Lamotrigine dosing

Lamotrigine is not approved for the acute treatment of depression, and the dose must be started low and slowly titrated up to decrease adverse effects if used for maintenance therapy of bipolar I disorder. A drug interaction and a severe dermatologic rash may occur when lamotrigine is combined with valproate (i.e., lamotrigine doses must be halved from standard dosing titration). 

Adjustments to Lamotrigine Dosing for Patients with Bipolar Disorder Following Discontinuation of Psychotropic Medications ... 

Current lamotrigine dose 100 mg/day Current lamotrigine dose 400 mg/day... 

Weeks onward Maintain current lamotrigine dose 200 200... 

Conversion to monotherapy for patients receiving valproic acid PO Titrate lamotrigine to 200 mg/day, maintaining valproic acid dose. Maintain lamotrigine dose and decrease valproic acid to 500 mg/day, no greater than 500 mg/day/wk, then maintain 500 mg/day for 1 wk. Increase lamotrigine to 300 mg/day and decrease valproic acid to 250 mg/day. Maintain for 1 wk, then discontinue valproic acid and increase lamotrigine by 100 m day each wk until maintenance dose of 500 mg/day reached. 

Reduce lamotrigine dose or stop dosage increase... 

Thus, if concomitant valproate is discontinued after lamotrigine dose is stabilized, then the lamotrigine dose should be cautiously doubled over at least 2 weeks in equal increments each week following discontinuation of valproate... 

Lamotrigine dose should be reduced by perhaps 50% if used with valproate, as valproate inhibits metabolism of lamotrigine and raises lamotrigine plasma levels, theoretically increasing the risk of rash... 

May also be useful for bipolar disorder In combination with lamotrigine, but must reduce lamotrigine dose by half when combined with valproate... 

Messenheimer JA, Guberman AH. Rash with lamotrigine dosing guidelines. Epilepsia 2000 41(4) 488. 

Information appears to be limited to these reports, but the interaction between lamotrigine and rifampicin would appear to be established. Be aware that rifampicin could reduce the efficacy of lamotrigine, and that increased lamotrigine doses are likely to be required. 

Cimetidine 400 mg twice daily for 5 days had no effect on the pharmacokinetics of a single 25-mg dose of lamotrigine in 10 healthy subjects. No change in lamotrigine dose appears to be needed during concurrent use. ... 

However, note that if they are also taking valproate in addition to phenytoin, the lamotrigine dose should be reduced, see Lamotrigine + Vd-proate , below. The lamotrigine dosage may need to be reduced if phenytoin is withdrawn. 

A study in 14 patients taking olanzapine in doses of 10 mg to 20 mg daily, and who were also given lamotrigine in increasing doses over 8 weeks to 200 mg daily found no changes in the pharmacokinetics of olanzapine with a lamotrigine dose of 100 mg daily, but when the dose was increased... 

The pharmacokinetic interaction would appear to be established however, since the relationship between lamotrigine levels and efficacy is not clear, the clinical relevance of the decrease is uncertain. Lamotrigine efficacy should be monitored in patients taking lopinavir/ritonavir, and probably any ritonavir-boosted regimen. Anticipate the need to increase the lamotrigine dose. 

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