S1M2 Pharm: Antianemia Drugs

• *First of all: Anemia can be caused by many diseases and disorders:
• It is a disorder of hematopoiesis that can be treated with pharmacological agents

Caused by: low number of erythrocytes, quantity of hemoglobin (Hb) or volume of packed RBCs in blood(Hct)

• Iron Preps
• Vitamin B12 Preps
• Folic Acid Preps
• Erythropoiesis-stimulation agents

*Easy.!

• Ferrous (Fe2+)
• Ferric (Fe3+)

• Ferrous fumarate
• Ferrous gluconate
• Ferrous sulfate (hydrated and dessicated)
• Iron dextran
• Iron sucrose
• Sodium ferric gluconate complex

Because of poor solubility @ physiological pH

• Metal iron of the heme cofactor in Hb!!!!!!
• It is responsible for O2 binding and transport.

• 60-70% of our IRON is found in Hb!!!

IRON elimination. Noway for Iron to get out!!!

• Infants: 0.27 mg/day
• Children:: 7-10mg/day (depending on age)
• Adolescent females/males: 15/11 mg/day
• Adult females/males: 18/8 mg/day
• Pregnant women: 27 mg/day
• Lactating women: 9-10 mg/day

Meat

• Because heme Fe in meat Hb and myoglobin can be absorbed intact without having to be dissociated into elemental Fe.
• ***Note: Fe in other foods like grains/vegetables is often tightly bound to organic molecules and is much less available for absorption

Low Fe Stores OR Increased Fe requirements

• So for menstruating women: absorption inccreases 1-2 mg/day
• Pregnant women: absorb. increase of 3-4 mg/day

• Duodenum
• Proximal jejunum
• Distal small intestin can absorb if needed.

Ferroreductase (FR)

Think, you want Fe to be in the reduced or Fe2+ form. So Ferroreductase is the enzyme to do this!

• Active transport of ferrous (Fe2+) via the action of divalent metal transporter 1 DMT1
• or
• Absorption of heme-complexed Fe via action of heme carrier protein 1 (HCP1)

Rate of uptake is increased into the cell by DMT1

• Active transport into blood across basolateral epithelial cell membrane via ferroportin (Fe)
• transported ferrous Fe is then oxidized by ferroxidase into the ferric (fe3+) form

OR

Fe is stored as FERRITIN--water solublecomplex consisting of a core Fe(OH3) covered by a shell apoferritin, specialized storage protein!!!!

• Total body [Fe] &Requirements
• If [Fe] high, low need---Ferritin
• If [Fe] low, high need---Active tranport to BLOOD...Gotta Use that Fe!!!!

• the protein Transferrin (Tf)
• B-globulin binds two ferric ions (Fe3+)

** don't forget this easy crap!

As a Tf-(Fe3+)2 complex which is transported into the bone marrow via transferrin receptor (TfR)

Ferritin!

In macrophages in the liver, spleen, and bone and in parenchymal liver cells

A specialized Fe storage protein.

• Free Fe Levels!
• If Fe is low, AF synthesis is inhibited (less storage) and you get a shift towards transferritin production
• If Fe is high, AF synthesis is stimulated to sequester more Fe in order to protect organs from toxic effects of excess free Fe.

• Ferritin!!!
• Serum ferritin is in equilibrium with storage ferritin in reticuloendothelial cells

******Serum ferritin can be used to estimate the total body Fe stores!!!

[ferritin] serum

• Tenaciously conserved: no mechanism for excretion of Fe
• Small amounts lost in feces (exfoliatio of intestinal mucosal cells) bile, urine and sweat (about 1 mg/day)
• This elimination necessitates Fe be balanced in body, and it must be tightly regulated.

• Easily achieved by changing the intestinal absorption and storage of Fe in response to the body's needs

As a metal cofactor in heme (metalloprophyrin prosthetic group of Hb, myoglobin, cytochromes, and other enzymes)

• Iron deficency Anemia:treated with oral or parenteral Fe preps
• ***Oral prep correct probelm just as rapidly/completely as parenteral prep as long as GI absorption of Fe is not hindered

**ORAL admin of Fe is PREFERRED.

• Only as Ferrous salts (most efficently absorbed)
• Ferrous sulfate
• Ferrous gluconate
• Ferrous fumarate

KNOW: gluconate salts better tolerated than sulfate salts: g = "good"

• 50-100 mg of Fe can be incorporated into Hb daily.
• 25% of oral Fe from ferrous salt can be absorbed
• Deficent patients hould be given 200-400 mg of elemental Fe (lower doses for intolerant people)

• Treatment should continue for at least 3-6 months after the correction of the cause of Fe loss.
• This will correct the ANEMIA and REPLENISHES Fe Stores. ***

PTs with documented Fe deficency, who can't absorb oral prpe, and people with chronic anemia.

