The drug is well and rapidly absorbed with a high bioavailability when injected intramuscularly. The T max is 20 minutes in healthy individuals and minutes in patients with schizophrenia. The mean T 1/2 is hours.  The decanoate injectable formulation is for intramuscular administration only and is not intended to be used intravenously. The plasma concentrations of haloperidol decanoate reach a peak at about six days after the injection, falling thereafter, with an approximate half-life of three weeks. 
2 to 5 mg IM single dose initially; use if oral therapy is not appropriate; may administer as frequently as 1 hour intervals, though dosing every 4 to 8 hours is satisfactory for most patients. Max: 20 mg/day IM. Repeat doses based on clinical response and safety considerations. Geriatric patients may require a lower dose; use lower starting dose and titrate gradually. Use the lowest effective dose in all patients. Convert to oral therapy as soon as clinically indicated. Second generation antipsychotics with efficacy for this indication (oral or parenteral, ., risperidone, olanzapine, or ziprasidone), may be preferred due to cardiac and extrapyramidal risks of parenteral haloperidol. In some patients, the addition of a benzodiazepine may be needed. SWITCHING TO ORAL THERAPY: In general, the parenteral dose administered in the preceding 24 hours may be used as the total initial daily PO dosage. Thereafter, closely monitor and adjust oral dosage to efficacy and tolerance. Usually, the first oral dose should be given within 12 to 24 hours following the last IM dose.