Dr. Sanjib Das MD

VII.Drugs for Treating AnemiaA. PharmacologyUnderstand the basic concepts of erythropoiesis

and its regulation by erythropoietin and other hematopoietic factors (e.g., GM-CSF, interleukin-3)

Know the biochemical basis for microcytic hypochromic anemia and megaloblastic anemia.

For iron, vitamin B12 and folic acid, know the following: Sources Mechanisms regulating their intestinal absorption Factors that influence their bioavailability Transport Metabolism Storage Excretion

Know the phases of acute and chronic toxicity in iron poisoning and its treatment

Know how to treat chronic iron overload disease (e.g., chronic blood transfusion, iron malabsorption disease etc.)

Understand the role of vitamin B12 and folic acid in DNA synthesis and understand the additional role of vitamin B12 in lipid metabolism

Know the biochemical systems that are impaired in vitamin B12 and folic acid deficiency and the role of cyanocobalamin/hydroxocobalamin and folic acid in correcting these metabolic defects

Understand in biochemical terms why folic acid will correct the erythropoietic lesion but not the neurologic lesion in Addisonian pernicious anemia

Know the mechanisms by which various drugs can lead to folic acid deficiency

Know the potential uses of erythropoietin and other hematopoietic factors in treating anemia

B. Some Important DrugsIRON (FERROUS SULFATE, IRON DEXTRAN)DEFEROXAMINEERYTHROPOIETINFOLIC ACIDVITAMIN B12 (CYANO- AND HYDROXO-

COBALAMIN)SARGRAMOSTIM (GM-CSF)FILGRAMOSTIM (G-CSF)OPRELVEKIN (IL-11)

AGENTS TO TREAT ANEMIAAGENTS TO TREAT ANEMIA Anemia may arise from failure to make sufficient

red blood cells or to synthesize adequate quantities of hemoglobin

Types of anemiaMicrocyticMacrocyticOther anemia’s

Drugs Used to Treat AnemiaDrugs Used to Treat Anemia Microcytic anemiaFerrous sulfateFerrous gluconateFerrous fumarate Iron dextran Iron Antidote

Deferoxamine

Macrocytic anemiaFolic acidLeucovorinCyanocobalaminHydroxocobalamin

Other anemiaEpoetin alfa (Erythropoietin)Sargramostim (GM-CSF)Filgrastim (G-CSF)Oprelvekin (IL-11)

AnemiaAnemia Symptoms:PalenessFatigueShortness of breathExercise intolerance Increased heart rate

Causes of anemia: A decrease in the amount of hemoglobin per RBC

Microcytic, hypochromic anemiaMicrocytic, hypochromic anemia

A decrease in the number of circulating RBC’s Megaloblastic, hyperchromic anemiaMegaloblastic, hyperchromic anemia

A decrease in hemopoietic growth factors, especially erythropoietin

Normocytic anemia or mixedNormocytic anemia or mixed

MICROCYTIC HYPOCHROMIC ANEMIAMICROCYTIC HYPOCHROMIC ANEMIAIron deficiencyIron deficiency

Impaired hemoglobin synthesis

Small red cells with insufficient hemoglobin

Microcytic hypochromic anemiaMicrocytic hypochromic anemia

MEGALOBLASTIC ANEMIAMEGALOBLASTIC ANEMIAVitamin BVitamin B1212 or folic acid deficiency or folic acid deficiency

Impaired DNA synthesis

Impaired production and maturation of erythroid precursors

Macrocytic hyperchromic anemiaMacrocytic hyperchromic anemia

IronIron Physiological functions of iron:

Required for hemoglobin synthesis

Co-factor in such enzymes as the cytochromes

Required for myoglobin synthesis

Pharmacokinetic Properties of IronPharmacokinetic Properties of Iron Absorption: in duodenum and proximal jejunum

Involves active transport of ferrous ironferrous iron, which is oxidized to ferric ironferric iron in the intestinal mucosa

Ferric iron can be stored as ferritinferritin in the intestinal mucosa, or it can be transported by transferrintransferrin to other sites

Only 5-10%5-10% of dietary elemental iron (10 to 15 mg/day) is absorbed (mucosal (mucosal block)block)

Heme-iron from meat can be absorbed with iron in ferricferric state

Low iron stores (ferritinferritin in intestinal mucosal cells) increase iron absorption and the rate of erythropoiesis

Absorption is decreased by food, metal chelators, antacids, fluoroquinolones, and tetracycline

Absorption is increased by hydrochloric and large amounts of ascorbic acid

Gastric resection or surgical removal of the upper region of the small intestine impairs iron absorption

