Drugs Affecting Blood Coagulation

Drugs Affecting Coagulation And Bleeding

Haemostatic agents

They arrest bleeding either by vasoconstriction or by promoting coagulation of blood.

• Classification

Read And Learn More: Pharmacology for Dentistry Notes

1. Local haemostatics (styptics) These drugs are commonly used locally to control bleeding from capillaries and minute vessels, for example, bleeding following tooth extraction, abrasions and epistaxis.
   • Astringents: They precipitate proteins locally in the bleeding site and control capillary oozing, for example, a solution of tannic acid, ferric chloride and ferric sulfate. They are useful in bleeding gums.
   • Adrenaline: It causes vasoconstriction (α₁) and arrests bleeding. A cotton pad soaked in 0.1% adrenaline solution is applied on the bleeding site to control capillary oozing, for example, epistaxis, bleeding after tooth extraction or from other sites. Adrenaline should be avoided in patients with hypertension, congestive cardiac failure, arrhythmias, ischaemic heart disease and uncontrolled hyperthyroidism, as it may precipitate myocardial infarction (MI) or aggravate the existing condition.
   • Thrombin: It is a freeze-dried powder derived from bovine or human plasma. It is used topically to control bleeding from capillaries. It can cause hypersensitivity reactions. Thrombin should not be injected. Thrombin is placed in the tooth socket to arrest bleeding.
   • Fibrin: It consists of fibrinogen, factor 8, thrombin, Ca²⁺ and other clotting components. It is used to control bleeding during surgical procedures or as a spray on the bleeding surface. Fibrin sealant in combination with tranexamic acid mouthwash helps to reduce bleeding during dental extraction in haemophilic patients.
   • Gelatin: It is an absorbable haemostatic and is available as a sponge or a film. It produces haemostasis by providing a physical meshwork on which clotting can occur.
   • Oxidized cellulose: It is an absorbable haemostatic. It should be applied dry so that it swells up and helps in the formation of a clot. It is used to control bleeding from capillaries and arterioles where ligation is not possible. It may cause tissue necrosis, nerve damage or vascular stenosis.
   • Calcium alginate: It is obtained from seaweeds. It is an absorbable haemostatic and is used to promote wound healing.
   • Haemocoagulase: The Haemocoagulase enzyme complex is isolated from the venom of Bothrops atrox (viper).
     • Mechanism of action It has a powerful haemostatic effect. It promotes coagulation by converting fibrinogen to fibrin. It can also shorten the bleeding and clotting time, thereby controlling capillary bleeding.
     • Pharmacokinetics It is available for topical, intravenous, intramuscular and subcutaneous administration. It has a rapid onset of action – within 5–10 min of intravenous (i.v.), 20–30 min after intramuscular (i.m.) administration and within a minute of topical application (spray/soaked swab).
     • Indications
       1. To control bleeding following tooth extraction or any other dental procedure.
       2. For prevention and treatment of haemorrhagic conditions of different aetiology.
          • Adverse effects are rare; they may cause anaphylactic reactions on intravenous administration.
2. Systemic agents
   • Vitamin K Vitamin K, a fat-soluble vitamin, is required for the synthesis of clotting factors 2, 7, 9 and 10. Vitamin K exists in different forms: vitamin K₁ (phytonadione, fat-soluble) is obtained from plant and animal sources; vitamin K₂ (menaquinone) is produced by intestinal bacteria, whereas vitamin K3 (menadione– fat soluble; salts are water soluble) is a synthetic form. All three forms of vitamin K (K₁, K₂ and K₃) are naphthoquinone derivatives.
