The anti-emetic action of prochlorperazine may mask the signs and symptoms of overdosage of other drugs and may obscure the diagnosis and treatment of other conditions such as intestinal obstruction, brain tumor and Reye’s syndrome (see
WARNINGS).
When prochlorperazine is used with cancer chemotherapeutic drugs, vomiting as a sign of the toxicity of these agents may be obscured by the anti-emetic effect of prochlorperazine.
Because hypotension may occur, large doses and parenteral administration should be used cautiously in patients with impaired cardiovascular systems. To minimize the occurrence of hypotension after injection, keep patient lying down and observe for at least ½ hour. If hypotension occurs after parenteral or oral dosing, place patient in head-low position with legs raised. If a vasoconstrictor is required, Levophed
®* (norepinephrine bitartrate) and Neo-Synephrine
®† (phenylephrine hydrochloride) are suitable. Other pressor agents, including epinephrine, should not be used because they may cause a paradoxical further lowering of blood pressure.
Aspiration of vomitus has occurred in a few post-surgical patients who have received prochlorperazine as an anti-emetic. Although no causal relationship has been established, this possibility should be borne in mind during surgical aftercare.
Deep sleep, from which patients can be aroused, and coma have been reported, usually with overdosage.
Antipsychotic drugs elevate prolactin levels; the elevation persists during chronic administration. Tissue culture experiments indicate that approximately 1/3 of human breast cancers are prolactin-dependent
in vitro, a factor of potential importance if the prescribing of these drugs is contemplated in a patient with a previously detected breast cancer. Although disturbances such as galactorrhea, amenorrhea, gynecomastia and impotence have been reported, the clinical significance of elevated serum prolactin levels is unknown for most patients. An increase in mammary neoplasms has been found in rodents after chronic administration of antipsychotic drugs. Neither clinical nor epidemiologic studies conducted to date, however, have shown an association between chronic administration of these drugs and mammary tumorigenesis; the available evidence is considered too limited to be conclusive at this time.
Chromosomal aberrations in spermatocytes and abnormal sperm have been demonstrated in rodents treated with certain antipsychotics.
As with all drugs which exert an anticholinergic effect, and/or cause mydriasis, prochlorperazine should be used with caution in patients with glaucoma.
Because phenothiazines may interfere with thermoregulatory mechanisms, use with caution in persons who will be exposed to extreme heat.
Phenothiazines can diminish the effect of oral anticoagulants.
Phenothiazines can produce alpha-adrenergic blockade.
Thiazide diuretics may accentuate the orthostatic hypotension that may occur with phenothiazines.
Antihypertensive effects of guanethidine and related compounds may be counteracted when phenothiazines are used concomitantly.
Concomitant administration of propranolol with phenothiazines results in increased plasma levels of both drugs.
Phenothiazines may lower the convulsive threshold; dosage adjustments of anticonvulsants may be necessary. Potentiation of anticonvulsant effects does not occur. However, it has been reported that phenothiazines may interfere with the metabolism of Dilantin
®‡ (phenytoin) and thus precipitate Dilantin (phenytoin) toxicity.
The presence of phenothiazines may produce false-positive phenylketonuria (PKU) test results.
Long-Term Therapy
SPL UNCLASSIFIED SECTION
Given the likelihood that some patients exposed chronically to antipsychotics will develop tardive dyskinesia, it is advised that all patients in whom chronic use is contemplated be given, if possible, full information about this risk. The decision to inform patients and/or their guardians must obviously take into account the clinical circumstances and the competency of the patient to understand the information provided.
To lessen the likelihood of adverse reactions related to cumulative drug effect, patients with a history of long-term therapy with prochlorperazine and/or other antipsychotics should be evaluated periodically to decide whether the maintenance dosage could be lowered or drug therapy discontinued.
Children with acute illnesses (e.g., chicken-pox, CNS infections, measles, gastroenteritis) or dehydration seem to be much more susceptible to neuromuscular reactions, particularly dystonias, than are adults. In such patients, the drug should be used only under close supervision.
Drugs which lower the seizure threshold, including phenothiazine derivatives, should not be used with Amipaque
®§ (metrizamide). As with other phenothiazine derivatives, prochlorperazine should be discontinued at least 48 hours before myelography, should not be resumed for at least 24 hours postprocedure, and should not be used for the control of nausea and vomiting occurring either prior to myelography with Amipaque (metrizamide), or postprocedure.