What Factors Affect Lamotrigine Dosage?

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  • Written By: wiseGEEK Writer
  • Edited By: O. Wallace
  • Last Modified Date: 29 October 2019
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The simple explanation of Lamictal® or lamotrigine dosage is that it is based on age and size, with the biggest differences in the pediatric and adult populations, condition being treated, and patient response. The matter gets significantly more complicated when other medications are added. Carbamazepine (Tegretol®), valproate (Depakote®), phenytoin (Dilantin®), phenobarbital, and primidone (Mysoline®) — which may be used to treat seizure disorders and/or bipolar disorder — interact with lamotrigine in different ways, changing the dosage. Moreover, lamotrigine requires an initiation period that means the medication is started at a low dose and gradually increased into the therapeutic range.

Lamotrigine dosage for pediatric patients depends on their weight and age. Children who are between two and 12 years old being treated for epilepsy, begin with doses of two to five milligrams that might be increased to 200 mg, though the dose can be higher if the drug is used with other anti-seizure medications, except for valproate. Use of Depakote® almost always translates to a lower Lamictal® dose. A lower dose can also be appropriate if seizures are adequately controlled.


Adults have different lamotrigine dosage schema, which again depends on condition, response and other medications. People over 12 with bipolar disorder who are only taking Lamictal® start at a dose of 25 mg for weeks one and two, increase to 50 mg for weeks three and four, and in the next four weeks will double the dose twice to 200 mg. Some patients may take slightly more, though there is little clinical evidence that greater than 200 mg is more effective.

The 200 mg monotherapy dose is the same in seizure disorders. Dosage may climb more slowly, and takes several more weeks to reach the therapeutic range. As mentioned, lamotrigine may not always be the best monotherapy for some seizure disorders and more than one medication could be required to treat these conditions or bipolar disorder.

Using additional medications means the lamotrigine dosage may need to be titrated up or down. For people with seizure disorder or bipolar disorder, who take carbamazepine, phenytoin, phenobarbital, and primidone, initial dose is usually higher and begins at 50 mg. Target dose is 400 mg. In contrast, those who take valproate begin by taking 25 mg every other day and by climbing to a target of 100 mg over a period of several weeks.

One medication used in bipolar disorder that is not mentioned in lamotrigine dosage is the anti-manic drug, lithium. It is quite possible for lithium and Lamictal® to be combined. Though lithium has a substantial number of drug interactions, it tends not to influence or be influenced by lamotrigine. Expected doses for the two might remain the same at 900-1200 mg for lithium and 200 mg for lamotrigine. Both drugs are effective as monotherapy in bipolar disorder for a substantial percentage of people, and they are certainly not always combined.


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