Introduction
The drug Risperdal® contains the active ingredient risperidone and is used in the treatment of schizophrenia and delusional disorders due to its antipsychotic and sedative effect. It is also used to treat hallucinations, psychoses, obsessive-compulsive disorders and aggressive behavior. Risperdal® belongs to the subgroup of atypical neuroleptics, which have fewer adverse effects than conservative neuroleptics. Risperdal® is highly effective.
Mechanism of action of Risperdal®
In order to understand the origin of the different side effects, it is important to understand the mechanism of action. Today, mental disorders are most often attributed to malfunctioning of the neurotransmitters dopamine and serotonin, which is why the corresponding structures in the brain involved in the production, transmission or action of the transmitters are inhibited. The drugs inhibit the influence of the transmitters on the brain and the psyche.
Risperdal® primarily inhibits the target structures of the transmitter serotonin, thus blocking the effect of serotonin. Risperdal® responds little to dopamine receptors and therefore causes fewer side effects specific to dopamine receptors. However, the active ingredient still has a certain affinity to two other transmitter systems: Adrenaline receptors, to which adrenaline, for example, binds, and histamine receptors (histamine is responsible, among other things, for the development of allergic reactions).
Further side effects are derived from the affinity to these two receptors. Risperdal® triggers a large number of side effects. Some of the most important ones are discussed and presented below.
A common side effect of drugs used to treat schizophrenia is the occurrence of persistent extrapyramidal motor movement disorders caused by inhibition of the dopamine receptor. Dopamine is important for the initiation and harmonious flow of movements. Due to the blockage of dopamine receptors, movement disorders can now occur to varying degrees.
These range from early dyskinesias (cramping of the mimic and tongue muscles) to Parkinson-like symptoms (rigidity, trembling, inability to move, rigid facial expressions) and akathisia, an agonizing motor restlessness, to late dyskinesias, which can persist even after months and years and even after discontinuing medication. Due to the low affinity of Risperdal® for the dopamine receptors, extrapyramidal motor movement disorders (EPS) are comparatively low. The EPS that occur are related to the dose of Risperdal®.
At low doses, EPS hardly ever occurs. However, at doses of 6 mg or more per day, symptoms are similarly severe and frequent as with classic preparations. Therefore application safety (therapeutic range) of the drug is very narrow (less than 6mg/day).
The transmitter dopamine is also important for regulating the release of other transmitters. Dopamine suppresses the release of the hormone prolactin. Prolactin is an important hormone in pregnancy, as it is responsible for the growth and differentiation of the mammary gland.
It also stimulates milk production. If dopamine is now suppressed by Risperdal® and other drugs, it cannot continue its original effect and the release of prolactin cannot be inhibited. The increased prolactin levels lead to mammary gland growth in both sexes.
In addition, the male libido is reduced by the increased release of the hormone. In women, additional side effects include milk flow from the mammary gland and the absence of menstruation. This increased prolactin secretion with its consequences is therefore also a side effect of Risperdal®.
Risperdal® also inhibits histamine receptors and adrenal receptors (especially alpha-1 receptors). By blocking these receptors, Risperdal® triggers other side effects: dry mouth, gastrointestinal complaints (diarrhoea, constipation, nausea, stomach pain, abdominal pain, indigestion, altered appetite), visual disturbances with blurred vision, confusion, palpitations, fatigue, tendency to sleep and listlessness. Taking Risperdal® can also trigger a change in the ECG, in particular the transition is often prolonged because Risperdal® blocks the excitation of the heart.
These changes are particularly common when several drugs are taken.Risperdal® can also cause or aggravate cardiac arrhythmia. The drugs also have an effect on blood formation (fewer white blood cells) and blood count in general, which is why the blood count should be checked regularly during long-term therapy with neuroleptics (not only Risperdal®). Serious side effects rarely occur.
If all neuroleptic drugs (including Risperdal®) are taken, a malignant neuroleptic syndrome may occur in the first two weeks of neuroleptic therapy. The symptoms are: High fever, EPS, vegetative disorders, metabolic acidosis (hyperacidity), comatose states and an increase in renal enzymes. In this very rare case the therapy must be stopped immediately.