     • Dietary source: Vitamin K is found in spinach, cabbage, cauliflower and tomatoes. It is also present in butter, meat, milk, liver and pears. The average daily intake for an adult is estimated to be 70–140 mcg/day.
     • Pharmacokinetics: Vitamin K₁ and menadione require the presence of bile for their absorption. Vitamin K is transported along with low-density lipoprotein (LDL) and is stored mainly in the liver. It undergoes glucuronide conjugation; metabolites are excreted in bile and urine.
     • Actions: Vitamin K acts as a cofactor for γ-carboxylation of glutamic acid residues of clotting factors (2, 7, 9 and 10) and osteocalcin (bone protein which is important for bone development).
     • Deficiency: Vitamin K deficiency may occur due to inadequate absorption (lack of bile salts), loss of vitamins (chronic diarrhoea) and administration of broadspectrum antibiotics (suppression of bacterial flora). In vitamin K deficiency, there is an increased tendency to bleed – epistaxis, haematuria, gastrointestinal bleeding and postoperative bleeding.
   • Preparations
     • Phytonadione (vitamin K₁): It is available for oral, subcutaneous (s.c.), i.m. and i.v. administration.
     • Menadione sodium diphosphate (vitamin K₃): It is a water-soluble preparation and is available for i.v., i.m. and oral administration. Menadione and its water-soluble salts have low efficacy and are toxic; hence, they are not commonly used.
   • Uses For prevention and treatment of bleeding associated with vitamin K deficiency:
     • In obstructive jaundice with haemorrhagic symptoms, parenteral vitamin K₁ is preferred. It is also administered to treat vitamin K deficiency resulting from prolonged antimicrobial therapy.
     • Vitamin K₁ (1 mg phytonadione, i.m.) is given routinely to all neonates to prevent bleeding, as the intestinal flora, which is necessary for the synthesis of vitamin K, is not developed.
     • To control bleeding due to oral anticoagulant therapy, phytonadione is used.
     • Adverse effects: Oral vitamin K is safe. Intravenous injection may cause flushing, sweating, dyspnoea, cyanosis, collapse and anaphylactic reaction. Menadione may cause haemolysis, hyperbilirubinaemia and kernicterus in newborns.
   • Fibrinogen is obtained from human plasma. It is used to control bleeding associated with hypofibrinogenaemia and is infused intravenously.
   • Antihaemophilic factor It contains coagulation factor 8 with von Willebrand’s factor. It is used to control bleeding episodes in haemophiliacs. It is administered as i.v. infusion. Adverse effects include fever with chills, headache and skin rashes.
   • Adrenochrome mono semicarbazone It is available for oral and parenteral administration. It is used to control capillary oozing following tooth extraction, epistaxis, etc.
   • Ethamsylate It is a haemostatic, available for oral, i.m. and i.v. administration. It corrects abnormal platelet adhesion and maintains the stability of the capillary wall. It is well absorbed after oral administration, secreted in breast milk and excreted unchanged in the urine. It is used to prevent and control bleeding from small blood vessels, For Example, bleeding following tooth extraction and epistaxis. It may cause skin rashes, hypotension and headache.
   • Desmopressin is a synthetic analogue of vasopressin. It is used to control mild-to-moderate bleeding in haemophilia A and von Willebrand’s disease. It is infused intravenously slowly.

