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Theophylline PK
Theophylline PK - Final Exam
Question | Answer |
---|---|
What are the 3 major determinants of theophylline dosing interval? | - Rate of product ABSORPTION - The patient's rate of ELIMINATION - Amount & acceptability of [SERUM] FLUX in relation to DZ-ctrl ~ (Regimen ADHERENCE can be considered a possible 4th) |
What dosage formulation of theophylline is preferred? | ORAL, slow-released formulations |
2 reasons there might be a lack of bioavailability info accessible | - Decreased use & amount of available products |
Primary 2 reasons generic substitutions are NOT recommended | - Varying ABSORPTION characteristics - NARROW therapeutic range (aka LOW therapeutic index) |
Selected product should have __________ & ___________ bioavailability. | KNOWN & CONSISTENT bioavailability |
It's much more important to consider the drug _______ than _______. ( Manufacturer or Distributor? ) | Manufacturer! |
How would you convert the dose of IV theophylline to PO theophylline? | Calculate total daily dose admin by IV & divide by frequency for PO admin (depndent on product/formulation) |
When would you start giving oral theophylline after conversion from IV? | Best = start giving oral theophylline when the IV stops - Slow released formulations can be overlapped ~1-2hours - Rapid release formulations must AVOID overlapping! (but they are rarely used anyways) |
What is the relationship between dose/[serum] & the airway bronchodilation fx? | Bronchodilation is PROPORTIONAL to the LOG [serum] between 5-20mcg/mL |
Which dosage change would elicit a larger airway response? 1. A change from 5-->10 or 2. A change from 11-->16 | 1. A change from 5-->10 (since the dose is associated with the log [serum] |
How is [serum] flux related to the therapeutic & SE response? | Flux parallels the therapeutic & SE response (we want the dose with the greatest amount of fx while minimizing flux as much as possible) |
What would the initial dose be for (a) a <1yo child & (b) adults & children >1yo assuming there are no risk factors that might reduce clearance? | Child <1yo: Dose (in mg/kg/day) = 0.2 (age in weeks) + 5 Adult & child >1yo: 10mg/kg/day with a max dose of 300mg |
What would the 2nd & 3rd titration steps be for a normal adult assuming there are no SE? | 2nd: 13mg/kg/day (max of 450mg/day) 3rd: 16mg/kg/day (max of 600mg/day) * Note: dose is titrated in 3-DAY intervals! * |
What would the IV loading dose (note: rarely done) be for a patient who currently has no theophylline on board? This dose would be infused over a time period of ______________. | Infuse 5mg/kg over 30-60minutes (to avoid CV-irritability) |
If a patient already has theophylline on board what would be the TARGET LEVEL you would aim to achieve when beginning the IV LD? If a patient was not at that level, what dose & rate would you initiate? | Target theophylline level = 12 mcg/mL - If not at target, infuse 1mg/kg for each 2mcg/mL increase needed over 30-60min |
When would you check theophylline levels after starting an IV loading dose? | Check theophylline levels ONE HOUR after the infusion is completed |
Generally, the optimal [serum] range associated with the reduction of asthma Sx is: | 10-20 mcg/mL |
What [serum] levels are generally associated with adverse fx? | >20 mcg/mL |
How would a patient present if experiencing theophylline-associated SE? | Typically this pt would have GI & CNS related SE: GI = N/V/D, reflux --- CNS = nausea, nervous, jittery, insomnia |
Transient theophylline SE are related to: | Dose absorption (particularly, the peak levels (fx would be similar to having too much caffeine) |
When would you monitor levels after starting an initial dose? How would this change if the pt was experiencing SE? | - Monitor @ end of dosing scheme aka once maintenance dose is achieved or Css - If pt has SE, REDUCE the dose & check the level to direct next steps |
When would you check blood levels to assess maintenance therapy? What was assessed to come up with that time? | Measure blood levels 3-DAYS after continuous maintenance tx - This value should represent the Css (assuming no doses were missed or added |
The PEAK occurs _____________ after a rapid releasing product & The PLATEAU (pseudo-peak) occurs _____________ after a SR product | IR Peak = 2 hours SR Plateau = 4 hours |
How often would you monitor a patient for routine care in: - Children (during rapid growing years) - Adults | - Children (during rapid growing years) --> q6mo - Adults --> annually |
Name 3 other situations that may indicate checking levels during routine care | - Complaints are similar to the SE-profile - Poor DZ-control - If any factors that can modify CL are introduced (ie. new drugs/DDI or conditions) |
Theophylline is metabolized by: | Primarily CYP1A2 (with a little help from 3A4) |
What physiologic conditions can effect theophylline levels/metabolism? | CHF (bc hepatic Q changes), hepatic failure, fever (requires lower theophylline doses) |
How would renal impairment effect theophylline CL? | Little-no fx from renal impairment (surprising since urinary excr is the primary elimination for most metabolites bc of water solubility) |
Elimination is... | * Dose-dependent * Saturable (zero-order) - use caution when changing doses close to therapeutic range |