Armodafinil

Indications

• FDA-approved in adults to improve wakefulness in excessive sleepiness associated with narcolepsy, at 150 to 250 mg each morning.
• FDA-approved as adjunctive treatment for residual excessive sleepiness in obstructive sleep apnea alongside ongoing positive airway pressure use.
• FDA-approved for excessive sleepiness of shift work disorder, given about one hour before the start of the work shift.
• Used off-label as adjunctive treatment for bipolar I depression, where randomized trials show small and inconsistent benefit over placebo.
• Used off-label for fatigue in multiple sclerosis, Parkinson disease, cancer, and traumatic brain injury after treatable causes are excluded.
• Used off-label for residual sedation and hypersomnia in major depressive disorder, jet lag, and sedating antipsychotic regimens.

Mechanism of action

• Weakly binds and blocks the dopamine transporter, raising extracellular dopamine without reversing transporter flux as amphetamines do.
• Activates orexin and histaminergic tuberomammillary wake circuits in the hypothalamus, supporting cortical arousal rather than global stimulation.
• Increases cortical glutamate and reduces GABA tone, contributing to sustained alertness with relatively little peripheral sympathetic effect.
• As the pure R-enantiomer it avoids the rapidly cleared S-isomer, so plasma concentrations stay higher 6-14 hours after a morning dose.
• Reinforcing effects exist but are weaker than with stimulants, consistent with schedule IV rather than schedule II placement.

Pharmacokinetics

• Tmax is about 2 hours in the fasted state, and food delays the peak by 2-4 hours without changing overall exposure.
• Terminal half-life is roughly 15 hours, and steady state is reached in about 7 days with once-daily dosing.
• Cleared mainly by hepatic amidase hydrolysis to inactive modafinil acid, with a lesser CYP3A4 route and minimal unchanged renal excretion.
• Moderately induces CYP3A4 and inhibits CYP2C19, the two effects behind nearly all of its clinically significant drug interactions.
• Severe hepatic impairment markedly raises exposure and requires dose reduction; renal impairment needs no adjustment but data are limited.

Dosing

• Narcolepsy and obstructive sleep apnea: 150-250 mg PO once daily in the morning; doses above 150 mg add little in sleep apnea.
• Shift work disorder: 150 mg PO approximately 1 hour before the start of the shift, rather than at a fixed clock time.
• Severe hepatic impairment: reduce the dose by about half and titrate slowly with attention to psychiatric and cardiovascular effects.
• Older adults should generally start at 50-100 mg/day because clearance declines with age and adverse effects are more frequent.
• Available as 50, 150, 200, and 250 mg tablets, which allows dose splitting for tolerability rather than fixed 150 mg increments.
• No taper is required, and stopping produces return of sleepiness rather than a physiologic withdrawal syndrome.

Adverse effects

• Headache in about 17 percent, nausea in 7 percent, insomnia, dizziness, anxiety, and dry mouth are the most common adverse effects.
• Serious rash including Stevens-Johnson syndrome, toxic epidermal necrolysis, and DRESS has been reported; any new rash should stop the drug.
• Angioedema and anaphylactoid reactions plus multi-organ hypersensitivity reactions are labeled warnings that require permanent discontinuation.
• Psychiatric adverse effects include anxiety, agitation, insomnia, mania, psychosis, and rarely suicidal ideation, especially in bipolar disorder.
• Blood pressure and heart rate can rise slightly, and some patients need antihypertensive adjustment during ongoing therapy.
• Insomnia is more likely than with modafinil when dosed later in the day because of higher afternoon and evening concentrations.

Monitoring

• Confirm the sleep diagnosis and, in obstructive sleep apnea, verify ongoing positive airway pressure adherence before and during treatment.
• Check blood pressure and pulse at baseline and periodically, particularly in patients with hypertension or established cardiac disease.
• Ask about rash, mucosal ulceration, fever, or facial swelling at each visit and instruct the patient to stop the drug and call immediately.
• Measure sleepiness with the Epworth Sleepiness Scale or maintenance of wakefulness testing rather than relying on subjective energy reports.
• Screen for insomnia, anxiety, mood elevation, and suicidal thinking, particularly when used off-label in bipolar depression.

Interactions

• Induces CYP3A4 and reduces ethinyl estradiol exposure, so hormonal contraceptives can fail; add a nonhormonal method during use.
• The contraceptive interaction persists for one month after armodafinil is stopped, so backup contraception must continue beyond the last dose.
• Inhibits CYP2C19, raising concentrations of phenytoin, diazepam, propranolol, omeprazole, and clomipramine, sometimes requiring dose reduction.
• Lowers levels of cyclosporine, midazolam, triazolam, and some antiretrovirals through CYP3A4 induction, which can cause therapeutic failure.
• Strong CYP3A4 inducers such as carbamazepine and rifampin reduce armodafinil exposure, while ketoconazole raises it modestly.

Special populations

• Pregnancy: pregnancy registry data for modafinil and armodafinil suggest increased major congenital malformations, so avoid where alternatives exist.
• Lactation: human milk data are limited; if used, watch the infant for irritability, poor feeding, and disturbed sleep.
• Pediatric: safety and effectiveness have not been established in patients under 17 years, and serious rash risk argues against off-label pediatric use.
• Geriatric: reduced clearance justifies lower starting doses and closer monitoring for insomnia, agitation, and blood pressure changes.
• Severe hepatic impairment requires dose reduction; no renal adjustment is defined although modafinil acid accumulates in severe renal failure.

Clinical pearls

• Same wakefulness effect as modafinil but higher afternoon levels, so evening insomnia is the usual complaint.
• Treat any rash as potential Stevens-Johnson syndrome and stop the drug before investigating.
• It reduces hormonal contraceptive efficacy during use and for a month afterward; document a backup method.