pharmcokinetics Allie punke

phenytoin

the basics What is the volume of distribution: Regular floor patient: Critically ill patient: What percent is protein bound? Max rate of infusion of phenytoin? Max rate of infusion of fosphenytoin? Floor pt=0.6, 0.7 Critically ill=0.8-1 90% protein bound 50 mg/min 150 mg PE/min (aqueous vehicle)

The basics SE of giving phenytoin too fast? What should phenytoin ONLY be mixed with? Phenytoin or fosphenytoin can be given IM? Therapeutic range? What is special about the kinetics of phenytoin? Hypotension and bradycardia due to propylene glycol solvent NS. Dextrose could cause it to precipitate Fosphenytoin 10-20 or 1-2 free Saturable kinetics

the basics You are reviewing medications for a long-term care facility. One of your new patients, NP, is in stable condition and her medication regimen includes phenytoin. How should we avoid the interaction of phenytoin with her enteral feeds? 1. Hold feedings 1-2 hours before & after 2. Switch to bolus feedings and separate phenytoin dosing 3. Switch to IV phenytoin

phenytoin When reviewing labs, you notice that one of your patients in the ICU is on phenytoin with a level of 8. What other information should we look at to interpret this dose? 1. Albumin level (critically ill patient) 2. Medications (inducers/inhibitors) 3. Other things--Time of the level, time of dose given before the level, CrCl, how long patient has been on therapy, seizure activity or signs of toxicity

phenytoin HS (100 kg, 69 in) is admitted due to status epilepticus. What LD of phenytoin should we give her? 1. What weight do we use? 2. What LD dose (mg/kg) should we use in this patient? 3. How fast can we give it? 4. When/should we draw a level? Adjusted body weight if >130% IBW Target concentration of 20…since pt is in status. 1547 mg For phenytoin, max of 50 mg/min…so if we give 1550 mg, it would take about 31 minutes to infuse the dose. 4. If active seizures, get level soon after LD or partial LD. Follow up with another level in 4-5 days (if no seizures before this time).

phenytoin HS (100 kg, 69 in) is admitted due to status epilepticus. She is on phenytoin at home and has a phenytoin level of 4. What LD should we give her? ~990 mg

phenytoin HS (100 kg, 69 in) is admitted due to status epilepticus. She is on phenytoin at home and has a phenytoin level of 4. Albumin level=2.3. CrCl=57. What LD should we give her? ~804 mg

phenytoin HS is now stable and is in the ICU for close observation. What should HS’s daily maintenance dose be? Range 4-8 mg/kg. Floor/ambulatory. 6-8 mg/kg critically ill. 6 mg/kg*77.35 kg=464 mg

phenytoin In your ambulatory clinic, you adjusted the phenytoin dose appropriately for a patient. When should a level be drawn? A. The next day B. At the end of the dosing interval (>12 hours) C. 2-4 weeks D. 5-7 days C

phenytoin A patient with severe renal dysfunction (CrCl<10) has a phenytoin level of 7. Albumin level=2.7. What is her corrected phenytoin concentration? 18.9

phenytoin A patient is being managed with phenytoin. Because of concern for toxicity (uncoordinated movement, arrhythmias), a level was drawn (phenytoin=32). What should be done? A. Hold the next two doses B. Decrease dose by 50-100 mg/day and hold for 1-2 days C. Stop phenytoin, get daily levels, and restart when level is <20. D. Continue normal dose, symptoms most likely not due to phenytoin. B= IF 20-30 and patient had nystagmus C= Correct.

Questions? Good luck!