Pharmacology
Pharmacodynamics
Iron
In case of iron-deficiency anaemia, the initial response of iron given orally is
1 week. Haemoglobin may increase 1.5 to 2.2 g/dl/week for the first 2 weeks and
then 0.7 to 1.6 g/dl/week until normal haemoglobin levels are achieved. Reticulocyte
count increases in 3 to 4 days and peaks in 7 to 10 days.
Given orally, subjects with normal iron stores absorb 10 - 35%; iron-deficient patients
absorb 80 - 95%. The percent absorption is affected by the salt form, the amount
administered, the dosing regimen, and the size of the iron stores. Oral iron is
poorly absorbed by patients on continuous peritoneal dialysis. Vitamin C enhances
absorption of non-haem iron. Ferrous iron is more bioavailable than ferric iron.
The absorption of a pharmacological dose of iron was assessed by determination of
mucosal uptake, mucosal transfer and retention of 33 mg Fe (II) as ferrous sulphate
and ferrous ascorbate in 11 subjects with normal iron stores and 9 subjects with
iron deficiency. There was no difference in absorption between the two iron compounds
in normal subjects. Absorption of ferrous ascorbate averaged 52% higher than ferrous
sulphate in subjects with iron deficiency. The difference was the result of higher
mucosal uptake, probably because the oxidation of Fe (II) in the alkaline milieu
of the intestine, which leads to formation of non-absorbable Fe (III) complexes,
was prevented.
For purposes of comparison, all studies currently refer to 40% absorption of the
reference dose of ferrous ascorbate since it corresponds to that which is obtained
in borderline iron-deficient populations.
The main dietary enhancers of absorption of non-haem iron are muscle tissue (cysteine-containing
proteins) and ascorbic acid. The main dietary inhibitors of absorption of non-haem
iron are phytic acid, polyphenols, calcium and certain proteins.
The elimination half-life of the parent compound is 6 hours. Excretion takes place
in trace amounts through the kidneys and the faeces.
Folic acid
The therapeutic drug concentration of folic acid in a healthy adult ranges from
4 - 20 ng/mL. It appears in the plasma approximately 15 to 30 minutes after an oral
dose; peak concentration is generally reached within 60 to 90 minutes.
The bioavailability of folic acid ranges from 76% to 93%. Folic acid is absorbed
by a carrier-mediated process primarily in the proximal part of the small intestine.
There is little absorption in the distal jejunum and practically none in the distal
ileum. Its absorption is reported to be impaired in patients with celiac disease
in the proximal jejunum, but absorption is reported to be comparable to that for
healthy individuals from the distal jejunum. Pregnancy does not appear to impair
the absorption of folic acid.
Folate derivatives are bound by plasma proteins. The greatest affinity for plasma
protein-binding occurs with the non-methylated analogs. Other distribution sites
include the liver (50%) and tissues. Once absorbed, folate and its derivatives are
rapidly distributed to all body tissues. Normal serum, cerebrospinal fluid and erythrocyte
levels of folate have been reported to be 5 - 15 ng/mL; 16 - 21 ng/mL and 0.175
- 0.316 mcg/mL, respectively. In general, folate serum levels below 5 ng/mL indicate
folate deficiency, and levels below 2 ng/mL usually result in megaloblastic anaemia.
Folic acid is metabolized in the liver to 7,8-dihydrofolic acid and, eventually,
to 5,6,7,8-tetrahydrofolic acid with the aid of a reduced diphosphopyridine nucleotide
(DPNH) and folate reductases. This conversion occurs primarily in the liver and
not to any significant degree during absorption through the intestinal mucosa. Tetrahydrofolic
acid derivatives are distributed to all body tissues, but are stored primarily in
the liver. Maternal Zinc deficiency may compromise infant development & lead to
poor birth outcomes5
The kidneys excrete 30% of folic acid. After a single oral dose of 100 mcg of folic
acid in a limited number of normal adults, only a trace amount of the drug appeared
in the urine. The other route of excretion is bile. Following oral administration,
folic acid is found in concentrations ranging from 15 - 400 ng/mL in the bile, with
peak levels occurring in approximately 120 minutes. Small amounts of orally administered
folic acid have also been recovered in the faeces. Folic acid is also excreted in
the milk of lactating mothers.
Warnings and Precautions
General
Do not exceed the recommended dose. The type of anaemia and the underlying cause
or causes should be determined before starting therapy with this medication. Since
the anaemia may be a result of a systemic disturbance, such as recurrent blood loss,
the underlying cause or causes should be corrected, if possible.
