G7iii / 21B09 / 19B14: Outline the classification and effects of beta-blocking drugs with examples (50% marks). Compare and contrast the pharmacokinetics of metoprolol with esmolol (50% marks)
21B09: Exam Report
Outline the classification and effects of beta-blocking drugs, including examples (50% marks). Compare and contrast the pharmacokinetics of metoprolol with esmolol (50% marks)
59% of candidates passed this question.
This was a two-part question with marks and thus timing of the answers given as a percentage. There are generally many ways to classify drugs within the same class. These are usually well described in the relevant recommended pharmacological texts. Receptor distribution throughout the body and the effect of the drug-receptor interaction are useful ways to organise systemic pharmacodynamic responses, as opposed to a list of organ systems with associated vague statements of interaction.
19B14: Exam Report
Outline the classification and effects of beta-blocking drugs with examples (505 of marks). Compare and contrast the pharmacokinetics of metoprolol with esmolol (50% of marks).
47% of candidates passed this question.
Beta-blocking drugs were generally well classified. Selectivity, membrane stabilising activity and ISA should have been mentioned. Many candidates omitted or poorly answered the ‘effects’ of beta blockers. Candidates who performed well answering the pharmacokinetics of metoprolol and esmolol provided a table of the two drugs. Superficial statements such as “hepatic metabolism and renal excretion” attracted minimal marks. The mechanism of action of beta blockers was not requested.
G7iii / 21B09 / 19B14: Outline the classification and effects of beta-blocking drugs with examples (50% marks). Compare and contrast the pharmacokinetics of metoprolol with esmolol (50% marks)
Definition
Β blockers are antagonists of the effects of catecholamines at β adrenoreceptors
Chemical
- All are derivatives of β agonist ISOPRENALINE
- Benzene ring substitutions determine whether drug will be an agonist/antagonist
- Levorotary more potent
Classification
Competitive antagonists – all are competitive antagonists & occupy β receptor to cause no activation
- Selectivity:
- Non-selective: β1 & β2 → PROPANOLOL
- Selective: β1 = cardioselective → METOPROLOL, ATENOLOL, ESMOLOL
- Intrinsic sympathomimetic activity – ∴ classified as partial agonist, better tolerated with poor LV function → LABETALOL
- Membrane stabilising activity → PROPANOLOL, LABETAOLOL have MSA effects similar to Class IA antiarrythmics
- Other → SOTALOL which exhibits K channel blocking activity
PK
A
Metoprolol
50% OBA
Esmolol
IV only
Comparison
LIPID SOLUBILITY: Metoprolol > esmolol
PK
D
Metoprolol
10% PPB
Esmolol
55% PPB
Vd 3.5L/kg
Comparison
Both have very high lipid solubility and cross BBB
PK
M
Metoprolol
Hepatic; 60% 1st pass metabolism
Inactive metabolites
Esmolol
Plasma hydrolysis by RBC esterase
Comparison
Esterase metabolism governs esmolol’s very short t1/2
PK
E
Metoprolol
Metabolites cleared in urine
<10% unchanged
t ½ B 6hrs
Esmolol
Renal <1% unchanged
T ½ 10mins
Comparison
Half life of metoprolol is much longer and usually has bd dosing
Author: Krisoula Zahariou