Aditia Retno FitriDepartment of PharmacologyFaculty of Medicine Diponegoro UniversityIndonesia

OverviewHematinic Agents

Iron Folic Acid and Vitamine B12

Haemopoetic Growth Factors

- a porphyrin like ring with a central cobalt

(Co ) atom attached t o a nucleotide

Cyanocobalamin Hydroxocobalamin

Mostly animal products:

▪ Meat ▪ Fish▪ Eggs▪ Milk and Milk

products like yogurt fortified with

Vitamin B12:▪ Breakfast Cereals▪ Bread

Ultimate source: microbial synthesis▪ not synthesized by animals /plants.

Must be converted to methyl-B12or ado-B12

Daily diet = 5-25 μg Daily requirement = 2-3 μg. = extrinsic factor Role: DNA synthesis

Conversion of methyl-FH4 to FH4 synthesis DNA

Isomerisation of methylmalonyl-CoA to succinyl-CoA.

Methyl-FH4 donates the methyl group to B12, the cofactor.

The methyl group is then transferred to homocysteine to form methionine

Deficiency: “methylfolate trap”

Synthesis of DNA

Vit B12 deficiency : acummulation of methyl malonate-CoA basis of neuropathy in vit B12 deficiency

Cobalamin is a cofactor for the enzyme Methylmalonyl-CoA mutase which converts methylmalonyl-CoA to succinyl-CoA.

Succinyl-CoA enters the Krebs cycles and goes into nerves to make myelin.

If no Vitamin B12, methylmalonyl-CoA goes on to form abnormal fatty acids and causes subacute degeneration of the nerves. Only B12 can correct this problem.

Normal B-12 absorption: Dietary B-12 binds to R factor in saliva and

gastric juices. In duodenum, pancreatic enzymes promote

dissociation from R factor and binding to Intrinsic Factor (IF)

IF-B12 complex taken up by ileal receptor cubilin.

Released into plasma bound to transcobalamines TC I, II, or III.

Enters cells through receptor mediated endocytosis and metabolized into two coenzymes: adenosyl-Cbl and methyl-Cbl.

Another mechanism for B12 absorption involves diffusion and not IF : jejunum

In circulation, cobalamin binds to transcobalamin II; transporting the vitamin from the enterocyte to the liver and other organs

Biliary excretion of B12 is much higher than excretion in urine or feces

It can take up to 20 years to show symptoms of deficiency in people who have recently changed to low-B12 diets!!! Vitamin B12 is excreted in bile, but the body is able to

reabsorb a large percentage. People who consume diets very low in B12 may actually be reabsorbing more than they absorb from diet. This is why It can take up to 20 years to show symptoms of deficiency in people who have recently changed to low-B12 diets. If there is a complete absorption failure, however, deficiency symptoms can occur in 3 years.

Vegetarian

PerniciousAnemia

Ileal disease

Iiverdisease

Pernicious anaemia :deficiency IF Dietary deficiency: vegetarian Malabsorption syndromes (>>>) :

stagnant loop syndrome ,Crohn’s disease, Fish tape worm infestation, gastrectomy

↑requirements: pregnancy, hemolytic anemia, hepatic disease

Vit b12 absorption test Neurologic syndrome: Vit B12 deficiency

Caused by ↓ absorption ↓ intrinsic factor Interference of absorption in the terminal ileum

▪ e.g. Colon resection in Crohn's disease

Clinical form: Pernicious anemia Neurological disease

▪ peripheral neuropathy, Dementia, subacute combined degeneration of the spinal cord

Abnormalities of epithelial tissue, ▪ e.g. sore tongue andmalabsorption

Lab: ↓serum vit B12 (N: 170-925 nanogram/1)

Blood film: pancytopenia, anisopoikilocytosis with

oval macrocytes and hypersegmented neutrophils; the marrow is megaloblastic

Schilling test : distinguish between gastric and

intestinal causes

Schilling Test Stage I

▪ Give 1mcg of radiolabeled B-12 orally 1000 mcg of B-12 IM one hour later A 24-hr urine collection count radiolabeled B-12 excretion (N: 8-35%).

Stage II▪ only if Stage I is abnormal. ▪ Repeat Stage I, except with the addition of added

oral IF which should normalize B-12 absorption in P.A., but not intestinal malabsorption.

