What is the pharmacokinetics of phenytoin?

Hepatic microsomal enzymes primarily metabolize phenytoin. Much of the drug is excreted in the bile as an inactive metabolite, which is then reabsorbed from the intestinal tract and ultimately excreted in the urine. Less than 5% of phenytoin is excreted unchanged in the urine.

What is the mechanism of action of phenytoin?

Mechanism of action Phenytoin is believed to protect against seizures by causing voltage-dependent block of voltage gated sodium channels. This blocks sustained high frequency repetitive firing of action potentials.

How is phenytoin metabolised?

Phenytoin is metabolized by cytochrome P450 (P450) enzymes primarily to 5-(p-hydroxyphenyl-),5-phenylhydantoin (HPPH), which may be further metabolized to a catechol that spontaneously oxidizes to semiquinone and quinone species that covalently modify proteins.

What is the half-life of phenytoin?

The plasma half-life in man after oral administration of phenytoin averages 22 hours, with a range of 7 to 42 hours. Steady-state therapeutic levels are achieved at least 7 to 10 days (5–7 half- lives) after initiation of therapy with recommended doses of 300 mg/day.

What happened when phenytoin given with TCAs?

Phenytoin may act through a similar mechanism as lidocaine, although experimental studies suggest that it does not compete directly for the same sodium channel binding site as TCAs. Allosteric modulation of the TCA binding site may occur in the setting of phenytoin use.

What happened when phenytoin given with TCA cycle?

What is status epilepticus?

A seizure that lasts longer than 5 minutes, or having more than 1 seizure within a 5 minutes period, without returning to a normal level of consciousness between episodes is called status epilepticus. This is a medical emergency that may lead to permanent brain damage or death.

How long does it take for phenytoin to leave your system?

In our patient the DPH took 204 hours to drop below the toxic level (20 mg/L), whereas by using a linear regression with only two different concentrations a figure of 155 hours was obtained.

How is TCA overdose treated?

Administration of sodium bicarbonate might be beneficial for patients with severe or life-threatening TCA toxicity if a prehospital protocol exists for its use (Grades B/D). Benzodiazepines are recommended for TCA-associated convulsions (Grade D).

What are TCA medications?

Tricyclic antidepressants (TCAs) are drugs used to treat depression, bipolar disorder, and other conditions such as chronic pain and insomnia. While newer classes of antidepressant have far fewer side effects, TCAs still have their place in the treatment of these and other disorders.

What are the long term side effects of phenytoin?

Side effects of phenobarbital and phenytoin during long-term treatment of epilepsy. Especially susceptible to the neurotoxic effects of phenytoin are epileptic children with severe brain damage who are on multiple drugs. In those children, balance disturbance may develop and be followed by gradual loss of locomotion.

Does phenytoin cause hyperglycemia?

Phenytoin, particularly in high dosages, may cause hyperglycemia by inhibiting insulin release. The drug may also raise serum glucose levels in diabetic patients. Therapy with phenytoin should be administered cautiously in patients with diabetes mellitus, glucose intolerance, or a predisposition to hyperglycemia.

Does phenytoin cause hyponatremia?

Phenytoin does not cause hyponatremia (low sodium levels). However, Phenytoin is known to cause hypernatremia (high serum sodium level >145 mmol/L). The information given above is for Phenytoin which is the active ingredient of Phenytoin.

Does phenytoin cause thrombocytopenia?

Drug‐induced thrombocytopenia is a well‐recognized phenomenon. Phenytoin has been reported to induce various hematologic reactions, including thrombocy‐topenia, and usually begins several weeks after initiation of therapy. Most described cases in the literature occurred following phenytoin initiation.