Re: Drug interactions Ritalin, Clonidine, Risperdal

Dear Karen,

At first I wasn’t sure where you were going with this, but I think I've got at what you wanted to know. Let me know if I'm not quite on target.

First the basics:

Ritalin is the trade name of methylphenidate hydrochloride. Methylphenidate is a central nervous sytem and respiratory stimulant whose mechanism of action is still unknown. It is widely used in the treatment of attention deficit hyperactivity disorder (ADHD).

Clonidine is a well known anti-hypertensive drug. It is an agonist of alpha 2 adrenergic receptors. It primarily causes decreased heart rate and blood pressure.

Resperdal is the trade name for respiridone. Respiridone is an antipsychotic agent which is an antagonist of type 2 serotonin receptors, type 2 dopamine receptors, alpha 1 and alpha 2 adrenergic receptors and type 1 histominergic receptors. It is primarily used to treat schizophrenia, but how it allieviates symptoms is unknown.

If you want more specific information, you can look up the drugs in the Physicians Desk Reference (PDR) or in the American Hospital Formulary Service Drug Information Book.

Interactions:

The PDR makes no reference of clonidine being used for anything other than treatment of high blood pressure. A quick search on Medline, however, showed that clonidine has been used for the past few years in conjuction with methylphenidate to treat ADHD.

Based on the pharmacology of the drugs, it seems quite probable they would interact, particularly in their effects on heart function. Possible adverse reactions of methylphenidate include abnormally fast heart rate, arrhthmia, and/or increased or decrease blood pressure, depending on the individual and the dose. Both clonidine and respiridone act at the alpha 2 adrenergic receptor, a critical receptor for proper cardiovascular function; clonidine as an agonist and repiridone as an antagonist.These drugs should definitely interact in some fashion. In fact, the PDR lists the use of hypotensive drugs (clonidine is a hypotensive drug) under the list of precautions to consider before prescribing respiridone. However, I was unable to uncover any well controlled studies which examined the interactions of clonidine and methylphenidate, and no literature dealing with interactions between respiridone and either of the other drugs. It appears that the nature of the interaction between these drugs is being primarily determined in the field (i.e. by actually giving them to patients)

A few cases studies are in the literature regarding the actions of the methylphenidate/clonidine combination, as well as some reports concerning possible dangerous interactions. There have been scattered reports of deaths associated with methylphenidate/clonidine intake. The Tourette’s Syndrome Association issued this release stating that they agreed with an FDA judgement that 3 cases of death associated with methylphenidate/clonidine were not due to the drug. However, a debate still seems to be going on in the medical journals regarding the safety of the regimen (see Cantwell et al., Journal of the American Academy of Child and Adolescent Psychology, 36(4), 539, 1997).

One potential danger is the rebound effect that occurs when clonidine is abruptly discontinued. If a person with ADHD forgot to take a dose, their blood pressure might rise to dangerous levels. This rise would be especially dangerous if coupled with some known or unknown cardiovascular problem. Some doctors are therefore advocating cardiac monitoring prior to putting patients on methylphenidate/clonidine; others believe this sort of testing is an overreaction, and believe that it should be done only if there is a known pre-existing heart condition.

If you have any questions or comments, or would like a list of some of the other references I used to construct this answer, please send me an email.