Pharmacokinetic Properties of IronPharmacokinetic Properties of IronDistribution: TransferrinTransferrin is a specific ferric iron transport protein

Erythroid cells have transferrin receptorstransferrin receptors, thus, iron is actively transported into hemoglobin-synthesizing cells in the bone marrow

Ceruloplasmin converts ferrousferrous iron to the ferricferric state, and this copper-containing, plasma protein appears to be important for cellular uptake of iron

10-20% total iron stored in ferritinferritin and hemosiderin, which are stored in macrophages in liver, spleen and bone marrow

70% in hemoglobin (red cells)(red cells)

10% in myoglobin (muscles)(muscles)

1% in cytochromes cytochromes and transferrin transferrin

Pharmacokinetic Properties of IronPharmacokinetic Properties of Iron

Excretion:

There is no specific mechanism for excreting iron

Iron balance is regulated by intestinal absorption

About 1 mg of iron is lost daily by such processes as exfoliationexfoliation of mucosal cells, which contain ferritinferritin

Causes of Iron DeficiencyCauses of Iron Deficiency Inadequate dietary intake: rare in USAMalabsorption Increased requirements: growth, pregnancy, and menstruationgrowth, pregnancy, and menstruationBlood loss (bleeding, cancer)(bleeding, cancer)

Iron deficiencyIron deficiency

Storage iron decreases then disappearse.g.,e.g., loss of hemosiderin granules in bone marrow loss of hemosiderin granules in bone marrow

Serum ferritin decreases (< 10 (< 10 g/L)g/L)

Good indicator of iron statusGood indicator of iron status

Serum iron decreases (< 40 (< 40 g/dL)g/dL)

Total iron-binding capacity of transferrin increases (> 400 (> 400 g/dL)g/dL)due to decreased saturation (< 10%)(< 10%)

Onset of anemiaOnset of anemia

40/400 = 10 %40/400 = 10 %

Treatment of Iron-deficiency AnemiaTreatment of Iron-deficiency Anemia Oral: ferrous salts are DOC for iron deficiency anemia:Ferrous sulfateFerrous gluconateFerrous fumarate

Treatment results in a rapid increase in reticulocytosis, and a measurable response to iron therapy should be detectable within one week

Normal hemoglobin levels should be reached in 1-3 months Normal hemoglobin levels:

14-18 g/dL for men14-18 g/dL for men 12-16 g/dL for women12-16 g/dL for women

Treatment should last 3-6 months or longer if the dose of iron was decreased due to intolerance

Parenteral iron: Iron dextran >>>> should be used rarelyPatients with gastric or small bowel resectionsPatients with inflammatory bowel disease involving the proximal small

intestine

Adverse Effects of Iron Gastrointestinal irritation

Acute toxicity from oral iron: seen as acute poisoning in children; treat with iron-chelating drug, deferoxaminedeferoxamineSymptoms: G.I. irritation; necrosis; nausea, cyanosis; Symptoms: G.I. irritation; necrosis; nausea, cyanosis;

hematemesis; green and tarry stools; cardiovascular hematemesis; green and tarry stools; cardiovascular collapse; metabolic acidosiscollapse; metabolic acidosis

Acute toxicity from iron dextran: Headache, Light headedness, Fever, Arthralgia, Nausea, Vomiting, Back pain, Flushing, Urticaria, Bronchospasm, Anaphylaxis (rare)

Small doses of iron dextran should be given first to check for signs of immediate hypersensitivity

Can cause deathCan cause death

Chronic Toxicity of IronChronic Toxicity of Iron Men with high meat diet?

HemochromatosisHemochromatosis: Excessive iron absorption (inherited disorder)

Hemosiderosis:Hemosiderosis: Result of numerous blood transfusions

Iron overload may also occur in the presence of anemia other than that caused by iron deficiency, such as the anemia of chronic disease or hemolytic anemia.

Excess iron deposited in heart, liver, pancreas and other organs.

In the absence of anemia, iron overload is treated by phlebotomyphlebotomy. One unit of blood removes 250-mg iron.

