Long-acting depot injections are used for maintenance therapy especially when compliance with oral treatment is unreliable. However, depot injections of conventional antipsychotics may give rise to a higher incidence of extrapyramidal reactions than oral preparations; extrapyramidal reactions occur less frequently with atypical antipsychotics such as risperidone. Depot antipsychotics are administered by deep intramuscular injection at intervals of 1 to 4 weeks. When initiating therapy with sustained-release preparations of conventional antipsychotics, patients should first be given a small test-dose as undesirable side-effects are prolonged. In general not more than 2–3 mL of oily injection should be administered at any one site; correct injection technique (including the use of z-track technique) and rotation of injection sites are essential. If the dose needs to be reduced to alleviate side-effects, it is important to recognise that theplasma-drug concentration may not fall for some time after reducing the dose; therefore it may be a month or longer before side-effects subside.
FLUPENTHIXOL DECANOATE:
Indications: maintenance in schizophrenia and other psychoses.
Contraindications: hepatic impairment; renal impairment; pregnancy; breast-feeding.
Dose and Administration: By deep intramuscular injection into the gluteal muscle, test dose 20 mg, then after at least 7 days 20–40 mg repeated at intervals of 2–4 weeks, adjusted according to response; max. 400 mg weekly; usual maintenance dose 50 mg every 4 weeks to 300 mg every 2 weeks; elderly initially quarter to half adult dose; child not recommended.
RISPERIDONE:
Indications: Bipolar Disorder in Remission, Schizophrenia and other psychoses in patients tolerant to risperidone by mouth.
Contraindications: Akathisia, Constipation, Dizziness, Drowsy, Dyspepsia, Extrapyramidal Disease, Fatigue, Headache Disorder, Parkinsonism, Rhinitis, Weight Gain, Xerostomia.
Dose and Administration: By deep intramuscular injection into the gluteal muscle, patients taking oral risperidone up to 4 mg daily, initially 25 mg every 2 weeks; patients taking oral risperidone over 4 mg daily, initially 37.5 mg every 2 weeks; dose adjusted at intervals of at least 4 weeks in steps of 12.5 mg to max. 50 mg (elderly 25 mg) every 2 weeks; child and adolescent under 18 years not recommended.
ZUCLOPENTHIXOL DECANOATE:
Indications: maintenance in schizophrenia and other psychoses, particularly with aggression and agitation.
Contraindications: hepatic impairment; renal impairment; pregnancy; breast-feeding.
Dose and Administration: By deep intramuscular injection into the gluteal muscle, test dose 100 mg, followed after at least 7 days by 200–500 mg or more, repeated at intervals of 1–4 weeks, adjusted according to response; max. 600 mg weekly; elderly quarter to half usual starting dose; child not recommended.
