You should be suspicious about any new medication that your son has started to take. The two medications you ask, could actually cause neurological problems:
Antihistaminics such as loratadine, may potentially cause seizures, although it is very rare. In the list of side effects from the brand, these side effects are listed: seizures, central nervous system stimulation.
Montek can cause psychiatric adverse reactions such as: aggressive behavior, hallucinations, depression, anxiety, tremors.
So the combination is not a good choice, particularly in your son that is already prone to get seizures, and is already taking anti-seizure medications,
Make sure the valaparin dosage is adequate (a blood test can be done to check the level). If there is too much valaparin in the blood, then the patient can have high "ammonia" levels in the blood, which can cause alterations in his mental status. If the level is too low, then he might not be protected against seizures.
Make sure he follows up with his doctor and neurologist.
Hope that helped.

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