But Ca2+ channel blocker like Diphenyl alkyl amine( eg. Verapamil) should not prescrib in combination with β- blockers when indicated for patients with myocardial infarction.Because verapamil blocks AV nodal conductance,thus leading to bradycardia.
Nifedipine is primarily vasodilator while verapamil and diltiazem have both vasodilator and cardio-depressant actions. The increased heart rate has seen with nifedipine, because of the reflex mechanism which tries to overcome the vasodilatation and subsequent drop in blood pressure caused by nifedipine. In contrast the compensatory mechanism does not occur to the same extent with either verapamil or diltiazem. This is in part due to the ability of Verapamil & diltiazem to block AV nodal conductance, and in part due to the ability of nifedipine to activate the baro-receptor reflex.
So β blockers are prescribed in combination with nifedipine/diltiazem (DihydropyridineClass | M/A | Side effects | Examples |
β- adrenoreceptor antagonist | It reduces the action of β1-adrenoreceptor on the heart,thus reduces cardiac output.It also inhibit the release of renin from the kidneys.Thus decreasing the formation of angiotensin 2 & secretion of aldosterone.Thus reduces the Na & water retension, blood volume and blood pressure. | · Hypotension · Bradycardia · Fatigue · Insomnia · Sexual dysfunction | Atenolol Metoprolol Labetalol |
ACE (Angiotensin converting enzyme) Inhibitor | These drugs block the ACE that cleaves Angiotensin-1 to form the potent vasoconstrictor angiotensin-2.Thus lower the blood pressure by reducing peripheral vascular resistence. | · Dry cough · Hypertension · Skin rash · Hypotension · Fever · Renal failure · Taste disturbance | Ramipril Lisinopril Captopril enalapril |
Ca- channel blocker | Dihydropyridine group work almost exclusively on L-type Ca2+ channel in the peripheral arterial and reduce blood pressure by reducing total peripheral resistance. | · Bradycardia · Oedema · Constipation(verapamil only) · Headache · Flushing | 3 classes of drugs · Diphenyl alkyl amine Eg. Verapamil · Benzothiazepines Eg. Diltiazem · Dihydropyridine Eg. Nifedipine |
AT-1 antagonist | It is a competetive Angiotensin-2 receptor type-1 antagonist, reducing the responses to ang-2 and thus resulting in a decrease in total peripheral resistence. | · Renal failure · Edema · Headache | Losartan Candesartan |
α1 –adrenoreceptor antagonist | Causes α1- adrenoreceptor block , thus results in vasodilation. | · Oedema · Postural hypotension. | Prazosine Doxazosin Terazosin |
Diuretic | ⬆ excretion of Na+ & water in the urine and reduce blood volume & thus reduce blood pressure. | · Hypokalaemia · Gout · Impotence · Uraemia · Dehydration | 3 classes · Loop diuretics: eg. Furosemide · K-sparing: eg. Spironolactone. · Thiazide: |
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