Active Ingredients

Primidone – Effect, Application & Risks

Primidone

Primidone is an anticonvulsant from the pharmacologically active group of antispasmodic drugs. It is used for long-term therapy of various forms of epilepsy .

What is primidone?

Primidone records an antispasmodic effect in patients with epilepsy. It is assigned to the drug group of antiepileptics. The chemical classification is in the group of barbiturates .

It is a prodrug, a precursor of the medically active substance. The human organism converts primidone into the powerful phenobarbital (deoxyphenobarbital), which dissolves epilepsy spasms . It is a breakdown substance (metabolite). Doctors administer this drug for special forms of epilepsy.

Pharmacological action

The medical mechanism has not yet been conclusively researched. However, doctors assume that primidone affects the membrane (cell wall) of the nerve cells and thus develops an anti-seizure effect.

Primidone is known from the long-term therapy of various forms of epilepsy. These special forms include grand mal epilepsy, petit mal epilepsy, status epilepticus, and myoclonic seizures. In children with petit mal epilepsy, primidone acts to prevent the development of grand mal epilepsy. These disorders present as temporal lobe seizures and primary generalized seizures affecting the whole brain (grand mal epilepsy).

Another group consists of secondary generalized seizures that affect individual areas of the brain (petit mal epilepsy). Gran mal seizures are also known as tonic-clonic seizures. The tonic phase lasts about 10 to 30 seconds and is characterized by muscle tension and spasms. During the clonic phase, muscle tremors and irregular spasms occur with great intensity. This phase can last from thirty seconds to three minutes. Symptoms include a short, intense cry immediately before the onset of cramps, salivation, twitching, wetting, rolling of the eyes, sudden end of the cramps, loss of consciousness, and then an increased feeling of tiredness .

Since it is not possible to accurately predict when seizures will occur, the only option is preventive or palliative treatment with suitable drugs such as primidone. This drug is second-line for anesthesia preparation and treatment of essential tremor when first-line drugs have proved ineffective.

Medical Application & Use

After the substance has been absorbed by the organism, it is immediately metabolized or converted into phenobarbital. Another active ingredient that develops through this process is phenylethylmalonamide, but it is of minor importance.

Primidone works together with the breakdown product phenobarbital at the central switching point of the neurotransmitter gamma-aminobutyric acid (GABA). Alongside glutamate , it is the most important inhibitory neurotransmitter in the central nervous system . It plays a prominent role in many neuronal processes of the CNS. It has a modulating effect and acts as an opponent (antagonistic) to the excitatory (exciting) effect of glutamate. Phenobarbital has a strengthening effect on the concentration of the messenger substance gamma-aminobutyric acid and reduces the readiness for seizures.

Risks & side effects

Primidone also has side effects and drug interactions. The drug must not be administered if there is a known hypersensitivity to the drug substance or other barbiturates. Centrally depressant drugs such as antidepressants , sleeping pills , opioid painkillers and neuroleptics are contraindicated because their mode of action is enhanced by primidone.

Simultaneously taking the calcium blocker nimodepin to treat angina pectoris (chest tightness), hypertension ( high blood pressure ) and tachycardia ( palpitations ) can be life-threatening. This drug is not administered to patients with signs of acute alcohol intoxication.

A careful risk-benefit analysis must be carried out in patients with cardiac arrhythmias , respiratory system diseases , severe sepsis , and functional disorders of the liver and kidneys . The reason for a possible contraindication lies in the considerable delay in the breakdown of the substance in the event of previous damage to the organism. In most cases, doctors use a reduced dose of primidone with careful monitoring of the patient.

The barbiturate may only be administered in very small doses during pregnancy and lactation if treatment is absolutely necessary. Common side effects are nausea , vomiting , headache , dizziness , increased excitability , memory and speech disorders , coordination disorders , perception disorders , indigestion , convulsions, tremor, drowsiness and delayed reaction time .

Cardiac arrhythmias, pigment disorders , haematopoietic disorders, anemia , skin changes, allergies , muscle fatigue and liver dysfunction occur rarely .

Long-term therapy increases the risk of developing osteoporosis . Increased excitability, aggressiveness and moodiness were often observed in the elderly and children. The breakdown of beta-blockers , used to treat heart problems and high blood pressure, is accelerated while their effectiveness is reduced.

Primidone reduces the effect of cardiac glycosides such as digitoxin and cytostatics used in the treatment of tumor diseases . The effect of antiepileptic drugs such as diazepam , clonazepam , phenytoin , carbamazepine is reduced.

Side effects and toxicity of methotrexate for the treatment of cancer are increased. Regular checks of the liver enzyme values ​​and the blood count are particularly indicated in the initial phase. There is an increased risk of osteoporosis in patients with previous illnesses who are taking [cortisone] at the same time.

Primidone can affect the effectiveness of contraceptives, so additional contraceptive measures should be taken .

Experts assume that there is an increased risk of suicide when taking the drug, so regular monitoring of the patient is essential. As with most drugs, there is also the possibility of a habituation effect with primidone. In order to avoid withdrawal symptoms, the drug must not be discontinued suddenly, but must be gradually reduced. Brain seizures are possible with cold turkey.

Due to the unfavorable side effect profile, primidone is a drug of second choice. It is only used when no alternative drugs with a more favorable appearance are available, or when the first-line drugs have proven to be ineffective.

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.