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Promethazine may cause marked drowsiness. Ambulatory patients should be cautioned against such activities as driving or operating dangerous machinery until it is known that they do not become drowsy or dizzy from promethazine therapy.
The sedative action of promethazine hydrochloride is additive to the sedative effects of central nervous system depressants; therefore, agents such as alcohol, narcotic analgesics, sedatives, hypnotics, and tranquilizers should either be eliminated or given in reduced dosage in the presence of promethazine hydrochloride. When given concomitantly with promethazine hydrochloride, the dose of barbiturates should be reduced by at least one-half, and the dose of analgesic depressants, such as morphine or meperidine, should be reduced by one-quarter to one-half.
Promethazine may lower seizure threshold. This should be taken into consideration when administering to persons with known seizure disorders or when giving in combination with narcotics or local anesthetics which may also affect seizure threshold. Sedative drugs or CNS depressants should be avoided in patients with a history of sleep apnea. Antihistamines should be used with caution in patients with narrow-angle glaucoma, stenosing peptic ulcer, pyloroduodenal obstruction, and urinary bladder obstruction due to symptomatic prostatic hypertrophy and narrowing of the bladder neck.
Administration of promethazine has been associated with reported cholestatic jaundice.
Because phenylephrine is an acirenergic agent, it should be given with caution to patients with thyroid diseases, diabetes mellitus, and heart disease or those receiving tricyclic antidepressants. Men with symptomatic, benign prostatic hypertrophy can experience urinary retention when given oral or nasal decongestants.
Phenylephrine can cause a decrease in cardiac output, and extreme caution should be used when administering the drug parenterally or orally to patients with arteriosclerosis, to elderly individuals, and/ or to patients with initially poor cerebral or coronary circulation.
Phenylephrine should be used with caution in patients taking diet preparations, such as amphetamines or phenylpropanolamine, because synergistic adrenergic effects could result in serious hypertensive response and possible stroke.
Animal reproduction studies have not been conducted with the drug combination - promethazine and phenylephrine. It is not known whether this drug combination can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. Promethazine and phenylephrine should be given to a pregnant woman only if clearly needed.
Promethazine should be used cautiously in persons with cardiovascular disease or impairment of liver function. Phenylephrine should be used with caution in patients with cardiovascular disease, particularly hypertension.
Drug/ Laboratory Test Interactions
The following laboratory tests may be affected in patients who are receiving therapy with promethazine hydrochloride.
Glucose Tolerance Test: An increase in blood glucose has been reported in patients receiving promethazine.
Carcinogenesis, Mutagenesis, Impairment of Fertility
Promethazine: Long-term animal studies have not been performed to assess the carcinogenic potential of promethazine, nor are there other animal or human data concerning carcinogenicity, mutagenicity, or impairment of fertility with this drug. Promethazine was nonmutagenic in the Salmonella test system of Ames.
Phenylephrine: A study which followed the development of cancer in 143,574 patients over a four-year period indicated that in 11,981 patients who received phenylephrine (systemic or topical), there was no statistically significant association between the drug and cancer at any or all sites. Long- term animal studies have not been performed to assess the carcinogenic potential of phenylephrine, nor are there other animal or human data concerning mutagenicity.
A study of the effects of adrenergic drugs on ovum transport in rabbits indicated that treatment with phenylephrine did not alter incidence of pregnancy; the number of implantations was significantly reduced when high doses of the drug were used.
Pregnancy Category C:
Promethazine: Teratogenic effects have not been demonstrated in rat- feeding studies at doses of 6.25 and 12.5 mg/ kg of promethazine. These doses are 8.3 and 16.7 times the maximum recommended total daily dose of promethazine for a 50-kg subject. Specific studies to test the action of the drug on parturition, lactation, and development of the animal neonate were not done, but a general preliminary study in rats indicated no effect on these parameters. Although antihistamines, including promethazine, have been found to produce fetal mortality in rodents, the pharmacological effects of histamine in the rodent do not parallel those in man. There are no adequate and well-controlled studies of promethazine in pregnant women.
Phenylephrine: A study in rabbits indicated that continued moderate overexposure to phenylephrine (3 mg/ day) during the second half of pregnancy (22nd day of gestation to delivery) may contribute to perinatal wastage, prematurity, premature labor, and possibly fetal anomalies; when phenylephrine (3 mg/ day) was given to rabbits during the first half of pregnancy (3rd day after mating for seven days), a significant number gave birth to litters of low birth weight. Another study showed that phenylephrine was associated with anomalies of aortic arch and with ventricular septal defect in the chick embryo.
Promethazine and phenylephrine should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
Promethazine taken within two weeks of delivery may inhibit platelet aggregation in the newborn.
Labor and Delivery
Administration of phenylephrine to patients in late pregnancy or labor may cause fetal anoxia or bradycardia by increasing contractility of the uterus and decreasing uterine blood flow. (See also Pregnancy: Nonteratogenic Effects above).
It is not known whether promethazine or phenylephrine are excreted in human milk. Caution should be exercised when promethazine and phenylephrine is administered to a nursing woman.
This product should not be used in pediatric patients under 2 years of age because safety for such use has not been established.
Last reviewed on RxList: 12/8/2004
This monograph has been modified to include the generic and brand name in many instances.
Additional Phenergan Vc Information
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