ABSTRACT
Adjuvant drugs that can delay tolerance to morphine analgesia may lead to improved management of pain in chronic disease such as cancer. This study was aimed to investigate effect of buspirone, as a partial agonist of 5-HT1A receptor, on tolerance induced to morphine analgesic effect in animals with skin cancer. Study was carried on female Swiss albino mice. For skin tumorigensis, mice were treated with single dose of 7,12-dimethylbenz(a)anthracene (DMBA) and promoted by multiple dose of croton oil. Tolerance to morphine analgesia was induced by daily subcutaneous (sc) injection of morphine (5mg/kg for 30 days) and assayed by using the hot plate method. Results obtained from this study showed that pain threshold in mice with skin cancer were significantly lower. Tolerance to analgesic effect of morphine (5 mg/kg, sc) was appeared at day 15, whereas, in normal and skin tumor bearing mice co-treated daily with morphine (5 mg/kg, sc) and three different intraperitoneal (ip) doses of buspirone (5, 7.5 and 10 mg/kg) tolerance was observed at days 25 and 30. In conclusion our data indicate that concurrent use of morphine with buspirone may produce good cancer pain control and attenuate development of tolerance.