As noted, the manufacturing process is entirely different in biologic drugs than in traditional drugs. Most drugs are chemically synthesized, and their structure is known whereas biologics are much more complex mixtures that are not easily characterized or even identified. Biologics are extremely vulnerable to heat and are much more likely to be contaminated by microbials than traditional chemically synthesized drugs. Traditional drugs like penicillin and aspirin, or even a statin like Lipitor, are small molecule drugs. They have dozens of atoms and are made in bulk in a chemistry lab. Biologics contain large proteins with hundreds of thousands of atoms and are made inside living cells. Because DNA in those living cells is altered, biologics are difficult to manufacture. After a specific number of years of exclusivity, traditional drugs must yield the way to generics which drive down spending on a specific class of drugs. There are no generic versions of biologics, allowing drug companies to continue to bring in profits years after losing patent protection because there is virtually no incentive for lowering the cost. This at least partially explains why a single prescription for a biologic drug that treats rheumatoid arthritis can cost as much as $3,000.