MLT GlobeChemistry: TDM, toxicology & vitamins – page 2
109 Chemistry MCQs on TDM, toxicology & vitamins with answers and explanations.
Transamination, decarboxylation and many other amino acid reactions share one vitamin-derived cofactor. Which vitamin is it?
Pyridoxal phosphate forms a Schiff base with amino acids and supports transamination, decarboxylation, deamination and racemisation. B12 is used in only two human enzymes.
Advising a patient with iron-deficiency anaemia, which vitamin taken with meals improves absorption of non-haem iron?
Ascorbate reduces Fe3+ to the absorbable Fe2+ form and chelates it, which improves uptake by DMT1 in the duodenum.
An undernourished patient with alcohol dependence arrives confused. Which vitamin should be given before intravenous dextrose?
A glucose load increases demand for thiamine (for pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase) and can bring on or worsen Wernicke encephalopathy. Thiamine is given first.
Which finding is NOT expected in scurvy?
Vitamin C deficiency weakens collagen, causing bleeding gums, bruising, loose teeth and poor healing. Liver failure is not a feature.
Which feature is NOT part of pellagra?
Niacin deficiency classically causes the '3 Ds' (dermatitis, diarrhoea, dementia), with death as a fourth. Alopecia is typical of biotin or zinc deficiency.
Which of these vitamins is water-soluble?
Vitamin C is water-soluble and not stored in large amounts. Vitamins D (cholecalciferol), A (retinol) and E (tocopherol) are fat-soluble.
A patient who drinks a lot of carrot juice has yellow-orange palms, but the sclerae are white and bilirubin is normal. What is the cause?
Excess beta-carotene deposits in skin (carotenodermia) and spares the sclera. It is harmless because conversion to retinol is regulated, so it does not cause vitamin A toxicity.
Pregnant women are warned against high-dose supplements of which vitamin because it is teratogenic?
Excess preformed vitamin A and retinoids such as isotretinoin cause craniofacial, cardiac and CNS defects. Folic acid is recommended in pregnancy to prevent neural tube defects.
Which situation is LEAST likely to cause a rapid functional vitamin K deficiency?
Citrus fruit supplies vitamin C, not vitamin K. Antibiotics reduce bacterial menaquinone, neonates have low stores, and warfarin blocks vitamin K epoxide reductase.
Periconceptional supplements are advised to lower the risk of spina bifida and anencephaly. Which vitamin?
Folate is needed for nucleotide synthesis during neural tube closure, and folic acid supplements reduce neural tube defects. Raised maternal serum AFP is a screening marker for these defects.
Exposing some foods, such as mushrooms or milk, to ultraviolet light raises their content of which vitamin?
UV-B converts sterol precursors (ergosterol, 7-dehydrocholesterol) to vitamin D2 or D3. This is the basis of UV-treated vitamin D-enriched foods.
A newborn not given prophylaxis at birth bleeds from the umbilical stump on day 3 with a prolonged PT. Which vitamin was omitted?
Haemorrhagic disease of the newborn (vitamin K deficiency bleeding) happens because neonates have low vitamin K stores and a sterile gut. A single dose of vitamin K at birth prevents it.
A man on a diet with no fresh fruit or vegetables for months develops swollen bleeding gums and corkscrew hairs. Which vitamin is lacking?
These are signs of scurvy. Collagen hydroxylation fails without ascorbate, which weakens vessels and connective tissue.
A toddler has bowed legs, widened wrists, low phosphate and raised alkaline phosphatase. Which vitamin is deficient?
Rickets is poor mineralisation of growing bone, usually from vitamin D deficiency. Osteoblast activity raises ALP, and secondary hyperparathyroidism lowers phosphate.
Which protein, secreted by gastric parietal cells, is needed for vitamin B12 to be absorbed in the terminal ileum?
The intrinsic factor–B12 complex binds cubilin receptors in the ileum. Lack of intrinsic factor, as in autoimmune gastritis, causes pernicious anaemia.
The daily pyridoxine requirement rises mainly with a higher intake of which nutrient?
Pyridoxal phosphate is the cofactor for most amino acid reactions, so more dietary protein means a higher B6 requirement.
For therapeutic drug monitoring, a trough level should be drawn:
The trough is the lowest concentration, just before the next dose, and shows whether levels stay therapeutic without accumulating. Peaks are timed after absorption and distribution.
After starting a fixed dosing schedule, a drug reaches steady state after about:
After about 5 half-lives, the amount given equals the amount eliminated (about 97% of steady state). TDM samples are usually taken after this point.
Tacrolimus and cyclosporine are measured in which specimen?
These drugs are concentrated in red cells, and plasma levels depend on temperature and hematocrit. EDTA whole blood gives the most reliable results.
N-acetylcysteine is effective in acetaminophen overdose because it:
The toxic metabolite NAPQI is normally conjugated with glutathione. NAC replenishes glutathione and protects the liver. Fomepizole, not NAC, inhibits alcohol dehydrogenase.