Anticoagulants

Anticoagulants are drugs that prevent or reduce coagulability of blood.

1. Classification
   • Used in vitro:
     • Heparin
     • Sodium citrate: Used in blood banks to store blood
     • Sodium oxalate: Used As an anticoagulant in the laboratory
     • Sodium Edetate: Used As an anticoagulant in the laboratory
   • Used in vivo:
     • Parenteral anticoagulants
       • Indirect thrombin inhibitors
         1. Heparin (unfractionated heparin, UFH)
         2. Low-molecular-weight heparins (LMWHs): Enoxaparin, dalteparin, tinzaparin, ardeparin, reviparin
         3. Fondaparinux
       • Direct thrombin inhibitors: Bivalirudin, argatroban
     • Oral anticoagulants
       • Coumarin derivatives: Warfarin, dicumarol
       • Indandione derivative: Phenindione
       • Direct thrombin inhibitor: Dabigatran
       • Factor Xa inhibitor: Rivaroxaban
2. Parenteral anticoagulants
   • Indirect thrombin inhibitors
     • Heparin (unfractionated heparin) Heparin, the strongest organic acid in the body, was discovered by a medical student, McLean. It was later isolated and identified by Howell as a sulfated mucopolysaccharide. It is strongly electronegative. Commercially, heparin is obtained from ox lung and pig intestinal mucosa
       • Differences between Heparin (Parenteral Anticoagulant) and Warfarin (Oral Anticoagulant)
     • Mechanism of action Heparin binds to plasma antithrombin 3 (AT 3) and activates it. The heparin–antithrombin 3 complex enhances the rate of inactivation of activated clotting factors 10a, 2a, 9a, 11a, 12a and 13a.
       At low concentrations, heparin selectively inhibits the conversion of prothrombin to thrombin. Heparin thus prevents further thrombus formation. Heparin, in high doses, has antiplatelet action and prolongs the bleeding time. It releases lipoprotein lipase, which hydrolyses triglycerides, resulting in the clearing of lipemic plasma.
     • Pharmacokinetics Heparin is not absorbed after oral administration because of its high negative charge and large molecular size. Therefore, it must be given parenterally – intravenously or subcutaneously. On i.v. administration, the anticoagulant effect starts immediately, whereas through s.c. route, it takes 1–2 h. Heparin is highly protein-bound. It does not cross the blood-brain barrier or placental barrier and is safe for use during pregnancy. It is rapidly inactivated in the liver by heparinase and the metabolites are excreted in the urine.
     • Mode of administration Heparin is administered by i.v. infusion (for treatment) or s.c. route (for prophylaxis). Intramuscular administration may cause haematomas, hence should not be used. During heparin therapy, activated partial thromboplastin time (aPTT) monitoring is necessary and it should be maintained at 1.5–2.5 times the control.
     • Adverse effects and contraindications
       1. Bleeding: The main side effect is bleeding. Overdosage may cause serious and fatal haemorrhage. Bleeding can occur in the urinary and gastrointestinal tract or anywhere in the body. Hence, heparin therapy requires aPTT monitoring. No antagonist is required in cases of mild bleeding as the effect of heparin disappears within hours of the stoppage of therapy. If heparin-induced bleeding is life-threatening, it can be controlled rapidly by slow i.v. infusion of protamine sulfate (heparin antagonist). It is a strongly basic protein, and hence rapidly neutralizes the anticoagulant effect of heparin.
          • Protamine sulfate, a specific heparin antagonist, is obtained from fish sperm. One milligram of protamine sulfate approximately neutralizes 100 units of heparin (chemical antagonism).
       2. Heparin-induced thrombocytopenia (HIT): Heparin rarely causes thrombocytopenia, but it is a dangerous complication. The incidence is higher with unfractionated heparin (UFH) than with LMWHs.
       3. Hypersensitivity reactions can occur rarely. They are skin rashes, urticaria, fever, etc.
       4. Osteoporosis: Dose-dependent osteoporosis with spontaneous fractures may occur during long-term therapy.
       5. Reversible alopecia has been reported.
          • Heparin is contraindicated in haemophiliacs, patients with HIT, severe hypertension, intracranial haemorrhage, bacterial endocarditis, active tuberculosis, peptic ulcer, threatened abortion, cirrhosis, etc.
   • Low-molecular-weight heparins Enoxaparin, dalteparin, tinzaparin, ardeparin, reviparin, etc. are LMWHs and are obtained from standard heparin by fractionation. LMWHs produce anticoagulant effects mainly by inactivation of factor 10a through antithrombin. LMWH therapy usually does not require aPTT monitoring but patients with chronic renal failure may need monitoring by measuring factor 10a activity. LMWHs are given subcutaneously. The following are the advantages of LMWHs:
     • They have a higher s.c. bioavailability as compared to UFH.
     • They have a longer t_1/2; and can be administered once a day.
     • They do not routinely require aPTT monitoring.
     • There is a lower incidence of thrombocytopenia and osteoporosis as compared to UFH.
     • (Uses, adverse effects and contraindications are the same as other anticoagulants.)
