Corrected phenytoin level equation
When should phenytoin be corrected for albumin?
Corrects serum phenytoin level for renal failure and/or hypoalbuminemia. Use in patients with albumin ≤3.2 g/dL (32 g/L). The “Sheiner-Tozer Equation” is the official name of this correction.
How does albumin affect phenytoin levels?
Serum albumin concentrations < 3.5 g/dL have previously been shown to affect phenytoin binding ratios and to contribute to phenytoin intoxication. Decreased protein binding leads to an increase in the free fraction of the drug.
What is a free Dilantin level?
The therapeutic ranges for most adults have been established at 10.0-20.0 mcg/mL for total phenytoin (bound plus unbound) and 1.0-2.0 mcg/mL for free phenytoin (unbound only). This reference range for unbound phenytoin (free) was established based on an assumed 10% unbound drug fraction.
What can affect phenytoin levels?
Phenytoin interacts with a number of antiepileptic drugs: Carbamazepine, phenobarbital, valproic acid, sodium valproate can either increase or decrease phenytoin levels. Lamotrigine, valproic acid, topiramate, zonisamide and levetiracetam can all have their effect reduced by phenytoin.
How do you calculate corrected albumin?
Thus, the calcium level should be corrected in patients with low serum albumin levels, using the following formula: Corrected calcium (mg/dL) = measured total Ca (mg/dL) + 0.8 (4.0 – serum albumin [g/dL]), where 4.0 represents the average albumin level.
What does phenytoin do to the brain?
Phenytoin is used to control certain type of seizures, and to treat and prevent seizures that may begin during or after surgery to the brain or nervous system. Phenytoin is in a class of medications called anticonvulsants. It works by decreasing abnormal electrical activity in the brain.
What causes high phenytoin levels?
Phenytoin toxicity can occur from an increase in the daily dose of phenytoin, changes in the formulations or brands as well as changes in the frequency of administration. It can also occur when patients are started on new medications that interact with the metabolism or binding capacity of phenytoin to plasma proteins.
How do you check phenytoin levels?
Laboratories often report the value in g/L instead (g/dL = g/L x 0.1). After a patient has received a loading dose of intravenous phenytoin, levels can be checked one hour after the dose. If loading is achieved by oral dosing, phenytoin levels can be checked 24 hours after the last dose10.
What is a toxic Dilantin level?
Signs and symptoms of phenytoin toxicity typically correspond to the serum level, and progress from occasional mild nystagmus at 10-20 mcg/mL (the therapeutic range) to coma and seizures at levels above 50 mcg/mL (see Presentation and Workup). Treatment is supportive (see Treatment and Medication).
What should Dilantin level be?
Although the reference range is between 10 and 20 µg/mL, about half of patients’ seizures are controlled at values lower and higher than the therapeutic range. Some adverse effects of phenytoin are related to specific serum levels.
What causes low phenytoin levels?
Drugs which may decrease phenytoin levels include: carbamazepine, chronic alcohol abuse, reserpine. Moban brand of molindone HCl contains calcium ions which interfere with the absorption of phenytoin.
What is the antidote for phenytoin?
There is no antidote, and there is no evidence that any method of gastrointestinal decontamination or enhanced elimination improves outcome. Activated charcoal should be considered if the patient presents early; however, the role of multiple-dose activated charcoal is controversial.
What can I monitor with phenytoin?
Generally, situations which alter phenytoin pharmacokinetics (e.g. body weight changes, initiation of interacting drugs, changes in renal or liver function) should prompt the physician to revisit the phenytoin regimen and review the need to check drug levels.