Equations Flashcards
Dosing rate
Dosing rate = CL x CSS
Clearance
CL = rate of elimination/ concentration
Systemic clearance
CL = CLrenal + CLhepatic + CLother
extraction ratio
CL = Q[(CA – CV)/ CA] = Q x E
where E is referred to as the extraction ratio.
where Q is the blood flow to the organ.
Vd = Amount of drug in body / C (Blood concentration )
elimination half life
elimination constant
CL / Vd = (ml/min) / ml = 1/min = elimination constant (Ke)
Ke= 0.7/ t 1
clearance in a multicompartment model
CL = dose / AUC
bioavailability (F)
F x Dosing rate = CL x Css
dosing rate
dose / T
steady state concentration
dose
* Css = (F x Dose) / (CL x T)
Dose = (Css x CL x T) / CL x T F
IV infusion concentration steady state
Css = infusion rate / total body clearance
Loading dose
Loading dose (LD) = (Css x Vd) / F
zero order elimination kinetics
LD = (Vd x Css)/F
Css = (Km x DR)/(Vm- DR)
DR = (Css x (Vm – DR))/ Km
- Km is the dose that produces 50% of the maximal elimination rate
- Vm is the maximum rate of the process
HH equation for weak base
pH = pKa + log [B]/[BH+]
[Unprotonated]/[Protonated]
nonionized / ionized
Michaelis-Menton kinetics.
V = Vmax[S]/(Km+[S])
If the drug is filtered but not secreted or reabsorbed the renal clearance will be about 120 ml/min in normal subjects
(CLr = GFR)
If the renal clearance is less than 120 ml/min then drug show net reabsorption
(CLr < GFR)
If the renal clearance is greater than 120 ml/min then tubular secretion must be contributing to the elimination process.
(CLr > GFR)
Rising phase of effect
Abs > Met + Exc
Falling phase of drug results
Met + Exc > Abs
Therapeutic Index
MTC/MEC
- MTC (minimal toxic concentration)
- MEC (minimal effective concentration)
Fick’s law
Diffusion rate = -DAK (C out-C in) / X
- The diffusion coefficient (D): inversely related to the size of the drug.
- partition coefficient (K): reflects the lipid solubility of the drug (oil:H20)
- Surface area (A): larger surface area promotes diffusion.
- Membrane thickness (X): The thinner the membrane the quicker the diffusion.
- Concentration gradient (C out-C in): larger gradients promote drug diffusion.
- Ionization (affects K): is a major determinant of the ability of a drug to cross membranes. It is dictated by the environment (pH) of the bodily fluid in which the drug is dissolved in.
weak acid HH
pH = pKa + log [A-] / [HA]
unprotonated / protonated
ionized / non-ionized
Volume of Distribution
Vd = amount of drug administered / plasma drug concentration