   • Fondaparinux It is a synthetic parenteral anticoagulant. It binds to antithrombin and selectively inactivates factor Xa without any effect on thrombin. It does not require routine laboratory monitoring. Fondaparinux is administered subcutaneously. It is useful in pulmonary embolism and deep vein thrombosis (DVT). The incidence of thrombocytopenia is lower with fondaparinux. Its effects are not reversed by protamine sulfate.
   • Parenteral direct thrombin inhibitors Bivalirudin and argatroban bind directly to thrombin and inactivate it. They do not bind to antithrombin III. They are used intravenously as anticoagulants in patients who are at risk of HIT. The adverse effect is bleeding.
3. Oral anticoagulants Among oral anticoagulants, coumarin derivatives are commonly used. Oral anticoagulants act only in vivo. They are vitamin K antagonists.
   1. Mechanism of action Clotting factors 2, 7, 9 and 10 are synthesized in the liver as inactive proteins. These factors are rich in glutamic acid residues and are carboxylated in the liver where vitamin K acts as a cofactor. Vitamin K is converted to inactive epoxide form by oxidation and is regenerated to its active form by the vitamin K epoxide reductase enzyme. Warfarin is a coumarin derivative and has a structure similar to that of vitamin K. It competitively inhibits epoxide reductase, thus inhibiting the synthesis of vitamin K–dependent clotting factors – 2, 7, 9 and 10 and produces anticoagulant effects.
      • The onset and duration of the anticoagulant effect of warfarin depends on the half-lives (in hours) of clotting factors, which are as follows: 7 (6), 9 (24), 10 (36) and 2 (50). There is always a delay in the onset of the anticoagulant effect because the levels of clotting factors already present in plasma decline slowly over a period of 1–3 days. Oral anticoagulant therapy is monitored by measuring the international normalized ratio (INR).
   2. Pharmacokinetics Warfarin is almost completely absorbed after oral administration. It is highly bound to plasma proteins, freely crosses the placental barrier, is metabolized in the liver and the inactive metabolites are excreted in urine and stool. It has a long half-life of about 40 hours, and the duration of action is 3–6 days.
   3. Adverse effects
      • Bleeding: Bleeding is the most important and common side effect of warfarin. Bleeding can occur anywhere – skin, pulmonary, gastrointestinal urinary tract, etc. It can be controlled by oral or parenteral vitamin K₁ (depending on severity). Fresh frozen plasma should be given in severe bleeding. Warfarin therapy is monitored by measuring the international normalized ratio (INR).
      • Teratogenic effect: Warfarin is contraindicated during pregnancy as it may cause CNS abnormalities, foetal haemorrhage, abortion or intrauterine death.
   4. Drug interactions
      • Oral anticoagulants × barbiturates/carbamazepine/rifampicin/griseofulvin: They are enzyme inducers, increase the metabolic clearance of oral anticoagulants and decrease the anticoagulant effect.
      • Warfarin × phenytoin/sulfonamides: Warfarin is highly protein-bound. These drugs displace warfarin from the plasma protein binding site, increasing the free plasma concentration of warfarin, which can result in bleeding.
      • Warfarin × erythromycin/metronidazole: They decrease the metabolism of warfarin and increase the anticoagulant effect.
      • Warfarin × cefoperazone/ceftriaxone: Severe bleeding can occur due to hypoprothrombinaemia.
      • Warfarin × tetracyclines: Tetracyclines suppress bacterial flora and decrease vitamin K production, hence potentiating the warfarin effect.
      • Warfarin × aspirin and other NSAIDs: NSAIDs have an antiplatelet effect and also displace warfarin from the plasma protein binding site, thus potentiating the warfarin effect.
   5. Contraindications The contraindications for warfarin are similar to heparin. In addition, warfarin is contraindicated in pregnancy.
   6. Oral direct thrombin inhibitor: Dabigatran etexilate is a prodrug, which is converted to dabigatran. No laboratory monitoring is required during dabigatran therapy.
   7. Factor Xa inhibitor: Rivaroxaban directly inhibits factor 10a. It acts rapidly and is as efficacious as LMWHs. No laboratory monitoring is required during rivaroxaban therapy.
      • Therapeutic uses of anticoagulants:  The main aim of anticoagulant therapy is to prevent the formation of intravascular thrombus or further extension of an already formed clot. They do not break the clot or thrombus once it is formed.
        1. Venous thromboembolism: Venous thrombi are mainly formed of fibrin networks with a long tail that can easily detach and result in embolization of pulmonary arteries. Anticoagulants are used for the treatment and prevention of thromboembolism. For treatment of venous thrombosis and pulmonary embolism, heparin/LMWH is administered. Warfarin is also started simultaneously. Heparin/LMWH is continued for about 4–5 days till the effect of warfarin is obtained. For patients undergoing major surgery or requiring prolonged immobilization, anticoagulants are prescribed to prevent thromboembolism.
        2. Myocardial infarction (MI): Antiplatelets are the primary agents used in MI. In patients undergoing stenting, a short course of parenteral anticoagulants is administered.
        3. Other uses: Unstable angina, atrial fibrillation and prosthetic heart valves to prevent thromboembolism.

