Modafinil

Indications

• FDA-approved in adults to improve wakefulness in excessive daytime sleepiness from narcolepsy, including type 1 and type 2 presentations.
• FDA-approved as an adjunct for residual sleepiness in obstructive sleep apnea, only alongside continued positive airway pressure therapy.
• FDA-approved for excessive sleepiness associated with shift work disorder, dosed one hour before the start of the work shift.
• Used off-label for fatigue and sleepiness in multiple sclerosis, Parkinson disease, and traumatic brain injury when sleep disorders are excluded.
• Used off-label to augment antidepressants for residual fatigue, hypersomnia, and low energy in major depressive and bipolar depression.
• Used off-label for ADHD in adults, though it is not FDA-approved for ADHD and a pediatric application was rejected over serious rash risk.

Mechanism of action

• Binds the dopamine transporter with weak affinity and blocks reuptake, raising extracellular dopamine in striatum and nucleus accumbens.
• Unlike amphetamines it does not reverse transporter flux, and the slow rise in dopamine is thought to explain its lower abuse potential.
• Increases hypothalamic orexin and histamine signaling and activates tuberomammillary wake-promoting nuclei, supporting cortical arousal.
• Raises glutamate and reduces GABA tone in cortex and hypothalamus, and elevates norepinephrine in wake-regulating regions.
• The wakefulness effect is relatively selective, producing less peripheral sympathetic activation and less rebound hypersomnia than stimulants.

Pharmacokinetics

• Absorbed with Tmax at 2-4 hours; food delays absorption by about an hour but does not reduce total bioavailability.
• Racemic, with the R-enantiomer half-life near 15 hours and the S-enantiomer near 4 hours, giving an effective half-life of about 15 hours.
• Cleared mainly by hepatic amidase hydrolysis to inactive modafinil acid, with a smaller CYP3A4 pathway and under 10 percent renal excretion.
• Moderately induces CYP3A4 and CYP1A2 while inhibiting CYP2C19, the combination that drives most of its clinically relevant interactions.
• Severe hepatic impairment roughly doubles exposure and requires halving the dose; renal impairment does not require adjustment.

Dosing

• Narcolepsy and obstructive sleep apnea: 200 mg PO once daily in the morning, taken with or without food.
• Shift work disorder: 200 mg PO taken approximately 1 hour before the start of the work shift rather than on a fixed clock time.
• Doses up to 400 mg/day have been used and are tolerated, but controlled trials show no consistent added benefit over 200 mg.
• Severe hepatic impairment: reduce to 100 mg/day; no adjustment is required for renal impairment, though data in severe disease are sparse.
• In older adults consider starting at 100 mg daily because clearance falls with age and psychiatric side effects are more common.
• No taper is required and physiologic withdrawal is not seen, though sleepiness returns promptly when the drug is stopped.

Adverse effects

• Headache in about 34 percent, nausea in 11 percent, nervousness, anxiety, insomnia, dry mouth, and diarrhea are the common complaints.
• Serious rash including Stevens-Johnson syndrome, toxic epidermal necrolysis, and DRESS has been reported; stop the drug at the first rash.
• Angioedema and anaphylactoid reactions, along with multi-organ hypersensitivity, are labeled warnings requiring immediate discontinuation.
• Psychiatric effects include anxiety, agitation, insomnia, and rarely mania, psychosis, or suicidal ideation, particularly in bipolar disorder.
• Small mean rises in blood pressure and heart rate can require antihypertensive adjustment, especially in patients with sleep apnea.
• Abuse potential is low but real, and euphoria and psychoactive effects consistent with other schedule IV stimulants have been documented.

Monitoring

• Confirm the sleep diagnosis before starting, including polysomnography and adherence to positive airway pressure in obstructive sleep apnea.
• Baseline and periodic blood pressure and heart rate, since small pressor effects can matter in patients with cardiovascular disease.
• Ask about rash, mucosal lesions, fever, or facial swelling at every visit during the first several months and instruct patients to stop and call.
• Track daytime sleepiness with the Epworth Sleepiness Scale or maintenance of wakefulness testing rather than by report of energy alone.
• Screen for emergent anxiety, insomnia, mania, and suicidal ideation, especially in patients with bipolar or psychotic disorders.

Interactions

• Induces CYP3A4 and lowers ethinyl estradiol exposure, reducing effectiveness of oral, patch, ring, and implant contraceptives; use an additional nonhormonal method.
• Contraceptive failure risk persists for one month after modafinil is stopped, so backup contraception must continue past the last dose.
• Inhibits CYP2C19, raising levels of phenytoin, diazepam, omeprazole, propranolol, and clomipramine; monitor and reduce doses as needed.
• CYP3A4 induction lowers concentrations of cyclosporine, midazolam, triazolam, and some direct oral anticoagulants and protease inhibitors.
• Strong CYP3A4 inducers such as carbamazepine and rifampin lower modafinil levels, while inhibitors such as ketoconazole raise them modestly.

Special populations

• Pregnancy: registry data suggest an increased rate of major congenital malformations, so avoid unless there is no reasonable alternative.
• Lactation: limited data on transfer into human milk; if used, monitor the infant for agitation, poor feeding, and disrupted sleep.
• Pediatric: not approved at any age, and a pediatric ADHD application was not approved because of serious rash including Stevens-Johnson syndrome.
• Geriatric: clearance is reduced, so consider starting at 100 mg/day and watch for agitation, insomnia, and blood pressure elevation.
• Severe hepatic impairment requires halving the dose; no renal adjustment is defined, but modafinil acid accumulates in severe renal failure.

Clinical pearls

• Modafinil makes hormonal contraception fail; document a backup method and continue it a month after stopping.
• Any rash on modafinil is a stop-the-drug event until Stevens-Johnson syndrome is confidently excluded.
• In sleep apnea it treats residual sleepiness only, never as a substitute for positive airway pressure.