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ADHD Prescription Drugs (cont.)

Medical Editor:

What are the drug interactions of ADHD drugs?

Absorption and excretion of amphetamines -- and therefore blood levels --- are affected by pH. Fruit juices, vitamin C, and some drugs (guanethidine, reserpine) acidify the stomach, decreasing absorption. Alkalinizing agents, such as antacids, increase amphetamine absorption. Amphetamines should not be used along with tricyclic antidepressants or decongestants.

A 14-day clearing period is required between use of an MAOI and amphetamine. Otherwise, severe hypertension may occur.

Methylphenidate should not be used within 14 days of using an MAOI. Otherwise, a hypertensive crisis might occur. Because it raises blood pressure and heart rate, methylphenidate should be used with caution with other drugs that can affect blood pressure and heart rate. Dosage adjustment may be necessary for:

  • Warfarin (Coumadin)
  • Phenytoin (Dilantin)
  • Antidepressants (tricyclics and selective serotonin reuptake inhibitors)

Using methylphenidate with clonidine may result in serious adverse events.

Atomoxetine should not be used within 14 days of an MAOI, otherwise severe, possibly fatal reactions could occur. Increases in heart rate and blood pressure may occur if atomoxetine is administered with other medications that can increase heart rate or blood pressure.

The sedative effect of alcohol, barbiturates, or other drugs may be increased by clonidine and guanfacine. Clonidine may also interact with some cardiac agents, including digoxin, beta-blockers, and calcium channel blockers.

Bupropion should not be used within 14 days of an MAOI. Medications that can interact with bupropion include:

  • Tricyclic and SSRI antidepressants (nortriptyline, desipramine, imipramine, norfluoxetine, sertraline, paroxetine, fluvoxamine)
  • Atomoxetine (Strattera)
  • Stimulants
  • Anticonvulsants (carbamazepine, phenytoin, phenobarbital)
  • Antipsychotics (haloperidol, risperidone, thioridazine)
  • Beta-blockers (metoprolol, propranolol)
  • Antiarrhythmics (propafenone, flecainide)
  • Orphenadrine
  • Thiotepa
  • Cyclophosphamide
  • Diabetes medications

Bupropion may increase adverse effects seen with levodopa and amantadine. Some medications increase the likelihood of seizures (antidepressants, theophylline, steroids) and should be used with caution in patients taking bupropion. Adverse events or reduced tolerance is possible when bupropion is combined with alcohol. Using bupropion with nicotine patches may increase the risk for high blood pressure.

Tricyclic antidepressants (TCAs) should not be used within 14 days of an MAOI. Severe, even fatal, reactions may occur. Many drugs may interact TCAs. These include:

  • Quinidine (Quinidex)
  • Cimetidine (Tagamet)
  • Phenothiazines
  • Other antidepressants (such as fluoxetine, sertraline, paroxetine)
  • Anticonvulsants (barbiturates, phenytoin)

TCAs may increase side effects from decongestants. TCAs can also increase the effects of anticholinergics, blood pressure-lowering drugs, and CNS depressants, including alcohol.

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