Folic AcidFolic AcidPhysiological functions:

Essential for normal synthesis of DNA and normal mitosis of proliferating cells

Conversion of folic acid to cofactors required for purine and pyrimidine synthesis

Folate (F)Folate (F)

Dihydrofolate reductase (DHFR)Dihydrofolate reductase (DHFR)

Dihydrofolate (FHDihydrofolate (FH22))

Dihydrofolate reductase (DHFR)Dihydrofolate reductase (DHFR)

Tetrahydrofolate (FHTetrahydrofolate (FH44))

1-carbon donors1-carbon donors

5-CH5-CH33-FH-FH44 5-CHO-FH 5-CHO-FH44 10-CHO-FH 10-CHO-FH44 5,10-CH 5,10-CH22-FH4 5,10-CH+=FH-FH4 5,10-CH+=FH44

DietaryDietaryFolate Folate RequiresRequiresB-12 forB-12 forUtilizationUtilization

Folate supplementsFolate supplements

Folic AcidFolic AcidSources: Diet (not synthesized) from plants and animals.

Yeast, liver, kidney and green vegetablesYeast, liver, kidney and green vegetables

Pharmacokinetic properties: Absorption: Readily and completely absorbed from small intestine by active transport

system 50-200 g folate absorbed daily (10-25% of folate in diet) Absorption is increased in pregnancy, but so is demand

Polyglutamate forms of folate (5-CH(5-CH33-FH-FH44))

Conjugase (glutamyl transferase)

Monoglutamate forms of 5-CH5-CH33-FH-FH44

Active and passive transport in proximal jejunum

Requires B-12 forRequires B-12 for utilizationutilization

Folic AcidFolic AcidDistribution:Distribution:

Liver and other tissues store 5-20 mg of folate Major dietary and storage form is 5-CH3-FH4

Because the body stores relatively little folic acid (relative to the high demand), megaloblastic anemia can develop in 1-61-6 months following folate deficiency

Excretion:Excretion:Folates are metabolized and excreted in urine and

feces.Serum levels decline within days when intake is

diminished.

Deficiency can occur relatively fastDeficiency can occur relatively fast

DeficiencyDeficiency Inadequate dietary intake

Alcoholics

Increased requirement:During pregnancypregnancyRenal dialysis (blood folates are removed by dialysis)Proliferative disorders (e.g., cancer, leukemia, certain chronic

diseases and skin disorders)Hemolytic anemia

Interference with utilization by other drugs: anticonvulsant drugs such as: phenytoin, primidone, and mephobarbital, also oral contraceptivesoral contraceptives and isoniazid

Malabsorption syndromes: patients with high rates of cell turnover (hemolytic anemia); alcoholism/poor liver function

Occurs frequentlyOccurs frequently

Therapeutic UseTherapeutic Use Treatment of folate deficiency

Give during pregnancy -- maternal folate deficiency is associated with neural tube defects (spina bifida)neural tube defects (spina bifida)

Coronary heart disease: HyperhomocystinemiaHyperhomocystinemia (high levels of homocysteine) is a possible

risk factor

Conversion of homocysteine to methionine requires folic acid and vitamin B12

Thus, low methioninelow methionine levels with folic acid folic acid or B B12 12 deficiencydeficiency

Clinical studies are ongoing to determine whether folic acid and/or vitamin B12 supplements reduce the risk of coronary heart disease

Vitamin BVitamin B1212 Physiological function: essential for normal

synthesis of DNA and for maintenance of myelin throughout the nervous system DNA synthesis: vitamin B12 is required to convert 5-5-

CHCH33-FH-FH44 (the dietary form) to FH4; FH4 (more specifically its derivative 5,10-CH5,10-CH22-FH-FH44) is required to convert dUMP to dTMP

Lipid synthesis: vitamin B12 is required to convert methylmalonyl-CoA methylmalonyl-CoA to succinyl-CoA succinyl-CoA

Amino acid synthesis: vitamin B12 and folate are required to convert homocysteine homocysteine to methionine methionine

Vitamin BVitamin B1212 Deficiency and the Deficiency and the Methylfolate TrapMethylfolate Trap

5-CH5-CH33-FH-FH44(Major dietary and storage form)

vitamin Bvitamin B1212

Tetrahydrofolate (FHTetrahydrofolate (FH44))

Other 1-carbon donorsOther 1-carbon donors

Nucleotides (dUMP & dTMP)Nucleotides (dUMP & dTMP)

In vitamin B12 deficiency, levels of 5-CH3-FH4 increase (trapped) with a decrease in the other forms of folate required for nucleotide synthesis

This defect can be circumvented by administration of folic acid, which can be reduced to tetrahydrofolate by dihydrofolate reductase (DHFR)

Thus, the defects in nucleotide synthesis caused by vitamin B12 deficiency can be corrected by folic acid treatment

Structure of Vitamin BStructure of Vitamin B1212 Porphyrin-like ring system complexed with cobalt

