Clonidine, ADHD and Autism

Clonidine has been used for more than half a century as an antihypertensive drug, to lower blood pressure.

It later found favour as a treatment for ADHD, drug withdrawal treatment, tobacco withdrawal treatment and a wide range of psychiatric disorders.  Off label usage of Clonidine includes autism.

Until recently it appeared to researchers to be a centrally acting α₂ adrenergic agonist, but recent research indicates than instead it is a centrally as an imidazoline receptor agonist.  This would account for its actions other than lowering blood pressure. Maybe it is both.  The good thing is that it is centrally acting (i.e. acting on the brain and the CNS) and it does appear to work. 

Adrenergic Agonist

As a centrally-acting α-adrenergic receptor agonist, Clonidine has more affinity for α₂ than α₁. It selectively stimulates receptors in the brain that monitor catecholamine (epinephrine, norepinephrine and dopamine) levels in the blood. These receptors close a negative feedback loop that begins with descending sympathetic nerves from the brain that controls the production of catecholamines.  By fooling the brain into believing that catecholamine levels are higher than they really are, clonidine causes the brain to reduce its signals to the adrenal medulla, which in turn lowers catecholamine production and blood levels. The result is a lowered heart rate and blood pressure.

Imidazoline Receptors

There are three classes of imidazoline receptors:

• I₁ receptor – mediates the sympatho-inhibitory actions of imidazolines to lower blood pressure
• I₂ receptor – an allosteric binding site of monoamine oxidase and is involved in pain modulation and neuroprotection.
• I₃ receptor – regulates insulin secretion from pancreatic beta cells

L-Monoamine oxidases (MAO)

MAOs are enzymes that act as catalysts.  There are two types of MAO: MAO-A and MAO-B

MAO- A is an enzyme that degrades amine neurotransmitters such as dopamine (DA), norepinephrine (NE), and serotonin (5-HT).

MAO-B is an enzyme that catalyzes the oxidation of arylalkylamine neurotransmitters, including dopamine (DA).

The differences between the selectivity of the two enzymes are utilized clinically.  MAO- A inhibitors have been used in the treatment of depression, and MAO-B inhibitors are used in the treatment of Parkinson's disease

Selective MAO-B inhibitors preferentially inhibit MAO-B, which mostly metabolizes DA. If MAO-B is inhibited, then more DA is available for proper neuronal function, especially in Parkinson's Disease. 

Clinical significance

Because of the vital role that MAOs play in the inactivation of neurotransmitters, MAO dysfunction (too much or too little MAO activity) is thought to be responsible for a number of psychiatric and neurological disorders. For example, unusually high or low levels of MAOs in the body have been associated with schizophrenia, depression, attention deficit disorder, substance abuse, migraines, and irregular sexual maturation.

MAO inhibitors are one of the major classes of drug prescribed for the treatment of depression, although they are often last-line treatment due to risk of the drug's interaction with diet or other drugs. Excessive levels epinephrine, norepinephrine or dopamine may lead to a hypertensive crisis, and excessive levels of serotonin may lead to serotonin syndrome.

MAO-A inhibitors act as antidepressant and antianxiety agents, whereas MAO-B inhibitors are used to treat Alzheimer’s and Parkinson’s diseases.

Clonidine in ADHD

In the US, the FDA has licensed clonidine for use in children with ADHD.

Pediatric doses of clonidine are calculated based on the child's body weight. Clonidine dosage for ADHD in children is 5 micrograms per kilogram of body weight per day orally in four divided doses. Children who require a daily dosage of 0.2 mg usually can use the 0.3 mg trans-dermal patch. If ADHD is associated with sleep disturbances, low to moderate doses of clonidine can be taken at bedtime.

Clonidine in Autism

Not surprisingly, since clonidine is effective in ADHD, it also shows promise in autism. 

Other ADHD drugs, like Ritalin, have problematic side effects.  The US Center for Disease Control reported in 2012 that an estimated 6.4 million children ages 4 to 17 had been diagnosed with ADHD at some point, a 53 percent increase over the past decade. Approximately two-thirds of those currently diagnosed have been prescribed drugs such as Ritalin or Adderall. Those drugs can help patients with both mild and severe symptoms, but they can also cause addiction, anxiety and psychosis.  In the UK, it is suggested that about 3% of children may have ADHD.  Drug use is far lower than in the US, but 657,000 prescriptions were written by doctors for drugs like Ritalin in 2012.

Use of ADHD drugs 'increases by 50% in six years'

There have been studies of clonidine in autism; here a fairly recent one:-

Use of clonidine in children with autism spectrum disorders

Perhaps even more interesting is a lively debate among parents who have tried it:-

Clonidine for autism?

It does seem to work, but nobody seems to be following it up.

Clonidine Stimulation Test

Regular readers will know my interest in TRH and GH.  At least there is no doubt about Clonidine’s effect on GH (growth hormone).  If you want to test pituitary function to see how well GH is being produced, the standard test is the:-

Clonidine GH stimulation Test

For those interested in GH, if you were to take Clonidine, smoke a cigarette and then have your GH measured, the Endocrinologist would have a surprise.

Nicotine from cigarette smoking enhances clonidine-induced increase of serum growth hormone concentrations in men

“These findings suggest that in man nicotinic cholinergic and adrenergic mechanisms might interact in the stimulation of GH secretion.”
 

Interestingly, one of the milder side effects of the ADHD drug Ritalin is growth retardation. According to Professor Tim Kendal, who created the national guidelines in the UK for treating ADHD: - “In children, without doubt, if you take Ritalin for a year, it's likely to reduce your growth by about three-quarters of an inch.

Conclusion

Clonidine looks like another old drug that has been stumbled upon by somebody doing some off label experimentation.  It does seem to have good results in ADHD and Autism.  The good thing is that it is FDA approved and is available in both oral and time release transdermal forms.

I do not think anybody really understands how it works in ADHD or other psychiatric disorders; undoubtedly, there is another, as yet unidentified, mode of action.

 

For those who want more info:- 

The Clinical Utility of Clonidine

Note ulcerative colitis, ADD and even growth delay.

 

Clonidine treatment for short stature