Seriously. Anyway. Prevention of a subtherapeutic phenytoin level is important for seizure control. Plus there’s not that much exciting here, but for completeness, we’ll mention it.Phenytoin may be oxidized by hepatic CYP enzymes, but it is excreted by the kidneys following glucuronidation.
Less than 5% is excreted as unchanged drug, so that gives you an idea of how much work the body does on this med! You may be asking yourself why on earth do we have both? Elsevier Science But that was before drug shortages hit in earnest. residency, should I do a residency?, PGY1, PGY-1, Pharmacy residency, Pharmacy student, Pharmacy school, midyear, ashp midyear, the showcase, residency applications, residency interviews, pharmacy residency interviews, pharmacy residency applicationsseven figure pharmacist, student debt, student loans, student pharmacist, pharmacy student, finances, your financial pharmacist Which we do with total levels. Fosphenytoin is dosed in phenytoin equivalents (or PEs). If you take absolutely nothing else away from this post, remember these main points:You'll also receive updates from our blog and exclusive, members-only content.
For these reasons, we love fosphenytoin and are super hopeful that it’s back for real this time.Regardless of whether you use phenytoin or fosphenytoin, we need to I guess while we’ve wandered into adverse effects, we might as well do it right.Here are some more adverse effects to be aware of when maintaining people on phenytoin:Leukopenia, thrombocytopenia, agranulocytosis, pancytopenia +/- bone marrow suppressionDecreased bone mineral density (vitamin D deficiency)Dermatologic reactions, including Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN)CNS depression (including coma and possible respiratory failure)One of the reasons phenytoin is so difficult to predict is because it is highly protein bound.
Oral or nasogastric administration should be … We know he’s out there…there have been sightings…but we’re not 100% certain he’s for real back. Wouldn’t it be easier to just worry about one?Sure. These equations are used in place of obtaining a (pricey) free level and calculating a patient specific free fraction.While they supposedly take into account hypoalbuminemia and uremia, their accuracy has been shown to be limited in studies that compared equation-calculated versus measured free levels, especially in hypoalbuminemic patients. Not to mention the variability that comes from genetics (CYP polymorphisms) and drug interactions.So, basically, if possible, actually measure your patients’ free levels to establish a free fraction!LO is a 55 YOF (5’7”, 115 kg) admitted to the hospital for new onset seizure disorder. How can I tell if the phenytoin concentration is therapeutic? I want you pumped and ready to take it down. We have to have a hot minute for fosphenytoin. No further seizures have occurred.No, free level is below therapeutic range of 1-2 mcg/mL, and total is below her specific goal range of 5.8-11.6 mcg/mLGive mini loading dose of 10 mg/kg either IV or PO to ensure adequate seizure protectionGo ahead and increase maintenance dose by 50 mg/day (since approaching steady state by day 5). Only the free phenytoin is actually fighting the Dark Side of seizures. ).Of course, the caveat is if your patient goes into renal failure…or has a new interacting medication added to their regimen…anything that can change the ff. After a patient has received a loading dose of intravenous phenytoin, levels can be checked one hour after the dose. Interacts with enteral feeds (stop feed 2 hrs before and after dose). Her albumin is 1.8 g/dL, and her SCr is 0.8 mg/dL. Epub 2011 Nov 26.Clin Pharmacokinet. If you remember nothing else from this post, take this away:Phenytoin is metabolized by several CYP enzymes (mainly 2C19, and 2C9, but a little of 3A4 too), and so there are multiple medications that can affect its metabolism.So regardless of mechanism of altered phenytoin concentrations (aka changes in distribution versus metabolism), see below for a sampling of medications that can affect phenytoin serum concentrations:Although the focus for this post is on phenytoin dosing, it’s hard to mention drug interactions of phenytoin and ONLY discuss the ones that affect phenytoin. No spam, ever. Ideal sampling time At least 4 to 6 hours post IV dose Immediately prior to next oral dose (trough) Major factors influencing serum levels Liver impairment, hypoalbuminaemia. Once established on phenytoin, take a level 2-4 weeks after change in dose or oral formulation, or after stopping/starting a potentially interacting drug (see list below). Which ultimately decreases the excitability of neurons and slows neuronal transmission. We'll treat it with courtesy and respect.
