5 Flashcards
(20 cards)
What is a Levey-Jennings chart used for in QC?
To plot control sample results over time against the mean and ±2 standard deviation limits, identifying trends or shifts in assay performance.
In QC terminology, what defines a ‘shift’?
Six or more consecutive QC results on one side of the mean, indicating a sudden change in assay accuracy.
In QC terminology, what defines a ‘trend’?
Six or more consecutive QC results moving steadily upward or downward, indicating gradual drift in assay performance.
What does ALTM stand for, and how is it calculated?
All Laboratory Trimmed Mean: the average QC result after removing the top and bottom 5% of values to set a target value.
How is ‘bias’ defined in QC for TDM assays?
Bias is the percentage deviation of the laboratory’s measured value from the target (ALTM) value for a control sample.
What is ‘rolling bias’ in QC parameters?
The mean of current and previous five QC results, indicating short-term assay accuracy trends.
What is ‘rolling variability’ in QC?
The average deviation (ignoring direction) of the current and previous five QC results, reflecting assay precision over time.
Define ‘Bias Index Score (BIS)’ in QC.
BIS compares each QC result’s deviation from the target to assess overall laboratory performance across multiple analytes.
Why is TDM indicated in cases of suspected toxicity?
To determine if high drug or metabolite levels (due to overdose, impaired metabolism/excretion, or interactions) are causing toxicity.
Give three examples of drugs requiring TDM due to narrow therapeutic index.
Digoxin (cardiac glycoside), Lithium carbonate (psychiatric), and Carbamazepine (anticonvulsant).
What laboratory method is commonly used to measure Digoxin levels?
Immunoassay techniques (e.g., immunofluorescence or immunoenzymatic assays).
Which drugs can elevate Digoxin concentrations via CYP450 interactions?
Amiodarone, Quinidine, and Verapamil can inhibit Digoxin clearance, raising serum levels.
Why is TDM critical for patients with renal or hepatic impairment?
Because reduced metabolism (hepatic) or excretion (renal) can lead to drug/metabolite accumulation and toxicity.
Name three patient populations for whom TDM is especially important.
Pediatric (especially neonates), geriatric, and patients undergoing dialysis or hemofiltration.
Why is TDM generally not required for drugs with a broad therapeutic index?
Because dosage variations are less likely to cause toxicity or loss of efficacy, and clinical endpoints can often be monitored functionally.
What defines a ‘hit-and-run’ drug for which TDM is not typically needed?
Drugs with rapid onset and offset of action, minimal toxicity risk, and easily measurable functional effects (e.g., omeprazole, MAO inhibitors).
Which class of antibiotics often requires TDM and why?
Aminoglycosides (e.g., Gentamicin, Streptomycin) require TDM due to nephrotoxicity and ototoxicity risks at high concentrations.
Describe the pharmacokinetic properties of aminoglycoside antibiotics relevant to TDM.
Poor oral absorption, wide distribution (Vd ≈ 0.25 L/kg), negligible plasma protein binding, renal excretion via glomerular filtration, and a half-life of ~2–3 hours.
What toxic effects are associated with aminoglycoside accumulation?
Nephrotoxicity (tubular cell damage via phospholipid metabolism disruption) and reversible ototoxicity (inner ear free radical generation).
Name two anti-epileptic drugs that require TDM and their metabolic considerations.
Phenytoin (zero-order kinetics near enzyme capacity) and Phenobarbital (administered as prodrug Primidone, hepatic metabolism).
