Azacitidine (Page 4 of 5)

12.1 Mechanism of Action

Azacitidine for Injection is a pyrimidine nucleoside analog of cytidine. Azacitidine for Injection is believed to exert its antineoplastic effects by causing hypomethylation of DNA and direct cytotoxicity on abnormal hematopoietic cells in the bone marrow. The concentration of azacitidine required for maximum inhibition of DNA methylation in vitro does not cause major suppression of DNA synthesis. Hypomethylation may restore normal function to genes that are critical for differentiation and proliferation. The cytotoxic effects of azacitidine cause the death of rapidly dividing cells, including cancer cells that are no longer responsive to normal growth control mechanisms. Non-proliferating cells are relatively insensitive to azacitidine.

12.3 Pharmacokinetics

The area under the curve (AUC) and peak concentration (Cmax ) of subcutaneous administration of azacitidine in patients with cancer were approximately dose proportional within the dose range of 25 mg/m2 (0.33 times the lowest approved recommended dosage) to 100 mg/m 2 (the maximum approved recommended dosage). The mean and standard deviation (SD) of Cmax was 750 ± 403 ng/mL after a single subcutaneous administration of 75mg/m2 azacitidine. Multiple dosing at the recommended dose-regimen does not result in drug accumulation.


Azacitidine is rapidly absorbed after subcutaneous administration with a median time to Cmax (Tmax ) of 0.5 hour. The bioavailability of subcutaneous azacitidine relative to intravenous azacitidine is approximately 89%, based on AUC.


Mean volume of distribution following intravenous dosing is 76 ± 26 L.


Mean apparent subcutaneous clearance is 167 ± 49 L/hour and mean half-life after subcutaneous administration is 41 ± 8 minutes.


Published studies indicate that urinary excretion is the primary route of elimination of azacitidine and its metabolites. Following intravenous administration of radioactive azacitidine, the cumulative urinary excretion was 85% of the radioactive dose. Fecal excretion accounted for less than 1% of administered radioactivity over 3 days. Mean excretion of radioactivity in urine following subcutaneous administration of 14 C-azacitidine was 50%. The mean elimination half-lives of total radioactivity (azacitidine and its metabolites) were similar after intravenous and subcutaneous administrations, about 4 hours.

Specific Populations

The effects of hepatic impairment, gender, age, or race on the pharmacokinetics of azacitidine have not been studied.

Patients with Renal Impairment

The exposure of azacitidine increased by approximately 70% after single and 41% after multiple subcutaneous administrations of 75 mg/m2 /day azacitidine in patients with cancer and severe renal impairment (CLcr less than 30 mL/min) relative to patients with cancer and normal renal function (CLcr greater than 80 mL/min). This increase in exposure was not correlated with an increase in adverse events. The exposure was similar to exposure in patients with normal renal function receiving 100 mg/m2 [see Use in Specific Populations ( 8.6)].

Drug-Drug Interactions

No formal clinical drug interaction studies with azacitidine have been conducted.

An in vitro study of azacitidine incubation in human liver fractions indicated that azacitidine may be metabolized by the liver. Whether azacitidine metabolism may be affected by known microsomal enzyme inhibitors or inducers has not been studied.

An in vitro study with cultured human hepatocytes indicated that azacitidine at concentrations up to 100 µM (intravenous Cmax = 10.6 µM) does not cause any inhibition of cytochrome P450 (CYP) 2B6 and 2C8. The potential of azacitidine to inhibit other CYP enzymes is not known.

In vitro studies with human cultured hepatocytes indicated that azacitidine at concentrations of 1.0 µM to 100 µM does not induce CYP 1A2, 2C19, or 3A4/5.


