Pharmacodynamics of Vitamins and Minerals
Session 15: Pharmacodynamics of Vitamins and Minerals
Total Session Time: 120 minutes
Prerequisites
None
Learning Tasks
By the end of this session students are expected to be able to:
Describe mechanism of action of Vitamins and Minerals Drugs
Describe drug interactions associated with Vitamins and Minerals
Describe side effects of Vitamins and Minerals
Describe contraindications of Vitamins and Minerals
Resources Needed:
Flip charts, marker pens, and masking tape
Black/white board and chalk/whiteboard markers
Computer and LCD projector
SESSION OVERVIEW
Step
Time
Activity/
Content
Step
Time
Activity/
Content
Step
Time
Method
Content
Method
Method
1
1
05 minutes
05 minutes
Presentation
Introduction, Learning Tasks
Introduction, Learning Tasks
2
2
45 minutes
45 minutes
Presentation/
Mechanism of Action of Vitamins and
Mechanism of Action of Vitamins and
2
2
45 minutes
45 minutes
Buzzing
Minerals Drugs
Minerals Drugs
Buzzing
Minerals Drugs
Minerals Drugs
3
3
20 minutes
20 minutes
Presentation/
Drug Interactions Associated With Vitamins
Drug Interactions Associated With Vitamins
3
3
20 minutes
20 minutes
brainstorming
and Minerals
and Minerals
brainstorming
and Minerals
and Minerals
4
4
20 minutes
20 minutes
Presentation
Side Effects of Vitamins and Minerals
Side Effects of Vitamins and Minerals
5
5
20 minutes
20 minutes
Presentation/
Contraindications of Vitamins and Minerals
Contraindications of Vitamins and Minerals
5
5
20 minutes
20 minutes
Brainstorming
Contraindications of Vitamins and Minerals
Contraindications of Vitamins and Minerals
Brainstorming
6
6
05 minutes
05 minutes
Presentation
Key Points
Key Points
7
7
05 minutes
05 minutes
Presentation
Evaluation
Evaluation
PST 05104 Pharmacology & Therapeutics 122 NTA Level 5 Semester 1 Facilitator Guide
SESSION CONTENTS
STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)
READ or ASK students to read the learning tasks and clarify
ASK students if they have any questions before continuing.
STEP 2: Mechanism of Action of Vitamins and Minerals (45 minutes)
Activity: Buzzing (5 minutes)
ASK students to pair up and buzz on the following question for 2 minutes
How do Vitamins and Minerals produce their pharmacological effects?
ALLOW few pairs to respond and let other pairs add on points not mentioned
WRITE their response on the flip chart/board
CLARIFY and SUMMARIZE by using the content below
Vitamins and minerals have different mechanisms of action as discussed below:
Vitamin D
o The two major forms of vitamin D replacements are vitamin D2 and vitamin D3.
o Vitamin D is an important regulator of calcium and phosphate homeostasis and bone metabolism. It works in conjunction with PTH. The overall effect of vitamin D is to increase serum calcium concentrations. These effects are mediated via the following:
o Increased calcium absorption from the intestine
o Regulation of bone resorption and formation. This occurs via stimulation of both osteoblastic and osteoclastic processes. Osteoblasts form bone, and osteoclasts dissolve bone.
o Increased calcium reabsorption in the distal renal tubules
o Vitamin D results in a negative feedback loop and decreases transcription and secretion of PTH. The overall effect of PTH is to increase serum calcium levels, so increased vitamin D inhibits the actions of PTH so that both mechanisms do not drive up calcium levels too high.
o Vitamin D is lipophilic (it is one of the fat-soluble vitamins—A, D, E, and K) and thus freely crosses the cytoplasmic membrane. Intracellularly, it binds vitamin D receptors (VDRs) and binds DNA, where it regulates transcription of genes in the intestine, bone, kidney, and parathyroid gland.
o Vitamin D also has actions in macrophages and T cells and in proliferation and differentiation of a large number of cells, including cancer cells.
PST 05104 Pharmacology & Therapeutics 123 NTA Level 5 Semester 1 Facilitator Guide
Through these actions, it has immunomodulating and potentially, anticancer actions.
Also, these actions are the basis of the mechanism whereby it is effective in psoriasis.
Vitamin B1 (Thiamine)
Thiamine is used in the treatment of beriberi and other states of thiamine deficiency, or in their prevention. Such conditions include alcoholic neuritis, Wernicke‘s
encephalopathy and the neuritis of pregnancy, as well as chronic diarrhoeal states and after intestinal resection.
