MLT GlobeChemistry: TDM, toxicology & vitamins – page 3
109 Chemistry MCQs on TDM, toxicology & vitamins with answers and explanations.
When collecting blood for a legal blood alcohol test, the site should be cleaned with:
Alcohol-based swabs can contaminate the sample and falsely raise the result. A non-alcohol antiseptic and a sealed tube, with chain of custody, are used.
A urine drug screen by immunoassay is positive for amphetamines. What should be done before reporting a legal (forensic) result?
Immunoassays are sensitive screens but cross-react with other drugs. A different, more specific method such as mass spectrometry is required for confirmation.
Which test best reflects a person's vitamin D status?
25-OH vitamin D has a long half-life and reflects body stores. 1,25-(OH)2 D is tightly regulated and may be normal or even high in deficiency.
Therapeutic drug monitoring is most useful for drugs that have:
TDM is valuable when toxic and effective concentrations are close and patients handle the drug differently. Drugs with a wide margin or easily measured effects rarely need routine level monitoring.
For a patient taking oral digoxin once daily, when should blood be drawn for a digoxin level?
Digoxin distributes slowly from blood to tissue. Samples taken earlier than 6–8 hours after the dose show falsely high levels that do not reflect tissue (effect-site) concentration.
Urine drug screens for cocaine use detect which main metabolite?
Cocaine is quickly hydrolyzed to benzoylecgonine, which stays in urine for several days and is the target of screening and confirmation. THC-COOH is the cannabis metabolite.
A 5-day-old baby who did not receive vitamin K at birth has umbilical bleeding. PT is prolonged; platelet count is normal. Which additional marker supports vitamin K deficiency?
Without vitamin K, factors II, VII, IX and X are not gamma-carboxylated, so non-functional forms like PIVKA-II circulate. Low fibrinogen and raised D-dimer suggest DIC.
A serum sample for vitamin A (retinol) should be handled by:
Retinol and carotenoids are destroyed by light, so samples are wrapped or kept in amber tubes. Fluoride prevents glycolysis and is used for glucose, not vitamins.
The therapeutic range of a drug is the blood concentration range that:
The therapeutic range lies between the minimum effective concentration and the concentration at which toxicity becomes likely. TDM aims to keep levels within it.
Which drug used for bipolar disorder is routinely monitored by measuring its serum level?
Lithium has a narrow therapeutic range, and toxicity (tremor, confusion, arrhythmia) can occur just above it, so serum levels are checked regularly, usually 12 hours after the last dose.
Vitamin B12 is found naturally almost only in which foods?
Vitamin B12 is made by bacteria and enters the diet through animal products such as meat, eggs and milk. Strict vegans are at risk of deficiency.
Aminoglycoside antibiotics such as gentamicin are monitored mainly to avoid damage to which organs?
Aminoglycosides are nephrotoxic and ototoxic, and the risk rises with high trough levels, so peak and trough levels are monitored.
A large paracetamol (acetaminophen) overdose mainly damages which organ?
Excess paracetamol produces the toxic metabolite NAPQI, which causes hepatocellular necrosis, often with very high ALT a few days after ingestion.
Theophylline, a drug monitored by TDM, is used mainly to treat:
Theophylline is a bronchodilator used in asthma and COPD. It has a narrow therapeutic range, and toxicity causes vomiting, arrhythmias and seizures.
Which red cell finding on a blood film is classically associated with lead poisoning?
Lead inhibits pyrimidine 5′-nucleotidase, so ribosomal RNA remnants remain and appear as coarse basophilic stippling in red cells.
A patient with macrocytic anaemia has normal folate. Which raised urinary metabolite best supports cobalamin deficiency?
Methylmalonyl-CoA mutase needs vitamin B12; without it methylmalonic acid accumulates and is excreted. Folate deficiency raises homocysteine but not methylmalonate.
Which vitamin has an entirely open-chain (acyclic) structure?
Pantothenic acid is pantoic acid joined to β-alanine, with no ring. Riboflavin has an isoalloxazine ring, thiamine a pyrimidine and thiazole, and vitamin D a secosteroid.
Which antibacterial drug blocks bacterial folate synthesis by competing with p-aminobenzoic acid (PABA)?
Sulfonamides are PABA analogues that inhibit dihydropteroate synthase. Trimethoprim acts later on bacterial dihydrofolate reductase, and methotrexate targets human DHFR in cancer therapy.
Thymidylate synthase needs a one-carbon donor derived from which vitamin?
N5,N10-Methylene-tetrahydrofolate supplies the methyl group that turns dUMP into dTMP. B12 deficiency affects this only indirectly by trapping folate as methyl-THF.
Convulsions in infants fed a vitamin B6-deficient formula result from low GABA, because glutamate decarboxylase requires:
Amino acid decarboxylases, including glutamate decarboxylase, are PLP-dependent, so B6 deficiency reduces inhibitory GABA and lowers the seizure threshold.