• Summary of Mechanism of Action of Anticoagulants

Fibrinolytic (Thrombolytics)

In response to stimuli (injury, stasis), tissue plasminogen activator (t-PA) is released from the vascular endothelium. It binds to fibrin-bound plasminogen and converts it to plasmin, which degrades fibrin.

Fibrinolytics are drugs that lyse thrombi rapidly by promoting the conversion of plasminogen to plasmin. Plasmin degrades fibrin and rapidly dissolves the blood clot.

Streptokinase, urokinase, alteplase, reteplase and tenecteplase are plasminogen activators.

• Pharmacological Properties of Fibrinolytic

Reteplase and tenecteplase are obtained from DNA recombinant technology. They have longer plasma half-lives than alteplase.

1. Uses of fibrinolytic
   • Acute MI: The main aim of fibrinolytic therapy is to restore coronary artery patency. These drugs dissolve the clot by promoting the conversion of plasminogen to plasmin. Thrombolytic therapy is most effective if they are administered within 1 h of the onset of symptoms. As the time between the onset of symptoms and to administration of fibrinolytic increases, the benefits of therapy decline.
   • Deep vein thrombosis: Thrombolytic therapy helps to provide symptom relief and prevent pulmonary embolism.
   • Pulmonary embolism: Fibrinolytics are used to lyse the clot.
   • Stroke: Fibrinolytics like alteplase are useful in selected cases of stroke.
2. Contraindications These include recent trauma, recent surgery, recent abortion, recent stroke, severe hypertension, severe diabetes, severe liver damage, peptic ulcer and bleeding disorders.

Antifibrinolytics

Antifibrinolytics block the conversion of plasminogen to plasmin and thus inhibit the fibrinolytic activity.

1. Epsilon aminocaproic acid (EACA) is administered orally or intravenously. It is used mainly to control bleeding due to overdose of fibrinolytics, after tooth extraction and surgery in haemophiliacs. It rarely causes myopathy and muscle necrosis.
2. Tranexamic acid It is available for oral, i.v. and topical administration. It is more potent than EACA. It is used to control excessive bleeding due to fibrinolytic overdose, following tooth extraction in haemophiliacs, tonsillectomy, prostatectomy, etc. Its main side effects are nausea, vomiting, diarrhoea, headache, etc.

