From the Guidelines
The oral equivalent of Consta 37.5mg is approximately 2mg of oral risperidone daily. When considering the management of delirium symptoms in adult patients, as outlined in the ESMO clinical practice guidelines 1, it's crucial to understand the pharmacological interventions that may have a role. According to the guidelines, risperidone is listed with a suggested starting dose of 0.5 mg p.o. stat, and it's mentioned that the dose should be reduced in older patients and patients with severe renal or hepatic impairment. The guidelines also note that risperidone may cause insomnia, agitation, anxiety, drowsiness, and orthostatic hypotension.
In the context of transitioning from the long-acting injectable form of risperidone (Consta 37.5mg) to oral medication, patients should begin taking the oral risperidone immediately after their last injection is due. The 37.5mg injectable dose is designed to provide steady blood levels equivalent to what would be achieved with a daily 2mg oral dose, based on the pharmacokinetic properties of risperidone. Key points to consider when making this transition include:
- Monitoring patients for efficacy and side effects during the transition period
- Individual responses may vary, and some patients may require dose adjustments based on their clinical response
- The importance of making this transition under medical supervision to ensure symptom control is maintained throughout the process
- Being aware of potential side effects such as EPSEs, especially if the dose exceeds 6 mg/24 h, as noted in the guidelines 1.
From the Research
Equivalent Oral Dose of Risperidone
The equivalent oral dose of risperidone can be determined based on the studies that compared oral risperidone with risperidone long-acting injection.
- A study published in 2007 2 found that patients who were originally on an oral risperidone dose of more than 3 mg/day but of 5 mg/day or less should receive 37.5 mg of risperidone long-acting injection.
- This suggests that 37.5 mg of risperidone long-acting injection is equivalent to an oral dose of approximately 3-5 mg/day of risperidone.
Pharmacokinetics of Risperidone
The pharmacokinetics of risperidone are well understood, with an absolute oral bioavailability of nearly 70% and a peak plasma level reached at about 1 hour after oral administration 3.
- The active metabolite of risperidone, 9-hydroxyrisperidone, is equally active with the parent compound and contributes to the clinical activity of the drug.
- The plasma concentrations of risperidone and its active metabolite remain dose-proportional even at doses exceeding the therapeutic range.
Clinical Efficacy of Risperidone
Risperidone has been shown to be effective in the treatment of schizophrenia, with a therapeutic activity comparable to that of haloperidol 3, 4.
- Risperidone has a greater effect on negative symptoms and produces fewer extrapyramidal side effects than haloperidol.
- The clinical success of risperidone suggests that the development of compounds with selective affinity for 5-HT2 or other serotonin receptors may result in further improvements in the pharmacotherapy of psychiatric disorders.