Influence of plasma-protein binding on analgesic effect of methadone in rats with spontaneous withdrawal
Autor: | M J Garrido, R Calvo, E Gomez, R Jiminez |
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Rok vydání: | 1996 |
Předmět: |
Male
Narcotics media_common.quotation_subject Pharmaceutical Science Alpha (ethology) Pharmacology Rats Sprague-Dawley Pharmacokinetics Oral administration Blood plasma medicine Animals media_common Pain Measurement Morphine business.industry Orosomucoid Abstinence Rats Substance Withdrawal Syndrome Analgesics Opioid Abstinence Syndrome business Methadone medicine.drug Protein Binding |
Zdroj: | ResearcherID |
ISSN: | 0022-3573 |
Popis: | The effect of spontaneous withdrawal on α1-acid glycoprotein (AAG) levels and methadone protein binding has been studied in the rat. Animals were made physically dependent on morphine by providing morphine HCl in drinking water for three weeks. The natural opiate withdrawal was induced in rats by substituting the morphine solution with drinking water. The severity of the abstinence syndrome was assessed at various time intervals. After 12 h of withdrawal, the animals showing abstinence signs and low morphine levels were injected with intravenous methadone (0.35 mg kg−1) and the analgesic effect was measured by the tail-flick method and compared with animals receiving water. The oral administration of morphine produced an increase in AAG levels from 0.64 ± 005 g L−1 in control animals to 1.47 ± 0.92 g L−1 in experimental animals at the point of withdrawal and 1.21 ± 009 g L−1 24 h after withdrawal. The percentage of methadone unbound was significantly lower in morphine-treated than in control animals. A significant correlation between AAG levels and percentage of methadone bound was observed. A parallel analgesic effect after intravenous methadone, as measured by AUC in the tail-flick test, was less in abstinence animals than in control (287.6 ± 24.8 compared with 401.0 ± 37.06 s min). We suggest that in the withdrawal syndrome an adjustment of methadone dose may be necessary because of changes in protein binding. |
Databáze: | OpenAIRE |
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