Antiplatelet Drugs

Drugs that inhibit platelet aggregation are called antiplatelet drugs

1. Classification
   • Thromboxane (TXA₂) synthesis inhibitor: Low-dose aspirin
   • Phosphodiesterase inhibitor: Dipyridamole
   • Purinergic (P2Y₁₂) receptor antagonists: Ticlopidine, clopidogrel, prasugrel
   • Glycoprotein (GP)-receptor antagonists: Abciximab, eptifibatide, tirofiban
2. TXA₂ synthesis inhibitor Low-dose aspirin (50–325 mg/day) irreversibly acetylates platelet COX-1 and reduces the production of TXA₂. Since platelets cannot synthesize new enzymes, the antiplatelet effect lasts for the life-time of the platelets, i.e. 7–10 days. In higher doses, aspirin inhibits both TXA₂ and PGI₂; hence, antiplatelet efficacy is reduced. Common adverse effects are gastric irritation and bleeding.
3. Phosphodiesterase inhibitor Dipyridamole is a vasodilator. It inhibits phosphodiesterase and increases the concentration of cyclic adenosine monophosphate (cAMP) levels which inhibits platelet aggregation. It is occasionally used in combination with warfarin during the postoperative period in patients with prosthetic heart valves.
4. Purinergic receptor antagonists Ticlopidine, clopidogrel and prasugrel are prodrugs and structurally related. They inhibit adenosine diphosphate (ADP)-mediated platelet aggregation by irreversibly blocking purinergic (P2Y₁₂) receptors on the platelets. They are administered orally. They produce a synergistic effect when combined with aspirin or GP antagonists. Bleeding is an important adverse effect; the other side effect is diarrhoea. Neutropenia and thrombocytopenia are serious adverse effects of ticlopidine but rare with clopidogrel.
5. GP- receptor antagonists Abciximab, eptifibatide and tirofiban block GP IIb/IIIa receptors on platelet surface to inhibit the final step of platelet aggregation. They are useful as adjunctive therapy in high-risk patients with acute coronary syndrome undergoing percutaneous intervention (PCI). The main side effects of these drugs are bleeding and thrombocytopenia.
   • Uses
     • Acute coronary syndrome: It includes myocardial infarction and unstable angina. Aspirin alone or in combination with clopidogrel is used.
     • They can also be used in transient ischaemic attacks (to prevent recurrent attacks), patients with prosthetic heart valves (to prevent valve thrombosis), peripheral artery disease, etc.

Haematinics

Haematinics, such as iron, vitamin B₁₂ and folic acid are required for the formation of blood and are used in the treatment of anaemia. In anaemia, there is decreased oxygen-carrying capacity of blood due to a reduction in blood haemoglobin level and number of circulating RBCs. Anaemia results from a deficiency of nutrients (iron, vitamin B₁₂, folic acid), depression of bone marrow (due to cytotoxic drugs, radiation, etc.), blood loss (for example hookworm infestation, GI bleeding) and RBC destruction.

