M Dawes Flashcards
Why can’t you give warfarin to pregnant women?
Because it will cross the placenta
How is warfarin metabolised?
By cytochrome P450 - other drugs interfere with P450
What are the adverse events of warfarin?
Haemorrhage - older age,
Teratogenic - first trimester - bone disease and haemorrhages in the brain in the last trimester.
Should be avoided in those with risk: Pregnancy Uncontrolled alcohol/drug abuse Unsupervised dementia Falls Poor concordance/insight
What determines how much warfarin should be given and for how long?
The duration of treatment depends on the condition:
3-6 months for transient causes and 6-12 months idiopathic causes of DVT.
If the disorder is lifelong or long-term, such as cancer thrombophilia, then can give lifelong. Warfarin doesnt work for these conditions.
Give a loading dose
The INR that you are trying to achieve also depends on the condition. Huge individual variants - such as haw much vitamin K in the persons diet, liver disease, absorption issues, drugs.
Concomitant drugs
What are some drugs that inhibit cytochrome P450?
Alcohol Amiodarone Antibiotics Anti-fungals Antacids Analgesics Allopurinol
What drugs inhibit warfarin by activating P450?
Alcohol Barbiturates Phenytoin Contraceptives Rifampicin
What do you do if someone is bleeding on warfarin?
Vitamin K - IV (slow onset)
IV prothrombin X
Withhold warfarin
What are the problems of warfarin?
Narrow therapeutic window
Lifetime risk of haemorrhage
Drug interactions
Regular INR required
What does dabigatran do?
Inhibits thrombin - oral.
Not cytochrome P450 dependent P-glycoprotein substrate Half-life 12 hours Excreted renally.
Good alternative to warfarin. for atrial fibrilation and VTE (DVT and PE)
Should not be used for metal heart valves.
Idarucizumab - antidote.
What are some drugs that inhibit platelet function?
Aspirin
Clopidogrel
Tricagrelor
What are the indicators for anticoagulants?
For arterial disease (antiplatelets + anticoagulants)
- coronary artery disease
- cerebrovascular disease
- peripheral vascular disease
Thrombo-embolic disease (anti-coagulatns)
- atrial fibrillation
- Venous thrombo-embolism (DVT, PE)
- Prosthetic cardiac valves
What is unfractionated heparin used for?
Has to be given intravenously.
Acute coronary syndrome (MI) Thromboembolism - venous (DVT, PE) Arterial - AF Temporary warfarin therapy - such as in pregnancy
Has to be given intravenously. But has a rapid offset. Can just stop to reduce effects.
How does unfractionated heparin work?
Binds to and increase the activity of anti-thrombin III, which inactivates thrombin and factor Xa. Also inhibits IXa, XIa and XIIa.
Requires APTT monitoring
What are the adverse events of unfractionated heparin?
Brusing/bleeding
Heparin induced thrombocytopenia - check platelets levels - it is an autoimmune antibody generated against the heparin but recognizes platelets - only treatment is to stop treatment
How do you reverse fractionated heparin?
Stop heparin - short half-life
Protamine i.v.
Monitor APTT
Protamine dissociates heparin from antithrombin
irreversible binding to heparin
How does low molecular weight heparin work?
Binds anti-thrombin III Inhibits factor Xa only More predictable than unfractionated Patients can administer it themselves No monitoring required Can give subcutaneously
Less thrombocytopenia than unfractionated, but can’t be monitored by APTT or reversed by protamine.
Care needs to be taken with renal failure. - excreted by kidneys
When is LMWH used?
Non-stemi
STEMI
Initial DVT/PE Rx
Warfarin alternative
How do you treat PE/DVT?
Give LMWH for arround 5 days and give warfarin. When the INR is therapeutic then stop heparin
When do you give warfarin?
Treatment of venous or arterial thrombosis.
- DVT/PE
- Mural thrombosis (post anterior MI to reduce the risk of embolism).
Prevention of venous or arterial thromboembolism
- mechanical, heart valves
- Atrial fibrilation
What are the main ACE inhibitors?
They all end in pril
Cilazapril
Captopril
Renally excreted.
What are the main angiotensin antagonists?
They all end in sartan
Candesartan
Losartan
Renally excreted.
What does the RAAS system do?
Regulates
- blood pressure
- intravascular volume (Na/K)
- Fetal development
- sympathetic system regulation
Juxta-glomerular cell produce circulating renin
Locally produced RAA - myocardium, vascular endothelium and adrenal
It is also involved in pathology:
Increased activity in heart failure and hypertension
Involved in chronic heart failure progression
- Cardiac hypertrophy
-Atherosclerosis development and plaque rupture
-Proinflammation
What do ACE inhibitors do?
Prevent the conversion of angiotensin I into angiotensin II.
Also prevents the breakdown of bradykinin and substance P, which also have beneficial vascular effects.
The excess Angiotension I then goes to angiotensin (1-9) then (1-7), which have anti-hypertensive functions
Over time, other things begin to produce Ang II in the presence of an ACE inhibitor.
What do angiotensin II antagonists do?
Inhibit angiotensin II type I receptors
Angiontensin II is still formed but can only bind AT-2,
Type II receptor stimulation is beneficial - induces tissue repair, vasodilarion, kidney development
What does angiotensin II do?
