Adult ADHD: Pharmacologic treatment in the DSM-5 era

A noradrenergic medication

Atomoxetine is a potent, selective inhibitor of the presynaptic noradrenaline transporter that increases the availability of extracellular noradrenaline in the prefrontal cortex.^48,49 Atomoxetine may be a good alternative for adult patients with ADHD and comorbid anxiety.⁵⁰

For adults, the optimal starting dosage is 40 mg in the morning for 1 week, followed by an increase to 80 mg. Insufficient dosing is common with atomoxetine, and the dosage could be increased to 100 mg/d.⁵¹ Dosing twice per day may be associated with higher rates of insomnia.

Atomoxetine’s efficacy for managing ADHD in adults has been consistently demonstrated by 6 placebo-controlled trials of 10 to 16 weeks, 3 placebo-controlled 6-month trials, and a 1-year maintenance-of-response trial.⁵² Atomoxetine was found to have an effect size of 0.45 (medium) (number needed to treat [NNT] = 5).^53-55The most common adverse effects include nausea, dry mouth, insomnia, and erectile dysfunction. Small increases in heart rate and blood pressure have been reported, so use this medication with caution in patients for whom this might be problematic. Atomoxetine is metabolized by CYP2D6; 7% of white individuals have a genotype corresponding to a nonfunctional CYP2D6 enzyme.^56-58

Alpha-2 adrenergic agonists

Clonidine and guanfacine are antihypertensive drugs that induce peripheral sympathoinhibition via the stimulation of receptors. Clonidine binds equally to adrenergic receptor subtypes α-2A, α-2B, and α-2C (as well as to α-1 and β subtypes, histamine receptors, and possibly dopamine receptors).^59,60 Guanfacine binds preferentially to postsynaptic α-2A adrenoceptors in the prefrontal cortex, which have been implicated in attentional and organizational functions.^61,62

ER guanfacine and ER clonidine are FDA-approved as monotherapy for ADHD in children and adolescents.

Efficacy in adults. A small (N = 17), double-blind, placebo-controlled, crossover study comparing immediate-release guanfacine and dextroamphetamine found that both medications significantly reduced adult ADHD symptoms, as measured with the DSM-IV Adult Behavior Checklist for Adults.⁶³

No trials have been published regarding the efficacy of ER clonidine in adults with ADHD; adverse effects including sedation, bradycardia, and hypotension may limit its use. One study compared the supplemental use of ER guanfacine (1 to 6 mg/d) or a matching placebo in 26 adults with ADHD who had suboptimal response to stimulant-only treatment. After 10 weeks, both the guanfacine ER and placebo groups showed statistically significant improvements in ADHD symptoms and general functioning. The treatments did not differ in efficacy, safety, or tolerability.⁶⁴

Adverse events. Compared with clonidine, guanfacine has less CNS depressant and hypotensive activity.⁵⁸ A phase I trial of ER guanfacine in healthy adults found its single-dose pharmacokinetic properties in 1-, 2-, and 4-mg tablets appeared to be statistically linear. Somnolence—the most common treatment-emergent adverse effect—occurred in 33 of 52 participants (63.5%). All mean vital-sign measurements and ECG parameters remained within normal limits after dosing, and no marked changes from baseline measurements were noted.⁶⁵

Antidepressants

Antidepressants used in ADHD treatment include bupropion and tricyclic antidepressants.
Bupropion is a noradrenaline and dopamine reuptake inhibitor and is considered to be a mild psychostimulant because of its amphetamine-derived chemical structure.^66,67 It generally is considered a third-line medication when stimulants have not improved ADHD symptoms or are not tolerated.

A 2011 meta-analysis examined 5 randomized, controlled trials including 175 adults treated with bupropion for ADHD. Bupropion was found to be more effective than placebo (NNT = 5), although bupropion’s therapeutic benefits were not observed until weeks 5 and 6. Its effects were less pronounced than those of methylphenidate. Mean daily dosages were 362 mg for the bupropion SR trials and 393 mg for the bupropion XL trial.⁶⁸

Tricyclics. Desipramine and nortriptyline have been found to be efficacious in childhood ADHD,^69,70 although cardiovascular risk and toxicity in overdose limit their use.⁷¹