What are the precautions when prescribing antihistamines (anti-histamine medications) and anti-seizure (antiepileptic) medications together?

From the Guidelines

When prescribing antihistamines and anti-seizure medications together, healthcare providers should prioritize monitoring for increased sedation and cognitive impairment, as both drug classes can cause central nervous system depression, particularly with first-generation antihistamines and certain antiepileptic drugs like carbamazepine and valproate 1.

Key Considerations

• First-generation antihistamines pose a higher risk for interaction with antiepileptic drugs due to their sedative effects and potential for pharmacokinetic interactions.
• Antiepileptic drugs such as carbamazepine and phenytoin can increase the metabolism of antihistamines, potentially reducing their effectiveness, while some antihistamines may inhibit the metabolism of certain antiepileptics, leading to increased serum levels and potential toxicity 1.
• Second-generation antihistamines are generally safer options with minimal sedative effects and fewer drug interactions.
• Dosage adjustments may be necessary when these medications are used together, and patients should be advised to avoid activities requiring mental alertness until their response to the combination is known.

Patient Counseling

• Patients should be counseled about avoiding alcohol and other CNS depressants while taking these medications together, as this could dangerously amplify sedative effects.
• Individualized guidance is crucial to ensure safe driving for each patient, considering factors such as drug dosage, drug interactions, and pharmacokinetics, while prioritizing seizure control 1.

Clinical Practice

• The effects of antiseizure medications on driving performance should be considered, with some medications like carbamazepine, valproate, lamotrigine, lacosamide, and levetiracetam potentially resulting in clinically meaningful driving impairment under acute administration but not under chronic administration 1.
• Healthcare providers should be aware of the complex pharmacological effects of antiseizure medications and their potential impact on driving, emphasizing the need for personalized patient care and monitoring.

From the Research

Precautions for Prescribing Antihistamines and Anti-Seizure Medications Together

• When prescribing antihistamines and anti-seizure medications together, it is essential to consider the potential risks of seizures induced by antihistamines, particularly in patients with a history of epilepsy 2, 3.
• Antihistamines, especially first-generation H1-antagonists, have been known to provoke convulsions in healthy children and epileptic patients 2.
• Second-generation antihistamines, such as desloratadine, are considered to be effective and safe but may still pose a risk of seizures in certain individuals 2.
• A study found that antihistamines were the most common causative drug for new-onset seizures, highlighting the need for caution when prescribing these medications to patients with a history of seizures or epilepsy 3.

Considerations for Anti-Seizure Medication Selection

• The choice of anti-seizure medication depends on the type of seizure, and certain medications may be more suitable for specific types of epilepsy 4, 5.
• Newer-generation anti-seizure medications, such as lamotrigine and levetiracetam, have unique mechanistic and pharmacokinetic properties and may be better tolerated than older medications 4, 5.
• However, certain anti-seizure medications, such as valproate, may have teratogenic effects and should be avoided in women of childbearing potential 4.

Potential Interactions and Contraindications

• Antihistamines and anti-seizure medications may interact with other medications, including herbal supplements, and reduce their efficacy or increase the risk of adverse effects 6.
• Ginkgo biloba, a popular herbal supplement, may induce seizures or interact with anti-seizure medications, such as Depakote and Dilantin, and reduce their efficacy 6.
• It is crucial to consider potential interactions and contraindications when prescribing antihistamines and anti-seizure medications together to ensure safe and effective treatment 4, 5, 2, 3, 6.