Different ligands attached to cobalt produce several forms of cobalamin Active form: R = 5’-deoxyadenosyl or methyl group Drugs: R = Cyano (CN-) or hydroxy (OH-)group Food: R = various ligands

Drugs and dietary cobalamins are converted to active forms in the body

Vitamin BVitamin B1212Sources:Sources:

Food (microbial origin); meat (liver), eggs and dairy productsNot synthesized in humans (Extrinsic factor)(Extrinsic factor)

Pharmacokinetic properties:Pharmacokinetic properties:Absorption: requires intrinsic factor (IF):intrinsic factor (IF):

Glycoprotein synthesized by parietal cells of stomach IF binds vitamin B12, and this complex is absorbed in ileum Intrinsic factor is not used as a drug

Distribution:Distribution: Transported via transcobalamin II, a plasma glycoprotein Excess stored in liver: thus it takes 3-6 years3-6 years to deplete stores from

body (since it has long half-life, only given once a month in patients who cannot absorb it from diet)

Excretion:Excretion: occurs in bile but undergoes enterohepatic circulation and most is reabsorbed from small intestine; when transcobalamin II is saturated excess is excreted in urine

IF is IF is never used as a drug used as a drug

Deficiency occurs very very slowDeficiency occurs very very slow

Causes of Vitamin BCauses of Vitamin B1212 Deficiency Deficiency Lack of intrinsic factor: pernicious anemiapernicious anemia

Treat with Vitamin B12 not with intrinsic factor

Lack of receptors for IF/B12 complex in ileum

Fish tapeworm infections

Patients with gastrectomy

Therapeutic UsesTherapeutic Uses Therapeutic uses:

Only approved use is treatment of vitamin B12 deficiencyUsually given by intramuscular injectionVitamin B12 is nontoxic even in large amounts

Preparations: CyanocobalaminCyanocobalamin:

Available nasally, orally, and parenterally, usually given parenterally Unlike hydroxocobalamin, cyanocobalamin does not cause an

antibody response to hydroxocobalamin-transcobalamin II complex Preferred agent for long-term use

Hydroxocobalamin: Is highly protein bound and remains in circulation longer Some patients produce antibodies against hydroxocobalamin-

transcobalamin II complex Also, now used for treatment of cyanide poisoning (known or

suspected)

Vitamin BVitamin B1212 versus Folic Acid versus Folic Acid DeficiencyDeficiency It is important to diagnosis the cause of

megaloblastic anemia so that corrective therapy can be initiated appropriately with either vitamin vitamin BB1212 or folic acidfolic acid..

Clinical tests:Red cell levels of folic acid (more reliable than Red cell levels of folic acid (more reliable than

serum levels)serum levels)

Serum levels of vitamin BSerum levels of vitamin B1212

Since folic acid can reverse the hematological damage due to vitamin B12 deficiency but not the neurological changes, one must differentiate between folate deficiencyfolate deficiency and vitamin Bvitamin B1212 deficiency deficiency

Two-stage Schilling TestTwo-stage Schilling Test Used to determine the cause of vitamin B12

deficiency.The test involves the oral administration of radioactive

vitamin B12 withwith and withoutwithout pig intrinsic factor, after which the presence of radioactivity in the urine is determined (a positive result proving that vitamin B12 was absorbed).

A negative result (i.e., impaired absorption) of both both free vitamin B12 and vitamin B12 complexed with pig intrinsic factor indicates malabsorption in the distal ileum (perhaps due to inflammatory bowel disease or (perhaps due to inflammatory bowel disease or small bowel resection).small bowel resection).

A negative result (i.e., impaired absorption) of just just vitamin Bvitamin B1212 indicates malabsorption due to lack of intrinsic factor (perhaps due to gastrectomy or (perhaps due to gastrectomy or pernicious anemia).pernicious anemia).

(Addisonian) Pernicious Anemia(Addisonian) Pernicious Anemia Megaloblastic anemia due to B12 deficiency resulting from lack

of production of intrinsic factor by the parietal cells of the gastric mucosa.

Accompanied by achlorhydria.

Generally observed in older men and women of northern European extraction (e.g., Scandinavians).

Five yearsFive years or more may elapse between loss of intrinsic factor and the development of megaloblastic anemia, which is how long it takes to deplete liver stores of vitamin B12.

Treatment with parenteral vitamin Bparenteral vitamin B1212 should not be delayed after gastrectomy (or surgical procedures and diseases that would impair B12 absorption), and should be continued for life.