In general, people with a history of kidney disease, intestinal disease, peptic
ulcer disease, enteritis, colitis, pancreatitis, hepatitis, who consume excessive
alcohol, who plan to become pregnant, or who are over 55 years of age and have a
family history of heart disease should consult a doctor and pharmacist before taking
iron. Individuals with blood disorders who require frequent blood transfusions are
also at risk of iron overload and should not take iron supplements without direction
by a qualified healthcare provider. Long-term use of high doses of iron can cause
haemosiderosis that clinically resembles haemochromatosis. Iron overload is associated
with several genetic diseases, including haemochromatosis. Accumulation of excess
iron is being investigated as a potential contributor to neurodegenerative diseases
such as Alzheimer's and Parkinson's disease.
Vitamin B12 deficiency that is allowed to progress for longer than 3 months may
produce permanent degenerative lesions of the spinal cord. Folic acid in doses above
0.1 mg daily may obscure pernicious anaemia in that haematologic remission can occur
while neurological manifestations remain progressive. This may result in severe
nervous system damage before the correct diagnosis is made. Neurological manifestations
will not be prevented with folic acid, and if not treated with vitamin B12, irreversible
damage will result. Adequate doses of vitamin B12 may prevent, halt, or improve
the neurological changes caused by pernicious anaemia.
Administration of folic acid alone is improper therapy for pernicious anaemia and
other megaloblastic anaemias in which vitamin B12 is deficient. Doses of cyanocobalamin
exceeding 10 mcg daily may produce a haematologic response in patients with folate
deficiency. Indiscriminate administration may mask the true diagnosis.
Caution should be used in patients undergoing angioplasty since an intravenous loading
dose of folic acid, vitamin B6, and vitamin B12, followed by oral administration
taken daily after coronary stenting, might actually increase restenosis rates. Due
to the potential for harm, this combination of vitamins should not be recommended
for patients receiving coronary stents.
Drug Interactions
• The administration of the following with iron salts results in decreased iron
effectiveness: Aluminium hydroxide, aluminium phosphate, calcium , aluminium carbonate
(basic), chloramphenicol, dihydroxyaluminium aminoacetate, dihydroxyaluminium sodium
carbonate, magaldrate, magnesium carbonate, magnesium hydroxide, magnesium oxide,
magnesium trisilicate, methacycline, minocycline, oxytetracycline, rolitetracycline,
sodium bicarbonate.
• The administration of the following with iron salts results in decreased effectiveness
of the following molecules: Cefdinir, cinoxacin, ciprofloxacin, enoxacin, gatifloxacin,
gemifloxacin, grepafloxacin, levofloxacin, lomefloxacin, moxifloxacin, norfloxacin,
ofloxacin, penicillamine, sparfloxacin, temafloxacin, trovafloxacin mesylate, levothyroxine.
• The administration of the following with iron salts results in decreased effectiveness
of the molecule as well as iron: Zinc (with decreased gastrointestinal absorption),
acetohydroxamic acid, trientine (with decreased gastrointestinal absorption).
• The administration of the following with iron salts results in reduced iron absorption/bioavailability:
Esomeprazole, desferrioxamine, gossypol, lansoprazole, omeprazole, pantoprazole,
rabeprazole, soybean, soy protein, vanadium, cholestyramine, colestipol, pancrelipase.
• The administration of the following molecules with iron decreases the absorption
of the molecules: Ciprofloxacin, ofloxacin, levofloxacin, tiludronate, risedronate,
alendronate, etidronate, ibandronate, levodopa, methyldopa, levothyroxine, mycophenolic
acid, minocycline, doxycycline, tetracycline, demeclocycline.
• Allopurinol may increase iron storage in the liver and should not be used in combination
with iron supplements.
• Aminosalicylic acid may cause a malabsorption syndrome (weight loss, iron and
vitamin depletion, steatorrhoea).
• Aspirin and NSAIDs can cause mucosal damage and bleeding throughout the gastrointestinal
tract. Chronic blood loss associated with the long-term use of these agents may
contribute to iron deficiency anaemia. Since iron supplements may also irritate
the gastrointestinal tract, patients should not use them concurrently with NSAIDs
unless recommended by a physician.
• Chloramphenicol can reduce the response to iron therapy in iron-deficiency anaemia.
• Iron supplements and dimercaprol may combine in the body to form a harmful chemical.
• Adequate dietary iron intake is recommended when taking H2 blockers like cimetidine,
ranitidine, famotidine or nizatidine. Iron supplements are not usually required
unless they are being used for another indication.
• The administration of the following with folic acids results in decreased effectiveness
of the molecule: Fosphenytoin, phenytoin, pyrimethamine.
• The administration of the following with folate results in reduced folate absorption:
Aminosalicylic acid, antacids, antibiotics, aspirin, carbamazepine, cholestyramine,
colestipol, cycloserine, cimetidine, famotidine, nizatidine, ranitidine, pancrelipase,
sulfasalazine, triamterene.
• The administration of the following with folate results in reduced serum folate
levels: Oestrogens conjugated, oral contraceptives pills, methotrexate, methylprednisolone
sodium succinate (noted in people with multiple sclerosis), intravenous pentamidine,
phenobarbital and primidone, pyrimethamine.
