Primidone

About Primidone

Primidone and two substances the body makes from it, phenobarbital and phenylethylmalonamide (PEMA), all have anticonvulsant activity; exactly how it controls seizures is not known. The label covers grand mal, psychomotor and focal epileptic seizures, alone or with other anticonvulsants, and notes it may control grand mal seizures that resist other treatment. It is started low and built up over ten days: for adults and children 8 and older, 100 to 125 mg at bedtime for three days, then twice a day, then three times a day, and from day ten usually 250 mg three times a day, raised if needed but never above 2 g a day. Children under 8 follow a lower schedule.

There is no boxed warning. It must not be taken by people with porphyria or anyone allergic to phenobarbital. Stopping it suddenly can set off status epilepticus, seizures that do not stop, and like other antiepileptic drugs it can increase suicidal thoughts or behavior, so new or worse depression or mood changes should be reported at once. Unsteadiness (ataxia) and vertigo are the most frequent early side effects and usually fade; nausea, loss of appetite, tiredness, irritability, double vision, drowsiness and rash can occur, and rarely blood problems, including a megaloblastic anemia that responds to folic acid. Because treatment is long, the label recommends a complete blood count and a chemistry panel every six months.

Although part of each dose becomes phenobarbital, which the DEA lists in Schedule IV, the primidone label carries no controlled-substance schedule and primidone is not on the DEA list of controlled substances, so federal controlled-substance rules do not apply to it. In pregnancy, the label encourages patients to join the North American Antiepileptic Drug Pregnancy Registry and recommends vitamin K for the mother in the month before and during delivery, because newborns have had bleeding resembling vitamin K deficiency. It passes into breast milk in substantial amounts, and excessive drowsiness in a nursing baby is a sign to stop breastfeeding. A switch from another anticonvulsant to primidone alone takes at least two weeks.

Taking Primidone

How to take it

Exactly as prescribed, usually three or four times a day once the starting schedule is finished. Keep taking it even if you feel well, and do not stop without the prescriber, since a sudden stop can bring on seizures that do not stop.

If you miss a dose

Take the missed dose as soon as you remember, unless it is almost time for the next one; then skip it. Do not take a double dose.

Storage

At room temperature (68°F to 77°F) in the original container, tightly closed, away from light, excess heat and moisture, out of reach of children.

Interactions to know about

It can cause drowsiness, so do not drive or operate machinery until you know how it affects you, and ask the prescriber about the safe use of alcohol. Tell the prescriber and pharmacist about every prescription and nonprescription medicine, vitamin, supplement and herbal product, and about porphyria or an allergy to phenobarbital.

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 Primidone differs from pharmacy to pharmacy

Primidone is an old generic with several makers of the 50 and 250 mg tablets, so quotes for those differ mostly by the pharmacy’s fee and markup, and a prescription that names Mysoline and blocks substitution is filled at the brand price. The 125 mg tablet comes from fewer sources, so not every pharmacy stocks it. A maintenance dose of several tablets a day is a large monthly count, so the price per tablet matters more than the dispensing fee.

Ways to pay less for Primidone without insurance

• Ask for generic substitution, and make sure the prescription does not name Mysoline with substitution blocked.
• Ask for a ninety-day supply once your dose is stable.
• Ask whether primidone is on the pharmacy’s flat-price generic list, and compare more than one pharmacy.
• If you take the 125 mg strength, confirm a new pharmacy stocks it before moving your prescription, since running out risks the seizures a sudden stop can cause.
• 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 Primidone

1. 1.When will my blood count and other blood tests be checked?
2. 2.What should I do if I run short or miss several doses?
3. 3.Which of my medicines add to its drowsiness?
4. 4.What should I know about vitamin K and the pregnancy registry if I plan a pregnancy?

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