Treatment of Epilepsy. The recommended initial dosage of Gabapentin (Neurontin) for adults being treated for epilepsy is 300 mg taken once up to three times a day. The usual maintenance dose is 900 mg per day given in 3 divided doses.If necessary, the maintenance dose may be increased up to the maximum daily dose of 1,800 mg, until the condition is under control. Children (aged 3 to 12 years old) should be given individualized dosage of gabapentin based on child’s body weight.our gabapentin dosage depends on several of factors that include your age and weight, the medical condition being treated, other medications currently taken, and other underlying medical conditions. The following information provides only the average dosage as indicated by the manufacturer.