A Phenytoin test is conducted to get a measure of the amount of Phenytoin in the blood. So, what is Phenytoin? It is a drug used to treat certain seizure disorders (also called epilepsy). As a result of seizure disorders the...
Introduction
A Phenytoin test is conducted to get a measure of the amount of Phenytoin in the blood. So, what is Phenytoin? It is a drug used to treat certain seizure disorders (also called epilepsy). As a result of seizure disorders the brain's ability to transmit electrical impulses is impaired and it hinders in regulating nerve activity.
When a patient encounters a seizure, he or she experiences changes in consciousness, alterations in sight, smell, and taste, and may go through uncontrolled muscular convulsions in one or more parts of the body.
Why do seizures occur?
Seizures can befall anyone at any age. There could be an array of causes that may trigger seizures in people. They may cause as a result of high fevers, head trauma, decrease in oxygen supply, getting exposed to certain toxins or drugs, withdrawal from alcohol especially after acute drinking problems, severe infections, metabolic disorders, extremely low blood sugar, and brain tumors.
Even newborns could have seizures due to head trauma that may have occurred in the uterus or during the process of birthing. Moreover, in many of the cases, it is not even known why a seizure occurred in the first place. The frequency and severity of seizures also vary among patients and also susceptible to change in the long run. Some patients may have a single seizure and after that could never have another one for life. At times they may experience occasional seizures or may have recurrent ones.
In some rare cases, some people may have a seizure that won’t stop until intervened medically. There is no residual damage for most patients from seizures, but the threat is from muscle contractions during attacks, which may likely cause acute injuries. They could also lose consciousness and fall. In some cases, there is also a danger of progressive brain damage as a result of recurrent seizures.
How does Phenytoin help?
People who have recurrent seizures are given Phenytoin to thwart them. Ever since it was developed in 1938, Phenytoin has found wide acceptance to curb and reign in seizures in patients. It is still used rampantly, but gradually newer drugs are also emerging.
It is important to maintain Phenytoin levels within a narrow therapeutic range. If it is too little the patient will deal with seizures, and when it is too much the patient will suffer from Phenytoin toxicity, which will manifest in loss of balance and falling, confusion, nystagmus (eye movement from side to side), slurred speech, tremors, and low BP.
Maintaining a steady Phenytoin level challenging
It is difficult to keep the Phenytoin level in the blood constant because it is processed by the liver and excreted through urine. Enzymes present in the liver process Phenytoin at varying rates and a lot depends from patient to patient, influenced by a patient's age and liver health. Children can metabolize it more quickly compared to the elderly.
Moreover, once the body reaches its capacity to process Phenytoin, even a small increase in the dosage can snowball into large increases in blood concentrations. This may raise the intensity of side effects, which is called Phenytoin toxicity.
Most of the Phenytoin in the bloodstream is bound to protein, and it is the unbound, free portion that remains active. If a patient has lower levels of protein in their blood than usual, it could lead to an excess of active Phenytoin. Moreover, Phenytoin frequently interacts with other medications, which can further complicate matters, either by enhancing or diminishing the effectiveness of the other drugs, as well as impacting the effectiveness of Phenytoin itself.
It is important to adjust the dosages of Phenytoin very slowly until there is a steady concentration in the blood. The actual amount of drug needed to reach this steady level is not uniform and varies from person to person and is also likely to change over time. It is paramount that doctors evaluate their patients for side effects and negative reactions during the adjustment of initial dosage over time. These may include:
- Swelling of the gums
- Hirsutism
- Insomnia
- Difficulty swallowing
- Nausea
- Confusion
- Fatigue
- Rashes
In certain cases, the patient has to be given another anti-seizure drug due to its powerful side effects.
The process of the Phenytoin test
The Phenytoin test, which helps to measure and monitor the amount of Phenytoin in the blood, is generally ordered every few days. It is because when the patient begins to take the drug it is important to adjust the dose to a desired level. And from then onwards it is regularly ordered to closely watch the blood concentrations. One or more Phenytoin tests are ordered if a patient begins or stops any extra medicines. It is advised to look at any reactions with other drugs. It is also ordered if a patient has a seizure or there is toxicity suspected by the doctor.
