Precise pharmacokinetic data of long-acting neuroleptics: apparent half life (T 1/2), time of peak plasma concentration (Tmax), bioavailability, has been a major contribution to determine optimal dosage of the drug. If the aim of the depot neuroleptic is to obtain a stable plasma concentration of the neuroleptic after . injection of the ester form equivalent to that following oral administration, it is logical to obtain the same pharmacological effect; this is true for haloperidol decanoate. Mean value of T 1/2 of clopenthixol decanoate and haloperidol decanoate are 19 and 21 days, respectively, they thereby justify monthly administration. Flupenthixol decanoate and fluphenazine enanthate should be injected with dosing intervals of 3 and 1 weeks, respectively in respect with their half-lives: 17 and 4 days. Fluphenazine decanoate have a half-life of 14 days, however, the longer time the treatment, the longer the apparent half-life, suggesting to reduce the dose or to enlarge the dosing interval. Optimal dose has been determined from the bioavailability of the oral formulation and the interval between two injections, it averages 15, 20 times the oral daily dose for haloperidol decanoate. A lower conversion factor is frequently used ( to 5 times) for other depot-neuroleptics such as pipotiazine palmitate, fluphenazine enanthate or decanoate; these low factors are not entirely explainable by the low bioavailability of the oral forms and produces more lower plasma concentration than after oral administration.
Drug has few CV adverse effects and may be preferred in patients with cardiac disease.
Dose of 2 mg is therapeutic equivalent of 100 mg chlorpromazine.
When changing from tablets to decanoate injection, patient should initially receive 10 to 20 times the oral dose once monthly (not more than 100 mg).
Assess patient periodically for extrapyramidal reactions and tardive dyskinesia.
Don’t withdraw drug abruptly except when required, because abrupt withdrawal may cause severe adverse reaction. Taper dosage over several weeks.
Safety and efficacy of drug injection in children haven’t been established, and oral drug isn’t recommended for children younger than age 3.
Drug is especially useful for agitation related to senile dementia. Tardive dyskinesia may occur more often, especially in elderly women.
Elderly patients usually need lower initial doses and a more gradual dosage adjustment.
The intravenous route is not FDA approved and is generally not recommended except when no other alternatives are available. Intravenous administration appears to be associated with a higher risk of QT prolongation and torsade de pointes (TdP) than other forms of administration. The manufacturer recommends ECG monitoring for QT prolongation and arrhythmias if IV administration is required. A dose in the range of 1 to 5 mg IV has been suggested, with the dose being repeated at 30 to 60 minute intervals, if needed. A maximum IV dose has not been established. The lowest effective dose should be used in conjunction with conversion to oral therapy as soon as possible.