 5. Prior and or concomitant treatment with drugs known to induce or inhibit cytochrome P450 3A4: phenytoin, carbamazepine, barbiturates, rifampicin, imidazole antifungals such as ketoconazole, fluconazole, itraconazole, metronidazole, omeprazole and ritonavir. Patients who are taking gastric acid-lowering agents such as H2 antagonist or antacids will be evaluated regarding the need to continue with these medications. If discontinuation of these medications is medically contraindicated, the patient will be excluded as these agents are known to lower the solubility of sorafenib and hence may limit their efficacy. 