Conclusion
Normally, when Phenytoin results are within the therapeutic range, it means the patient does not have recurrent episodes of seizures, and there are also no significant side effects. It portrays that the Phenytoin dosage the patient is receiving is adequate. Moreover, patients shouldn't increase or decrease or ceases to take their medication on their own. It may heighten the risk of having a seizure and may interact with other medications that they are presently taking. Determining the dosage and further adjustments depend on individual cases.
Patients usually take Phenytoin or for that matter any anti-seizure drugs every day and sometimes many times a day for an entire lifetime. It is because maintaining a therapeutic serum Phenytoin level is crucial for the patient’s health. It is important to mention that patients who suffer seizures due to a temporary condition may not take them for a lifetime but only for a short duration.
FAQs
What is serum Phenytoin level?
Phenytoin is characterized by a narrow therapeutic range, which is between 10-20 mg/L. To monitor Phenytoin levels in the blood, doctors measure the total concentration of the drug. However, Phenytoin is typically bound to plasma proteins, mainly albumin, to an extent of 90%. Only the unbound form of Phenytoin is biologically active and responsible for its pharmacological effects.
How do you measure Phenytoin levels?
Phenytoin levels are often reported by laboratories in g/L instead (g/dL = g/L x 0.1). Once a patient receives a loading dose of intravenous Phenytoin, the levels are ready to be checked one hour after the dose. If loading is done orally, it is better to check the Phenytoin levels after 24 hours from the last dose.
Why check the Phenytoin level?
When a person who is already taking Phenytoin faces epilepticus, it can help providing a 'top-up' loading dose to achieve therapeutic levels. To determine the current plasma concentration and calculate the necessary 'top-up' loading dose, measuring a Phenytoin level becomes imperative.
Why is Phenytoin important?
Phenytoin is a medication useful in managing and treating epilepsy, generalized tonic-clonic seizures, status epilepticus, and complex partial seizures.
What is the warning of Phenytoin?
One should always consult the doctor about the risks of using Phenytoin to address a condition. The risk factors of taking Phenytoin include developing osteopenia, osteoporosis, or osteomalacia and issues with the lymph nodes including Hodgkin's disease.
What is the antidote for Phenytoin?
There is no antidote as such for Phenytoin. There is a lack of evidence that any method of gastrointestinal decontamination or enhanced elimination can enhance the results.
What are the common side effects of Phenytoin?
Common side effects of Phenytoin are:
- Headaches: One should rest and drink plenty of fluids
- Feeling drowsy, sleepy, or dizzy: As the body gets used to Phenytoin, these side effects should wean off
- Feeling nervous, unsteady, or shaky
- Sore or swollen gums
- Constipation
How does Phenytoin affect vitamin D?
Phenytoin is extensively used as an anti-seizure drug. It has several side effects that are well-documented including hypocalcemia, especially in patients with concomitant vitamin D deficiency. Decreased serum calcium levels may cause seizures.
Can Phenytoin cause liver damage?
Phenytoin is an anticonvulsant drug, which may rarely cause acute idiosyncratic drug-induced liver disease. It can be severe or potentially fatal. There is liver damage due to Phenytoin resulting from a hypersensitivity reaction.
Can Phenytoin cause brain damage?
Phenytoin is an anti-seizure medication and has been linked to changes in the cerebellum, cerebellar signs, and permanent cerebellar damage.
Can Phenytoin cause diabetes?
The research found that Phenytoin can cause an increase in blood sugar levels (hyperglycemia). The reason behind this has been attributed to the inhibition of insulin release. However, recently there has been a patient who experienced hyperglycemia while taking Phenytoin and the rise in insulin requirements showed the presence of insulin resistance.
Is Phenytoin removed by dialysis?
Yes, Phenytoin can be removed by dialysis in emergencies, and hence, ESRD patients should be dosed following dialysis.
Does Phenytoin cause anemia?
Administering Phenytoin is believed to be associated with 3.5 fold increased risk of aplastic anemia in patients.
Can Phenytoin be given IV?
It is advisable to inject Phenytoin Injection BP slowly and directly into a large vein with the help of a large-gauge needle or intravenous catheter.
