CLINICAL HANDBOOK OF SCHIZOPHRENIA

16. Antipsychotics 165are not available at the current time. Equivalent dosing of this medication with SGA medicationsis provided in Table 16.4.Basic Pharmacological Parameters of Antipsychotic MedicationsThe pharmacokinetics of all antipsychotics are summarized in the following general statements(differences may occur with specific medications and patients):• All medications are highly lipophilic, which helps with fast central nervous systempenetration.• All medications are highly protein bound, which may limit central nervous systempenetration.• The majority of medications have long half-lives that allow once-daily dosing (seeTables 16.3 and 16.4).• Most medications do not have established therapeutic blood concentrations.• In patients with renal or hepatic disease the dose should be started at 50% usualdaily dose.• Improvements are gradual with time; maximal improvement can be observed at 4–6 months (Table 16.1).Antipsychotic Drug InteractionsThere is a large potential for drug–drug interactions with the antipsychotic medications.Although many of these are not clinically important, some common interactions must beTABLE 16.4. Dosing of the Second- and Third-Generation AntipsychoticsDose rangeApproximateequivalent dosages(oral)Half life(hours)Intramuscular dosing(short acting)Clozapine 300–450 mg 400 mg 12–66 N/AOlanzapine 5–20 mg 15 mg 20–50 5–10 mg every 2–4hours, maximum dailydose of 30 mgRisperidone 0.5–6 mg 4 mg 20 (3–6 dayswith long-actinginjection)Ziprasidone40–160 mg (dividedtwice daily withfood); twice theincreasedbioavailabilitywith foodN/A (25–50 mg longactinginjection)120 mg 7 10 mg every 2 hoursor 20 mg every 4hours, maximum dailydose of 40 mg (20 mgintramuscular =120 mg oral)Quetiapine 200–800 mg 600 mg 6 N/AAripiprazole 5–30 mg 15 mg 75–96 9.75 mg every 2hours, maximum dailydose of 30 mgPaliperidone 6–12 mg 6 mg a 23 N/Aa Dosing equivalence for paliperidone, the active metabolite of risperidone, has not been established in comparison toother second-generation antipsychotics.