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All about Bio pharmacology quiz
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  Ya rabb Salima Ednan Copyright protected Page 1 BBB IIIOOOPPPHHHAAARRRMMMAAACCCEEEUUUTTTIIICCCSSS AAANNNDDD  PPP HHHAAARRRMMMAAACCCOOOKKKIIINNNEEETTTIIICCCSSS   B IOAVAILABILITY :   it’s the relative amount of the drug that is biologically available in blood compared to the amount of the drug in the dosage form administered. The primary proof of a drug’s bioavailability is the pro duction of its pharmacological (clinical) effect, and in order to do so, the drug must always achieve adequate concentration at its site of action. e.g. Antibiotics should reach its MIC to produce its effect rather than its blood conc. D RUG A BSORPTION :  the transfer of most drugs across biological membranes occurs by passive diffusion from a region of high conc. to a region of low conc. i.e. with a conc. gradient. With no consumption of energy since the membrane is semi-permeable composed of lipids and proteins.   P  ASSIVE T RANSPORT P ROCESS :  it’s the transfer of the drug from an area of high conc. to an area of low conc. till equilibrium is reached (according to conc. gradient). N.B. The greater the conc. difference, the greater is the transfer rate.    A CTIVE T RANSPORT P ROCESS :  it’s also called carrier mediated transfer. The carrier such as enzymes in the membrane aids in transporting moles of drug across the membrane. It’s a continuous process that can work against the conc. gradient, and continue until the entire drug has been transported, with the consumption of energy, and equilibrium doesn’t occur.  Certain chemicals like Poisons can reduce active transport through inactivation of carriers. The active transport process is structure specific because carriers are often very specific in respect to the drug they will transfer, and because of the chemical specificity and the limited capacity of the carrier, this process may become saturated. When this occurs, the active transport rate becomes a constant value until the drug conc. is reduced  –  i.e. Z ERO O RDER K INETIC . N.B. The carrier may be selective for certain types of drugs and at high conc. of the drug, the carrier system may be saturated. R ATES AND O RDERS OF R EACTIONS : Rate of chemical reaction = velocity with which chemical reaction occurs Order way conc. of drug influence rate of chemical reaction. 1. Z  ERO O  RDER R  EACTION  :   it is the rate of elimination or absorption of drug with respect to the time is constant. N.B. it doesn’t depend on drug conc.  i.e.  –   dc = K dt 2. First Order Reaction:    it’s the rate of elimination or absorption with respect to time and depends on the conc. of the drug. Most drugs obey First Order Kinetic Reaction.  –   dc = Kc where K = rate constant  –  C = conc of drug in plasma dt dc/dt = rate of change of drug conc. with respect to time.  Ya rabb Salima Ednan Copyright protected Page 2 Loading Dose: it’s the I.V. infusion dose and it’s used to give an initial I.V. injection of drug that produces a steady state conc. (CSS) as rapidly as possible. N.B. the volume of distribution (Vd) of a drug = amount of drug in the body    Amount of drug in blood Vd = AB Cp Thus knowing “Vd” of a drug can permit calculation of total amount in the body.   AB = Vd X Cp Loading dose = (Vd)(Cp) (S)(F) Where: Vd = volume of distribution Cp = plasma conc. S = portion of the salt form that in active drug (e.g. aminophylline is 80  –  85%, thiophylline S = 0.8085) F = fraction of dose absorbed. N.B. CSS = time needed to reach maximum drug conc. in blood in a constant rate IV infusion, and it’s indepen dent on rate of the infusion but is dependent on t ½. G ASTRIC E MPTYING :   It’s an exponential process, with a normal half time between 50 –  60 minutes.    It’s slowed by vigorous exercise, pain, hot meals & emotional stress.   Accelerated by hunger, mild exercise, cold meals, dilute solutions & laying on the right side. T HE R ATE OF M ETABOLISM OR E LIMINATION OF D RUG that follows Zero Order Kinetics is constant and expressed by: -   dc = K dt Where: dc/dt = the rate of change of drug conc. in the blood with respect of time. K = zero order rate constant of elimination. N.B. Most drugs are metabolized or eliminated from the body by First Order Kinetics, where the rate of metabolism or elimination changes with time and is dependent only on the conc. of the drug in the blood. Thus: -   dc = KC dt Where: C = conc. of the drug in plasma.  