Often seen firstOften seen first

Other AnemiasOther Anemias Bone marrow failure, causing decreased red cell

production, may result from:Myelofibrosis and Multiple myeloma: affect bone Myelofibrosis and Multiple myeloma: affect bone

marrow directlymarrow directly

Myelosuppressive chemotherapy: antitumor Myelosuppressive chemotherapy: antitumor agents; drugs used to treat AIDS; agents; drugs used to treat AIDS; immunosuppressive agentsimmunosuppressive agents

Deficiency of hematopoietic growth factors: Deficiency of hematopoietic growth factors: chronic renal failure (erythropoietin deficiency)chronic renal failure (erythropoietin deficiency)

Drugs Used to Treat Bone Marrow Drugs Used to Treat Bone Marrow FailureFailure

Epoetin alpha (Erythropoietin):Epoetin alpha (Erythropoietin): A glycoprotein that stimulates red cell production Derived from genetically modified cells of Chinese hamster ovary Used in treatment of anemia patients with chronic renal failure and in cancer patients

receiving chemotherapy

Sargramostim (GM-CSF):Sargramostim (GM-CSF): Recombinant granulocytic-macrophage colony stimulating factor Promotes myeloid recovery in patients with non-Hodgkin's lymphoma, acute

lymphoblastic leukemia, and Hodgkin's disease who are undergoing bone marrow transplantation

Promotes myeloid recovery after standard-dose chemotherapy Treats drug-induced bone marrow toxicity or neutropenia associated with AIDS

Filgrastim (G-CSF):Filgrastim (G-CSF): Recombinant colony stimulating factor Prevents and treats chemotherapy-related febrile neutropenia, for promotion of myeloid

recovery in patients undergoing bone marrow transplantation

Oprelvekin (IL-11)Oprelvekin (IL-11) Promotes megakaryopoiesis See Immunopharmacological Agents

Summary on Agents Used to Treat AnemiaSummary on Agents Used to Treat AnemiaCause Inadequate iron Inadequate globin synthesis InadequateRBC synthesis

Deficiency Iron Folic acid Vitamin B12 ErythropoietinLow stores, Large stores,quick onset slow onset

Differential Microcytic Megaloblastic Megaloblastic plus Normocytic/normochromic

Diagnosis Hypochromic neurologic defects Mixed-type anemia

Low iron, ferritin Low folic acid Low vitamin B12 Low erythropoietin Schilling testSchilling test

Major factors Blood loss Decrease intake Decreased intake Kidney failureDietary insufficiency No intrinsic factor Chronic diseaseMalabsorption Malabsorption CancerImpaired metabolism InfectionDHFR inhibitors InflammationIncreased utilization Cytotoxic drugsPregnancyMalignancyHemolytic anemiaRenal dialysis

TreatmentTreatment Ferrous ironFerrous iron Folic acidFolic acid CyanocobalaminCyanocobalamin ErythropoietinErythropoietin

Drugs used to treat anemia

Other anemia

Epoetin alpha (Erythropoietin) Sargramostim (GM-CSF)

Filgrastim (G-CSF) Oprelvekin (IL-11)

Macrocytic anemia

Folic acid Cyanocobalamin

Microcytic anemia

Ferrous sulfate

Antidote Deferoxamine

Folate vs. B-12 deficiencyFolate vs. B-12 deficiency

Which of the following would be most Which of the following would be most appropriate for the treatment of normocytic appropriate for the treatment of normocytic anemia in a 62-year-old woman with chronic anemia in a 62-year-old woman with chronic renal failure?renal failure?

A.A. ErythropoietinErythropoietinB.B. Ferrous sulfateFerrous sulfateC.C. Folic acidFolic acidD.D. OprelvekinOprelvekinE.E. Vitamin B-12Vitamin B-12

Answer: AAnswer: AErythropoietin is made in theErythropoietin is made in thekidney; lack of it causeskidney; lack of it causesnormocytic anemianormocytic anemia

A 25-year-old pregnant woman in her 4A 25-year-old pregnant woman in her 4thth month of pregnancy was diagnosed with month of pregnancy was diagnosed with macrocytic anemia. Which of the following macrocytic anemia. Which of the following would her infant have a higher than normal would her infant have a higher than normal risk of?risk of?

A.A. Cardiac abnormalityCardiac abnormalityB.B. Congenital neutropeniaCongenital neutropeniaC.C. Liver damageLiver damageD.D. Limb deformityLimb deformityE.E. Neural tube defectNeural tube defect

Answer: EAnswer: EFolic acid deficiencyFolic acid deficiencyleads to neural tubeleads to neural tubedefectsdefects