• People on Hemodialysis (renal disease), EPO stimulating agents
• People with IBD (inflammatory bowel disease)
• People with malabsorption syndromes

Limit the dose administered idiot!

• Iron dextran
• Sodium ferric gluconate complex
• Iron sucrose

KNOW THESE THREE

• Parenteral prep of of Iron, stable ferric oxyhydroxide and dextran polymers with 50 mg/ml of elemental Fe
• Administered by deep IM injection or IV
• IV admin eliminates local pain and tissue staining that occurs with IM route

administered by IV

• Parenteral Fe prep.
• Oral is the desired route!

• Oral Fe Therapy:
• -nausea, epigastric discomfort, abdominal cramps constipation, diarrhea usually dose-related can be overcome by lowering daily does or taking tabs with meals
• -black stools****not clinically significat but black stools that occur during oral Fe therapy can obscure any GI blood loss

Although the black stools are not clinically significant the black stool may obscure the diagnosis of continued GI blood loss

Chronic treatment necessitates monitoring of Fe storage levels to avoid toxicity of iron overload.

• Iron Dextran: IM:local pain tissue staining
• IV: headache, lightheadness, fever, arthralgias, nausea/vomiting, back pain, flushing, urticaria (hives), brochospasm, anaphylaxis (rare)
• -DEATH.

• Acute Fe Toxicity:
• almost exclusive to children who accidently ingest Fe tablets. 10 tablets are lethal!
• Poisoned Children experience necrotizing gastroenteritis, vomiting, abdominal pain, bloody diarrhea, shock, lethargy, dyspnea, metabolic acidosis, coma, death.
• = URGENT treatment
• Whole bowel irrigation should be performed to flush out unabsorbed pills
• Systemic administration of iron antidote

• Also called Fe overload or hemochromatosis*****
• Most commonly occurs in patients with inherited hemochromatosis and in patients who recieve many RBC transfusions over a long period time (pts with thalassemia major)
• chronic Fe toxicity can occur when excess Fe is deposited in the heart, liver, pancream and other organs (can cause DEATH)

• Intermittent phlebotomy in the absence of anemia!!!!***
• Save your patients!
• One unit of blood can be removed per week until all the excess Fe is removed
• OR
• administer an Fe antitode

• Anemias NOT caused by Fe deficency!
• State of Fe overload (only people who are deficent!)
• Parkinson's disease: Fe supplements appear to increase the rate at which disease progressses!!!!!!--aggregates the protein responsible and makes the disease worse
• Increases in gastric pH and phosphates (which decreases Fe absorption)
• Decreased absorption of certain drugs (tetracycline, quinolones, thyroid hormone)-->avoid this by spaces seperate doses of Fe from these drugs by 2hrs.

• Deferoxamine (used most often)
• Deferasirox

• First of all memorize, it's an Fe chelator.
• It binds metal irons (Fe3+ specific) and pulls them out of the blood
• It has low oral availability
• Administered IM or IV

• It's an Fe chelator (antidote) remember**most commonly used one!
• It has a very very very high affinity for Ferric (fe3+) iron
• It binds ferric Fe forming a pharmacologically inactive chelate complex
• It can remove Fe from hemosiderin (poorly organized form), ferritin (storage) and Tf (transferritin) but NOT from Hb or cytochromes.

• Iron poisoning (too much Fe)
• or
• Transfusional Fe overload (thalassemia, sickle cell disease)

• Hypotension
• Allergic rxn (rash, uticaria (hives))
• Neurotoxicity (after long time use)
• Acute respiratory distress syndrome (in high doses)

• Know its an Tridentate iron chelator
• Pharmokinetics: good absorption, oral admin

Chronic Iron overload due to blood transfusions

• Fever, Rash, Headache
• Abdominal pain, diarrhea, nausea/vomitting
• Increased [creatinine] in serum

*it's an Fe chelator

• Cyanocobalamin
• &
• Hydroxocobalamin

Consists of a porphyrin-like rink with a central cobalt atom attached to a nucleotide

• Deoxyadenosylcobalamin
• Methylcobalamin

microbially derived vitamin b12 in meat (liver especially) eggs, dairy products

• Avg US diet: 5-30 micrograms/day
• Daily Requirement 2 micrograms/day

• Primarily in LIVER
• about 3000-5000 micrograms
• Would take 5 YEARS to deplete B12 in liver stores....