Contraindication Inconclusively diagnosed anaemia Allergic to cobalt

Interaction Alcohol, aminosalicylic acid, neomicine

and colchicine may decrease the absorption of oral vit B12

Hydroxocobalamin is preferred to cyanocobalamin: First choice : injection Initial dose:

hydroxocobalamin 1 mg i.m. every 2-3 days for 5 doses to induce remission and to replenish stores

Maintanance dose: 1 mg/3 months Response:

Feel better : 2 days Reticulocyte peak : 5-7 days Hb, RBC, Ht ↑ : first week normalize: 2 months Watch: hypokalemia!!

If injections are refused rare allergy, bleeding disorder Alternative: snuff , aerosol , oral Large daily oral doses (1000 micrograms)

▪ depleted stores must be replaced by parenteral cobalamin before switching to the oral preparation;

▪ the patient must be compliant; ▪ monitoring of the blood must be more frequent ▪ adequate serum vitamin B12 levels must be

demonstrated.

Synthetic vitamin B12 Cyanocobalamin, hydroxocobalamin Oral cyanocobalamin : well absorbed, highly

protein bound to the transcobalamins Metabolize in the liver, followed by biliary and

urinary excretion T1/2 is about 6 days Cyanocobalamin injection containing benzyl

alcohol : should not be used for neonates or immature infants

Reduction of absorption of B12 from GI tract

excessive consumption of ethanol for longer than 2 weeks

prolonged use of cholestyramine, colchicine large doses of ascorbic acid may destroy

B12

Folate (Folic Acid) can mask signs of B12 deficiency

because it can correct macrocytic anemia, which is often the first symptom experienced in B12

deficiency. The folate won’t correct the deficiency, however, and because it goes undetected severe nerve damage can occur.

Usually do not occurwhen a megaloblastic anaemia due

to pernicious anaemia is incorrectly diagnosed as due to folate deficiency; here folic acid, if used alone (see below) may accelerate progressionof subacute combined degeneration of the nervous system.

Exposure to Nitrous Oxide can cause B12 deficiency in cases of abuse, anesthesia usage during surgery, or occupational exposure for hospital workers.

NO actually inactivates B12, so while those affected have enough in their system, they are effectively B12 deficient.

needs an 'intrinsic factor' for absorption in terminal ileum. It is stored in the liver.

It is required for: synthesis of purines and pyrimidines (see

above) isomerisation of methylmalonyl-CoA to

succinyl-CoA. Deficiency : pernicious anaemia, Vitamin B12 is given by injection to treat

pernicious anaemia.

composed of a heterocycle, p-aminobenzoic acid, and glutamic acid

Folate: Pharmacodynamics

5-FU

methotrexate

Human requirement : varies from 25-35 mcg/d in infancy to up to 100

mcg/d in adults Total body folic acid stores :

5-10 mg, half of which is stored in the liver as N-5-methyltetrahydrofolate

> 2% is degraded daily so a continuous dietary is essential

Active absorption : mainly in the proximal part of the small intestine

Conjugate in the epithelial cells converts the polyglutamates into absorbable monoglutamates

Pharmaceutical product : completely absorbed in the upper duodenum, even in the presence of malabsorption

Excretion: entirely as metabolites by the kidney

Folate: Pharmacokinetics

Inadequate dietary supply

Small intestinal disease

Uremiaalcoholism,hepatic disease

Vitamin B12 deficiency

Etiology : Most causes : inadequate diet, alcoholism,

pregnancy, malabsorption syndrome Other causes : increased requirement, enhanced

metabolism, interference in the metabolism

Several reasons for folate def. in alcoholics reduced dietary intakes, inactivation of folate

conjugate, impaired enterohepatic cycling, depletion of liver folate stores

More often malnourished than those with cobalamin deficiency

Gastrointestinal manifestations More widespread and more severe than

those of pernicious anemia Diarrhea is often present Cheilosis Glossitis

Neurologic abnormalities do not occur

1. Negative folate balance (decreased serum folate)

2. Decreased RBC folate levels and hypersegmented neutrophils

3. Macroovalocytes, increased MCV, and decreased hemoglobin

Diagnosis : Megaloblastosis

possibly due to folic acid deficiency must be interpreted in the light of B12 status

