*Hematinics- Maturation Factors*Erythropoetin

Dr Advaitha M. VPharmaceutical PhysicianS. DemonstratorK.S. Hegde Medical Academy,Mangalore, India

• Hematinics are the nutrients required for the formation of RBCs.

1. Fe ( ↓↓ microcytic Hypochromic Anemia)

2. Vit B12, Folic Acid are maturation Factors

(↓↓ Megaloblastic Anemia; Premature RBCs will have hard time to synthesize DNA.)

Cobalamin (vitamin B12) • COBALAMIN exists in a number of different

chemical forms. • All have a cobalt atom at the center of a corrin

ring.

• Natural or Active or coenzyme forms of Cobalamin:2-deoxyadenosyl (ado) form located in

mitochondria. Methylcobalamin present in plasma and in cell

cytoplasm (given therapeutically).

• Dietary Forms or Stable forms (are generally called Vit B12)

CyanocobalaminHydroxocobalaminUsed therapeutically.

DIETARY SOURCES :• Cobalamin is synthesized solely by

microorganisms.

• Only source for humans is food of animal origin e.g., meat, fish, and dairy products.

• Vegetables, fruits, and other foods of non-animal origin are free from cobalamin unless they are contaminated by bacteria

• Daily requirement: *1–3 μg** Pregnancy and lactation : 3–5 μg.

• Body stores are of the order of 2–3 mg, sufficient for 3–4 years if supplies are completely cut off.

Pharmacokinetics

• Vit B12 present in food as protein conjugates is released by cooking or by proteolysis in stomach facilitated by gastric acid.

• Intrinsic factor (a glycoprotein) secreted by stomach forms a complex with B12

• They attach to specific receptors present on intestinal mucosal cells at the ileum.

• Absorbed by active carrier mediated transport

• Vit B12 is transported in blood in combination with a β globulin, transcobalamin II (TCII).

• Excess Vit B12 is stored in liver cells as 5’- deoxyadenosylcobalamin.

• It is not degraded in the body.

• It is secreted in bile (normally) or excreted in urine by glomerular filtration (when administered in therapeutic doses).

Folic (Pteroylglutamic) acid• Contains 2 to 8 molecules of glutamic acid.

• Humans do not synthesize FA and meet the need from green leafy vegetables (spinach), egg, meat, milk.

• It is synthesized by gut flora, but this is largely unavailable for absorption

• Daily requirement of an adult : 0.2 mg/day.• During pregnancy, lactation: 0.8 mg/day.

-----------------------------------------------------• Folate is easily destroyed by heating, particularly

in large volumes of water.

• Total body folate in the adult is ~10 mg, (Mainly stored in liver),

• Stores are sufficient for only 3–4 months.

Pharmacokinetics:• Absorbed in proximal Jejunum.

• Folic acid is present in food as polyglutamates (absorbable but less efficient).

• So, in the lumen or inside the mucosa, they are hydrolysed to monoglutamates (5- Methyl Tetra Hydro Folate OR 5-MeTHF ,easily absorbable), before entering portal circulation.

• Folate is transported in plasma about one-third is loosely bound to albumin, and two-thirds is unbound.

• Methyltetrahydrofolate (Me-THF) is the principal folate congener supplied to cells.

• Folic acid is rapidly extracted by tissues and stored in cells as polyglutamates.

• Liver takes up a large part and secretes methyl-THFA in bile which is mostly reabsorbed from intestine (enterohepatic circulation).

• Alcohol interferes with release of methyl-THFA from hepatocytes.

• Pharmacological doses are excreted in urine.

Relationships Between Vitamin B12 and Folic Acid

• Property : Its all about Methylation and one carbon transfer !!!!

Metabolic functions of cobalamin

• The active forms are essential for cell growth and replication.

• 5-Deoxyadenosylcobalamin is required for the re-arrangement of methylmalonyl CoA to succinyl CoA (for fatty acid synthesis in neural tissue)

• Methylcobalamin is required for the conversion of homocysteine to methionine.

• In vitamin B12 deficiency , MeTHF becomes "trapped" as to cause a functional deficiency of other required intracellular forms of folic acid.

(Folate trap or Methyl Folate trap !!!!)

• So, B12 is required to support folate metabolism.

Etiology : Vit B12 deficiency• Addisonian pernicious anaemia

• Gastric mucosal damage: chronic gastritis, gastric carcinoma, gastrectomy, etc.

• Malabsorption due to bowel resection, inflammatory bowel disease.

• Consumption by abnormal flora in intestine (blind loop syndrome) or fish tape worm.

• Nutritional deficiency in strict vegetarians.

• Increased demand in pregnancy, infancy.

Manifestations of B12 deficiency

• Megaloblastic anaemia (generally the first manifestation), neutrophils with hypersegmented nuclei, giant platelets.

• Glossitis, g.i. disturbances.

• Neurological: subacute combined degeneration of spinal cord.

*peripheral neuritis, diminished vibration and position sense, paresthesias.

• Neuropsychiatric: poor memory, mood changes, hallucinations, etc. are late effects.

Metabolic functions of Folic acid• Conversion of Homocysteine to Methionine:- Me-THF

(using vitamin B12 as a cofactor).

• Conversion of Serine to Glycine:- *THF acts as an acceptor of a methylene group from

serine (using pyridoxal phosphate as a cofactor). *It results in the formation of 5-Methylene THF an

essential coenzyme for the synthesis of thymidylate.

• Synthesis of Thymidylate:

5-Methylene THF donates a methylene group and reducing equivalents to deoxyuridylate for the synthesis of thymidylate—a rate-limiting step in DNA synthesis.

