Our group recently demonstrated in a rat model that pretreatment with morphine facilitates doxorubicin delivery to the brain in the absence of signs of increased acute systemic toxicity. Morphine and other drugs such as dexamethasone or ondansetron seem to inhibit MDR proteins localized on blood-brain barrier, neurons and glial cells increasing the access of doxorubicin to the brain by efflux transporters competition. We explored the feasibility of active modification of the blood-brain barrier protection, by using morphine dexamethasone or ondansetron pretreatment, to allow doxorubicin accumulation into the brain in a rodent model. Rats were pretreated with morphine (10 mg/kg, i.p.), dexamethasone (2 mg/kg, i.p.) or ondansetron (2 mg/kg, i.p.) before injection of doxorubicin (12 mg/kg, i.p.). Quantitative analysis of doxorubicin was performed by mass spectrometry. Acute hearth and kidney damage was analyzed by measuring doxorubicin accumulation, LDH activity and malondialdehyde plasma levels. The concentration of doxorubicin was significantly higher in all brain areas of rats pretreated with morphine (P < 0.001) or ondansetron (P < 0.05) than in control tissues. The concentration of doxorubicin was significantly higher in cerebral hemispheres and brainstem (P < 0.05) but not in cerebellum of rats pretreated with dexamethasone than in control tissues. Pretreatment with any of these drugs did not increase LDH activity or lipid peroxidation compared to controls. Our data suggest that morphine, dexamethasone or ondansetron pretreatment is able to allow doxorubicin penetration inside the brain by modulating the BBB. This effect is not associated with acute cardiac or renal toxicity. This finding might provide the rationale for clinical applications in the treatment of refractory brain tumors and pave the way to novel applications of active but currently inapplicable chemotherapeutic drugs.