Thiamine (in the form of thiamine pyrophosphate) is required for carbohydrate metabolism, as it is a coenzyme for decarboxylases and transketolases.
Vitamin B6 (Pyridoxine)
Pyridoxine hydrochloride is given to patients at risk (e.g. alcoholics) during long-term therapy with isoniazid to prevent peripheral neuropathy, and in deficiency states. Pyridoxine is also used to treat certain uncommon inborn errors of metabolism,
including primary hyperoxaluria.
Vitamin B6 occurs naturally in three forms, namely pyridoxine, pyridoxal and pyridoxamine. All three forms are converted in the body into pyridoxal phosphate, which is an essential cofactor in several metabolic reactions, including decarboxylation, transamination and other steps in amino acid metabolism.
Vitamin B3 (Niacin and Nicotinic Acid)
Niacin is used to treat and prevent pellagra. Nicotinic acid (or nicotinic acid analogues may be used to treat dyslipidaemia, but hypolipidaemic dosing is limited by vasodilatation/flushing.
Niacin is vital metabolic role is as a component of nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP).
Vitamin B12
Vitamin B12 is an organic molecule with an attached cobalt atom. Linked to the
cobalt atom may be a cyanide (cyanocobalamin), hydroxyl (hydroxocobalamin) or methyl (methylcobalamin) group. These forms are interconvertible.
Vitamin B12 is needed for normal erythropoiesis and for neuronal integrity. It is a cofactor needed for the isomerization of methylmalonyl coenzyme A to succinyl
coenzyme A, and for the conversion of homocysteine into methionine (which also utilizes 5-methyltetrahydrofolate).
Vitamin B12 is also involved in the control of folate metabolism, and B12 and folate are required for intracellular nucleoside synthesis.
Vitamin C (Ascorbic Acid)
Ascorbic acid is used in the prophylaxis and treatment of scurvy. The reducing properties of ascorbate may be used in the treatment of methaemoglobinaemia. In
PST 05104 Pharmacology & Therapeutics 124 NTA Level 5 Semester 1 Facilitator Guide
scorbutic patients, wound healing is delayed and this is restored to normal by administration of ascorbic acid.
Ascorbic acid is involved in several metabolic processes.
It is a potent water soluble anti-oxidant.
Vitamin E(Tocopherol)
Vitamin E protects erythrocytes against haemolysis, and is a fat-soluble anti-oxidant and detoxifies free radicals. Free radicals cause membrane and epithelial injury and have been implicated in the pathophysiology of numerous diseases, including cancer and atheroma.
Vitamin A (Retinoic Acid) and its derivatives
Vitamin A is used to prevent and treat deficiency states. Regular dietary or parenteral supplementation of vitamin A may be necessary in patients with steatorrhoea.
Vitamin A has many physiological functions including maintenance of epithelial cell
integrity, stabilization of membranes and normal soft tissue growth. Vitamin A is also a component of rhodopsin (essential for normal vision).
Vitamin A is a cofactor for microsomal drug-metabolizing enzymes, cholesterol synthesis and mucopolysaccharide synthesis.
Vitamin K
Vitamin K is key cofactor in the hepatic activation of four coagulation factors. The four vitamin K-dependent clotting factors are II, VII, IX, and X. To act as a cofactor, vitamin K must be in its reduced form, vitamin K hydroxyquinone.
The enzyme vitamin K epoxide reductase (VKOR) converts vitamin K to its reduced form which is the active form.
Iron
Iron plays a vital role in the body in many proteins including transport proteins (e.g. haemoglobin, myoglobin) and enzymes (e.g. CYP450s, catalase, peroxidase, and metalloflavoproteins). It is stored in the reticulo-endothelial system and bone marrow.
PST 05104 Pharmacology & Therapeutics 125 NTA Level 5 Semester 1 Facilitator Guide
STEP 3: Drug Interactions Associated with Vitamins and Minerals (20 minutes)
Activity: Brainstorming (5 minutes)
Ask students to brainstorm on the following question:
What are drug interactions associated with vitamins and minerals?
ALLOW few students to respond
WRITE their responses on the flip chart/ board
CLARIFY and SUMMARISE by using the content below
Vitamins and minerals exhibit very few interactions of action as discussed below:
Vitamin B6
o Isoniazid prevents the activation of pyridoxal to pyridoxal phosphate by inhibiting the enzyme pyridoxal kinase, and slow acetylators of isoniazid are at increased risk of developing peripheral neuropathy for this reason.
