The US Food and Drug Administration (FDA) has approved clonidine, like guanfacine, for the treatment of attention deficit hyperactivity disorder (ADHD), alone or with stimulants in 2010, for pediatric patients aged 6–17 years. According to the clinical trials submitted to FDA its effectiveness is comparable to stimulants commonly used for ADHD, when used alone it leads to ~35% improvement in symptoms,comparable to ~30% improvement when stimulants are used It was later approved for adults. In Australia, clonidine is an accepted but not approved use for ADHD by the TGA. Clonidine along with methylphenidate has been studied for treatment of ADHD. Some studies show clonidine more sedating than guanfacine -which may be better at bed time along with an arousing stimulant at morning. Clonidine can be used in the treatment of Tourette syndrome (specifically for tics). Clonidine may be used to ease withdrawal symptoms associated with the long-term use of narcotics, alcohol, benzodiazepine and nicotine (smoking). It can alleviate opioid withdrawal symptoms by reducing the sympathetic nervous system response such as tachycardia and hypertension, as well as reducing sweating, hot and cold flashes, and general restlessness. It may also be helpful in aiding smokers to quit. The sedation effect is also useful although its side effects can include insomnia, thus exacerbating an already common feature of opioid withdrawal.
Clonidine's effect on reducing circulating epinephrine by a central mechanism was used in the past as an investigatory test for phaeochromocytoma, which is a catecholamine-synthesizing tumour, usually of the adrenal medulla. In a clonidine suppression test plasma catecholamines levels are measured before and 3 hours after a 0.3 mg oral test dose has been given to somebody. A positive test occurs if there is no decrease in plasma levels.
Clonidine is classed by the FDA as pregnancy category C. It is classified by the TGA of Australia as pregnancy category B3, which means that it has shown some detrimental effects on fetal development in animal studies, although the relevance of this to human beings is unknown. Clonidine can pass into breast milk and may harm a nursing baby; caution is warranted in women who are pregnant, planning to become pregnant, or are breastfeeding.
Clonidine suppresses sympathetic outflow resulting in lower blood pressure, but sudden discontinuation can cause rebound hypertension due to a rebound in sympathetic outflow.
Clonidine therapy should generally be gradually tapered off when discontinuing therapy to avoid rebound effects from occurring. Treatment of clonidine withdrawal hypertension depends on the severity of the condition. Reintroduction of clonidine for mild cases, alpha and beta blockers for more urgent situations. Beta blockers never should be used alone to treat clonidine withdrawal as alpha vasoconstriction would still continue.
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