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WEEK 18:
Pharmacokinetics Applications:
| Question | Answer |
|---|---|
| F (bioavailability) | AUC oral / AUC IV |
| shape of overall plasma curve is influenced by (2) | rate of dissolution (if tablet) and rate of absorption |
| how many half lives are needed to achieve steady state (Css) | 5 |
| steady state concentrations are proportional to what | dose and F/CL |
| fluctuations are proportional to | dosing interval/ half life |
| dose = | CL x Css x t (tau) / F |
| dose given = | amount needed / F |
| t (tau) meaning | dosage interval |
| factors affecting design of dosage regimen (3) | therapeutic window (TW), urgency of onset of effect, and elimination half life |
| drugs with a large therapeutic window uses what | maximal dose strategy |
| drugs with a small therapeutic window uses what | target level strategy |
| loading dose = | target level x (V/F) |
| maintenance dose = | target level x (CL/F) |
| urgency of onset effect may have to give what | loading dose (LD) |
| when is a maintenance dose given | after LD to keep up with elimination |
| how long is a short elimination half life | less than 1 hour |
| how long is a long elimination half life | more than 24 hours |
| gentamicin | antibiotic (aminoglycoside) which has post-antibiotic effect |
| side effects of gentamicin | ototoxicity and nephrotoxicity |
| gentamicin function | management of septicaemia (sepsis) and endocarditis |
| how can gentamicin be given (3) | IV, IV infusion, and IM |
| post antibiotic effect | time required for an organism to regrow after antibiotic is removed |
| trough of gentamicin | more than 2mg/L to prevent toxicity |
| peak of gentamicin | 5-10mg/L |
| t1/2 of gentamicin in normal renal function | 2-3 hours |
| hartford gentamicin nomogram | standard graph showing when patient should take next dose |
| shape of fast oral curve on oral dosing curve | high peak, earlier peak, and has a shorter duration |
| shape of slow oral curve on oral dosing curve | lower peak, later peak, and has a longer duration |
| explain the area of an oral dosing curve from rise to peak | absorption is higher than elimination |
| explain the area of an oral dosing curve at the peak | absorption is equal to elimination |
| explain the area of an oral dosing curve from peak to fall | only elimination (curve is exponential decay - 1st order) |
| what type of curve is in an oral dosing curve from peak to fall | exponential decay curve (first order) |
| why cant half life or clearance be calculated on slow oral dosing curves | absorption happens for a long time so true elimination does not occur yet |
| what can oral dosing curves be used to estimate | absorption rate constant, time taken to reach peak, and bioavailability |
| fluctuations are blunted by | slow absorption |
| example of drug with large therapeutic window | penicillin |
| how long is a moderate elimination half life | 4-24 hours |
| describe dosage if the drug has a short elimination half life and large TW | give large dose in intervals eg every 6 hours |
| describe dosage if the drug has a short elimination half life and small TW | give by infusion + loading dose |
| loading dose | dose given to reach therapeutic window |
| maintenance dose | dose given after loading dose to maintain drug plasma concentration in therapeutic window |
| describe dosage if the drug has a moderate elimination half life | give normal starting dose then give half of that every half life |
| describe dosage if the drug has a long elimination half life | set a 24 hour dosage interval (once daily) |
| what does a long elimination half life mean | eliminated slowly |
| what does a small elimination half life mean | eliminated quickly |
| why is gentamicin an exception | since it reaches therapeutic window immediately with the first dose so no loading dose is needed |
| how are gentamicin doses given (2) | as 3 divided doses or single daily dose |
| t1/2 life of gentamicin in anephric patients | 30-60 hours |
| dose interval of gentamicin depends on | creatinine clearance and design regimen |
| dosing interval of gentamicin is calculated by | 2 x t1/2 |
| which patients should receive single daily dose of gentamicin (4) | those on cistplatin chemotherapy, children, those with a creatinine clearance of less than 20mL/min, and anyone with carditis |
| how would you given a single daily dose of gentamicin | give 7mg/kg in 100mL over 30-60 minutes and sample 6-14 hours after start of infusion to plot on a nomogram to see whether dose is safe/ how long dosing interval should be |
| when do you sample the single daily dose of gentamicin | 6-14 hours after start of infusion |
| why do you sample the single daily dose of gentamicin 6-14 hours after infusion | to plot on a nomogram to see whether dose is safe and how long dosing interval should be |
| where do you plot the single daily dose of gentamicin on after 6-14 hours | nomogram |
Created by:
kablooey
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