13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility

The potential carcinogenicity of azacitidine was evaluated in mice and rats. Azacitidine induced tumors of the hematopoietic system in female mice at 2.2 mg/kg (6.6 mg/m2 , approximately 8% the recommended human daily dose on a mg/m2 basis) administered IP three times per week for 52 weeks. An increased incidence of tumors in the lymphoreticular system, lung, mammary gland, and skin was seen in mice treated with azacitidine IP at 2.0 mg/kg (6.0 mg/m2 , approximately 8% the recommended human daily dose on a mg/m2 basis) once a week for 50 weeks. A tumorigenicity study in rats dosed twice weekly at 15 or 60 mg/m2 (approximately 20% to 80% the recommended human daily dose on a mg/m2 basis) revealed an increased incidence of testicular tumors compared with controls.

The mutagenic and clastogenic potential of azacitidine was tested in in vitro bacterial systems Salmonella typhimurium strains TA100 and several strains of trpE8, Escherichia coli strains WP14 Pro, WP3103P, WP3104P, and CC103; in in vitro forward gene mutation assay in mouse lymphoma cells and human lymphoblast cells; and in an in vitro micronucleus assay in mouse L5178Y lymphoma cells and Syrian hamster embryo cells. Azacitidine was mutagenic in bacterial and mammalian cell systems. The clastogenic effect of azacitidine was shown by the induction of micronuclei in L5178Y mouse cells and Syrian hamster embryo cells.

Administration of azacitidine to male mice at 9.9 mg/m2 (approximately 9% the recommended human daily dose on a mg/m2 basis) daily for 3 days prior to mating with untreated female mice resulted in decreased fertility and loss of offspring during subsequent embryonic and postnatal development. Treatment of male rats 3 times per week for 11 or 16 weeks at doses of 15 to 30 mg/m2 (approximately 20% to 40%, the recommended human daily dose on a mg/m2 basis) resulted in decreased weight of the testes and epididymides, and decreased sperm counts accompanied by decreased pregnancy rates and increased loss of embryos in mated females. In a related study, male rats treated for 16 weeks at 24 mg/m2 resulted in an increase in abnormal embryos in mated females when examined on day 2 of gestation.


Myelodysplastic Syndromes (MDS)

Study 1 was a randomized, open-label, controlled trial carried out in 53 U.S. sites that compared the safety and efficacy of subcutaneous Azacitidine for Injection plus supportive care with supportive care alone (“observation”) in patients with any of the five FAB subtypes of myelodysplastic syndromes (MDS): refractory anemia (RA), RA with ringed sideroblasts (RARS), RA with excess blasts (RAEB), RAEB in transformation (RAEB-T), and chronic myelomonocytic leukemia (CMMoL). RA and RARS patients were included if they met one or more of the following criteria: required packed RBC transfusions; had platelet counts less than or equal to 50 x 109 /L; required platelet transfusions; or were neutropenic (ANC less than 1 x 109 /L) with infections requiring treatment with antibiotics. Patients with acute myelogenous leukemia (AML) were not intended to be included. Supportive care allowed in this study included blood transfusion products, antibiotics, antiemetics, analgesics and antipyretics. The use of hematopoietic growth factors was prohibited. Baseline patient and disease characteristics are summarized in Table 3; the 2 groups were similar.

Azacitidine for Injection was administered at a subcutaneous dose of 75 mg/m2 daily for 7 days every 4 weeks. The dose was increased to 100 mg/m2 if no beneficial effect was seen after 2 treatment cycles. The dose was decreased and/or delayed based on hematologic response or evidence of renal toxicity. Patients in the observation arm were allowed by protocol to cross over to Azacitidine for Injection if they had increases in bone marrow blasts, decreases in hemoglobin, increases in red cell transfusion requirements, or decreases in platelets, or if they required a platelet transfusion or developed a clinical infection requiring treatment with antibiotics. For purposes of assessing efficacy, the primary endpoint was response rate (as defined in Table 4).

