Subcutaneous administration is used because many protein drugs are destroyed in the gastrointestinal tract when taken orally.
Oral drug delivery is the most common mode of convenient and inexpensive drug delivery. The main site of drug absorption is usually the small intestine, and drug bioavailability is affected by the amount of drug absorbed across the intestinal epithelium.
Oral administration is the most common form of drug administration due to the advantages of drug administration by the oral route such as convenience patient preference cost-effectiveness and ease of large-scale manufacturing of oral dosage forms. The main site of drug absorption is usually the small intestine.
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