Transdermal and oral dl-methylphenidate-ethanol interactions in C57BL/6J mice: transesterification to ethylphenidate and elevation of d-methylphenidate concentrations

Abstract

We tested the hypothesis that C57BL/6J mice will model human metabolic interactions between dl-methylphenidate (MPH) and ethanol, placing an emphasis on the MPH transdermal system (MTS). Specifically, we asked: (1) will ethanol increase d-MPH biological concentrations, (2) will MTS facilitate the systemic bioavailability of l-MPH, and (3) will l-MPH enantioselectively interact with ethanol to yield l-ethylphenidate (l-EPH)? Mice were dosed with MTS (¼ of a 12.5 cm(2) patch on shaved skin) or a comparable oral dl-MPH dose (7.5 mg/kg), with or without ethanol (3.0 g/kg), and then placed in metabolic cages for 3 h. MPH and EPH isomer concentrations in blood, brain, and urine were analyzed by gas chromatographic-mass spectrometry monitoring of N-(S)-prolylpiperidyl fragments. As in humans, MTS greatly facilitated the absorption of l-MPH in this mouse strain. Similarly, ethanol led to the enantioselective formation of l-EPH and to an elevation in d-MPH concentrations with both MTS and oral MPH. Although only guarded comparisons between MTS and oral MPH can be made due to route-dependent drug absorption rate differences, MTS was associated with significant MPH-ethanol interactions. Ethanol-mediated increases in circulating concentrations of d-MPH carry toxicological and abuse liability implications should this animal model hold for ethanol-consuming attention-deficit hyperactivity disorder patients or coabusers.

Figure 1

Enantiomers of MPH: d-MPH (left) and l-MPH (right).

Figure 2

Enantioselective transesterification of dl-MPH to l-EPH following concomitant ethanol.

Figure 3

Representative GC–MS-SIM chromatogram of d-MPH, l-MPH, and l-EPH from a C57 mouse brain extract (upper ion profile). The sample was collected 3.25 h after dosing with one quarter of a 12.5 cm² MTS and 3 h after dosing with 3.0 g/kg ethanol by gavage. Enantiospecific analysis used chiral derivatization and a deuterated internal standard (lower ion profile).

Figure 4

(a) In mice treated with one quarter of a 12.5 cm² MTS for 3.25 h, ethanol (3.0 g/kg, gavaged at 0.25 h) increased total excretion of d-MPH in urine and increased d-MPH concentrations in blood and brain relative to dH₂O. (b) In mice gavaged with dl-MPH (7.5 mg/kg), concomitant ethanol (3.0 g/kg) increased total 3 h urinary excretion of d-MPH, and increased 3 h d-MPH concentrations in blood and brain, relative to gavage dosing with dl-MPH (7.5 mg/kg) and dH₂O. ^*p < 0.05, ^**p < 0.01, and ^***p < 0.001.

Figure 5

(a) In mice treated with one quarter of a 12.5 cm² MTS for 3.25 h, ethanol (3.0 g/kg, gavage at 0.25 h) increased total excretion of l-MPH in urine and increased l-MPH concentrations in blood and brain relative to dH₂O gavage. (b) In mice gavaged with dl-MPH (7.5 mg/kg), concomitant ethanol (3.0 g/kg) increased total 3 h urinary excretion of d-MPH and increased 3 h l-MPH concentrations in blood and brain, relative to gavage dosing with dl-MPH (7.5 mg/kg) and dH₂O. ^*p < 0.05, ^**p < 0.01, and ^***p < 0.001.

Figure 6

(a) Ethanol (3.0 g/kg, gavage at 0.25 h) and one quarter of a 12.5 cm² MTS resulted in enantioselective l-EPH formation as quantified in 3.25 h urine, blood, and brain. (b) Concomitant gavage of ethanol (3.0 g/kg) and dl-MPH (7.5 mg/kg) resulted in greater 3 h urinary elimination of l-EPH than for d-EPH. EPH was not detectable (ND) in 3 h blood using dosing regimen. In brain, the mean l-EPH concentration was greater, but not significantly (NS) different from that of d-EPH. EPH offers the potential of serving as a biomarker for combined dl-MPH–ethanol exposure. ^*p < 0.05, ^**p < 0.01, and ^***p < 0.001.