One concept to reduce the adverse effects of opioids is the use of very small doses of opioid antagonists. 25 – 28 The rationale is that agents such as naloxone (Narcan) have a biphasic effect whereby very low doses reduce the incidence of opioid adverse effects and may augment the analgesic effect. 25 , 28 Much of the data are limited to the inpatient setting with intravenous administration of the opioid antagonist. 25 – 27 Concomitant administration of intravenous naloxone with morphine infusions has been studied, but the results have been mixed. 25 – 27 More research is needed before this treatment is implemented as part of routine practice.
There are no well controlled studies with Haldol (haloperidol) in pregnant women. There are reports, however, of cases of limb malformations observed following maternal use of Haldol along with other drugs which have suspected teratogenic potential during the first trimester of pregnancy. Causal relationships were not established in these cases. Since such experience does not exclude the possibility of fetal damage due to Haldol, this drug should be used during pregnancy or in women likely to become pregnant only if the benefit clearly justifies a potential risk to the fetus.
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 ).