Of the 191 patients included in the study, independent review (adjudicated diagnosis) found that 19 had the diagnosis of AML at baseline. These patients were excluded from the primary analysis of response rate, although they were included in an intent-to-treat (ITT) analysis of all patients randomized. Approximately 55% of the patients randomized to observation crossed over to receive Azacitidine for Injection treatment.

Table 3. Baseline Demographics and Disease Characteristics

Azacitidine for





Gender (n%)


72 (72.7)

60 (65.2)


27 (27.3)

32 (34.8)

Race (n%)


93 (93.9)

85 (92.4)


1 (1.0)

1 (1.1)


3 (3.0)

5 (5.4)


2 (2.0)

1 (1.1)

Age (years)




Mean ± SD

67.3 ± 10.39

68.0 ± 10.23


31 to 92

35 to 88

Adjudicated MDS diagnosis at study entry (n%)


21 (21.2)

18 (19.6)


6 (6.1)

5 (5.4)


38 (38.4)

39 (42.4)


16 (16.2)

14 (15.2)


8 (8.1)

7 (7.6)


10 (10.1)

9 (9.8)

Transfusion product used in 3 months before study entry (n%)

Any transfusion product

70 (70.7)

59 (64.1)

Blood cells, packed human

66 (66.7)

55 (59.8)

Platelets, human blood

15 (15.2)

12 (13.0)




Plasma protein fraction






Table 4. Response Criteria






Complete Response

(CR), duration

≥4 weeks


<5% blasts



Normal CBC if abnormal at baseline

Absence of blasts in the peripheral circulation



(PR), duration

≥4 weeks


No marrow requirements

≥50% decrease in blasts

Improvement of marrow dyspoiesis



≥50% restoration in the deficit from normal levels of baseline white cells,

hemoglobin and platelets if abnormal at baseline

No blasts in the peripheral circulation

For CMMoL, if WBC is elevated at baseline, a ≥75% reduction in the excess

count over the upper limit of normal

The overall response rate (CR + PR) of 15.7% in Azacitidine for Injection-treated patients without AML (16.2% for all Azacitidine for Injection randomized patients including AML) was statistically significantly higher than the response rate of 0% in the observation group (p<0.0001) (Table 5). The majority of patients who achieved either CR or PR had either 2 or 3 cell line abnormalities at baseline (79%; 11/14) and had elevated bone marrow blasts or were transfusion dependent at baseline. Patients responding to Azacitidine for Injection had a decrease in bone marrow blasts percentage, or an increase in platelets, hemoglobin or WBC. Greater than 90% of the responders initially demonstrated these changes by the 5th treatment cycle. All patients who had been transfusion dependent became transfusion independent during PR or CR. The mean and median duration of clinical response of PR or better was estimated as 512 and 330 days, respectively; 75% of the responding patients were still in PR or better at completion of treatment. Response occurred in all MDS subtypes as well as in patients with adjudicated baseline diagnosis of AML.

Table 5. Response Rates

Azacitidine for



Observation Before




n (%)

n (%)

P value

Overall (CR+PR)

14 (15.7)

0 (0.0)


Complete (CR)

5 (5.6)

0 (0.0)


Partial (PR)

9 (10.1)

0 (0.0)

Patients in the observation group who crossed over to receive Azacitidine for Injection treatment (47 patients) had a response rate of 12.8%.

Study 2, a multi-center, open-label, single-arm study of 72 patients with RAEB, RAEB-T, CMMoL, or AML was also carried out. Treatment with subcutaneous Azacitidine for Injection resulted in a response rate (CR + PR) of 13.9%, using criteria similar to those described above. The mean and median duration of clinical response of PR or better was estimated as 810 and 430 days, respectively; 80% of the responding patients were still in PR or better at the time of completion of study involvement. In Study 3, another open-label, single-arm study of 48 patients with RAEB, RAEB-T, or AML, treatment with intravenous Azacitidine for Injection resulted in a response rate of 18.8%, again using criteria similar to those described above. The mean and median duration of clinical response of PR or better was estimated as 389 and 281 days, respectively; 67% of the responding patients were still in PR or better at the time of completion of treatment. Response occurred in all MDS subtypes as well as in patients with adjudicated baseline diagnosis of AML in both of these studies. Azacitidine for Injection dosage regimens in these 2 studies were similar to the regimen used in the controlled study.

