The influence of renal impairment on the pharmacokinetics of haloperidol has not been evaluated. About one-third of a haloperidol dose is excreted in urine, mostly as metabolites. Less than 3% of administered haloperidol is eliminated unchanged in the urine. Haloperidol metabolites are not considered to make a significant contribution to its activity, although for the reduced metabolite of haloperidol, back-conversion to haloperidol cannot be fully ruled out. Even though impairment of renal function is not expected to affect haloperidol elimination to a clinically relevant extent, caution is advised in patients with renal impairment, and especially those with severe impairment, due to the long half-life of haloperidol and its reduced metabolite, and the possibility of accumulation (see section ).
One injectable preparation is the long-acting decanoate ester which is used to treat schizophrenia and related conditions in patients who have had difficulty adhering to other medication plans. This can happen if patients have a poor understanding of their illness or because they forget to take their tablets. Patients are administered an injection once every four weeks. Haloperidol decanoate must only be administered intramuscularly and is not for intravenous use. The drug is quickly absorbed and has a high bioavailability. In healthy individuals, the Tmax is around 20 minutes, while it is minutes in people with schizophrenia. The T1/2 is just under 21 hours. The blood plasma haloperidol level reaches peak concentration at around six days post-administration and the half-life is approximately six weeks.