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.
How do you adjust phenytoin levels?
If the phenytoin concentration is 7-12 mcg/mL, the dose may be increased by 50 mg/day. If the phenytoin concentration is >12 mcg/mL, the dose may be increased by 30 mg/day. If the phenytoin concentration is >16 mcg/mL, any change may result in a significant increase in serum level and should be done very carefully.
Does phenytoin bind to albumin?
Phenytoin is mainly bound to albumin, the percentage of bound drug being constant over a wide range of total drug concentrations. Palmitic acid and some acidic drugs, warfarin and phenylbutazone added to human serum albumin, decreased phenytoin binding in a non competitive way.
Can phenytoin cause hypoalbuminemia?
Phenytoin has a high protein binding (90%), so hypoalbuminemia condition will affect the free drug amount in the body, while it is known that only drug that unbound by protein (free drug) who can pass through the membrane and reach its target.
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 do you calculate corrected albumin?
Formula Used: Corrected Ca = [0.8 x (normal albumin – patient’s albumin)] + serum Ca level.
How do you interpret phenytoin levels?
Toxic phenytoin levels are defined as greater than 30 µg/mL. Lethal levels are defined as greater than 100 µg/mL. The reference range of free phenytoin is 1-2.5 µg/mL. In patients with renal failure associated with hypoalbuminemia, free phenytoin levels may be more accurate than total phenytoin levels.
Is phenytoin highly protein-bound?
Since phenytoin is highly protein-bound and free (unbound) phenytoin is the component producing the pharmacological effect, any factor which changes the protein binding of phenytoin would be expected to alter the free drug levels.
Does phenytoin bind to plasma protein?
The plasma protein binding of phenytoin was investigated in 100 epileptic patients, using equilibrium dialysis at 37 degrees C. The unbound fractions of phenytoin in plasma formed a skewed distribution, with a range of 9.7 to 24.7% and a median value of 12.3%.
How do you calculate corrected phenytoin?
If clcr < 20 mL/min then Corrected Phenytoin = Total Phenytoin Level / ( (0.1 x albumin) + 0.1) This is so cool!
When should Dilantin levels be drawn?
A level can be taken 2-4 hours following an IV loading or top-up dose (12-24 hours for oral doses) and levels should then be monitored every 24 hours until control is achieved and concentration has stabilised.
What is 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.