- Oral concentrate: 10 mg/mL;
- Oral solution: 5 and 10 mg per teaspoon;
- Oral tablet: 5 mg and 10 mg;
- Soluble tablet, 40mg;
- Solution for Injection 5 and 10 mg per teaspoon: 10 mg/mL.
- Methadone when taken with drugs that slow brain function, such as alcohol and barbiturates (phenobarbital), can increase the effects of these drugs.
- Because methadone causes constipation, taking antidiarrheal medications such as diphenoxylate (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.
- Anti-retroviral agents including abacavir (Ziagen), amprenavir (Agenerase), efavirenz (Sustiva), nelfinavir (Viracept), Nevirapine (Viramune, Viramune XR), Ritonavir (Norvir), and lopinavir/ ritonavir (Kaletra) have been shown to decreased the blood levels of methadone making it necessary to adjust the dose of methadone to prevent narcotic withdrawal effects.
- Some drugs that slow the heart rate for example, dofetilide (Tikosyn), procainamide (Pronestyl, Procan-SR), quinidine, and sotalol (Betapace), as well as laxatives and diuretics that cause low magnesium or low potassium in the body, for example, furosemide (Lasix), can cause rare serious and fatal irregular heartbeats.
PREGNANCY AND BREASTFEEDING SAFETY: Safety during pregnancy has not been established. Methadone has been shown to cross the placenta, and it is found in cord blood, amniotic fluid and in the newborn urine. Children born to mothers who were taking methadone for a prolonged period may exhibit respiratory depression or withdrawal symptoms. Methadone enters breast milk, and this can cause sedation and respiratory depression in the breast feeding infant. The benefit to the mother of taking methadone while breast feeding should be weighed against the risks to the infant.
STORAGE: Oral methadone and injection should be stored at room temperature between 15 C and 30 C (59 F and 86 F). Methadone injection also should be protected from light.
- The initial dose of oral methadone in patients who require continuous pain control throughout the day can range from 2.5 to 10 mg given every 8 to 12 hours.
- Those who are seriously ill may need to be started at an oral dose of 10 to 40 mg given every 6 to 12 hours.
- The initial total daily dose for detoxification usually is higher, and this can range from 20 to 120 mg daily.
- The usual dose for methadone solution for injection when treating moderate to severe pain in patients who require continuous pain control is 2.5 to 10 mg given as intravenous (I.V.), subcutaneous (SubQ) or intramuscular (I.M.) injection every 8-12 hours.
- The conversion ratio from oral methadone to methadone given as an injection (I.V., SubQ) or I.M.) is 2:1. The total daily amount of methadone that a person is prescribed is not fixed, and it will depend on many factors including the severity of the pain, prior use of methadone, medications that are being taken concomitantly, the response to treatment and other factors that may be specific to a person.
- Therefore, each person has to be monitored carefully while receiving methadone. When stopping therapy, the dose of methadone should be gradually reduced in order to avoid withdrawal symptoms.
DRUG CLASS AND MECHANISM: Methadone is a strong, synthetic (man-made) narcotic that acts on the central nervous system (brain) in a manner similar to other narcotics. It is used in the management of narcotic addiction and for pain control. Methadone was first approved by the Food and Drug Administration on August 13, 1947.
REFERENCE: FDA Prescribing Information.
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