Benefit was seen in patients who did not meet the criteria for PR or better, but were considered “improved.” About 24% of Azacitidine for Injection-treated patients were considered improved, and about 2/3 of those lost transfusion dependence. In the observation group, only 5/83 patients met criteria for improvement; none lost transfusion dependence. In all 3 studies, about 19% of patients met criteria for improvement with a median duration of 195 days.

Study 4 was an international, multicenter, open-label, randomized trial in MDS patients with RAEB, RAEB-T or modified CMMoL according to FAB classification and Intermediate-2 and High risk according to IPSS classification. Of the 358 patients enrolled in the study, 179 were randomized to receive azacitidine plus best supportive care (BSC) and 179 were randomized to receive conventional care regimens (CCR) plus BSC (105 to BSC alone, 49 to low dose cytarabine and 25 to chemotherapy with cytarabine and anthracycline). The primary efficacy endpoint was overall survival.

The azacitidine and CCR groups were comparable for baseline parameters. The median age of patients was 69 years (range was 38 to 88 years), 98% were Caucasian, and 70% were male. At baseline, 95% of the patients were higher risk by FAB classification: RAEB (58%), RAEB-T (34%), and CMMoL (3%). By IPSS classification, 87% were higher risk: Int-2 (41%), High (47%). At baseline, 32% of patients met WHO criteria for AML.

Azacitidine was administered subcutaneously at a dose of 75 mg/m2 daily for 7 consecutive days every 28 days (which constituted one cycle of therapy). Patients continued treatment until disease progression, relapse after response, or unacceptable toxicity. Azacitidine patients were treated for a median of 9 cycles (range 1 to 39), BSC only patients for a median of 7 cycles (range 1 to 26), low dose cytarabine patients for a median of 4.5 cycles (range 1 to 15), and chemotherapy with cytarabine and anthracycline patients for a median of 1 cycle (range 1 to 3, i.e. induction plus 1 or 2 consolidation cycles).

In the Intent-to-Treat analysis, patients treated with azacitidine demonstrated a statistically significant difference in overall survival as compared to patients treated with CCR (median survival of 24.5 months vs. 15.0 months; stratified log-rank p=0.0001). The hazard ratio describing this treatment effect was 0.58 (95% CI: 0.43, 0.77).

Kaplan-Meier Curve of Time to Death from Any Cause: (Intent-to-Treat Population)

(click image for full-size original)

Key: AZA = azacitidine; CCR = conventional care regimens; CI = confidence interval; HR = Hazard Ratio

Azacitidine treatment led to a reduced need for red blood cell transfusions (see Table 6). In patients treated with azacitidine who were RBC transfusion dependent at baseline and became transfusion independent, the median duration of RBC transfusion independence was 13.0 months.

Table 6. Effect of Azacitidine on RBC Transfusions in MDS Patients
Efficacy Parameter

Azacitidine plus BSC
(n= 179)
Conventional Care
(n= 179)
1 A patient was considered RBC transfusion independent during the treatment period if the patient had no RBC transfusions during any 56 consecutive days or more during the treatment period. Otherwise, the patient was considered transfusion dependent.

Number and percent of patients who were transfusion dependent at baseline who became transfusion independent on treatment1

Number and percent of patients who were transfusion-independent at baseline who became transfusion-dependent on treatment

50/111 (45.0%)

(95% CI: 35.6%, 54.8%)

10/68 (14.7%)

(95% CI: 7.3%, 25.4%)

13/114 (11.4%)

(95% CI: 6.2%, 18.7%)

28/65 (43.1%)

(95% CI: 30.9%, 56.0%)

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