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Agrylin - Scientific Information

Manufacture: Shire, Inc.
Country: Canada
Condition: Thrombocythemia
Class: Miscellaneous uncategorized agents
Form: Capsules
Ingredients: anagrelide hydrochloride, black iron oxide, crospovidone, gelatine, lactose anhydrous, lactose monohydrate, magnesium stearate, microcrystalline cellulose, povidone, silicone dioxide, sodium lauryl sulphate, titanium dioxide

Pharmaceutical Information

Drug Substance

Proper name:anagrelide hydrochloride
Chemical name:6,7-dichloro-1,5-dihydroimidazo[2,-1-b]-quinazolin-2(3H)-one monohydrochloride monohydrate
Molecular formula and molecular mass:C10H7Cl2N3O•HCl•H2O    310.55
Structural formula:

Physicochemical properties:

Anagrelide hydrochloride is an off-white, non-volatile powder. It is practically insoluble in water and very slightly soluble in dimethyl sulfoxide and dimethylformamide.

In aqueous solutions at 25°C, the solubility of anagrelide below pH 3 increased as the pH was decreased. The solubility at pH 0.96 was 236μg/mL. Between pH 4 and pH 8, the solubility remained constant at 1.2μg/mL. Above pH 8, the solubility increased with increasing pH consistent with ionization of the quinazoline moiety. The solubility at pH 11.4 was 992μg/mL.

The estimated pKa values were 2.9 and 9.8 and the melting point was above 300°C.

Clinical Trials

Study Demographics and Trial Design

A total of 942 patients with myeloproliferative disorders including 551 patients with Essential Thrombocythemia (ET), 117 patients with Polycythemia Vera (PV), 178 patients with Chronic Myelogenous Leukemia (CML), and 96 patients with other myeloproliferative disorders (OMPD), were treated with anagrelide in three clinical trials. Patients with OMPD included 87 patients who had Myeloid Metaplasia with Myelofibrosis (MMM), and 9 patients who had unknown myeloproliferative disorders.

Patients with ET, PV, CML, or MMM were diagnosed based on the following criteria:


  • Platelet count ≥900,000 on two determinations
  • Profound megakaryocytic hyperplasia in bone marrow
  • Absence of Philadelphia chromosome
  • Normal red cell mass
  • Normal serum iron and ferritin and normal marrow iron stores


  • A1 Increased red cell mass
  • A2 Normal arterial oxygen saturation
  • A3 Splenomegaly
  • B1 Platelet count ≥400,000/μL, in absence of iron deficiency or bleeding
  • B2 Leucocytosis (≥12,000/μL, in the absence of infection)
  • B3 Elevated leucocyte alkaline phosphatase
  • B4 Elevated serum B12


  • Persistent granulocyte count ≥50,000/μL, without evidence of infection
  • Absolute basophil count ≥100/μL
  • Evidence for hyperplasia of the granulocytic line in the bone marrow
  • Philadelphia chromosome present
  • Leucocyte alkaline phosphatase ≤lower limit of the laboratory normal range


  • Myelofibrotic (hypocellular, fibrotic) bone marrow
  • Prominent megakaryocytic metaplasia in bone marrow
  • Splenomegaly
  • Moderate to severe normochromic normocytic anemia
  • White cell count may be variable; (80,000- 100,000/μL)
  • Increased platelet count
  • Variable red cell mass; teardrop poikilocytes
  • Normal to high leucocyte alkaline phosphatase
  • Absence of Philadelphia chromosome

Diagnosis was positive if A1, A2, and A3 present; or, if no splenomegaly, diagnosis was positive if A1 and A2 are present with any two of B1, B2, or B3.

Study Results

The parameters used to determine the efficacy of anagrelide in the treatment of patients with thrombocythemia secondary to myeloproliferative disorders showed a clinically significant improvement over time of treatment. Anagrelide was shown to be an efficacious treatment for patients with thrombocytosis, decreasing the platelet count and the incidence of symptoms associated with a high platelet count. It is also effective in patients who have failed on or been intolerant of other anti-thrombocytotic therapy. Unlike other agents used to treat thrombocytosis, the action of anagrelide is specific to platelets and overall has no clinical effect on the plasma level of other formed elements in the blood.

