Pharmaceutical companies bringing a new prescription drug to market typically patent the medication, giving the developer exclusive rights to sell the drug for a set period of time. After the patent expires, other drug manufacturers are permitted to produce and sell a generic version of the drug. The U.S. Food and Drug Administration must approve a generic prescription drug before it can be sold, ensuring that the medication is of the same strength, purity, quality and stability as the brand-name drug.
Hydrocodone/Acetaminophen
Hydrocodone/acetaminophen was the top-selling generic prescription drug in the United States in 2009, with more than 120 million prescriptions filled, according to the pharmaceutical newsmagazine Drug Topics. Brand names for hydrocodone/acetaminophen include Lorcet, Lortab, Vicodin, Dolorex Forte, Liquicet, Hycet, Zamicet, Stagesic, Polygesic, Zydone, Maxidone and Xodol. Hydrocone is a narcotic pain reliever and acetaminophen is a nonnarcotic pain reliever. Hydrocodone/acetaminophen is used for short-term relief of moderate to moderately severe pain.
Lisinopril
Lisinopril is an angiotensin-converting enzyme inhibitor, also known as an ACE inhibitor. This medication is used to treat high blood pressure and heart failure, according to the Mayo Clinic. Lisinopril is the generic version of the brand name drugs Prinivil and Zestril. More than 74 million prescriptions were filled for lisinopril in the United States in 2009, according to Drug Topics.
Simvastatin
Simvastatin is the generic substitute for the brand name drug Zocor, which is a cholesterol-lowering statin medication. By reducing total cholesterol and LDL cholesterol, simvastatin diminishes the risk for atherosclerotic heart disease and stroke. Drug Topics reports that nearly 73 million generic simavastatin prescriptions were filled in the United States in 2009.
Levothyroxine
Levothyroxine is a man-made thyroid hormone used for the treatment of hypothyroidism, also known as underactive thyroid disease. Brand names of levothyroxine include Levothroid, Synthroid and Levoxyl. Pharmacies in the United States filled more than 63 million prescriptions for generic levothyroxine in 2009, according to Drug Topics.
Amoxicillin
Amoxicillin is an aminopenicillin used for the treatment of a variety of bacterial infections, including those of the skin, ears, throat, bladder, kidneys and lungs. Brand names for amoxicillin include Moxatag, Trimox and Amoxil. Amoxicillin ranked fifth on the Drug Topics 2009 top-selling prescription generic drugs list, with more than 51 million prescriptions filled.
Azithromycin
Azithromycin is the generic substitute for the brand name drugs Zmax and Zithromax. This medication is a macrolide antibiotic used to treat a range of bacterial infections, including those caused by pneumococcus, group A streptococcus, group B streptococcus, Haemophilus influenzae, Chlamydia trachomatis and pneumoniae, Mycoplasma pneumoniae and Staphylococcus aureus, according to the manufacturer's FDA-approved prescribing information. Pharmacists filled nearly 50 million prescriptions for generic azithromycin in the United States in 2009, according to Drug Topics.
Hydrochlorothiazide
Hydrochlorothiazide is a diuretic medication that increases the urinary excretion of sodium and water. This medication is used for the treatment of high blood pressure. Brand names of hydrochlorothiazide include Microzide, HydroDIURIL, Oretic, Aquazide H and Esidrix. Drug Topics reports that pharmacies in the United States filled more than 46 million prescriptions for generic hydrochlorothiazide in 2009.