Increases aldosterone
- Na retention
- K loss
to cardiac myocytes: - hypertrophy Apoptosis Increased O2 consumption Impaired relaxation
Peripheral artery:
Vasoconstriction
Hypertrophy
Decreased compliance
Causes fibrosis
Coronary artery: Vasoconstriction Endothelial dysfunction Atherosclerosis Thrombosis
What happens when you give ACEi or AIIA?
Vasodilation:
- decreased arterial and venous pressure
- decreased preload and afterload
Decreased blood volume
- natriuresis
- diuresis
Decreased sympathetic activity
Decreased cardiac and vascular hypertrophy
They are vasodilators but don’t cause tachycardia.
When do you give ACE inhibitors?
Hypertension
- monortherapy and combination therapy
- Diuretic + ACEi (synergistic combination)
Congestive heart failure
- as part of multiple treatments
- ACEi (or AIIA)
- Diuretic
- beta blocker
- aldosterone antagonist (spiralactalone)
When do you give AIIA ?
In patients who can’t get ACE inhibitors
- Hypertension
- Heart failure
What are the side effects of ACEi?
Dry cough, tickly
- because of bradykinin/substance P
Hyperkalaemia - because it reduces aldersterone
Renal function deterioration
Hypotension
Don’t give in pregnancy.
What are the side effects of AIIA?
No dry cough because of no increase in bradykinin
Hyperkalaemia - because it reduces aldersterone
Hypoension
Renal function deterioration
Don’t give in pregnancy.
What are the cautions with use of AIIA and ACEi?
Monitor potassium
Renal impairment
Volume depleted patients - because they depend on the RAAS system
Do not use in bilateral renal artery stenosis or pregnancy
What is bilateral renal artery stenosis?
Perfusion pressure in the glomerulus is reduced wehn the artery to the kidney is stenosed. Angiotensin II is produced to constrict the efferent arteriol to increase that pressure.
If you give AIIA or and ACEi then that reduces the efferent constriction and the GFR is reduced significantly
Need to monitor the creatinine.
Why don’t you give ACEi or AIIA in pregnancy?
It is important in kidney development.
ACEii/AIIA crosses placenta - only necessary in 2nd and 3rd trimester
What is the role of ANG II in diabetes?
It can promote abnormal glucose handling.
Reduces reduced insulin sensitivity.
It may prevent the development of diabetes
Should you give and AIIA and an ACEi?
No, adverse events really bad.
Future directions?
renin inhibitors
What are the likely causes of DVT?
Virchow’s triad: stasis, endothelial damage, hypercoaguability.
Stasis: flight, obese
Family history of VTE: factor V lieden, lupus anticoagulant,
Previous DVT
Tumour history: estrogen y
Drugs
Why is there swelling, redness and heat with a DVT?
Because the blockage increases the pessure in the capllaries ausing more fluid to leave the vessels at the capillaries causing oedema.
It is red and hot because of the imflammation.
What are the treatment options for DVT?
LMW Heparin (enoxaparin; clexane) - given sub cut.
Warfarin also if long term treatment. Can be given orally.
Analgesia
Elevate leg
What are the problems with warfarin and what else could be used?
Warfarin has drug interactions and the INR needs to be checked twice weekly.
Dabigatran does not need to be checked with blood tests but is required twice daily. blocks thrombin directly Given orally.
Rivaroxaban only once daily with no blood tests.
Both dabigatran and rivaroxaban are excreted renally, may need dose changes in poor kidney functionand shouldn’t be given with a GFR <30.
These are also not good for people with metal heart valves.
Is there an antidote for rivaroxaban?
No
What are the treatments for PE?
LMWH
Warfarin
You can do thrombolysis in those with severe PE with right heart impairment
What are the risks associated with atrial fibrillation?
High heart rate can cause heart failure because the high rate increases you cause ischaemia because of reduced ejection fraction that requires remodeling -> heart failure.
A thrombus can form in the left atrial appendage. This can cause a stroke. They need anticoagulation.
How do you treat someone with atrial fribulation?
Can either try and slow the heart rate or try to convert them to sinus rhythm.
Rate control:
- beta blocker
+/- diltiazem
Blood pressure control
Lipid control (cholestrol)
Anticoagulation:
- aspirin vs warfarin vs dabigatran other anticoagulant. CHAD-VAS score
Heparin is not needed. No rush for anti-coagulation.
When do you give warfarin with atrial failure?
CHADS-VAS score.
Congestive cardiac failure Hypertension Age >75 Diabetes Stroke Vascular damage Age (>65) Sex female
Score 2 or more = warfarin
How do you know the risk of haemorrhage on anti-coagulation?
HAS BLED score
Hypertension Abnormal blood results - (creatinine or liver function tests) Stroke Bleeding previously Labile INR Elderly >65 Drug use (alcohol)
3 or above = no treatment because its too risky.
What is a alpha 1 receptor blocker?
Doxazosin
Causes vasodilation and hypotension by acting on the postsynaptic receptors receptors and inhibiting NA induced vasoconstriction.
Also has an effect on prostatic smooth muscle.
Used once daily. Oral.
Mainly faecal elimination. Elimination half-life 22 hours. Linear kiertic. Peak plasma level in 2-3 hours. Reversible binding.
Side effects: Postural hypotension - take drug at night before bed or take a low does. Urinary incontenance in women Feeling tired Nasal stufiness
What is a alpha 2 receptor blocker?
Blocking increases norepinephrine release by blocking the presynaptic receptors that inhibit NA release.