DRUG INTERACTIONS: Methadone when taken with drugs that slow brain function, such as alcohol and barbiturates (phenobarbital), can increase the effects of these drugs. Since methadone causes constipation, taking antidiarrheal medications such as diphenoxylate and atropine (Lomotil) and loperamide (Imodium) along with methadone can result in severe constipation. Drugs that block narcotic (opioid) receptors including pentazocine (Talwin), nalbuphine (Nubain), naloxone (Narcan), butorphanol (Stadol) and buprenorphine (Subutex) can lead to withdrawal symptoms.
Rifampin (Rifadin), barbiturates, carbamazepine (Tegretol), phenytoin (Dilantin), primidone and St. John's wort preparations can increase the liver's ability to metabolize (eliminate) methadone and reduce its blood concentration which could result in withdrawal side effects, while drugs such as erythromycin (E-Mycin, Eryc, Ery-Tab), clarithromycin (Biaxin, Biaxin XL), ketoconazole (Nizoral), and itraconazole (Sporanox) can decrease the liver's ability to metabolize methadone thereby increasing the side effects of this drug.
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