Less than 5% is excreted as unchanged drug, so that gives you an idea of how much work the body does on this med! You may be asking yourself why on earth do we have both? Elsevier Science But that was before drug shortages hit in earnest. residency, should I do a residency?, PGY1, PGY-1, Pharmacy residency, Pharmacy student, Pharmacy school, midyear, ashp midyear, the showcase, residency applications, residency interviews, pharmacy residency interviews, pharmacy residency applicationsseven figure pharmacist, student debt, student loans, student pharmacist, pharmacy student, finances, your financial pharmacist Which we do with total levels. Fosphenytoin is dosed in phenytoin equivalents (or PEs). If you take absolutely nothing else away from this post, remember these main points:You'll also receive updates from our blog and exclusive, members-only content.
For these reasons, we love fosphenytoin and are super hopeful that it’s back for real this time.Regardless of whether you use phenytoin or fosphenytoin, we need to I guess while we’ve wandered into adverse effects, we might as well do it right.Here are some more adverse effects to be aware of when maintaining people on phenytoin:Leukopenia, thrombocytopenia, agranulocytosis, pancytopenia +/- bone marrow suppressionDecreased bone mineral density (vitamin D deficiency)Dermatologic reactions, including Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN)CNS depression (including coma and possible respiratory failure)One of the reasons phenytoin is so difficult to predict is because it is highly protein bound.
Oral or nasogastric administration should be … We know he’s out there…there have been sightings…but we’re not 100% certain he’s for real back. Wouldn’t it be easier to just worry about one?Sure. These equations are used in place of obtaining a (pricey) free level and calculating a patient specific free fraction.While they supposedly take into account hypoalbuminemia and uremia, their accuracy has been shown to be limited in studies that compared equation-calculated versus measured free levels, especially in hypoalbuminemic patients. Not to mention the variability that comes from genetics (CYP polymorphisms) and drug interactions.So, basically, if possible, actually measure your patients’ free levels to establish a free fraction!LO is a 55 YOF (5’7”, 115 kg) admitted to the hospital for new onset seizure disorder. How can I tell if the phenytoin concentration is therapeutic? I want you pumped and ready to take it down. We have to have a hot minute for fosphenytoin. No further seizures have occurred.No, free level is below therapeutic range of 1-2 mcg/mL, and total is below her specific goal range of 5.8-11.6 mcg/mLGive mini loading dose of 10 mg/kg either IV or PO to ensure adequate seizure protectionGo ahead and increase maintenance dose by 50 mg/day (since approaching steady state by day 5). Only the free phenytoin is actually fighting the Dark Side of seizures. ).Of course, the caveat is if your patient goes into renal failure…or has a new interacting medication added to their regimen…anything that can change the ff. After a patient has received a loading dose of intravenous phenytoin, levels can be checked one hour after the dose. Interacts with enteral feeds (stop feed 2 hrs before and after dose). Her albumin is 1.8 g/dL, and her SCr is 0.8 mg/dL. Epub 2011 Nov 26.Clin Pharmacokinet. If you remember nothing else from this post, take this away:Phenytoin is metabolized by several CYP enzymes (mainly 2C19, and 2C9, but a little of 3A4 too), and so there are multiple medications that can affect its metabolism.So regardless of mechanism of altered phenytoin concentrations (aka changes in distribution versus metabolism), see below for a sampling of medications that can affect phenytoin serum concentrations:Although the focus for this post is on phenytoin dosing, it’s hard to mention drug interactions of phenytoin and ONLY discuss the ones that affect phenytoin. No spam, ever. Ideal sampling time At least 4 to 6 hours post IV dose Immediately prior to next oral dose (trough) Major factors influencing serum levels Liver impairment, hypoalbuminaemia. Once established on phenytoin, take a level 2-4 weeks after change in dose or oral formulation, or after stopping/starting a potentially interacting drug (see list below). Which ultimately decreases the excitability of neurons and slows neuronal transmission. We'll treat it with courtesy and respect.