests [see WARNINGS AND PRECAUTIONS]

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 TRISENOX. 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 TRISENOX 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 TRISENOX at the recommended dose at a rate of 5% or more. Similar adverse event profiles were seen in the other patient populations who received TRISENOX.

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

The following additional adverse events were reported as related to TRISENOX 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.

Cardiac disorders : 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 TRISENOX for the treatment of malignancies other than APL [see BOX WARNING].

Manifestations

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

Management

If symptoms of TRISENOX (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.

Mechanism Of Action

The mechanism of action of TRISENOX is not completely understood. Arsenic trioxide causes morphological changes and DNA fragmentation characteristic of apoptosis in NB4 human promyelocytic leukemia cells in vitro. Arsenic trioxide also causes damage or degradation of the fusion protein promyelocytic leukemia (PML)-retinoic acid receptor (RAR)-alpha.

Pharmacodynamics

A dedicated QTc study was not performed with TRISENOX. However, in a single arm trial of TRISENOX (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 TRISENOX infusion, and then returned towards baseline by the end of 8 weeks after TRISENOX infusion.

Pharmacokinetics

The inorganic, lyophilized form of arsenic trioxide, when placed into solution, immediately forms the hydrolysis product arsenious acid (AsIII ). AsIII is the pharmacologically active species of arsenic trioxide. Monomethylarsonic acid (MMAV), and dimethylarsinic acid (DMAV ) are the main pentavalent metabolites formed during metabolism, in addition to arsenic acid (AsV) a product of AsIII oxidation. The pharmacokinetics of arsenical species ([AsIII], [AsV], [MMAV], [DMAV]) 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 (AsIII ), the primary active arsenical species were reached at the end of infusion (2 hours). Plasma concentration of AsIII 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 AsIII (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, MMAV and DMAV , 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 AsIII . The mean estimated terminal elimination half-lives of the metabolites MMAV and DMAV 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. AsV is present in plasma only at relatively low levels.

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

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

Approximately 15% of the administered TRISENOX dose is excreted in the urine as unchanged AsIII . The methylated metabolites of As (MMAV, DMAV ) are primarily excreted in the urine. The total clearance of AsIII 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.

The effect of renal impairment on the pharmacokinetics of AsIII , AsV , and the pentavalent metabolites MMAV and DMAV 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 AsIII was comparable among the normal, mild and moderate renal impairment groups. However, in the severe renal impairment group, the mean AUC0-∞ for AsIII was approximately 48% higher than that in the normal group.

Systemic exposure to MMAV and DMAV tended to be larger in patients with renal impairment; however, the clinical consequences of this increased exposure are not known. AsV plasma levels were generally below the limit of assay quantitation in patients with impaired renal function [see Use In Specific Populations]. The use of arsenic trioxide in patients on dialysis has not been studied.

The effect of pharmacokinetics of AsIII , AsV , and the pentavalent metabolites MMAV and DMAV 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 AsIII , AsV , MMAV or DMAV 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 MMAV and DMAV 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 [see Use In Specific Populations].

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 AsIII (mean AUC0-24h ) was 317 ng•hr/mL on Day 1 of Cycle 1 [see Use In Specific Populations].

Drug Interactions

No formal assessments of pharmacokinetic drug-drug interactions between TRISENOX and other drugs have been conducted. The methyltransferases responsible for metabolizing arsenic trioxide are not members of the cytochrome P450 family of isoenzymes. In vitro incubation of arsenic trioxide with human liver microsomes showed no inhibitory activity on substrates of the major cytochrome P450 (CYP) enzymes such as 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4/5, and 4A9/11. The pharmacokinetics of drugs that are substrates for these CYP enzymes are not expected to be affected by concomitant treatment with arsenic trioxide.

Clinical Studies

TRISENOX has been investigated in 40 relapsed or refractory APL patients, previously treated with an anthracycline and a retinoid regimen, in an open-label, single-arm, non-comparative study. Patients received 0.15 mg/kg/day intravenously over 1 to 2 hours until the bone marrow was cleared of leukemic cells or up to a maximum of 60 days. The CR (absence of visible leukemic cells in bone marrow and peripheral recovery of platelets and white blood cells with a confirmatory bone marrow ≥ 30 days later) rate in this population of previously treated patients was 28 of 40 (70%). Among the 22 patients who had relapsed less than one year after treatment with ATRA, there were 18 complete responders (82%). Of the 18 patients receiving TRISENOX ≥ one year from ATRA treatment, there were 10 complete responders (55%). The median time to bone marrow remission was 44 days and to onset of CR was 53 days. Three of 5 children, 5 years or older, achieved CR. No children less than 5 years old were treated.

Three to six weeks following bone marrow remission, 31 patients received consolidation therapy with TRISENOX, at the same dose, for 25 additional days over a period up to 5 weeks. In follow-up treatment, 18 patients received further arsenic trioxide as a maintenance course. Fifteen patients had bone marrow transplants. At last follow-up, 27 of 40 patients were alive with a median follow-up time of 484 days (range 280 to 755) and 23 of 40 patients remained in complete response with a median follow-up time of 483 days (range 280 to 755).

Cytogenetic conversion to no detection of the APL chromosome rearrangement was observed in 24 of 28 (86%) patients who met the response criteria defined above, in 5 of 5 (100%) patients who met some but not all of the response criteria, and 3 of 7 (43%) of patients who did not respond. RT-PCR conversions to no detection of the APL gene rearrangement were demonstrated in 22 of 28 (79%) of patients who met the response criteria, in 3 of 5 (60%) of patients who met some but not all of the response criteria, and in 2 of 7 (29%) of patients who did not respond.

Hyperleukocytosis (≥ 10 x 103/uL) developed in 20 of the 40 patients treated. A relationship did not exist between baseline WBC counts and development of hyperleukocytosis nor baseline WBC counts and peak WBC counts. Hyperleukocytosis was not treated with additional chemotherapy. WBC counts during consolidation were not as high as during induction treatment.

Responses were seen across all age groups tested, ranging from 6 to 72 years. The ability to achieve a CR was similar for both genders. There were insufficient patients of Black, Hispanic or Asian derivation to estimate relative response rates in these groups, but responses were seen in members of each group.

Another single center study in 12 patients with relapsed or refractory APL, where patients received TRISENOX (arsenic trioxide) injection doses generally similar to the recommended dose, had similar results with 9 of 12 (75%) patients attaining a CR.