Pharmacokinetics

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Pharmacokinetic (PK) data on modafinil were obtained from healthy male subjects. The possibility of PK variability in females or those with coexisting medical problems is largely unstudied. Modafinil is well-absorbed and it reaches peak plasma concentrations in 2.7 hours. The plasma half-life is approximately 15 to 17 hours and steady state is reached after two to four days. Modafinil is hepatically metabolized via P450 [cytochrome P (CYP)] isoenzymes to inactive metabolites (10). Modafinil impacts multiple isoenzymes and has the potential for significant drug interactions. It has been shown to induce CYP 3A/5 isoenzymes resulting in lower area under the curve (i.e., plot of drug concentration in plasma vs. time) of ethinylestradiol and triazolam (Halcion®), both substrates for CYP 3A4 (10,12). Modafinil can decrease the effectiveness of these drugs and other drugs metabolized by 3A4 including cyclosporine, verapamil (Calan®, Isoptin®, Verelan®), and lovastatin (Mevacor®, Altoprev®). Modafinil inhibits CYP 2C9 and 2C19 and therefore blood levels of phenytoin (Dilantin®, Phenytek®) and clozapine (Clozaril®) can be increased leading to possible toxicity (10,13).

Adverse Effects

The adverse events that were reported significantly more often in the modafinil group compared to placebo group in the clinical trials for OSA were headache (p < 0.05) and nausea (p = 0.01). In a 12-month extension study, the most commonly reported treatment-emergent adverse events in modafinil (dosage of 200-400 mg/day) recipients included infection, nervousness, headache, accidental injury, sinusitis, rhinitis, depression, anxiety, insomnia, and dizziness (5-11% of patients). Potential study participants were excluded if they had active clinical disease [e.g., hypertension, congestive heart failure, chronic obstructive pulmonary disease (COPD), depression] and so it is possible that adverse effects would be more common and significant in these groups of patients (10). Elevated blood pressure, increased heart rate, dizziness, nervousness, and insomnia have all been reported with regular use of modafinil (10).

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