General pharmacology

# Pharmacology terms

Dr. Alex Bianco

Use this section as a resource for interpreting articles and advanced materials.

# Definitions

Pharmacokinetics =What the body does to the drug. E.g. Metabolism, elimination
Pharmacodynamics =What the drug does to the body. E.g. Desired effects + adverse effects (AE)
Dosage =Amount of drug administered per unit body weight. Mg/kg, mg/lb, IU/kg
Dose =The amount of drug the animal receives. Total mg/tablets/mL
Initial concentration (C0)= [Drug] at first time point after administration (t=0)
Maximum concentration (Cmax) = The highest [drug] obtained after a single dose of drug
Concentration at steady state (Css) =Applies to repeated drug administration or CRI; the [drug] where drug administration and clearance equilibrate
CRI -constant rate infusion (an iv drip)
Terminal half life (t1/2) = The amount of time it takes to decrease the plasma [drug] by 50%
t1/2 =  (0.693 ∗Vd)/Cl = 0.693/k  where k = the elimination rate constant (slope of the elimination curve)

Clearance (Cl) = Rate at which drugs are eliminated from the body (urine or feces). Cl is inversely proportional to half-life

Cl = (0.693 ∗Vd)/(t1/2)
Volume of distribution (Vd) =Amount of drug in body relative to plasma volume
↑Vdss= more drug NOT IN plasma
↓Vdss= more drug IN plasma
Vd = (Dose (mg))/C0    Can only calculate from iv parameters
Time to maximum concentration (tmax) = How long it takes before reaching Cmax. Depends on rate of absorption vs. clearance
tmax always = 0 when given IV : highest drug concentration is immediately after administration
Bioavailability (F%)  =Percentage of drug administered that is ultimately absorbed in to bloodstream.
Calculated by comparing to same dose given IV (100% bioavailable). Measured by comparing area under the curve  using trapezoidal rule (fancy math)

C0 = Cmax
Cmax after IV dosing will ALWAYS be higher than other route of administration
A drug given IV  will always have a shorter withdrawal time than when given by other routes
Other routes
Once drug enters blood, it should behave as with IV dosing
Rate of absorption (ka) = the time it takes to reach the blood
Bioavailability is never 100%. Drug is simultaneously being cleared/absorbed
PO is generally a lower peak (Cmax) and a longer elimination
Some drug is never absorbed when given po.

# Parameters of interest

Time dependent antibiotics – we care about time above MIC
Concentration dependent antibiotics – we care about Cmax: MIC ratio and AUC: MIC ratio

# Other resources

Pharmacology chapter, Dairy Production Medicine ebook
Swine drugs, Dr. Z’s antibiotic ebook