Peripheral blood and bone marrow biopsy look exactly like B12 deficiency

Reduced folate tissue levels : erythrocyte folate concentration<140 ng/ml more reliable of tissue stores

Plasma folate level : <3 ng/ml—fluctuates Only increased serum homocysteine levels but NOT serum

methylmalonic acid levels

Management : Folic acid should not be given until B12 def. and

pernicious anemia have been excluded Oral dose: 1 mg/day Absorption is normal : 50-100 mcg/d Malabsorption : 250-500 mcg/d To replenish depleted folate stores, a daily

dose of 1-2 mg/d for 2-3 weeks Duration of therapy depend on underlying

causes : 3-4 months to clear folate-deficient erythrocytes from the blood

Prophylactic folate therapy : pregnancy, particularly in women with poor diets,

multiple pregnancies, or thalassemia minor : 300 mcg/d in the last trimester

Monitoring : Reticulocyte count : peaks 5-8 days after

treatment Increase Hct Decrease to normal MCV

• Vitamin B12 deficiency anemia can be temporarily

corrected by folate supplementation

• However, this does not correct the neurologic deficits

• Folate “draws” vitamin B12 away from neurologic

system for RBC production and can exacerbate combined systems degeneration

Megaloblastic Anemia due to inadequate dietary intake of folic acid due to chronic alcoholism, pregnancy, infancy,

impaired utilization: uremia, cancer or hepatic disease.

Anemia associated with dihydrofolate reductase inhibitors. i.e. Methotrexate (Cancer chemotherapy),

Pyrimethamine (Antimalarial) Administration of citrovorum factor

(methylated folic acid) alleviates the anemia.

Ingestion of drugs that interfere with intestinal absorption and storage of folic acid. Mechanism- inhibition of the conjugases that break off

folic acid from its food chelators. Ex. – phenytoin, progestin/estrogens (oral

contraceptives)

Malabsorption – Sprue, Celiac disease, partial gastrectomy.

Rheumatoid arthritis – increased folic acid demand or utilization.

Oral replacement therapy Folate prophylaxis

Women planning pregnancy are advised to take 400 g folic acid daily before conception and until 12 weeks of pregnancy to prevent neural-tube defects (5 mg/day for women with a previous affected pregnancy)

Folate fortification of cereal grains at 1·4 mg/kg has been made mandatory in the USA as an additional method of improving the folate status of the population.

Prophylactic folate is also recommended in other states of increased demand such as long-term hemodialysis and chronic haemolytic disorders

Dark green leafy vegetables, like spinach

Broccoli, asparagus, green peas and okra

Orange juice Papaya

• Beans, lentils and black-eyed peas

• Soybeans and tofu

• Peanut butter• Fortified foods:

Cereal, rice, pasta, tortillas, grits

Be sure to eat 5 servings of fruits & vegetables such as

these every day!

Drugs implicated in causing :* malabsorption ? * impaired metabolism

- phenytoin - methotrexate

- barbiturates - pyrimethamine- sulfasalazine - trimethoprim- cholestyramine - pentamidine- oral contraceptives

Alcohol Tobacco Aspirin, ibuprofen,

naprosyn and acetaminophen

Antacids & anti-ulcer medications

• Some antiseizure medications

• Some anticancer drugs

• Some antibiotics/ antibacterials

• Oral hypoglycemic agents

Source: Folicacid.net.

No known level at which it is toxic, even in high amounts

Even if you eat fruits and vegetables containing folic acid, eat a bowl of cereal and take a multivitamin with folic acid in one day, you would not have a problem with too much folic acid

do not occur even with large doses of folic acid

except possibly in vitamin B12 deficiency, the blood picture may improve and give

the appearance of cure while the neurological lesions get worse.

Important to determine whether a megaloblastic anaemia is caused by a folate or a vitamin B12 deficiency.

Mechanism Effect Indication Pharmacokinetic

Color atlas of pharmacologyGoodman & Gilman’s The

Pharmacological Basis of Therapeutics, 11th ed.

Clinical Pharmacology, 9th Ed USMLE Pharmacology Recall Pharmacology for the health care profession Pharmacology Rang et al 5th Edition Basic and Clinical Pharmacology 11th Ed,

Katzung Desk reference of clinical pharmacology