Megaloblastic Anemia if all absorption is lost

As a COMPLEX with Intrinsic Factor (IF) a glycoprotein secreted by parietal cellls of gastric mucosa

IF complexes with B12 liberated from dietary sources in stomach and duodenum.

IN the distal ILEUM! by highly selective receptor-mediated transport system

Malabsorption due to lack of INTRINSIC FACTOR

OR loss/malfunction of specific absorption mechanism in the distal ileum

Those freaking vegetarians!! or vegans! who have had many years without meat, eggs, or dairy products

to various cells of body by Transcobalamin I, II, III

to the Liver for storage!!!

• three essential enzymatic reactions!!!!!**
• 1) Methyl Transfers to make Folate, Methionine (Synthesis of these) Methylcobalamin serves as an intermediate in the transfer of a methyl group from N5-methyltetrahydrofolate to homocystein converting it into methionine. B12 deficiency can cause accumulation of homocysteine and increase in homocysteine serum concentration***
• 2.) Cobalamin is an intermediate recieve the methyl group from N5-methtetrahydrofolate to become tetrahydrofolate (THF) THF is the precursor for all FOLATE cofactors: in B12 deficency, the loss of folate cofactors and accumulation of N5-methyltetrahydrofolate is called the methylfolate trap and this prevents the synthesis of purines and hence DNA!!!!
• 3.) Deoxyadensoylcobalamin is necessary for the conversion of L-methylmalonyl CoA to succinyl-CoA by the enzyme methylmalonyl-CoA mutase
• Deficency of B12, causes accumulation of methylmalonyl-CoA and methylmalonic acid.
• Increased [methylmalonic acid] serum/urine levels can be used to support a diagnosis of vitamin B12 deficency (as can homocysteine)

• Accumulation of homocysteine and increase in its serum concentration
• B12 deficency causes loss of folate precursors, preventing synthesis of purines and DNA synthesis!!!! KNOW!
• ( correct with admin of folic acid)
• Increases methylmalonic acid concentration in urine and serum!

Treat or prevent B12 Deficency

• Megaloblastic, macrocytic anemia
• Also can cause neurologic syndrome associate with deficency is arrested but may not be fully revered if it has occured for several months.
• When Diagnosis of megaloblastic anemia is made, it must be determined if it is vitamin b12 or folic acid deficent --> CHECK serum levels of the vitamins

• Administration of radiolabeled vitamin B12 allows determination of the mechanisms of vitamin B12 deficency.
• Assayed by measuring amount of radiolabled B12 excreted in urine!

B12 was absorbed successfuly in the GI system! :)

B12 NOT absorbed successfully.

Pernicious anemia (lack of IF), Damage to distal ileum, bacterial overgrowth, ALMOST ALL CASES caused by MALABSORPTION--> so parenteral injections of B12 would be required (lifelong)

Shilling tests shows diminished absorption of radiolabeled Vitamin B12 which is corrected with concomitant admin of IF (intrinsic factor)

Schilling test shows non-absorption of radiolabeled vitamin B12 even in presence of Intrinsic factor***

If it is not absorbed in a dual labelled shilling test, then there is a problem with ABSORPTION!

Used in Vit B12 deficency!

Used in Vit B12 deficency!

Administer radiolabelled B12. Look @ amount of B12 excreted in urine: Any B12 that is present in URINE means it was absorbed!!!

This man obviously has pernicous anemia due to the fact that B12 with IF (Co-57) was excreted more in urine than just B12 (Co-58) (without IF). Without IF the B12 was not absorbed by GI system and went out via stool! (less than 0.82 total), man isn't making his own IF. he needs IF

• With IF/B12, you get uptake (on the left)
• If less than 1% in both? then it is a receptor problem!!!!

• This is a diagnostic test using B12 to determine the mechanism behind a person's B12 deficency.
• This means there is probably a receptor problem. Because if you're providing one radio-labelled form with IF/B12 and one that is just B12, and both are not being taken up, you know that the person probably has something wrong with the receptors involved with uptake of B12 and not neccissarily a lack of B12

Then you would know that maybe that patient is just not getting enough B12 in their diet! (they took up both forms in high amounts!!)

