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20 Cards in this Set
- Front
- Back
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Thiazides & related drugs
- Drugs in class |
Thiazides
Hydrochlorothiazide (HCTZ) Related drugs Chlorthalidone Indapamide |
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Thiazides & related drugs
- Mode of action |
Works in the distal convuluted tubule, blocking the Na-Cl co-transporter, reducing their reabsorption; also reducing the corresponding reabsorption of K (That is, increases excretion of water, Na, Cl and K)
However, when used in the recommended low doses, main effect is vasodilation |
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Thiazides & related drugs
- Indications |
1. Hypertension
2. Oedema associated with HF or hepatic cirrhosis (but caution required with both cases) 3. NEPHROGENIC diabetes insipidus (when kidneys can't respond to ADH) - chlorthalidone 4. calcium kidney stone prevention - HCTZ |
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Thiazides & related drugs
- CI & Precautions - RF/LF - Preg/BF |
Contraindications
1. Addison's disease (increased Na&H20 loss) 2. Severe RI/anuria (also ineffective <25ml/min) 3. Severe hepatic disease (electrolyte disturbance: encephalopathy) May worsen - Gout - HF with sig oedema (low Na) BF: unlikely to reduce milk; caution Preg Cat C. AVOID - neonatal thrombocytopenia, electrolyte disturbance, may diminish placental blood flow |
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Thiazides & related drugs
- Adverse effects |
Common
- polyuria, dizziness, orthostatic hypotension - cramps, weakness - low magnesium, sodium, potassium, hypochloric alkalosis - hyperuricaemia Infrequent - Hyperglycaemia, dyslipidaemia, impotence **All less likely in low doses Rare - pancreatitis, jaundice, blood dyscrasias, TEN |
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Thiazides & related drugs
- Comparative efficacy - Comparative SEs |
- same
- same (indapamide can still cause hypokalaemia and hyponatraemia) |
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Thiazides & related drugs
- Comment on the use of these drugs in HF for oedema - and with loops |
May be used to increase diuresis.
Small, intermittent doses should be used Careful monitoring is needed to ensure that we avoid: #1. hyponatraemia: more likely with oedema AND a low salt diet or spirinolactone #2. renal hypoperfusion |
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Thiazides & related drugs
- Comment on appropriate dosing |
- Low doses are preferred because high doses are more likely to cause hyperglycaemia, impotence and hyperlipidaemia
- 12.5mg HCTZ may be suboptimal - Also, combo products are inflexible and not appropriate for starting doses |
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Thiazides & related drugs
- Comment on prevention and treatment of hypokalaemia |
1. Prevent with ACEI/ATTA & by using minimal doses
2. May be difficult to correct if there is hypomagnesium (more likely with diuretics!) 3. If K is <3.5mmol/L, consider (a) potassium sparring diuretic (Easier) (b) potassium supplements (600mg or 8mmol: need 3-8 tab or 20-60mmol d) |
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HCTZ
- dose forms (& Brands) including combination products |
25mg.100 tabs (Dithiazide)
25mg/50mg.100 tabs (Hydrene: HCTZ/triamterene) 50mg/5mg tab (Moduretic(50), Amizide (100): HCTZ/amiloride) 20mg/6mg tab (Renitec Plus: enalapril/HCTZ) 10/12.5, 20/12.5 (Monoplus, Hyforil: fosinopril/HCTZ) 10/12.5, 20/12.5 (Accuretic: quinalapril/HCTZ) And also with every ATIIA except losartan (Cozaar) |
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HCTZ
- indications for combo products |
ALL the combos are only marketed for hypertension
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HCTZ
- the combination of HCTZ with triamterene has ONE additional CI - what is it? |
CI by manufacturer with other drugs which increase potassium (cyclosporin, trimethoprim)
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HCTZ
- doses |
HTN: 12.5-25mg d
Oedema: 25-100mg d (or intermitently on 3-5 days per week) Renal calculi prevention: 50-200mg d |
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HCTZ
- counselling |
1. L16
2. Take in the morning (if 2 doses, take second dose before 6 pm) |
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Thiazides & related drugs
- Drug Interactions |
1. Decrease BP
2. Increase BGL (in high doses) 3. Decrease potassium (e.g. amphotericin) 4. Care with NSAIDs (reduced RF, increased BP) Loops (electrolyte disturbance, renal hypoperfusion) ACEI/ATIIA: decreased renal perfusion, FIRST DOSE HYPOTENSION (not as bad as loops) 5. Li: May increase Li conc, esp in first 10 days; Avoid use; Sometimes co-prescribed for Li-induced diabetes insipidus: monitor closely) |
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There is an additional, rather uninteresting DI for HCTZ alone. What is it?
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Bile acid binding resins decrease absorption of HCTZ.
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Chlorthalidone
- brand - dose forms - dose |
Hygroton
25mg.100 tabs HTN: 12.5mg-25mg d Oedema, Diabetes insipidus: 12.5-50mg d |
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Hygroton counselling
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1. L16
2. Morning doses, or second dose before 6pm |
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Indapamide
- brand - dose forms (inc combos) - dose |
Natrilix, Dapa-Tabs, Insig, Indahexal, Napamide (2.5mg.x30, x60, x90)
Natrilix SR (1.5mg.30, 1.5mg.90) Coversyl Plus (2.5/0.625, 5/1.25) DOSE: (Just used for HTN) 1.25-2.5mg d in the morning (1.5mg SR = 2.5mg) |
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How does the risk of hypokalaemia compare between Natrilix SR and Natrilix?
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Lower in SR form but antihypertensive effect similar
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