Pharmacodynamics of Drugs for Heart Failure – PST05104 Pharmacology and Therapeutics
NTA Level 5 • Semester 1 • PST05104 Pharmacodynamics of Drugs for Heart Failure Pharmacology and Therapeutics • Source Session/Topic 33 Full source-text version: all educational wording from the extracted learning source is retained; only presenter/tutor metadata and web-layout noise are removed, while formatting is improved for readability. Session 33: Pharmacodynamics of Drugs for Heart Failure Total Session Time: 120 minutes Prerequisites None Learning Tasks By the end of this session students are expected to be able to: Describe mechanism of action of drugs for heart failure Describe drug interactions associated with drugs for heart failure Describe side effects of drugs for heart failure Describe contraindications of drugs for heart failure Resources Needed: Flip charts, marker pens, and masking tape Black/white board and chalk/whiteboard markers Computer and LCD projector SESSION OVERVIEW Step Time Activity/ Content Step Time Activity/ Content Step Time Method Content Method Method 1 1 05 minutes 05 minutes Presentation Introduction, Learning Tasks Introduction, Learning Tasks 2 2 45 minutes 45 minutes Presentation/ Mechanism of Action of Drugs for Heart Mechanism of Action of Drugs for Heart 2 2 45 minutes 45 minutes Buzzing Failure Failure Buzzing Failure Failure 3 3 20 minutes 20 minutes Presentation/ Drug Interactions Associated Drugs for Heart Drug Interactions Associated Drugs for Heart 3 3 20 minutes 20 minutes brainstorming Failure Failure brainstorming Failure Failure 4 4 20 minutes 20 minutes Presentation Side Effects of Drugs for Heart Failure Side Effects of Drugs for Heart Failure 5 5 20 minutes 20 minutes Presentation/ Contraindications of Drugs for Heart Failure Contraindications of Drugs for Heart Failure 5 5 20 minutes 20 minutes Brainstorming Contraindications of Drugs for Heart Failure Contraindications of Drugs for Heart Failure Brainstorming 6 6 05 minutes 05 minutes Presentation Key Points Key Points 7 7 05 minutes 05 minutes Presentation Evaluation Evaluation PST 05104 Pharmacology & Therapeutics 261 NTA Level 5 Semester 1 Facilitator Guide SESSION CONTENTS STEP 1: Presentation of Session Title and Learning Tasks (5 minutes) READ or ASK students to read the learning tasks and clarify ASK students if they have any questions before continuing. STEP 2: Mechanism of Action of Drugs for Heart Failure (45 minutes) Activity: Buzzing (5 minutes) ASK students to pair up and buzz on the following question for 2 minutes How do Drugs for Heart Failure produce their pharmacological effects? ALLOW few pairs to respond and let other pairs add on points not mentioned WRITE their response on the flip chart/board CLARIFY and SUMMARIZE by using the content below Drugs for Heart Failure Diuretics o In Chronic heart failure: a diuretic is used to control symptomatic oedema and dyspnoea in patients with heart failure. o For more information on adverse effects, interactions , contraindications and mechanism refer a session on Pharmacodynamics of drugs acting on urinal genital system o Spironolactone improves survival in patients with cardiac failure and counters diuretic-induced hypokalaemia. o Diuretic-induced hypokalaemia increases the toxicity of digoxin. Conversely, spironolactone and other K+-retaining diuretics (e.g. amiloride, triamterene) can cause severe hyperkalaemia, especially if given with ACEI or sartans to patients with renal impairment. o It is therefore important to monitor plasma K+ during treatment with all diuretic therapy. Angiotensin-Converting Enzyme Inhibitors For more information on adverse effects, interactions , contraindications and mechanism refer a session on Pharmacodynamics of drugs acting on urinal genital system (session ) and Pharmacodynamics of Antihypertensive drugs(session ) When symptoms are mild, diuretics can be temporarily discontinued a day or two before starting an ACEI, reducing the likelihood of first-dose hypotension. PST 05104 Pharmacology & Therapeutics 262 NTA Level 5 Semester 1 Facilitator Guide Angiotensin Receptor Antagonists, Sartans o For more information on adverse effects, interactions, contraindications and mechanism refer a session on Pharmacodynamics of Pharmacodynamics of Antihypertensive drugs (session). o As in hypertension, the pharmacodynamics of sartans are similar to those of ACEI apart from a lower incidence of some adverse effects, including, particularly, dry Inotropic action: Through the action of Na/K/ATP ion pump blockade, the following sequence of ionic events occurs: o ↓ Na exits the cell o ↑ Intracellular Na o ↓ Na electrochemical gradient for Na-Ca exchanger o ↓ Ca exits the cell o ↑ Intracellular Ca o The increase in intracellular calcium results in increased contractility, SV, and CO. o In heart failure, sympathetic tone is increased as a compensatory mechanism to increase CO. o Digoxin increases contractility and hence SV and CO, therefore reducing the need for sympathetic compensation cough. Thus digoxin reduces the sympathetic tone in heart failure Beta blockers o For more information on adverse effects, interactions , contraindications and mechanism refer a session on Pharmacodynamics of Antihypertensives o Beta-blockers are negative inotropes and so intuitively would be expected to worsen heart failure. o There is, however, a rationale for their use in terms of antagonizing counter regulatory sympathetic activation and several randomized controlled trials have demonstrated improved survival when a β-adrenoceptor antagonist is added to other drugs, including an ACEI. Beta1-Adrenergic Agonists: Dobutamine ,Dopamine, Amrinone and Milrinone o Improves cardiac performance by their positive inotropic effects and vasodilatation ((β-2), minimum effects on HR by dobutamine) Increase in intracellular cAMP → results in the entry of Ca2+ into the myocardial cells increases, thus enhancing contraction Diminished effects after long-time infusions and possible worsening upon withdrawal o Ibopamine which is a pro-drug and has actions at β-1, β-2, D1 and D2 is not preferred because of the non-selectivity hence increased toxicity. Glucagon o Glucagon increases cyclic AMP thus increasing myocardial contraction hence used in acute cardiac dysfunction due to overdose of β-blockers Inhibitors of Phosphodiesterase III o Inhibitors of phosphodiesterase III which is specific to the heart and responsible for degradation of cyclic AMP thus increases myocardial contractility are also used. PST 05104 Pharmacology & Therapeutics 263 NTA Level 5 Semester 1 Facilitator Guide STEP 3: Drug Interactions Associated with Drugs for Heart Failure (20 minutes) Activity: Brainstorming (5 minutes) Ask students to brainstorm on the following question: What are drug interactions associated with drugs for heart failure? ALLOW