224 Levorphanol
Abuse factors.Tolerance and dependence can develop. When dependent
rats were given a choice between water and a sweetened solution of levor-
phanol, they preferred the drug solution, but when the choice was between
the same drug solution and sweetened water they preferred the sweet water.
When experimenters offered another set of dependent rats straight water and
unsweetened levorphanol solution, those animals preferred straight water.
Such results imply that the drug has a low addiction potential, but an impli-
cation is not a fact. Also, animals do not always react to a substance in the
same way humans do.
In humans the drug can improve spirits and even produce euphoria, and
some users say they became addicted. A rat experiment demonstrated partial
cross-tolerance withalcohol, suggesting that the two drugs appeal to the same
kinds of people.
Some employer drug testing cannot distinguish between levorphanol and
dextrorphan.
Drug interactions.Simultaneous use of levorphanol with alcohol or other
depressants increases the possibility of cumulative overdose. In mice the an-
esthetic lidocaine boosts levorphanol’s pain relief actions. Antihistamines and
monoamine oxidase inhibitors (MAOIs, found in some antidepressants and
other medicine) should be avoided when taking levorphanol. Levorphanol can
also be dangerous when taken withalprazolam,diazepam,flurazepam,lor-
azepam,phenobarbital,ortemazepam.
Cancer.Levorphanol’s potential for causing cancer is unknown.
Pregnancy.Mice experiments with the drug have caused pregnancy failures
and birth defects. Offspring from male mice exposed to the drug weighed less
than normal, were slower to mature, and had abnormal motions in water. The
potential for similar outcomes with humans is unknown. Rabbit experiments
show the drug passing into the fetus of a pregnant animal, reducing fetal
respiration. Milk from a nursing mother who uses levorphanol is assumed to
contain enough of the drug to cause unwanted effects in a nursing infant, but
that possibility may be minimized by waiting long enough after a dose before
nursing (the delay can allow much of the drug to wash out of the woman’s
body).
Additional scientific information may be found in:Chernin, T. “Use of Opioids for Chronic Nonmalignant Pain.”Pharmacy Times65 (1999):
18–20, 23–25.
Coniam, S.W. “Withdrawal of Levorphanol.”Anaesthesia46 (1991): 518.
Friedler, G. “Effects of Limited Paternal Exposure to Xenobiotic Agents on the Devel-
opment of Progeny.”Neurobehavioral Toxicology and Teratology7 (1985): 739–43.
Fuchs, V., and H. Coper. “Development of Dependence on Levorphanol in Rats by
Oral Intake of the Drug—The Influence of Taste on Drinking Behaviour in Rats
Physically Dependent on Levorphanol.”Drug and Alcohol Dependence6 (1980):
373–81.
Knych, E.T. “Cross-Tolerance between Ethanol and Levorphanol with Respect to Stim-
ulation of Plasma Corticosterone.”Life Sciences31 (1982): 527–32.