drug action and monitoring Flashcards
what is pharmacokinetics
how the body handles drugs; affected by clearance rates and plasma conc
what is pharmacodynamics
the action of the drug on the body; affected by ion channels, enzymes, peak flow, BP; monitored using blood tests (CRP, LFT)
why do drugs need to be monitored?
no one responds in the same way and so decisions on prescribing need to be guided by monitoring
what is the aim of drug monitoring
maximise benefit and minimise harm
how should the effect of a drug be measured (6)
symptoms; signs; clinical measurement; lab/radiological markers; directly sample drug conc; combination of methods - don’t rely on a single measure!
examples of clinical measurements (4)
heart rate (w Beta blockers); BP (with CaCh blockers); resolution of ankle oedema (w furosemide); peak flow (with salbutamol)
what to look for if the patient is experiencing recurrent blackouts?
tachy/bradycardia
what to look for if the patient is experiencing fluid overload?
check body weight to see if fluid is being removed; check U&Es for renal toxicity
what to look for if the patient is experiencing heart failure?
creatine levels; K+ levels after starting ACE inhibitors
what are the problems with using plasma conc for therapeutic drug monitoring?
venous level may not equal conc at target (e.g. bc has to pass throught BBB); is there a correlation with clinical effect?; doesn’t account for metabolites; there is heterogeneity in the population
why would plasma conc be checked
good correlation between drug level and response/toxicity; good indication for a test
what drugs is TDM mainly used for? (6)
antibiotics; digoxin; antiepileptic; lithium; aminophylline; immunosuppressants e.g. ciclosporin
gentamicin standard dose
5-7mg/kg/24hrs; high trough levels may result in renal toxicity
vancomycin dosing procedure
- loading does + saline
2.12hrly infusion if eGFR >40ml/min - trough blood sample
- adjust dose accordingly
digoxin toxicity (3)
nausea; disturbed colour vision; unexplained ECG changes