Patients were enrolled in clinical trials if their platelet count was ≥900,000/μL on two occasions or ≥650,000/μL on two occasions with documentation of symptoms associated with thrombocythemia. The mean duration of anagrelide therapy for ET, PV, CML, and OMPD patients was 65, 67, 40, and 44 weeks, respectively; 23% of patients received treatment for 2 years. Patients were treated with anagrelide starting at doses of 0.5-2.0mg every 6 hours. The dose was increased if the platelet count was still high, but to no more than 12mg each day. Efficacy was defined as reduction of platelet count to or near physiologic levels (150,000-400,000/μL). The criteria for defining subjects as “responders” were reduction in platelets for at least 4 weeks to ≤600,000/μL, or by at least 50% from baseline value. Subjects treated for less than 4 weeks were not considered evaluable. The results are depicted graphically below:

Patients with Thrombocytosis Secondary to Myeloproliferative Disorders Mean Platelet Count During Anagrelide Therapy

Table 1: Patients with Thrombocytosis Secondary to Myeloproliferative Disorders - Mean Platelet Count During Anagrelide Therapy
Time on Treatment

* x 103μL

† Nine hundred and forty-two subjects with myeloproliferative disorders were enrolled in three research studies. Of these, 923 had platelet counts over the duration of the studies.

Detailed Pharmacology

Clinically, AGRYLIN (anagrelide hydrochloride capsules) was found to be an effective, highly specific platelet-reducing agent. Anagrelide's effects on platelets are fully reversible. Moreover, it has no clinically significant effect on the other formed elements in the blood. These findings were demonstrated both preclinically and clinically.

Preclinical pharmacology data that are available demonstrate anagrelide's specificity toward platelets. While anagrelide was found to be a potent inhibitor of platelet aggregation, it had no significant effect on other cellular components of the blood. Additional significant pharmacologic effects attributed to anagrelide administration are hypotension and positive inotropic activity.

Mechanism of Action

Anagrelide is a highly selective platelet-lowering agent. In vitro studies of human megakaryocytopoiesis suggested that, in vivo, its thrombocytopenic activity results primarily from an inhibitory effect on the post-mitotic phase of megakaryotic maturation. Anagrelide inhibited thrombopoietin-induced megakaryocytopoiesis in a dose-dependent manner with an estimated IC50 of approximately 30nM (= 7.7ng/mL), consistent with the in vivo C max of 7-13ng/mL after doses of 0.5-1mg. Three in vivo studies in humans (published in abstract form) have confirmed that anagrelide decreases circulating platelet counts in thrombocythemic subjects by inhibiting megakaryocyte maturation and ploidy.

Effect on Platelet Count

An effect on platelet count was demonstrated in only a few animal studies. In one rat study, a decreased platelet count was found in male Sprague-Dawley rats treated at 1,000mg/kg for 27 days. In another rat study, decreased platelet counts were observed in all female rats dosed for 1 year with 120.5, 361.5, and 1,205mg/kg/day of anagrelide hydrochloride. Platelet counts were decreased from pre-study values by 30 to 54% in male beagle dogs, and by 23 to 40% in females treated for 1 year at doses of 10, 300, and 600mg/kg/day.

Anti-Thrombotic Studies

The ability of anagrelide to inhibit thrombosis was demonstrated in four different animal models: rat, rabbit, dog, and rhesus monkey. Anagrelide was found to be a potent, broad-spectrum platelet aggregation inhibitor whose effects are dose-related. It is 50 times more potent than acetylsalicylic acid as an anticoagulant and was found to have a synergistic effect on platelet aggregation inhibition when administered in conjunction with heparin.

Cardiovascular Pharmacology

Preclinical cardiovascular information was obtained during the course of studies conducted in four different animal models: rat, guinea pig, ferret, and dog.

The key findings in these studies was that anagrelide has a significant direct positive inotropic effect and direct vasodilatory effect; and causes dose-related decreases in mean blood pressure and reflexogenic increases in heart rate. Anagrelide was also shown to be a potent vasodilator and cardiotonic agent in dogs. All of these effects were seen at doses higher than the recommended clinical dose of 2.0mg/day.