Cyanocobalamin and Hydroxocobalamin

• Extremely rare (almost always follows parenteral treatment)
• Hypersensitivity rxns (especially to cobalt)
• Hypokalemia and thrombocytosis (which is high platelet count) (occurs upon conversion of severe megaloblastic anemia to normal erythropoiesis--->due to the body switching from an anemia state to a normal state

Pteroylglutamic acid (which is NOT useful to the cell)

• it is composed of pteridine, p-aminobenzoic acid, glutamic acid (several numbers of glutamic acid moieties may be attached to the pteroyl potion of the molecule resulting in monoglutamates, tiglutamates or polyglutamates.
• Pteroyglutamic acid undergoes a reaction by dihydrofolate reductase to become dihydrofolic acid (which is the useful form that can feed into the folate cycle)

does not have a HUGE store. We do not have a huge store of folate--about 1-6 months you would develop an anemia due to folate deficency.

plant and animal tissues, richests sources are yeast, liver kidney and green veggies.

500-700 micrograms daily.

300-400 micrograms.

in the proximal jejunum!

• polyglutamate forms of N-methyltetrahydrofolate.
• In order to be absorbed, all but one glutamyl reside must be hydrolyzed by the alpha glutamyl transferase within the brush border of the intestinal mucosa.
• Monoglutamate N5-methyltetrahydrofolate is transported into the blood stream by both active a passive transport and is widely distributed throughout the bloodstream by both active and passive transport and is widely distributed throughout the body.

THF is tetrahydrofolate, and it requires cobalamin in order to convert the dietary folates that were converted to N⁵ methyltetrahydrofolate to tetrahydrofolate, which is used to convert serine into glycine. This is 1 of 4 reactions that require THF cofactors to participate in one-carbon transfer reactions.

They require B12 (cobalamin) to convert N5-methyltetrahydrofolate to THF which is then used in conversion of serine to glycine.

• Without folate you won't carry out these reactions!****
• Conversion of dUMP to dTMP (deoxy) via thymidylate synthatase to create nucleotides for DNA synthesis!!! need folic acid (#1)
• Conversion of AAs serine to glycine (catabolic rxn, going from more complex serine to glycine) via action of serine transhydroxymethylase (#2)
• Synthesis of purines required for nucleotide synthesis and then DNA synthesis-->we need purines for DNA synthesis for erythropoiesis!!! Cancer cells also depend on this part of the cycle (#3)
• Methylation of Vitamin B12 for the production of methionine. this is where B12 and Folate metabolism meet! B12 is required for the production of the AA methionine from methylcobalamin (#4)

Folic acid is brought into the cycle when it is converted to dihydrofolate by folate reductase. This is essential to bring folate into a usable form.

****KNOW this. This is an essential step.

• *** Very Important!
• Methotexate is an anti-folate drug, which blocks dihydrofolate reductase so no folic acid can be converted into dihydrofolate. This reaction is neccessary in order for folic acid to be converted into a useable form and to make dTMP, which is required for DNA synthesis. So what do cancer cells do? They divide over and over and over again. To divide, they need DNA and methotrexate is targeting folic acid synthesis or the folatic cycle is a good way to target cancer. BOOM!

• Treatment and prevention of megaloblastic anemia caused by folic acid deficency (this is microscopically indistinguishable from the megaloblastic anemia caused by B12 deficency!!!)

Prevention of neural tube defects! This is critical!

• *Parenteral administration of folate is rarely neccessary since folic acid is well absorbed even in patients with malabsorptive syndromes
• *Therapy with folate should be continues unti the underlying cause is removed or corrected. Patients with malabsorptive issues or dietary inadequacy may be treated indefinitely.

• *Folate typically doesn't have any adverse effects or toxicity

A therapeutic folic acid prep consisting of folinic acid or 5-formyltetrahydrofolate! It is a unique form of Folic acid

• It is completely abesent
• **Why is Leucovorin unique?

It bypasses the dihydrofolate reductase step in the synthesis of THF. from the small intestine and is converted into its active metabolites inside GI cells.

Leucovorin (5-formyltetrahydrofolate) can be used to rescue cells that have been exposed to folate antagonists (like cancer drugs methotrexate, trimethoprim, pyrimethamine) so what is does is provide THF to the folic acid cycle by bypassing the DHF reductase step--Folic acid doesn't have to be converted to dihydrofolate.. it comes in at the THF step it feeds in directly!!!!

• It is referring to one of the clinical uses of lecovorin, the prophylaxis of methotrexate toxicity.
• Because methotrexate targets all cells and not just cancerous ones you need a way to still get DNA synthesis, methionine synthesis, purine synthesis and keep the folate cycle going! So leucovorin at standard clinical doeses will provide normal cells with THF to keep the cycle moving because Leucovorin bypasses the DHF step.

