Final answer:
The seventh barrier a drug must overcome to reach its target organ is the blood-brain barrier (BBB), which is particularly important for drugs intended to affect the central nervous system. Overcoming the BBB is a complex task that involves addressing the physiochemical properties of the drug to allow passage into the brain while still maintaining the drug's therapeutic effect.
Step-by-step explanation:
The seventh barrier a drug must pass to reach its target organ is the blood-brain barrier (BBB). This particular barrier is significant for drugs aimed at affecting the central nervous system. The BBB restricts what can cross from circulating blood into the CNS, thereby protecting the brain from potential toxins but simultaneously posing a challenge for drug delivery. Due to the BBB’s selective permeability, only certain essential nutrients such as glucose or amino acids can pass through easily. However, pharmaceutical companies strive to design drugs that can cross the BBB effectively and have the desired therapeutic effects on the nervous system.
Nutrient molecules move through the bloodstream and can cross the BBB, but for pharmaceuticals, overcoming this tightly regulated barrier while maintaining therapeutic activity requires careful consideration of the drug's physiochemical properties, such as decreasing polar surface area or modifying the compound to escape efflux by transporters like P-glycoprotein (PgP).