Does phenytoin have zero order kinetics?
Phenytoin metabolism is dose dependent. Elimination follows first-order kinetics (fixed percentage of drug metabolized during a per unit time) at the low drug concentrations and zero-order kinetics (fixed amount of drug metabolized per unit time) at higher drug concentrations.
Does phenytoin have saturable metabolism?
The metabolism of phenytoin to the major metabolite, 5-(p-hydroxyphenyl)-5-(phenylhydantoin, is saturable, giving rise to a non linear dose-serum concentration relationship.
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.
When should phenytoin levels 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.
Which drugs follow first order kinetics?
Examples are Ethanol, Phenytoin, Salicylates, Cisplatin, Fluoxetin, Omeprazol….
| Elimination kinetics | First order | Zero order |
|---|---|---|
| Term in clinical pharmacology | Linear kinetics | Non linear kinetics |
| Concerns | 95 % of drugs, at therapeutic concentrations | The remaining 5 %, and ethanol |
What is saturable metabolism?
These metabolic and carrier-mediated excretory clearance pathways are capacity-limited, becoming saturated at sufficiently high substrate concentrations. Saturable metabolic clearance processes lead to dose-dependent pharmacokinetics for many chemicals.
What are the indications of an abnormal phenytoin serum level?
Between 20 and 30 – Nystagmus. Between 30 and 40 – Ataxia, slurred speech, nausea, and vomiting. Between 40 and 50 – Lethargy and confusion. Higher than 50 – Coma and seizures.
How do you adjust phenytoin levels?
A rough guide to making an adjustment to the daily dose that should increase a serum level without leading to supratherapeutic / toxic levels is: 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.
What does a high Dilantin level mean?
What is Dilantin toxicity? Dilantin, or phenytoin, toxicity happens when you have high levels of Dilantin in your body that become harmful. Dilantin is a medicine that is used to prevent and treat seizures. Dilantin toxicity can lead to a coma.
What kinetic process in the body can be considered saturable?
Examples of these saturable metabolic processes include glycine conjugation of salicylate, sulfate conjugation of salicylamide, acetylation of p-aminobenzoic acid, and the elimination of phenytoin (Tozer et al, 1981). Drugs that demonstrate saturation kinetics usually show the following characteristics.