Calcium and magnesium
o Impairs absorption of tetracyclines.
STEP 4: Side Effects of Vitamins and Minerals (20 minutes)
Vitamin D
o Side effects are related to long-term over administration of vitamin D supplementation. Symptoms are primarily induced by hypercalcemia, which include gastrointestinal pain, renal stones, and psychiatric disturbances.
Vitamin B1 (Thiamine)
o Anaphylactoid reactions following parenteral thiamine dosing have been reported, so parenteral administration should be restricted to situations where it is essential.
Vitamin B6
Vitamin B3 (Niacin and Nicotinic acid)
o In replacement therapy for pellagra, adverse effects are uncommon. High doses (as used for hyperlipidaemia) cause the following: vasodilatation due to prostaglandin D2 (this can be reduced by premedication with aspirin), itching, hyperglycaemia and exacerbation of hyperuricemia.
Vitamin C( Ascorbic Acid)
Vitamin A
PST 05104 Pharmacology & Therapeutics 126 NTA Level 5 Semester 1 Facilitator Guide
Long-term ingestion of more than double the recommended daily intake of vitamin A can lead to toxicity and chronic hypervitaminosis. Chronic toxicity includes: anorexia and vomiting, itching and dry skin, raised intracranial pressure (benign intracranial hypertension), irritability and headache, tender hyperostoses in the skull and long bones, hepatotoxicity and congenital abnormalities.
Folic Acid
Iron
Gastro-intestinal side effects, including nausea, heartburn, constipation or diarrhoea,
are common.
Patients with ulcerative colitis and those with colostomies suffer particularly severely from these side effects.
Accidental overdose with iron is not uncommon in young children and can be extremely serious, with gastro-intestinal haemorrhage, cardiovascular collapse,
hepatic and neurotoxicity.
Desferrioxamine (an iron-chelating agent) is administered to treat it.
STEP 5: Contraindications of Vitamins and Minerals (20 minutes)
Activity: Brainstorming (5 minutes)
Ask students to brainstorm on the following question:
What are the contraindications of Vitamins and Minerals? ALLOW few students to respond?
WRITE their responses on the flip chart/ board
CLARIFY and SUMMARISE by using the content below
Vitamin D o None
Vitamin A
o Excess vitamin A during pregnancy causes birth defects (closely related compounds are involved in controlling morphogenesis in the foetus). Therefore pregnant women should not take vitamin A supplements, and should also avoid liver in their diet.
o Most vitamins do not have significant contraindications
PST 05104 Pharmacology & Therapeutics 127 NTA Level 5 Semester 1 Facilitator Guide
STEP 6: Key Points (5 minutes)
Vitamin A toxicity is associated with gastro-intestinal upsets, headache (raised intracranial pressure), desquamation, hepatotoxicity and teratogenicity.
Vitamin are important for normal body function
Some of toxicities of vitamins are detrimental
STEP 7: Evaluation (5 minutes)
What are the indications of vitamin B6?
What are symptoms/signs associated with hypervitaminosis?
How does vitamin K produce its pharmacological effects?
What are the other forms of vitamin D?
PST 05104 Pharmacology & Therapeutics 128 NTA Level 5 Semester 1 Facilitator Guide
References
Katzung, B. G. (2018). Basic and clinical pharmacology. New York: Mcgraw Hill Education.
Santos, R. R., Rang, H. P., Dale, M. M., Ritter, J. M., & Flower, R. J. (2007). Rang & Dale Farmacologia. Rio de Janeiro: Elsevier.
Tripathi, K. (2018). Essentials of Medical Pharmacology. Place of publication not identified:
Jaypee Brothers Medical P.
Ministry of Health and Social Welfare. (2013). Standard Treatment Guidelines & National Essential Medicines List Tanzania Mainland (4th ed.). Dar es salaam, Tanzania government printers.
Sally S.R, Jeanne C.S. (2000). Introductory Clinical Pharmacology (6th ed) New York, Lippincott Williams and Wilkins.
School of Pharmaceutical sciences. (2011).Tanzania Pharmaceutical Handbook (2nd ed.).
Dar es Salaam, ARDHI University press.
The Royal Pharmaceutical Society of Great Britain. (2007). Martindale, the Extra Pharmacopoeia (5TH ed). London, pharmaceutical press.
The Royal Pharmaceutical Society of Great Britain. 2009. British National Formulary (59th ed). London, BMJ Group and RPS Publishing.
PST 05104 Pharmacology & Therapeutics 129 NTA Level 5 Semester 1 Facilitator Guide
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