General Pharmacology Studies

General pharmacologic effects of anagrelide were studied in five different animal models: rat, guinea pig, ferret, rabbit, and dog. The overall conclusions from these studies were that anagrelide causes the following:

  • simple competitive antagonism of peripheral 5-HT receptors in the rat fundus model
  • a decrease in diuresis sodium and chlorine excretion in the volume-loaded normotensive rat
  • a dose-related prolongation of bleeding time in the guinea pig extracorporeal shunt model
  • no behavioural or neurological changes in the conscious dog model
  • weak airway dilation in the anesthetized dog model
  • inhibition of both cyclic AMP (cAMP) phosphodiesterase (PDE) and cyclic GMP PDE activity in a study of supernatant and sonicate models
  • inhibition of cAMP PDE activity in another study of supernatant and sonicate models
  • an increase in cAMP level and cAMP-dependent protein kinase (cA-PK) ratio in the washed human platelet model
  • inhibition of platelet PDE and resultant elevation of cAMP in the intact platelet model


Studies on the absorption, distribution, metabolism, and excretion (ADME) in four different models (rat, dog, monkey, and human) revealed that the orally-administered anagrelide is generally well absorbed, widely distributed to tissues, extensively metabolized, and excreted in the urine.

The monkey most closely resembled man in the route, rate, and extent of excretion. Human and animal urinary metabolite profiles were quantitatively similar. Each of the 3 main metabolites present in human urine were present in animal urine, but quantities were generally smaller.

Oral administration in the monkey resulted in rapid absorption with peak plasma levels occurring 4 to 8 hours after dosing. Capsule dose absorption from the intestinal tract was 76%. The main route of elimination was the urine; by 6 days after drug administration, the mean cumulative urinary excretion level of the dosed radioactivity was 61%.

A secondary route of elimination was in feces, the mean cumulative fecal excretion level over 6 days after drug administration was 31% in monkeys. The amount of parent compound detected in the urine as unchanged drug was less than 3%. Bioavailability in the primate was 92%, with a terminal half-life of 2 days.

In humans, 61% of the administered radioactivity was excreted in the 24 hours following administration and over 90% had been excreted by 72 hours after administration; 79% was in the urine and 21% recovered in the feces. The data indicate that all radioactivity was recovered in the urine and feces within 168 hours (7 days) of oral administration.


Acute Toxicity

Acute oral doses of anagrelide as high as 2,500mg/kg in mice and 1,500mg/kg in the rat, caused decreased activity immediately after administration; all animals recovered within 1 to 2 days. Intraperitoneal administration of 500mg/kg of anagrelide to mice, resulted in the death of all animals within 3 days, while administration of 250mg/kg caused decreased activity with recovery by 2 days.

In dogs, diarrhea was observed 4 to 5 days after a single oral dose of 10mg/kg of anagrelide and after 1 to 2 days with doses of ≥50mg/kg. Emesis was also observed, 2 days after a dose of 100mg/kg and on the day of dosing with doses of ≥500mg/kg; all animals recovered.

Single oral doses of 200mg/kg of anagrelide in rhesus monkeys caused soft stools and a transient decrease in food consumption after 3 days; all animals recovered.

These results indicate that the acute oral LD50 is >2,500mg/kg in mice, >1,500mg/kg in the rat, >800mg/kg in dogs, and >200mg/kg in primates (rhesus monkey).

Long-Term Toxicity

Anagrelide was administered daily to rats by oral gavage for 27 days at doses of 50 to 1,000mg/kg/day. Findings included flushing of the ears, feet, and nose. Drug-related changes seen at 1,000mg/kg/day consisted of decreased platelet counts, retarded body weight gains in males, and mild fibrosis and myocarditis along with labored respiration and/or rales; one female died. In a 94-day study, administration of 4 to 12mg/kg/day of anagrelide resulted in dose-related intestinal tract lesions and increased liver, adrenal, and thyroid weights relative to body weight at the highest dose.

Administration of escalating oral doses up to 3,200mg/kg over a period of 7 days in dogs resulted in a decrease in food consumption, in females at doses as low as 100mg/kg, and in males at doses as low as 800mg/kg. Clinical signs of gastrointestinal upset were evident; all dogs exhibited loose stools, diarrhea, and ultimately vomited as the dose was increased. In a 28-day repeat-dose study in the dog, the only abnormalities reported with oral doses were diarrhea and vomiting at doses of 500 to 800mg/kg/day.