Ya rabb Salima Ednan Copyright protected Page 3 H ALF L IFE (t ½): it’s the time required for a concentration of a drug to be decreased to one half (50%) t ½ = 0.693 K N.B. In patients with renal impairment, the half-life of drugs excreted unchanged by the kidney is increased. In newborn and infants the half-life also is increasing due to their incomplete enzyme system. U RINARY T RACT A NTIMICROBIAL to be effective they should be: 1. Highly active against gram  – ve bacilli. 2. Low level of protein binding. 3. Short biological half-life (i.e. to produce rapid conc. in the urine). 4. It must not have high volume of distribution in the body (only distributes itself in U.T.). P RO -D RUG :   it’s a compound that liberates active drug in the body.  e.g. Geocillin (pro-drug) is more stable and will not be inactivated in stomach rather than Geopen (the active form). H ALF -L IFE (t ½) is independent on the initial drug conc. but it’s constant for each drug.  It increases in case of renal impairment.   Curve I  represents blood conc. level of a drug administered by IV injection.   Curve III  represents a drug conc. administered by IV infusion.   Curve II  represents absorption from either oral or IM injection. N.B.   In IV infusion, the resulting steady state plateau is directly proportional to the infusion rate.   The time in which the maximum drug blood level is obtained is independent on infusion rate but dependent on the biological t ½. I F AN ORALLY ADMINISTERED DRUG APPEARS IN FECES THIS MIGHT BE DUE TO : 1. Incomplete absorption. 2. The drug may be excreted through the bile. U RINARY E XCRETION D ATA :   For many drugs, bioavailability can be evaluated using Urinary Excretion Data. This is based on the assumption that a drug must first be absorbed into the systemic circulation before it can appear in the urine (as kidney is the major route of drug elimination for polar, water soluble, low molecular weight drugs). I II III  Ya rabb Salima Ednan Copyright protected Page 4 T HE R ATE OF C HANGE OF D RUG A MOUNT IN THE B ODY :   it’s a function of the rate of absorption and the rate of elimination. If the rate of absorption > rate of elimination   the conc. will increase. If the rate of elimination > rate of absorption   the conc. will decrease. If the rate of absorption = the rate of elimination   no change of the conc. T HE T IME OF P EAK S ERUM C ONC .  gives some indications of the relative rate of absorption. i.e. the lower the time of peak, the faster the rate of absorption. T HE A REA U NDER THE S ERUM C ONC .   (AUC)  Time Curves represents the amount of drug absorbed. F OR A S USTAINED R ELEASE P RODUCT (SR)  the rate-limiting step must be drug release from the dosage form. D RUGS H AVING T HESE P ROPERTIES S HOULD N OT BE FORMULATED INTO SR  FORMS : 1. Poor solubility (since the dissolution rate is a limiting step). 2. Very long half-life (not needed). 3. Very short half-life (need very large amount). 4. Very high potency (individual variation). 5. Narrow safety margin (e.g. digoxin). T HE MINIMAL INHIBITORY CONC .   (MIC):   is the minimal concentration of the antibiotic that prevents the growth of microorganisms. The lower the MIC   the more effective is the antibiotic. C REATININE C LEARANCE T EST : Creatinine clearance test is more effective in determining the kidney function rather than the serum creatinine and blood urea nitrogen (BUN test). N.B. Creatinine clearance is used for the measurement of glomerular filtration rate (GFR). Serum creatinine (S.Cr.) and Blood Urea Nitrogen (BUN) tests are less useful in indicating the renal function than the creatinine clearance test and GFR. Normal Creatinine Clearance: the normal creatinine clearance in adult of 70 kg weight is 100  –  120 ml/min. Elderly people have less production and clearance of creatinine of about 70 ml/min. Male Creatinine Clearance = (140  –   age in years)(wt in kg) 72 (serum creatinine in mg /L) Female Creatinine Clearance = Male Creatinine Clearance X  0.85 A   C OMPARTMENT :   it’s any body site or fluid that appears to contain drug and it may be considered as a compartment or pool in a model. T WO C OMPARTMENT M ODEL :  it may be observed when the drug is rapidly absorbed and distribution phase is slower (in order to distribute itself between two compartments  – ---- e.g. tissue and blood).
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