Rectal absorption of lamotrigine compressed tablets

Purpose: Interruption of oral drug administration poses a significant clinical problem for antiepileptic drugs that have no parenteral formulation. If a drug is absorbed rectally, rectal administration can be a useful alternative when the oral route of administration is not possible. The purpose of this study was to compare the single-dose pharmacokinetics of lamotrigine (LTG) compressed tablets after rectal and oral administration in healthy volunteers. Methods: A single LTG compressed tablet (100 mg) was administered orally and rectally to 12 volunteers in this single-dose, two- period, crossover study with a 2-week washout between doses. For rectal administration, tablets were crushed and suspended in 10 mL of water. Plasma samples were collected from 0 to 120 hr after each dose and analyzed for LTG by an HPLC method developed for this investigation. Results: LTG plasma concentrations were lower after rectal administration versus oral administration. The average area under the curve was 28.90 ± 9.5 μg/mL/hr after rectal administration and 51.71 ± 19.2 μg/mL/hr after oral administration. The average maximum LTG concentration was 0.53 ± 0.14 μg/mL after rectal administration and 1.45 ± 0.35 μg/mL after oral administration. The relative bioavailability for LTG compressed tablets was 0.63 ± 0.33 for rectal administration. There were no drug-related rashes or serious side effects. Conclusions: LTG suspension prepared from LTG compressed tablets is absorbed rectally, although not to the same extent or rate as when given orally.