What is the maximum daily dosage of Dexedrine (dextroamphetamine) for an adult or adolescent patient with Attention Deficit Hyperactivity Disorder (ADHD) when prescribing Dexedrine Spansule in the morning and potentially adding Dexedrine (dextroamphetamine) regular in the afternoon?

Maximum Daily Dosage of Dexedrine (Dextroamphetamine) When Combining Spansule and Immediate-Release Formulations

The maximum total daily dose of dexamphetamine (Dexedrine) is 40 mg per day for both adults and children aged 6 years and older, regardless of whether you combine Spansule (sustained-release) with immediate-release formulations. 1, 2, 3

Regulatory Maximum Dose

• The FDA label explicitly states that "only in rare cases will it be necessary to exceed a total of 40 mg per day" for ADHD treatment. 3
• The American Academy of Child and Adolescent Psychiatry reinforces this 40 mg/day maximum as the regulatory standard for amphetamines. 2
• For adults and older adolescents, some patients may be treated with total daily doses of up to 0.9 mg/kg of dextroamphetamine or 40 mg, whichever is lower. 1, 2

Practical Dosing Strategy When Combining Formulations

When prescribing both Dexedrine Spansule (morning) and immediate-release Dexedrine (afternoon), add the morning and noon doses together to determine the Spansule dose, then add a separate immediate-release dose in the afternoon if needed. 1

Example Dosing Approach:

• If a patient requires 10 mg in the morning and 10 mg at noon, prescribe Dexedrine Spansule 20 mg in the morning. 1
• If afternoon coverage is needed for homework or evening activities, add immediate-release Dexedrine 5-10 mg in the early afternoon (around 4 PM). 1
• Total daily dose must not exceed 40 mg. 2, 3

Timing Considerations

• Administer the Spansule dose upon awakening to provide coverage throughout the day. 1, 3
• The immediate-release afternoon dose should be given at the clinician's discretion, typically 4-6 hours after the morning dose. 1, 3
• Avoid late evening doses due to resulting insomnia. 3

When Higher Doses Might Be Considered (Rarely)

If you are considering exceeding 40 mg/day, you must clearly document that:

• Symptoms could not be controlled at lower doses. 1, 2
• The higher doses are not producing side effects such as weight loss, blood pressure increase, or agitation. 1, 2
• The patient should be monitored for signs of tolerance. 1, 2

However, if the 40 mg/day maximum does not provide adequate symptom control, consider switching to an alternative stimulant (methylphenidate) rather than further dose escalation, as approximately 90% of patients respond when both stimulant classes are tried sequentially. 1, 2

Critical Monitoring Requirements

At each visit, you must assess:

• Blood pressure and pulse (cardiovascular monitoring). 2
• Height and weight (growth parameters). 2
• Side effects, particularly insomnia, anorexia, irritability, and cardiovascular symptoms. 1, 4

Common Pitfalls to Avoid

• Do not exceed 40 mg/day without exceptional documentation and justification. 2, 3
• Do not add afternoon doses that defeat the purpose of using sustained-release formulations (i.e., avoiding in-school dosing). 1
• Do not ignore the fact that dexamphetamine causes more severe insomnia, appetite suppression, and emotional side effects compared to methylphenidate, so monitor these closely when using combination dosing. 4
• Do not advance doses too quickly—titrate in 5 mg increments at weekly intervals. 5, 3

Duration of Effect Considerations

Dexedrine Spansules provide sustained effects lasting 3-6 hours longer than immediate-release formulations, making them ideal for morning dosing, while immediate-release dexamphetamine demonstrates earlier onset but shorter duration. 6 This pharmacokinetic profile supports the strategy of using Spansules for daytime coverage and adding immediate-release for targeted afternoon/evening symptom control.