Drug absorption 1 Flashcards
Which of the following factor is the LEAST LIKELY to affect the absorption of 1/1 a drug? The drugs:
a) Liquid ionization
b) degree of ionization
c) size
d) therapeutic use
d) therapeutic use
Which of the following gives the BEST definition of ‘bioavailability’? The fraction of the drug:
a) absorbed from the GIT
b) metabolised in the first pass through the liver
c) reaching the systemic circulation
d) released from its pharmaceutical formulation
c) reaching the systemic circulation
Therapeutic index is the ratio of the dose producing the desired therapeutic effect to the dose producing adverse effects.
a) true
b) false
b) false
Therapeutic index is the ratio of the dose producing adverse effects to the dose producing the desired effect. The higher the therapeutic index, the “safer” the drug.
Aspirin is a weak acid with a pKa of 3.5. At which pH will it be mostly in its unionised form?
a) pH = 1.5
b) pH = 3.5
c) pH = 5.5
d) pH = 7.5
a) pH = 1.5
Remember when the PH = pKa the drug will be 50% ionised and 50% unionised. For an drug that is an acid, when the pH < pKa, it will accept an H+ and become unionised. When pH > pka it will lose the H+ and become more ionised. You may need to rewatch the video to help your understanding.
If a drug is present in the gastrointestinal tract in both its ionised and unionised form:
a) it can only be absorbed from areas where it is predominantly present in the unionised form
b) as the unionised form is absorbed, the relative proportions of ionised and unionised forms will be maintained,
c) the amount absorbed will be equivalent to the proportion that is unionised
d) both forms can be absorbed across the cell membrane in the intestine where there is a large surface area
b) as the unionised form is absorbed, the relative proportions of ionised and unionised forms will be maintained,
The relative proportions of ionised and unionised drug will be determined by the pH relative to the pKa and will remain constant. The unionised form will be able to cross cell membranes and be absorbed and this will decrease the total amount of drug in the GIT - but the relative proportions of ionised/unionised will not change.
Which of the following would be consistent with a drug that is highly bound to plasma proteins? It:
a) easily moves across cell membranes to interact with its target
b) is readily filtered into the kidney tubules as it passes through the glomerulus
c) would tend to be retained in the vascular compartment
d) would be extensively taken up into tissues
c) would tend to be retained in the vascular compartment
Read the section on Drug DISTRIBUTION on the Pharmacology Education Project website (https://www.pharmacologyeducation.org/pharmacology/drug-distribution) and then answer the following question.
Metabolism facilitates elimination by:
a) increasing the size of the drug molecule and limiting its movement
b) increasing the lipophilicity of the drug
c) making the drug inactive so reducing its effects
d) increasing the number of ionisable groups on the drug molecule
d) increasing the number of ionisable groups on the drug molecule
The primary objective of drug metabolism is to facilitate a drug’s excretion by increasing its water solubility (hydrophilicity).
Read the section on Drug METABOLISM on the Pharmacology Education Project website (https://www.pharmacologyeducation.org/pharmacology/drug-metabolism) and then answer the following questions.
Which of the following statements is NOT a similarity between phase I and phase II drug metabolism? Both phases:
a) decrease lipophilicity
b) largely occur in the liver
c) increase the size of the drug molecule
d) usually produce inactive metabolites
c)increase the size of the drug molecule
The amount of drug excreted in the urine will be equal to:
a) amount filtered + amount reabsorbed - amount secreted
b) amount filtered + amount reabsorbed + amount secreted
c) amount filtered - amount reabsorbed - amount secreted
d) amount filtered - amount reabsorbed + amount secreted
d) amount filtered - amount reabsorbed + amount secreted
In zero order elimination kinetics:
a) rate of elimination changes as plasma concentration changes
b) half-life is constant
c) an enzyme metabolism step is involved
d) increasing the dose will lead to an increase in clearance
c) an enzyme metabolism step is involved
Zero order elimination is when rate of elimination is constant and not changing as plasma concentration changes. This occurs when an enzyme involved in the metabolism of the drug becomes saturated so can not increase in activity with increased dose. Because rate of elimination is constant, half life is not constant and overdose is a potential concern.