cally toward driving skills, however, led researchers to conclude that people should not operate a motor vehicle for 24 hours after an intramuscular injection of meperidine. Anyone with enlarged prostate, urinary difficulty, Addison's disease, or underactive thyroid should be wary about using the drug. An unusual case report tells of a patient developing Parkinson's disease symptoms from meperidine; more commonly such reports arise from contaminated illicit substances related to meperidine. Another illicit peril occurs when persons grind up and inject oral meperidine tablets; the talc in those tablets can block tiny blood vessels throughout the body and also cause those vessels to bleed—serious business in the eyes or brain. Illicit intramuscular injection of the drug over a period of years can cause muscle damage. Injecting into an artery can lead to gangrene.

Abuse factors. Meperidine tolerance occurs. Dependence may develop faster than with morphine, but meperidine's withdrawal syndrome may be briefer; symptoms also tend to be more limited than with morphine, perhaps just muscle spasms and unrest. When medical personnel are withdrawing addicts from heroin, meperidine has enough cross-tolerance to control withdrawal symptoms.

Drug interactions. Meperidine should be avoided by persons taking mon-oamine oxidase inhibitors (MAOIs, found in some antidepressants). That combination can be dangerous or even fatal. Alcohol and other depressants should be used carefully with meperidine in order to avoid cumulative overdose. Amphetamines boost pain relief provided by meperidine. The HIV/AIDS (human immunodeficiency virus/acquired immunodeficiency syndrome) drug ri-tonavir is believed to lengthen a meperidine dose, meaning that too much of the opioid could build up in a person who is on a normal meperidine medication schedule. Experiments with the ritonavir-meperidine combination, however, have shown the risk to be less than expected. Air pressure affects a meperidine dose; the higher the altitude, the longer a dose lasts. Phenobarbital, the antipsychotic drug chlorpromazine (Thorazine), and the heartburn-ulcer medicine cimetidine interfere with meperidine. Brewer's yeast is said to produce a bad reaction with meperidine, such as raising blood pressure so high that a medical emergency occurs.

Cancer. One analysis of medical records in Great Britain found a statistical association between receiving meperidine at birth and subsequent development of childhood cancer. A statistical association, however, simply provides guidance for future research and does not demonstrate cause and effect. Analysis of a different and smaller set of records found no association.

Pregnancy. An experiment on pregnant mice produced no birth defects definitely attributable to the drug, but meperidine has caused congenital malformations in hamsters. Medical records from a few dozen women who used meperidine during pregnancy revealed no congenital malformations attributable to the substance. If a pregnant woman takes the drug, it will pass into the fetus, where the substance tends to build up. Difficulties have not been seen in infants from such women unless the drug has been administered during childbirth. In those latter cases a respiratory emergency can occur in infants who acquired the drug during birth, and less serious newborn behavioral abnormalities are common. Rhesus monkeys who received fetal exposure at time of birth were tested for perception and thinking ability. On one test they did worse than monkeys who had no meperidine exposure, and on another test they did better. In humans, meperidine enters the milk of nursing mothers, but the level is low enough to be considered safe for the infant.

Additional information. An injectable format of the drug called Mepergan is intended for deep intramuscular administration. Intravenous injection can diminish breathing and stop the heart. Subcutaneous administration can cause sores at the injection site and even kill patches of skin. The product ingredients include sodium metabisulfite, to which some persons have a dangerous allergy. Mepergan is to be used cautiously by asthmatics.

Additional scientific information may be found in:

Clark, R.F., E.M. Wei, and P.O. Anderson. "Meperidine: Therapeutic Use and Toxicity."

The Journal of Emergency Medicine 13 (1995): 797-802. Henderson, M.E. "Central Nervous System Effects of Meperidine." Hospital Pharmacy 20 (1985): 934.

Korttila, K., and M. Linnoila. "Psychomotor Skills Related to Driving after Intramuscular Administration of Diazepam and Meperidine." Anesthesiology 42 (1975): 685-91.

Miller, R.R., and H. Jick. "Clinical Effects of Meperidine in Hospitalized Medical Patients." Journal of Clinical Pharmacology 18 (1978): 180-89. Zacny, J.P., et al. "Subjective, Behavioral and Physiological Responses to Intravenous Meperidine in Healthy Volunteers." Psychopharmacology 111 (1993): 306-14.

Continue reading here: Pregnancy Category D

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