Drugs and the hematologic system

Drugs and the hematologic system

The hematologic system includes plasma (the liquid component of blood) and blood cells, such as red blood cells (RBCs), white blood cells, and platelets. Types of drugs used to treat disorders of the hematologic system include:

• hematinic
• anticoagulant
• thrombolytic.

Hematinic drugs

Hematinic drugs provide essential building blocks for RBC production. They do so by increasing hemoglobin, the necessary element for oxygen transportation.

Iron, vitamin B₁₂, folic acid

This section discusses hematinic drugs used to treat microcytic and macrocytic anemia’iron, vitamin B₁₂, and folic acid.

It also describes the use of erythropoietin agents to treat normocytic anemia.

Iron

Iron preparations are used to treat the most common form of anemia’iron deficiency anemia. Iron preparations discussed in this section include ferrous fumarate, ferrous gluconate, ferrous sulfate, iron dextran, and sodium ferric gluconate complex.

 

Pharmacokinetics (how drugs circulate)

Iron is absorbed primarily from the duodenum and upper jejunum of the intestine. Different iron formulations don’t vary in absorption, but they do vary in the amount of elemental iron supplied.

 

Low iron increases absorption

The amount of iron absorbed depends partially on the body’s stores of iron. When body stores are low or RBC production is accelerated, iron absorption may increase by 20% to 30%. On the other hand, when total iron stores are large, the body absorbs only about 5% to 10% of the iron available.

Enteric-coated preparations decrease iron absorption because, in that form, iron isn’t released until after it leaves the duodenum. The lymphatic system absorbs the parenteral form after I.M. injections.

Hemoglobin has it

 

Iron is transported by the blood and bound to transferrin, its carrier plasma protein. About 30% of the iron is stored primarily as hemosiderin or ferritin in the reticuloendothelial cells of the liver, spleen, and bone marrow. About 66% of the total body iron is contained in hemoglobin. Excess iron is excreted in urine, stool, sweat, and through intestinal cell-sloughing. It appears in breast milk and crosses the placenta.

Pharmacodynamics (how drugs act)

Although iron has other roles, its most important role is the production of hemoglobin. About 80% of iron in the plasma goes to the bone marrow, where it’s used for erythropoiesis (production of RBCs).

 

Pharmacotherapeutics (how drugs are used)

Oral iron therapy is the preferred route for preventing or treating iron deficiency anemia. It’s used to prevent anemias in children ages 6 months to 2 years because this is a period of rapid growth and development. Pregnant women may need iron supplements to replace the iron used by the developing fetus.

Warning!

Adverse reactions to iron therapy

The most common adverse reactions to iron therapy are gastric irritation and constipation. Iron preparations also darken stool, and liquid preparations can stain the teeth.

The most serious reaction is anaphylaxis, which may occur after administration of parenteral iron. To guard against such a reaction, administer an initial test dose before giving a full-dose infusion.

Ironclad options

 

Parenteral iron therapy is used for patients who can’t absorb oral preparations, aren’t compliant with oral therapy, or have bowel disorders (such as ulcerative colitis or Crohn’s disease). Patients with end-stage renal disease who are receiving hemodialysis may also receive parenteral iron therapy at the end of their dialysis session. While parenteral iron therapy corrects the iron store deficiency quickly, it doesn’t correct the anemia any faster than oral preparations would.

Iron preparations available for parenteral administration are iron dextran (given by I.M. injection or slow, continuous I.V. infusion) and iron sucrose. Iron sucrose is used for patients on hemodialysis. 

 

Drug interactions

Iron absorption is reduced by antacids as well as by such foods as coffee, tea, eggs, and milk. Other drug interactions involving iron include:

• Absorption of tetracyclines (demeclocycline, doxycycline, minocycline, oxytetracycline, and tetracycline), methyldopa, quinolones (ciprofloxacin, levofloxacin, lomefloxacin, moxifloxacin, norfloxacin, ofloxacin, and sparfloxacin), levothyroxine, and penicillamine may be reduced when taken with oral iron preparations.
• Cholestyramine, cimetidine, proton-pump inhibitors, and colestipol may reduce iron absorption in the GI tract

Safe and sound

Testing for parenteral iron sensitivity

Parenteral iron can cause acute hypersensitivity reactions, including anaphylaxis, dyspnea, urticaria, other rashes, pruritus, arthralgia, myalgia, fever, sweating, and allergic purpura. To test for drug sensitivity and prevent serious reactions, always give a test dose of iron dextran before beginning therapy.

 

Carefully assess the patient’s response to the test dose. If no adverse reactions occur within 1 hour, give the total dose. If adverse reactions occur, notify the prescriber immediately. To treat anaphylaxis, keep epinephrine and standard emergency equipment readily available.