What is the sheiner Tozer equation?
What is the sheiner Tozer equation?
Objective: In settings where free phenytoin concentrations are not available, the Sheiner-Tozer equation-Corrected total phenytoin concentration = Observed total phenytoin concentration/[(0.2 × Albumin) + 0.1]; phenytoin in µg/mL, albumin in g/dL-and its derivative equations are commonly used to correct for altered …
How do you calculate phenytoin correction?
If clcr < 20 mL/min then Corrected Phenytoin = Total Phenytoin Level / ( (0.1 x albumin) + 0.1) This is so cool!
What calculation is used to correct total phenytoin levels for a low albumin concentration?
The “Sheiner-Tozer Equation” is the official name of this correction. This updated formula uses an albumin coefficient of 0.275, and 0.2 for patients with renal failure (see Evidence for details).
Why do we correct phenytoin?
Total serum phenytoin levels reflect both bound and unbound drug. However, as protein-bound phenytoin cannot cross the blood-brain barrier, only free phenytoin is active. In healthy adults, approximately 90% of phenytoin is bound to albumin. Thus, phenytoin levels must be corrected according to albumin levels.
How do you Phtrate phenytoin?
In young adults, phenytoin should be started at 4–5 mg/kg per day (200–300 mg/d, in one or two doses) and titrated by increments of 30 mg to 100 mg per day, with at least 7–10 days between changes. Elderly patients generally require a lower initial dose (3 mg/kg per day) and especially cautious titration.
How do you calculate phenytoin Vmax?
Significant inter-patient variability may exist for many of the pharmacokinetic parameters. Here are some reported ranges: Vd: 0.52 – 0.78 L/kg Vmax: 6 – 8 mg/kg/day Km: 5.4 – 6.8 mg/L….Phenytoin dosing guidelines.
| Vmax | Maximum rate of drug metabolism |
|---|---|
| Km | Concentration at which the rate of drug metabolism is 50% of Vmax |
How do you adjust phenytoin?
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.
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.
How do you mix phenytoin IV?
For administration by intravenous infusion phenytoin injection should be diluted in 50 – 100 ml of normal saline, and the final concentration of phenytoin in the solution should not exceed 10 mg/ml, the infusion mixture should not be refrigerated.