• Excessive use of alcohol increases the requirement for folic acid.
• Chloramphenicol may antagonize some effects of folic acid on the blood (haematopoietic
system). Limited data suggests that diuretics may increase excretion of folic acid.
• Reduced vitamin B12 and, to a lesser extent, folate levels occur in some people
with diabetes and can contribute to hyperhomocysteinaemia, which adds to the already
increased risk of cardiovascular disease. The reduced folate levels seen in diabetics
have been linked to metformin use in some cases, possibly as a result of reduced
folic acid absorption. Symptomatic folate deficiency is unlikely to occur with metformin,
but people with diabetes may need folic acid supplements to reduce hyperhomocysteinaemia.
• Chronic cigarette smoking is associated with diminished folate status.
• One study found that administration of folic acid to pregnant women might not
interfere with the protective effect of the
• There is a general belief that folic/folinic acid supplements do not interfere
with the therapeutic effects of trimethoprim. However, this view has been challenged,
and failure of trimethoprim therapy has occurred rarely when folinic acid is given
concurrently.
Pregnancy
Nutritional supplement doses of vitamins and minerals are generally considered safe
during pregnancy.
The use of iron supplements during pregnancy is considered an accepted and safe
recommendation which benefits both the mother and the infant. Folate-dependent enzymes
have been inhibited in laboratory experiments by ibuprofen, naproxen, indomethacin
and sulindac.
Because of negative interactions of iron on intestinal absorption of other divalent
minerals, supplemental iron doses should be as low as possible while fulfilling
their purpose. It is not known if iron salts cross the placenta.
The incidence of foetal malformations was lower in the women who had taken iron
during pregnancy compared to those who did not use supplemental iron. In addition,
the women in the iron-treated group delivered infants with higher birth weights
and also had a lower incidence of preterm births.
Folic acid requirements are markedly increased during pregnancy and deficiency will
result in foetal damage. Folic acid is recommended for women who are contemplating
pregnancy or who are pregnant to avoid birth defects caused by folic acid deficiency.
Folic acid crosses the placenta.
Studies in pregnant women have not shown that folic acid increases the risk of foetal
abnormalities if administered during pregnancy. If the drug is used during pregnancy,
the possibility of foetal harm appears remote. However, because studies cannot rule
out the possibility of harm, folic acid should be used during pregnancy only if
clearly needed.
It is recommended that all women capable of becoming pregnant consume folate in
order to reduce the risk of the foetus developing a neural tube defect. Folic acid
supplementation in higher than recommended doses is categorized as the FDA Pregnancy
Category C.
Lactation
Available evidence and/or expert consensus are inconclusive or are inadequate for
determining infant risk when used during breastfeeding. The potential benefits of
drug treatment have to be weighed against the potential risks before prescribing
this drug during breastfeeding.
Folic acid is excreted in human breast milk. During lactation, folic acid requirements
are markedly increased; however, amounts present in human milk are adequate to fulfil
infant requirements, although supplementation may be needed in low-birth-weight
infants, in those who are breast-fed by mothers with folic acid deficiency, or in
those with infections of prolonged diarrhoea. Most likely, it is safe to use during
breastfeeding under the supervision of a qualified healthcare provider. Adverse
effects in breastfed infants related to the intake of normal daily requirements
of folic acid during lactation have not been documented. The potential benefits
of drug treatment have to be weighed against the potential risks before prescribing
this drug during breastfeeding.
Undesirable Effects
Adverse reactions with iron therapy may include constipation, diarrhoea, nausea,
vomiting, dark stools and abdominal pain. Adverse reactions with iron therapy are
usually transient. Gastrointestinal upset, including nausea, vomiting, constipation,
diarrhoea and dark stools, has been reported. Gastrointestinal side effects are
relatively common and corrective bowel regimens such as increasing dietary fibre
or over-the-counter medications might be recommended to balance these side effects.
Folate appears to be well-tolerated in recommended doses. Stomatitis, alopecia,
myelosuppression and zinc depletion have been reported.
Erythema, urticaria, skin flushing, rash, itching, nausea, bloating, flatulence,
cramps, bitter taste, and diarrhoea have been reported. The colour of the urine
may become more intense.
Irritability, excitability, general malaise, altered sleep patterns, vivid dreaming,
overactivity, confusion, impaired judgment, increased seizure frequency, and psychotic
behaviour have been reported. Very high doses can cause significant central nervous
system side effects. Supplemental folic acid might increase seizures in people with
seizure disorders, particularly in very high doses.
Folic acid may mask the symptoms of pernicious, aplastic or normocytic anaemias
caused by vitamin B12 deficiency and may lead to neurological damage.
Anaphylaxis and bronchospasm have also been reported.