1. Iron Iron is an essential element of the body. The important sources of iron are liver, fish, dry fruits, jaggery, spinach, banana, meat, etc. Iron is a component of haemoglobin (Hb), myoglobin and a number of enzymes necessary for oxygen transfer (cytochrome, catalases, etc.). The total amount of iron in an adult male is about 4 g.
   • Pharmacokinetics Dietary iron exists in ferric form, which is reduced to ferrous iron with the help of acid in the stomach. Absorption of most of the iron takes place in the duodenum and upper jejunum. Iron absorption is regulated by a protein, apoferritin, in the intestinal mucosal cells. Ferrous iron is oxidized in mucosal cells to ferric iron and this combines with apoferritin to form ferritin. From ferritin, iron is very slowly released; so iron (as ferritin) will be in the mucosal cells for a long time.
     The ferrous iron in plasma is oxidized again to ferric iron. This ferric iron gets bound to transferrin (transport protein). This is taken up by various tissues like reticulocytes in the bone marrow (Hb synthesis), reticuloendothelial cells in the liver, spleen, etc. and stored. A small amount of iron is excreted from the body mainly by shedding gastrointestinal mucosal cells, desquamated skin, very little in the bile, sweat and least urine.
   • Factors affecting iron absorption are enhanced by the acidic pH of the stomach, ascorbic acid, cysteine, etc., which reduce the ferric iron to the ferrous form. Iron-deficiency states also increase the absorption of iron. Iron absorption is inhibited by excess phosphates, oxalates, phytates, etc. Milk, antacids and tetracyclines reduce iron absorption by forming insoluble complexes. Absorption of oral iron is more in an empty stomach.
   • Preparations of iron
     • Oral preparations: Oral administration of iron is convenient for the patient. The amount of elemental iron in each compound is important. Various preparations are:
       • Ferrous sulfate contains 20% (hydrated salt) and 32% (dried salt) elemental iron. It is the oldest and cheapest iron preparation.
       • Ferrous fumarate contains 33% elemental iron.
       • Ferrous gluconate contains 12% elemental iron.
         • Other oral preparations are ferrous succinate, iron choline citrate, ferric ammonium citrate, colloidal ferric hydroxide (50% elemental iron) and carbonyl iron (highly purified metallic iron).
         • Adverse effects of oral iron are nausea, vomiting, epigastric discomfort, dyspepsia, metallic taste, constipation or diarrhoea and staining of teeth (with liquid preparation).
   • Parenteral preparations
     • Iron dextran: It can be administered intravenously or intramuscularly. To prevent staining of the skin, injections are given deep intramuscularly into the buttock using the ‘Z-track’ technique (pull the skin and underlying subcutaneous tissue at the site of injection to one side before injecting the drug). It can be administered as a total dose infusion. The total dose required is diluted in 500 mL of normal saline and infused slowly intravenously over 6–8 h, after administering a test dose, under constant supervision. It can also be given intravenously slowly in small doses of 2 mL daily.
     • Iron sorbitol citric acid complex: It is given intramuscularly, but never intravenously.
     • Newer formulations like ferrous sucrose and ferric carboxy-maltose are administered intravenously. Ferric carboxy-maltose is an iron hydroxide complex with iron bound to a carbohydrate. Hypersensitivity reactions are less frequent as compared to older formulations of parenteral iron.
       • Indications for parenteral iron therapy
         1. Intolerance to oral iron
         2. Malabsorption of iron
         3. Noncompliance with oral iron
         4. Severe iron deficiency
         5. Patients with renal disease receiving erythropoietin
   • Adverse effects The intramuscular injections are painful and may cause abscesses and discolouration of the skin at the site of injection. The systemic side effects following administration by i.m./i.v. routes are headache, pyrexia, nausea, vomiting, arthralgia, lymphadenopathy, urticaria and circulatory collapse. An anaphylactoid reaction can occur. All patients should be monitored when receiving i.v. infusion of iron preparations. Facilities for resuscitation should be available. Hypersensitivity reactions are more frequent with older than newer formulations.
   • Therapeutic uses of iron
     • To treat iron-deficiency anaemia (microcytic hypochromic anaemia): For treatment of iron-deficiency anaemia, 200 mg of elemental iron is required per day. Ferrous sulfate is the most commonly used preparation. Treatment should be continued till the Hb level returns to normal (usually 4–8 weeks), and later, iron should be continued for at least 3–6 months to replenish iron storage. The expected rise in Hb concentration after iron therapy is 0.7–1 g/dL/week.
     • Prophylaxis: Prophylactic iron therapy is usually indicated during pregnancy and infancy. Iron is required prophylactically to meet the increased demand by the growing foetus and uterus and to combat loss during labour. For prophylaxis, 100 mg of elemental iron is administered daily starting from the second trimester. Treatment of megaloblastic anaemia with vitamin B12/folic acid results in a brisk haematologic response. If iron stores are inadequate, increased demands for iron cannot be met. So, iron must be supplemented in such patients.

Maturation Factors

Maturation factors are vitamin B₁₂ and folic acid. Both vitamin B₁₂ and folate are essential for DNA synthesis. The deficiency of one or both results in defective DNA synthesis and megaloblastic anaemia.

