Sublingual and rectal drugs – do not pass through liver first (no first-pass metabolism)
Skin absorption – based on lipid solubility through the epidermis
CSF absorption – restricted to nonionized, lipid-soluble drugs
Albumin – largely responsible for binding drugs (PCNs and warfarin 90% bound)
Sulfonamides – will displace unconjugated bilirubin from albumin in newborns (avoid in newborns)
Tetracycline and heavy metals – stored in bone
0 order kinetics – constant amount of drug is eliminated regardless of dose
1st order kinetics – drug eliminated proportional to dose
Takes 5 half-lives for a drug to reach steady state
Volume of distribution = amount of drug in the body divided by amount of drug in plasma or blood
• Drugs with a high volume of distribution have higher concentrations in the extravascular compartment (eg fat tissue) compared with intravascular concentrations
Bioavailability – fraction of unchanged drug reaching the systemic circulation
• Assumed to be 100% for intravenous drugs, less for other routes (ie oral)
ED50 – drug level at which desired effect occurs in 50% of patients
LD50 – drug level at which death occurs in 50% of patients
Hyperactive – effect at an unusually low dose
Tachyphylaxis – tolerance after only a few doses
Potency – dose required for effect
Efficacy – ability to achieve result without untoward effect
Drug metabolism (hepatocyte smooth endoplasmic reticulum, P-450 system)
• Phase I – demethylation, oxidation, reduction, hydrolysis reactions (mixed function oxidases, requires NADPH/oxygen)
• Phase II – glucuronic acid (#1) and sulfates attached (forms water-soluble metabolite
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