• Potientiation of 5-fluorouracil therapy (a cancer drug)! basically makes 5-fluorouracil a better drug for cancer therapy!
• 5-FU inhibits thymidylate synthetase, binding depends on the presence of methylene-THF. Leucovorin is metabolized to methylene-THF and increases and stabilizes the binding of 5-FU and its cytotoxic effect.
• It can also be used for patients with a congential deficency in DHF reductase and can't get folate into the cycle!!!!

You would test B12 and folate levels in the serum.

• TWO USES: ONE TO DECREASE TOXICITY (Methotrexate) ONE TO INCREASE TOXICITY (5-FU).
• 1) Prophylaxis of methotrexate toxicity (see above picture)= the "leucovorin rescue"
• 2.) Potentiation of 5-FU (5-fluorouracil therapy) making it more cytotoxic! 5-FU inhibits the enzyme thymydlate synthetase to convert dUMP to dTMP for formation of DNA.

a cytotoxic drug that targets all cells (normal and cancerous) that blocks the dihydrofolate reductase step----we can use leucovorin to "rescue" normal cells by feeding directly into the THF step --and provide the necessary folic acid!

• Darbepoetin alfa
• Epoetin alfa
• Epoetin beta (approved by FDA, not available in US due to legal issues)
• 34-39 kDa glycoprotein
• As a drug: recombinant human protein
• -recombinant human EPO
• -produced in a mammalian cell expression system

• Administration is partenteral because EPO is a large protein that is broken down in the GI system by proteases.
• Epoetin alfa (3x week), 1/2 life of 4-13 hours in patients with chronic renal protein (not cleared by dialysis)
• Darbepoetin alfa (1x dose a week): modified from that is more heavily glycosylated and has a 2-3 fold longer half life
• Epoetin beta (1-2 doses/month): isoform that is covalently attached to a long polyethylene glycol polymer--long lived!!

Binds to erythropoietin receptors on the plasma membrane of red cell progenitors, which stimulates JAK/STAT signal transduction pathway.

• Erthyropoiesis-stimulating agents (ESAs) can be used successfully to impact different types of anemia
• What it does is increase: Hb and Hct
• Often it eliminates the need for blood transfusions
• Increases quality of life
• Used routinely for patients with anemia secondary to their chronic renal disease
• Most patients will require Fe and Folate supplementation to support the increased erythropoiesis.

• EPO also useful for treatment of anemia due to primary bone marrow disorders and secondary anemias
• Used for : aplastic anemia, other bone marrow failure states
• Multiple myeloma and other bone marrow malignancies
• Anemias associated with chronic inflammation, AIDS, and myelosuppresive cancer therapy
• Anemia produced by zidvudine treatment (AZT), a breakthrough aids drug
• Anemia of prematurity
• Used to reduce the need for transfusion in high-risk patients undergoing elective, non-cardiac, nonvascular surgery.
• Used to accelerate erythropoiesis after phlebotomies for autologous transfusion of elctive surgery
• Treatment of hemochromatosis (overload of Fe, deposited in RBCs instead of storage)

• Expression is upregulated by tissue hypoxia mediated stimulation of EPO transcription: this corrects the anemia (which is the cause of the tissue hypoxia) provided that the bone marrow response is not impaired by RBC nutritional deficency, primary bone disorders or bone marrow suppression from drugs or chronic diseases
• EPO stimulates erythroid proliferation and differentiation
• It induces release of reticulocytes from the bone marrow (shift to the left)*****

• Treatment of hemochromatosis (the overload of Fe)
• So instead of depositing Fe for storage, you make more RBCs for the Fe to go into.

The recombinant version of EPO, the use of EPO as a drug is in this form.

• typically 3x weekly (if given by epoetin alfa)
• Because it's a BIG protein. It can't cross the plasma membrane, and proteases break down in the GI system
• -This holds true for ALL recombinant proteins used as drugs. must be given parenterally

• Renal Failure
• Increased rate of deep venous thromboses (epoetin alfa) patients should be on deep venous thrombosis prophylaxis
• Thrombotic complications have a greater incidence in patients whith chronic renal failure or cancer in who ESAs rais HB serum levels >12g/dL or faster tumor growth in patients with head/neck cancers
• Allergic reactions are infrequent
• Small number of cases of pure red cell aplasia (PRCA) accompanied by neutralizing antibodies.
• Most commonly seen in dialysis patient treated SC with Eprex (specfic form of Epoetin Alfa)

• Contraindications:
• Use of epoetin beta to treat anemia caused by cancer chemotherapy---increases chance of death.

Because EPO stimulates erythropoiesis. If you are making new red blood cells you need more DNA, if you want more DNA you need folate to synthesize DNA. If you want to carry more oxygen in your RBCs you need more Fe.