Beta blockers
How they work
They block beta (β) receptors in the heart. This means that the heart slows down (negative chronotropic effect), and pumps less hard (negative inotrophic effect). Some types are selective, such as atenolol, and only work on β1 receptors, reducing the side effects resulting from blockage of β2 receptors, but not completely.
What are they used for
- Treating heart failure, since they make the heart work less hard.
- After someone has an MI, in order to prevent another one.
- Atrial fibrillation - alongside digoxin they control the heart rate.
- They are also used a bit to control hypertension, but not as much as they used to be.
- Other uses: treating anxiety, reducing eye pressure in glaucoma and preventing migraine.
Common types and dose
- Propanolol hypertension 160-320mg OD, angina and arrhythmias upto 40mg QDS.
- Atenolol hypertension 25-50mg OD, angina and arrhythmias 100mg BD.
- Sotalol ventricular arrhythmias and SVT
Side effects
They should not be used on patients with asthma, since they can cause bronchospasm. Whilst some b1 blockers are slightly better in this regard, they still should not be used, apart from in a few weird and wonderful situations that you don't need to know about.
They are also contraindicated in heart block, since they can cause or worsen it.
Patients sometimes complain of feeling light headed, or even losing consciousness. This implies the beta blockers are working a little too well, and it's time to cut the dose.