1. Vitamin B₁₂ Vitamin B₁₂ is a cobalt-containing compound which is synthesized by the colonic bacteria and is present in food of animal origin, such as meat, liver, egg, fish and cheese. Vitamin B₁₂ is essential for normal haemopoiesis and for the maintenance of normal myelin.
   • Functions. Vitamin B₁₂ acts as a coenzyme in certain metabolic pathways. Methylcobalamin (methyl B₁₂) and deoxy adenosylcobalamin (DAB₁₂) are the coenzyme forms of vitamin B₁₂. Methylcobalamin is necessary for the conversion of homocysteine to methionine, whereas for the conversion of methyl malonyl CoA to succinyl CoA, DAB₁₂ is required.
   • Pharmacokinetics The ingested vitamin B₁₂ complexes with intrinsic factor (IF) in the stomach, which is secreted by gastric parietal cells. The vitamin B₁₂–IF complex reaches the terminal ileum, where it binds to specific receptors and vitamin B₁₂ gets absorbed into the blood. In blood, vitamin B₁₂  is bound to transcobalamin-2 and is transported to various cells of the body. Excess vitamin B₁₂ is transported to the liver for storage. Vitamin B₁₂ is excreted in bile and undergoes enterohepatic cycling. Deficiency of vitamin B₁₂ can be due to pernicious anaemia, malabsorption, fish tapeworm infestation, increased demand and rarely, inadequate intake.
   • Preparations Cyanocobalamin (oral, i.m. or s.c.), hydroxocobalamin (i.m.) and methylcobalamin (oral). Vitamin B₁₂ is available for oral and parenteral administration (never intravenously, because of the risk of anaphylaxis). The choice of route depends on the cause of the deficiency.
   • Uses
     • Pernicious anaemia: It is due to autoimmune destruction of the gastric parietal cells that synthesize IF. Vitamin B₁₂ is administered lifelong.
     • Other uses. Prophylactic therapy with vitamin B₁₂ is indicated in patients at high risk of developing deficiency, for example, patients who have undergone gastrectomy.
     • Oral methylcobalamin has been used in the treatment of diabetes and other neuropathies
2. Folic acid is a combination of glutamic acid, para-aminobenzoic acid and pteridine nucleus. It is abundantly found in fresh green leafy vegetables, liver, yeast, kidney, fruits, etc. Much of it is destroyed by cooking. The minimum daily requirement of an adult is 50–100 mcg. The requirement of folic acid increases during pregnancy and lactation, i.e. 500–800 mcg/day.
   • Pharmacokinetics Most of the dietary folic acid is found as polyglutamate. It is readily absorbed in the proximal part of the jejunum. In the mucosa of the jejunum, it is reduced to tetrahydrofolate and then gets methylated. In blood, it is transported to various tissues as methyl tetrahydrofolate (MTHF). Constant supply of MTHF is maintained by food intake and enterohepatic cycling. Folate is stored mainly in the liver. The stores are exhausted in about 3–4 months, hence manifestations of folate deficiency appear in about 3–4 months. Folic acid itself is inactive. Its active form, tetrahydrofolate, is essential for the biosynthesis of amino acids, purines, pyrimidines, choline, DNA and therefore cell division.
   • Causes of folate deficiency
     • Dietary deficiency: most common.
     • Decreased absorption (malabsorption, tropical sprue).
     • Diminished storage (hepatic disease, vitamin C deficiency).
     • Drug-induced (phenytoin, antifolates, e.g. methotrexate, trimethoprim, pyrimethamine).
     • Increased demand (pregnancy, lactation, haemolytic anaemias).
   • Manifestations of folate deficiency
     • Megaloblastic anaemia – microscopically, the blood picture is similar in both folate and vitamin B₁₂ deficiency.
     • Glossitis, diarrhoea, general weakness and weight loss.
   • Preparations Folic acid is available for oral (tablet and liquid) and parenteral administration. Folinic acid (calcium leucovorin) is used in the treatment of methotrexate toxicity and as an adjuvant in methanol poisoning.
   • Uses
     • Megaloblastic anaemia due to nutritional folate deficiency, increased demand (pregnancy, lactation), pernicious anaemia (along with vitamin B₁₂) and antiepileptic therapy (for example, phenytoin).
       • Folic acid is given orally in a dose of 1–5 mg daily and continued for about 3–4 months. Administration of folic acid alone in vitamin B₁₂ deficiency may correct the megaloblastic anaemia but will aggravate or precipitate neurological abnormalities. This is due to the utilization of small quantities of
         vitamin B_{12 is} present in the body for haemopoiesis.
     • Prophylactic therapy: During pregnancy, routine prophylactic folic acid 0.5 mg/day is given from the first trimester to prevent neural tube defects.
     • Methotrexate toxicity: Folinic acid, active form of folic acid is used to antagonize methotrexate toxicity.
   • Adverse effects
     • Oral folic acid is safe, but injections may rarely cause hypersensitivity reactions.