• Histidine Metabolism:THF also acts as an acceptor of a formimino

group in the conversion of formiminoglutamic acid to glutamic acid.

• Synthesis of Purines:Helps to add carbon atoms into the growing

purine ring.

Folate deficiency : Etiology• Inadequate dietary intake

• Malabsorption: especially involving upper intestine.

• Chronic alcoholism: intake of folate is generally poor. Its release from liver cells and recirculation are interfered.

• Increased demand: pregnancy, lactation, rapid growth Periods.

• Drug induced:

Anticonvulsants on prolonged therapy (phenytoin, phenobarbitone)

Oral contraceptives: interfere with absorption and storage of folate.

Manifestations of folate deficiency

• Megaloblastic anaemia: indistinguishable from that due to vit B12 deficiency.

• Epithelial damage: glossitis, enteritis,

diarrhoea, steatorrhoea.

• Neural tube defects : including spina bifida in the offspring, due to maternal folate deficiency

• Neurological symptoms do not appear in pure folate deficiency.

BIOCHEMICAL BASIS OF MEGALOBLASTIC ANEMIA

• The common feature of megaloblastic anemias is a defect in DNA synthesis that affects rapidly dividing cells in the bone marrow.

• In deficiencies of either folate or cobalamin, *There is failure to convert deoxyuridine

monophosphate (dUMP) to deoxythymidine monophosphate (dTMP), the precursor of dTTP .

OR

*There is misincorporation of uracil into DNA

because of a buildup of deoxyuridine triphosphate (dUTP).

Preparations, dose, administration of Vitamin B12:

• Available for injection and oral administration.

• Combinations with other vitamins and minerals also can be given orally or parenterally.

• The choice of a preparation always depends on the cause of the deficiency.

• Oral preparations may be used to supplement deficient diets.

• They are of limited value in the treatment of patients with deficiency of intrinsic factor or ileal disease

• Cyanocobalamin: inj. 500 μg, 1000 μg• Hydroxocobalamin: inj. 100mcg• Methylcobalamin (Oral/I.M/I.V) 500mcg, 1500

mcg

• Cyanocobalamin injection is safe when given by the I.M or deep S.C (but never be given I.V).

*Rare reports of transitory exanthema and anaphylaxis after IV injection.

• Some popular trends of usage:

Cyanocobalamin: *100 μg i.m./s.c. daily for 1 week, * Then weekly for 1 month *Then monthly for maintenance indefinitely.

Methylcobalamin (Oral, 1500mcg) has been promoted for correcting the neurological defects in diabetic, alcoholic and peripheral neuropathy.

Important Note for Vit B12:

• In megaloblastic anemia, apart from b12, it is rational to add 1–5 mg of oral folic acid and an iron preparation.

(because reinstitution of brisk haemopoiesis

may unmask deficiency of these factors)

• Responses :Symptomatic improvement starts in 2 days--

appetite improves, patient feels better.mucosal lesions heal in 1–2 weeks --------------------Hb% and haematocrit start rising after 2 weeks.Time taken for complete recovery of anaemia

depends on the severity of disease. ---------------------Neurological parameters improve more slowly—

may take several months. (full recovery may not occur in chronic patients)

Folic acid in therapeutics1. Megaloblastic anaemia Oral folic acid 2–5 mg/day is adequate. In acutely ill patients, 5 mg/day (IV/IM/SC)Response occurs as quickly as with vit B12.

2. Increased demand: pregnancy, lactation upto 5mg/day.

3. Pernicious anaemia: Folic acid has only secondary and adjuvant role in this condition.

• Folic acid should never be given alone to patients with megaloblastic anemia.

• Because haematological response may occur, but neurological defect may worsen due to diversion of meagre amount of vit B12 present in body to haemopoiesis.

3. Methotrexate (anticancer, DHFRase inhibitor) toxicity

• Folinic acid (Leucovorin, citrovorum factor, 5-formyl-THFA)

It is an active coenzyme form which does not need to be reduced by DHFRase before it can act.

Dose : 3.0 mg i.v. repeated as required. Oral forms are also available (Dose upto 15mg).

Folinic acid is comparatively expensive.

4. In methanol Poisoning : folinic acid serves as THFA to eliminate formic acid formed.

Erythropoietin (EPO)

• Glycoprotein hormone (MW 34000) produced by peritubular cells of the kidney that is essential for normal erythropoiesis.

• Anaemia and hypoxia are sensed by kidney cells and induce rapid secretion of EPO

• It acts on erythroid marrow

Stimulates proliferation of colony forming cells of the erythroid series.

Induces haemoglobin formation and erythroblast maturation.

It induces erythropoiesis in a dose dependent manner.

Therapeutics • Epoetin α, β : The recombinant human

erythropoietin.

Administered by i.v. or s.c. injectionPlasma t½ of 6–10 hr, but action lasts several

days. Given thrice weekly , Max 600 U/kg/week

• Darbepoetin : longer acting, given once a week.

Indications of epoetin :

• Chronic kidney disease –Associated Anemia.

• Chemotherapy –Related Anemia.

• Preparation for surgery with high risk of blood loss.

• Anaemia in AIDS patients treated with zidovudine.

Adverse effects • Increased blood viscosity and peripheral vascular

resistance.

• Increased clot formation in the A-V shunts (most patients are on dialysis)

• Hypertensive episodes

• Serious thromboembolic events

• Flu like symptoms lasting 2–4 hr occur in some patients.

Thank you