Page 145 - Interactive Theoritical Notes of Bioharmaceutics and pharamcokinetics.docx compressed

PharmD clinical pharmacy program Level 3, Semester 2 Biopharmaceutics & Pharmacokinetics (PT608(

 Ex 2: If a patient who is taking tolbutamide (which is normally 95% bound)

is given a second drug like sulfonamide (which has higher affinity for the

plasma protein).
 So sulfonamide will now displace tolbutamide. This will lead to a rapid

increase in concentration of free drug (active drug) in the plasma (Now
100% free).

2. In hypoalbuminemia, binding may be reduced and high concentrations of free drug
may be attained e.g. Phenytoin and Furosemide.

3. Drugs that are highly plasma protein bound may have:
• a longer duration of action

• and hence longer half-life because the drugs in bound form cannot be metabolized

or excreted.

• Thus, they require less frequent dosing.

Distribution to the Brain & Blood–Brain Barrier

✓ Few drugs exhibit good penetration of the central nervous system.

✓ The anatomical structure of the capillary network in the brain creates a significant

barrier to the passage of many drugs and is commonly referred to as the blood-brain

barrier.

‒ Endothelial cells of the brain capillary membrane are very closely packed with

tight junctions.

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