PSYC62H3 Chapter Notes - Chapter 4: Haloperidol, Endothelium, Bioavailability
Chapter 4: Properties of Drugs
Pharmacokinetic Properties and Drug Passage Through the Body
→ Absorption (1)
• Passage of drug from site of administration to the bloodstream
• Drug must pass through different membranes
o Which membrane it needs to pass through depends on drug’s route of
administration
• For most drugs, absorption relies on its ability to passively diffuse through membranes
o Diffusion works best for non-ionized mol with neutral pH (7)
• Time needed for elimination will vary from drug to drug
• Important determinant for how much drug reaches the bloodstream and length of time
needed for drug absorption
• pKa → strength of an acid
o Lower the pKa value, stronger the acid
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• Drugs pKa and local pH impact drug’s ability to form non-ionized mol
o closer a pKa value is to the pH, the more non-ionized molecules are formed and
penetrate through cell membranes
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• Surface area of tissue matters as well to how much is absorbed
• Many therapeutic drugs administered orally
o Passes through stomach to intestines
• Liberation: process of drug mol separating from pill or solution it was delivered in
o Most drug absorption occurs in small intestine
• Inhalation
o Drugs enter circulatory system primarily through lungs and to some degree the
membranes in the nose, mouth, and throat
o Therapeutically, inhaling brings drug directly to area needing treatment
o Absorb more quickly than orally administered drugs
• Injection
o Intravenous injection: drug delivery into vein through hypodermic needle
o Rapid drug effects and avoids absorption limitations
▪ Full absorption
→ Distribution (2)
• Passage of drug from bloodstream to sites in the body
• Affects a drug’s bioavailability: ability of a drug to reach a site of action
o For psychoactive drugs depends on drug reaching the CNS
o To enter brain, drugs must possess sufficient properties to permeate BBB
• Blood-brain barrier → prevents substances in blood from entering brain
o Surrounds capillaries and other small vessels
o Astrocytes form the BB by forcing epithelial cells in capillaries and vessels to fit
together tightly
▪ ur.dtjunctions prevent pathogens, hormones, etc from entering the brain
o Nutrients and other important mol pass through either passive diffusion or active
transport
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