## How is free phenytoin level calculated?

If clcr < 20 mL/min then Corrected Phenytoin = Total Phenytoin Level / ( (0.1 x albumin) + 0.1) This is so cool!

## What is free phenytoin level?

The reference range of free phenytoin is 1-2.5 µg/mL.

**What is the difference between a free phenytoin level and a total phenytoin level?**

Measurement of the concentration of the free form of phenytoin is considered to better reflect clinical status than total concentration. Total concentration is easily measured, and then free concentration is predicted using that value.

**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.

### 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 the plasma concentration of phenytoin?

A phenytoin level should be taken to establish the current plasma concentration and can be used to calculate the required ‘top-up’ loading dose.

- Top-Up Phenytoin = (20 – (measured concentration (mg/L)) x 0.7 x weight (kg)
- Sodium Dose.
- Table 1: Expected Increase in Phenytoin Concentration with “Once Only” Top-
- Up Dosing.

**When should a free phenytoin level be drawn?**

Levels can be drawn at the point of admission, regardless of the patient’s normal dosing time. In normal healthy subjects after dose adjustment, the phenytoin level should be drawn within six to seven days with subsequent doses of phenytoin adjusted accordingly.

**What is the sheiner-Tozer equation?**

#### How do you calculate phenytoin Vmax?

The concentration at steady state can be estimated using the following equation if Vmax and Km are known (may use population averages if not available): Css = [Km x (S) x (F) x dose(mg/day)] / [Vmax – (S)(F)(dose(mg/day))]. To simplify further steps, Daily dose will be abbreviated: dd.

#### What is corrected phenytoin level?

Corrected phenytoin levels were calculated using the Sheiner-Tozer equation. Corrected phenytoin levels = Measured total phenytoin(micromol/l) [(albumin g/1 x 0.9)+ 0.1] 40.

**How do you draw phenytoin levels?**

Monitoring: Drawing levels: Draw peak 30 minutes after a 30 infusion or 60 minutes after an IM injection. Draw trough within 30 minutes prior to next dose or at least one half-life after the peak.

**What are phenytoin equivalents?**

CEREBYX® (fosphenytoin sodium injection) is a prodrug intended for parenteral administration; its active metabolite is phenytoin. 1.5 mg of fosphenytoin sodium is equivalent to 1 mg phenytoin sodium, and is referred to as 1 mg phenytoin sodium equivalents (PE).

## How do you titrate phenytoin?

If the phenytoin concentration is < 7 mcg/mL, the dose may be increased by 100 mg/day. 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.

## What is phenytoin 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.

**How is IV phenytoin given?**

Phenytoin Injection BP should be injected slowly and directly into a large vein through a large-gauge needle or intravenous catheter. It must be administered slowly. Intravenous administration should not exceed 50 mg/minute in adults.

**How do you calculate phenytoin km?**

Other Equations The concentration at steady state can be estimated using the following equation if Vmax and Km are known (may use population averages if not available): Css = [Km x (S) x (F) x dose(mg/day)] / [Vmax – (S)(F)(dose(mg/day))]. To simplify further steps, Daily dose will be abbreviated: dd.

### How is phenytoin measured?

### How do you dilute IV phenytoin?

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.

**What is the Sheiner-Tozer equation for total phenytoin concentration?**

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 phenytoin binding to albumin.

**What is the Sheiner-Tozer equation used for?**

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 phenytoin dosing?

Phenytoin dosing guidelines. Projected loading doses required to increase sub-therapeutic concentrations to the therapeutic range are determined by using the following equation: Cadj = (Concentration desired – Concentration observed) x Vd, where Vd = 0.7 x adjusted body weight. The usual range for Vd is 0.52 to 0.78 L/kg.

#### What is the winter-Tozer equation used for?

The Winter-Tozer equation was developed to help clinicians estimate an unbound (free) phenytoin concentration based on a total phenytoin level and a serum albumin level. In patients with hypoalbuminemia, a corrected equation must be used to account for reduced phenytoin protein binding.