Section 3.7.1

Sympathomimetics

General Description

The sympathomimetic drugs used in psychiatry are dextroamphetamine (dexedrine), methylphenidate (ritalin) and pemoline (cylert). These drugs are also known as psycho-stimulants and analeptics.

The sympathomimetic drugs are approved for use in narcolepsy and attention deficit hyperactivity disorder. The sympathomimetic drugs are also sometimes used in the treatment of depression.

Indications for Medication

The major indications for sympathomimetic drugs are attention deficit/hyperactivity disorder in children and adults and narcolepsy. Sympathomimetic drugs are an effective treatment in about 75% of patients with attention deficit/hyperactivity disorder.

Methylphenidate is the most commonly used drug for attention deficit/hyperactivity disorder. However, dextroamphetamine is equally effective. The clinical data on the efficacy of pemoline is less robust; but some clinicians prefer to prescribe pemoline because of the lower abuse potential and because pemoline does not require a triplicate prescription.

The sympathomimetic drugs may be used for the treatment of narcolepsy; and they may be used for the treatment of depressive disorders. Possible indications for the use of sympathomimetic drugs include treatment resistant depressions, depressions in the elderly and in the medically ill.

Clinical Guidelines

The pretreatment evaluation should include an evaluation of cardiac function, with particular focus on the presence of hypertension or tachyarrhythmias.

Patients should also be examined for the presence of movement disorders, such as tics and dyskinesia, because those conditions can be exacerbated by the administration of sympathomimetic drugs. Liver function and renal function should also be assessed. The dosages of sympathomimetic drugs should be reduced if their metabolism is impaired.

Dextroamphetamine and methylphenidate are usually prescribed on a three times a day basis, while pemoline can be prescribed once daily. The usual dosage range for dextroamphetamine is 2.5-40 mg a day. The dosage range for methylphenidate is 10-80mg a day. Pemoline is given in dosages from 37.5-112.5mg daily.

Controversy still exists whether chronic administration of these sympathomimetic drugs is justified, especially in adults. The potential development of tolerance and dependence of these drugs must be thoroughly discussed and the utilization of these drugs must be closely monitored.

In depression, sympathomimetic drugs usually provide only short-term benefit (2-4 weeks), because tolerance to the antidepressant effects of the drug develop rapidly in most patients. The use of these drugs in depression must be carefully evaluated, and the duration of treatment must be closely monitored. The clinician may want to seek consultation in these cases.

Adverse Effects

The most common adverse effects associated with sympathomimetic drugs are anxiety, irritability, insomnia and dysphoria. Sympathomimetic drugs cause a decreased appetite, although tolerance develops to that side effect. These drugs may also cause an increase in heart rate and blood pressure; and these drugs may cause heart palpitations.

Less common adverse effects from the sympathomimetic drugs include the induction of movement disorders, such as tics, including Tourette's disorder-like symptoms and dyskinesia. These drugs may exacerbate glaucoma, hypertension, cardiovascular disorders, hyperthyroidism, anxiety disorders, psychotic illnesses and seizure disorders.

High doses of sympathomimetic drugs can cause dry mouth, pupillary dilation, bruxism, formication and emotional lability. Long-term use of high dosages can cause a delusional syndrome. The most limiting effect of long-term use of these drugs is the association with psychological and physical dependence.

There is virtually no indication for the use of sympathomimetic drugs during pregnancy. Dextroamphetamine and methylphenidate pass into the breast milk. It is not known whether pemoline passes into breast milk. These drugs should not be used in pregnancy or with nursing mothers.

Drug-Drug Interactions

The co-administration of sympathomimetic drugs with tricyclic or tetracyclic anti-depressants, warfarin, primidone, phenobarbital or phenytoin decreases the metabolism of those compounds, resulting in higher plasma levels.

Sympathomimetic drugs decrease the therapeutic efficacy of many hypertensives, especially guanethidine. Sympathomimetic drugs must be used with extreme caution in any patients on hypertensive medications.

Methylphenidate should be used with caution in patients treated with MAOIs. Amphetamines should not be used during treatment with MAOIs or within 2 weeks of taking MAOIs.

The consent form for these medications is " Sympathomimetic Amines."