PhenytoinPhenytoin Sodium

About Phenytoin

Phenytoin is thought to work by blocking sodium channels in nerve cells. It is labeled for tonic-clonic (grand mal) and psychomotor (temporal lobe) seizures and for seizures during or after neurosurgery. Extended capsules can be taken once a day if the prescriber decides; the chewable tablets are labeled not for once-a-day dosing.

The gap between an effective and a toxic level is narrow, and near the top of the range a small dose increase can raise the level sharply, so blood levels, usually aimed at 10 to 20 mcg/mL, are checked after starting, after dose changes and when other medicines change. Jerky eye movements, unsteadiness, slurred speech, drowsiness and confusion are the common side effects and are usually dose-related.

Serious skin and allergic reactions, liver injury and blood disorders can occur. The label notes that the HLA-B*1502 gene variant in people of Asian ancestry, and the CYP2C9*3 variant, may raise the risk of severe skin reactions, and suggests considering avoiding phenytoin as a substitute for carbamazepine in carriers. Long-term use can overgrow the gums and thin the bones, it can harm an unborn baby, and it carries the seizure-medicine warning about suicidal thoughts. Stopping suddenly can bring on seizures, and it is not used after liver injury from phenytoin or with the HIV medicine delavirdine.

The chewable tablets and suspension contain phenytoin itself and the capsules phenytoin sodium, so equal milligrams do not deliver quite the same amount, and the Phenytek label calls for careful level monitoring whenever the form or brand changes. The hospital injection carries a boxed warning that infusing it too fast can cause severe low blood pressure and heart rhythm problems.

Taking Phenytoin

How to take it

At the same times every day. Swallow extended capsules whole; chewable tablets can be chewed thoroughly or swallowed whole. Shake the suspension well and measure it with an accurate device. Ask how to space it from tube feeds. Do not stop it without your prescriber.

If you miss a dose

Take it when you remember, unless the next dose is almost due; then skip it. Do not take a double dose.

Storage

At room temperature, away from light, heat and moisture, and out of reach of children. Do not freeze the suspension.

Interactions to know about

Azole antifungals, fluoxetine, sertraline, cimetidine, omeprazole and some seizure medicines can raise its level; carbamazepine, some HIV medicines and long-term heavy drinking can lower it. It makes hormonal birth control less reliable, so another method is needed, and it changes the effect of warfarin and corticosteroids. Take antacids at a different time of day.

This summarizes the official prescribing information. Your prescriber’s and pharmacist’s instructions, and the leaflet that comes with your medicine, take priority.

Why the cash price for Phenytoin differs from pharmacy to pharmacy

Generic 100 mg extended capsules have several makers and cost pharmacies little, so a quote is mostly fee and markup. Doses using the 30 mg Dilantin capsule or Phenytek are priced as brands, and the chewable tablets and suspension have few makers. A pharmacy that stocks a different maker from your usual one may need to order yours.

Ways to pay less for Phenytoin without insurance

• Ask the prescriber whether your dose could use generic 100 mg capsules; any change of product is their call and may need a level check.
• Once stable, ask the pharmacy to keep the same manufacturer and warn you before any change.
• Ask for a ninety-day supply once your levels are settled.
• Upload the prescription to Script Unlock so licensed pharmacies can quote their cash price. You pay the pharmacy directly.

Questions to ask your pharmacist about Phenytoin

1. 1.Is this the same manufacturer and form as last time?
2. 2.When is my next phenytoin level due?
3. 3.How should I space it from antacids or tube feeds?
4. 4.Does it affect my birth control or blood thinner?
5. 5.Which rash or other symptoms mean I should call straight away?

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