Most Common Adverse Reactions in Clinical Trials

Adjunctive Therapy in Patients with Epilepsy: Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared with rates in the clinical trials of another drug and may not reflect the rates observed in practice. 

In these 2 trials, adverse reactions led to withdrawal of 4 (2%) patients in the group receiving placebo and 10 (5%) patients in the group receiving lamotrigine extended-release tablets. Dizziness was the most common reason for withdrawal in the group receiving lamotrigine extended-release tablets (5 patients [3%]). The next most common adverse reactions leading to withdrawal in 2 patients each (1%) were rash, headache, nausea, and nystagmus.

Table 4 displays the incidence of adverse reactions in these two 19-week, double-blind, placebo-controlled trials of patients with PGTC and partial onset seizures.

Note: In these trials the incidence of nonserious rash was 2% for lamotrigine extended-release tablets and 3% for placebo. In clinical trials evaluating immediate-release lamotrigine, the rate of serious rash was 0.3% in adults on adjunctive therapy for epilepsy [see Boxed Warning] . 

Adverse reactions were also analyzed to assess the incidence of the onset of an event in the titration period, and in the maintenance period, and if adverse reactions occurring in the titration phase persisted in the maintenance phase.

The incidence for many adverse reactions caused by treatment with lamotrigine extended-release tablets was increased relative to placebo (i.e., treatment difference between lamotrigine extended-release tablets and placebo ≥2%) in either the titration or maintenance phases of the trial. During the titration phase, an increased incidence (shown in descending order of percent treatment difference) was observed for diarrhea, nausea, vomiting, somnolence, vertigo, myalgia, hot flush, and anxiety. During the maintenance phase, an increased incidence was observed for dizziness, tremor, and diplopia. Some adverse reactions developing in the titration phase were notable for persisting (>7 days) into the maintenance phase. These persistent adverse reactions included somnolence and dizziness.

There were inadequate data to evaluate the effect of dose and/or concentration on the incidence of adverse reactions because, although patients were randomized to different target doses based upon concomitant AEDs, the plasma exposure was expected to be generally similar among all patients receiving different doses. However, in a randomized, parallel trial comparing placebo with 300 and 500 mg/day of immediate-release lamotrigine, the incidence of the most common adverse reactions (≥5%) such as ataxia, blurred vision, diplopia, and dizziness were dose related. Less common adverse reactions (<5%) were not assessed for dose-response relationships.

Monotherapy in Patients with Epilepsy: Adverse reactions observed in this trial were generally similar to those observed and attributed to drug in adjunctive and monotherapy immediate-release lamotrigine and adjunctive lamotrigine extended-release tablets placebo-controlled trials. Only 2 adverse events, nasopharyngitis and upper respiratory tract infection, were observed at a rate of >3% and not reported at a similar rate in previous trials. Because this trial did not include a placebo control group, causality could not be established [see Clinical Studies ( 14.3)] .