Metoprolol
Metoprolol is a cardioselective beta blocker. It reduces the effect of adrenaline on beta-1 receptors in the heart, slowing the rate and easing the force of contraction, which lowers blood pressure and the heart's oxygen demand. It is used for hypertension, arrhythmia and angina, and also to prevent migraine. It is prescription-only.
It is taken with food, which steadies absorption. It is not stopped abruptly, since sudden withdrawal can provoke chest pain or rhythm problems. Terbinafine blocks the liver enzyme that clears it, so blood levels rise and the heart slows further, and it works against salbutamol at the airways, which is why asthma calls for caution. Glucose and triglycerides are monitored, as beta blockers can shift both and can hide the early warning signs of low blood sugar.
A persistently slow pulse, dizziness or fainting, new breathlessness, or wheezing that a reliever does not settle are reasons to see a doctor rather than adjust anything alone.
Reference information, not medical advice. Discuss any change with your doctor.