Multidose studies were performed in primates using oral doses of 10mg/kg/day for 14 days or 4 to 12mg/kg/day of anagrelide for up to 92 days of treatment. Clinical signs related to anagrelide treatment consisted of diarrhea, emesis, soft and/or loose stools and decreased food consumption.

Chronic toxicity studies were carried out for up to 12 months in rats and dogs. In the rat, doses of 120.5, 361.5, and 1,205mg/kg/day of anagrelide were administered orally by diet. Treatment-related findings included the following: hunched posture; dilated vagina in females; increases and decreases in body weight; increased food consumption; mild transient increases in mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH), decreased platelet counts in females; changes in serum chemistry indicative of mild to moderate liver and kidney damage in all groups; increased cholesterol, decreased triglycerides, decreased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in males, increased creatinine in males, marginal increases in basal urea nitrogen (BUN) and creatinine in females, increased urine volume; liver and kidneys in all treated rats and adrenals in males were significantly increased in weight relative to body weight and/or brain weight; focal hyperplasia at the highest dose and pheochromocytomas at doses ≥361.5mg/kg/day. There were 24 deaths during the study (see Table 2); though none were attributed to anagrelide treatment, necropsy findings indicated kidney and liver damage.

Table 2: Unscheduled Deaths
Anagrelide (mg/kg/day)
Cause of Death *
Inflammation/infection and/or
1M2M2M2M; 1F
Heart failure1M
Total1M6M; 1F6M; 1F8M; 1F

* Animals may have had more than one finding at necropsy/histopathology

In the chronic dog toxicity study, repeated exposure to 10 to 600mg/kg/day of anagrelide were associated with a variety of toxicities, including: diarrhea and emesis; significant reductions in red cell counts, hemoglobin, hematocrit, and platelet counts; a tendency toward increased kidney weight in both sexes and increased liver weight in females; dose-related cardiac changes consisting of minimal to marked hemorrhage and chronic inflammation were present in the myocardium of the right atrium and left AV valves along with proliferative changes in some cardiac vessels.

Reproduction and Teratology

A comprehensive range of fertility, organogenesis, and peri/postnatal toxicity studies were performed in rats at oral doses of 60 to 900mg/kg/day of anagrelide.

In these studies, females were dosed from Days 6 to 15 or 18 of gestation, Day 6 gestation through Day 7 lactation, or Day 15 gestation to Day 21 lactation. The average number of live pups was significantly reduced on Day 1 postpartum in the 60 and 120mg/kg/day dosage groups; Days 4 and 21 postpartum in the 120 and 240mg/kg/day dosage groups and Day 7 postpartum in the 120mg/kg/day dosage group. Average body weights of pups were significantly reduced in all anagrelide-treated groups at Day 1 postpartum; in the 120 and 240mg/kg/day groups on Days 4 and 7 postpartum, and in the 240mg/kg/day group on Day 14 postpartum. Administration of anagrelide did not adversely affect the averages for implantations and live litter sizes, number of dams with all stillbirths, number of dams with all pups dying during lactation, sex ratios, or clinical and necropsy observations of the pups.

Doses of 240mg/kg/day and higher were associated with an increase in the incidence of pups dying on Days 1 to 4 postpartum, a decrease in the percentage of pups surviving to Day 7 postpartum, and a decrease in the average pup weight/litter.

Fetal body weights were significantly reduced by 5 to 7% in groups receiving 300 and 900mg/kg/day. Significant reversible delays in fetal ossification occurred in groups given doses of 100mg/kg/day or higher. No fetal malformations were attributable to doses of anagrelide as high as 900mg/kg/day. Deaths occurred when rats were continued to be dosed during delivery and early lactation.

In organogenesis studies with rabbits, oral doses of 30 to 480mg/kg of anagrelide, administered from Days 6 to 18 of gestation revealed that doses of ≥60mg/kg/day caused body weight loss, severe decreases in food consumption, decreased live litter sizes, and increased number and percentages of resorptions per litter. Deaths occurred in all dosed groups and there were two deformed fetuses, one at 30 and another at 240mg/kg/day. A second study of similar design employed doses of 1 to 20mg/kg/day. Body weight gains were significantly increased with 10 or 20mg/kg/day while food consumption significantly decreased during dosing. There were no deaths, abortions, premature deliveries, changes in litter parameters, or fetal malformations with oral doses of ≤20mg/kg/day.