219 - References

References

Schizophrenia and related psychoses CHAPTER 1 Intramuscular clozapine Intramuscular clozapine is a short-­term intervention for patients with a treatment-­ refractory psychotic disorder who refuse oral medication. It is always used with a view to converting to oral clozapine once treatment is established.1 IM clozapine has also been used for patients who are unable to take oral medication because of physical illness.2 Although evidence is relatively limited, observational data indicate that initiating treatment with IM clozapine does not adversely affect long-­term adherence to oral treatment.1,3 IM clozapine is similar to oral clozapine in respect to short-­term safety and tolerability.4,5 The IM preparation is unlicensed in the UK and many other countries, so adequate precautions should be taken and patient or carer consent obtained. General recommendations for prescribing intramuscular clozapine in adults are summarised in Table 1.51. References

1. Casetta C, et al. A retrospective study of intramuscular clozapine prescription for treatment initiation and maintenance in treatment-­resistant psychosis. Br J Psychiatry 2020; 217:506–513.
2. Gee S, et al. Intramuscular clozapine in the acute medical hospital: experiences from a liaison psychiatry team. SAGE Open Med Case Rep 2021; 9:2050313x211004796.
3. Henry R, et al. Evaluation of the effectiveness and acceptability of intramuscular clozapine injection: illustrative case series. BJPsych Bull 2020:1–5.
4. Schulte PF, et al. Compulsory treatment with clozapine: a retrospective long-­term cohort study. Int J Law Psychiatry 2007; 30:539-­545.
5. Gee S, et al. Alternative routes of administration of clozapine. CNS Drugs 2022; 36:105–111. Table 1.51  General recommendations for prescribing intramuscular clozapine. Strength 25mg/mL Maximum dose* 100mg (4mL) per site Oral equivalent dose The oral bioavailability of clozapine is about half that of the IM injection (e.g. 50mg IM injection daily = 100mg tablets/oral solution daily) Site of administration† The manufacturer states deep intramuscular gluteal injection Maximum treatment length‡ Before administering each injection, the patient should be offered oral clozapine. Clozapine injection should be used for the shortest duration possible (maximum 2 weeks consecutively). Dosing frequency To minimise the number of injections, once daily dosing is preferred Monitoring After each administration, patients should be observed every 15 minutes for the first 2 hours to check for excess sedation. Routine clozapine monitoring also applies. * For doses >100mg, the dose may be divided and administered into two sites. † Case series data report administration via lateral thigh or deltoid –­ note that the injection is painful3 and the ­maximum volume for the deltoid route is 2mL (50mg). ‡ Case series data report use of intramuscular clozapine for up to 96 days.3,4 Injection site reactions become common with longer-term treatment. Note: Simultaneous injection of IM clozapine and parenteral benzodiazepines has not been studied. If IM benzodiapines are required leave at least 1 hour between administration of IM clozapine and IM benzodiapines.