Pharma MCQ 7 Flashcards
The half life of a drug affects the steady-state plasma concentration during constant rate infusion? T/F
False. The time to achieve steady state concentrations depends on half life but the absolute concentrations at steady state depend on the infusion rate.
How is the half life of a drug related to the elimination constant?
half life is inversely related to the elimination constant.
What can be calculated from the concentration-time AUC?
calculate CLEARANCE (Cl = dose/AUC).
What factors effect the duration of a drug?
Duration of action is determined by several factors including metabolism, redistribution, mechanism of action (e.g. drugs which bind irreversibly) and elimination half life.
Lidocaine protein binding?
65%
Alfentanil protein binding?
92%
What is diazepam metabolised to?
Diazepam is extensively metabolised to N-desmethyldiazepam (nordiazepam), temazepam and oxazepam.
What is the main determinant of clearance of drugs with high hepatic clearance?
liver blood flow
How does hypocapnia affect biotransformation of drugs with high hepatic clearance?
Decreased as hypocapnia reduces hepatic blood flow.
T/F: The biotransformation of drugs having a high hepatic clearance is unaffected by drug protein binding.
True.
It is relatively insensitive to changes in protein binding, or enzyme activity.
Drugs whose pharmacological actions involve receptor site competition include:
Select true or false for each of the following statements.
A. atropine B. bisoprolol C. diltiazem D. rocuronium E. phentolamine
A. True. Atropine competitively blocks muscarinic acetylcholine receptors.
B. True. Bisoprolol competitively blocks Beta1-adrenergic receptors.
C. False. Calcium channel blocker. Diltiazem is a benzothiazepine which acts on the alpha1 subunit of the L-type voltage-gated calcium channel.
D. True. Rocuronium competitively blocks nicotinic acetylcholine receptors at the neuromuscular junction.
E. True. Phentolamine is a non-selective antagonist at alpha-adrenergic receptors.
The following drugs may be presented as a single stereoisomer:
Select true or false for each of the following statements.
A. bupivacaine B. lidocaine C. ketamine D. morphine E. norepinephrine
A. True. Bupivacaine is available as a racemic mixture but may be presented as the single stereoisomer levobupivacaine.
B. False.
C. True. Ketamine is available as a racemic mixture but may be presented as the single stereoisomer S-ketamine.
D. False.
E. True. Norepinephrine is presented only as the R(-) form, l-norepinephrine, because d-norepinephrine is much less potent.
Early signs of cyanide poisoning?
Progressive metabolic acidosis,
- Cyanide toxicity inhibits cellular metabolic processes.
Increased mixed venous O2 tension as cyanide impairs cellular oxygen utilisation so mixed venous oxygen concentration increases.
How does cyanide toxicity affect Hb saturations?
Oxyhaemoglobin concentrations are unaffected, although nitrites administered to counteract cyanide toxicity cause methaemoglobinaemia.
Mechanism of cyanide toxicity?
- Binds the ferric (Fe3+) ion of cytochrome oxidase causing ‘histotoxic hypoxia’ and lactic acidosis
- Stimulates biogenic amine release causing pulmonary and coronary vasoconstriction, which results in pulmonary oedema and heart failure
- Stimulates neurotransmitter release, such as N-methyl-D-aspartate (NMDA), causing neurotoxicity and seizures
