DRUG INTERACTIONS: This product should not be used with the following medications because very serious, possibly fatal, interactions may occur: cisapride, pimozide, astemizole, terfenadine. If you are currently using any of these medications, tell your doctor or pharmacist before starting this product. Before using this medication, tell your doctor of all nonprescription and prescription medication you may use, especially of: cyclosporine, tacrolimus, certain protease inhibitors (e.g., lopinavir, ritonavir), theophylline, warfarin, digoxin and other heart medications, zidovudine, certain "statin" drugs for high cholesterol (e.g., atorvastatin, lovastatin, simvastatin), drugs for blood pressure (e.g., propranolol), drugs for diabetes (e.g., glyburide), bromocriptine, sildenafil, rifabutin, methylprednisolone, cilostazol, tolterodine, anti-seizure medications (e.g., carbamazepine, phenytoin, valproate), drugs for migraines (e.g., dihydroergotamine, ergotamine), benzodiazepines (e.g., alprazolam, triazolam), barbiturates (e.g., hexobarbital), certain narcotic pain relievers (e.g., alfentanil). Other drugs besides clarithromycin which may affect the heart rhythm (QTc prolongation in the EKG) include dofetilide, disopyramide, quinidine, droperidol, sotalol, procainamide, and sparfloxacin among others. QTc prolongation can infrequently result in serious, rarely fatal, irregular heartbeats. Consult your doctor or pharmacist for details. Ask for instructions about whether you need to stop any other QTc-prolonging drugs you may be using in order to minimize the risk of this effect. Lansoprazole can decrease the effectiveness of certain drugs which require stomach acid in order to be absorbed. Before using this medication, consult your doctor or pharmacist on how to manage such a potential interaction if you are taking the following drugs: ampicillin, azole antifungals (e.g., ketoconazole, itraconazole), iron supplements. This drug may interfere with the effectiveness of birth control pills. Discuss using other methods of birth control with your doctor. Do not start or stop any medicine without doctor or pharmacist approval.