Drugs acting in the bloodstream

Question 1

Regarding the anticoagulant effect of warfarin:

It is exerted directly on the blood

Answer 1

False

Warfarin prevents the reduction of vitamin K which is a co-factor in producing clotting factors II, VII, IX and X.

Question 2

Regarding the anticoagulant effect of warfarin:

It is readily excreted in the urine

Answer 2

False

It is almost entirely metabolized in the liver by mixed function oxidases. The metabolites are excreted in the urine.

Question 3

Regarding the anticoagulant effect of warfarin:

It is antagonized by salicylates

Answer 3

False

Question 4

Regarding the anticoagulant effect of warfarin:

It is potentiated by phenylbutazone

Answer 4

True

Question 5

Regarding the anticoagulant effect of warfarin:

It is potentiated by barbiturates

Answer 5

False

Question 6

Regarding heparin:

It affects the coagulation pathway mainly by binding to ATIII (Antothrombin III); it has no direct antiplatelet activity

Answer 6

True. Its antiplatelet effects are mediated through its effects on fibrin.

Question 7

Regarding heparin:

Haemorrhage and anaphylaxis are the commonest adverse drug reactions occurring after heparin therapy

Answer 7

False. Haemorrhage, hypotension and thrombocytopenia are the commonest adverse reactions.

Question 8

Regarding heparin:

LMWH (Low Molecular Weight Heparin) is only partly reversed by protamine

Answer 8

True. Only anti-IIa activity is fully reversed, anti- Xa activity is partially reversed.

Question 9

Regarding heparin:
For LMWH the APTT (Activated Partial Thromboplastin Time) ratio is a far more reliable indicator than INR (International Normalized Ratio)

Answer 9

False. Factor Xa assays are required to monitor effect of LMWHs, but owing to their safe profile, this is seldom performed.

Question 10

Regarding heparin:

Heparin-induced thrombocytopenia is not dose-dependent

Answer 10

True. It can occur after the first dose of heparin.

Question 11

Regarding warfarin, which of the following statements are true?
Protein C production is limited in patients on warfarin therapy

Answer 11

True. Protein C and S production are also inhibited by warfarin.

Question 12

Regarding warfarin, which of the following statements are true?
It is 70% eliminated by renal filtration

Answer 12

False. It is almost entirely metabolized by the liver via inducible enzymes.

Question 13

Regarding warfarin, which of the following statements are true?
It is highly protein bound

Answer 13

True. It is highly protein bound (99%) resulting in numerous drug interactions.

Question 14

Regarding warfarin, which of the following statements are true?
Amiodarone, gliclazide or metronidazole can increase a patient’s INR

Answer 14

True. Gliclazide and amiodarone displace warfarin from albumin. Metronidazole is an enzyme inhibitor reducing warfarin metabolism.

Question 15

Regarding warfarin, which of the following statements are true?
Unlike warfarin, heparin does not cause increased risk of stillbirths and abortions

Answer 15

False. Heparin causes an increased risk of fetal death and morbidity, but the incidence is less than warfarin.

Question 16

Regarding low-molecular-weight heparin:

It has a similar effect on platelets as unfractionated heparin

Answer 16

False. LMWH interacts less with platelets than unfractionated heparin.

Question 17

Regarding low-molecular-weight heparin:

It has a longer half-life than unfractionated heparin

Answer 17

True. The half-life of most low-molecular-weight heparins is 2–3 times longer than unfractionated heparin.

Question 18

Regarding low-molecular-weight heparin:

Guidelines suggest at least 12 hours should elapse after dosing before attempting central neuraxial block

Answer 18

True. At least 12 h should elapse after dosing before attempting central neuraxial block, which is in accordance with the American Society of Regional Anesthesia (ASRA) guidelines; anti-Xa activity is about 50% of peak 12 h after dosing.

Question 19

Regarding low-molecular-weight heparin:

It can be given 2-4 hours after uneventful spinal or epidural block

Answer 19

True. Low-molecular-weight heparin can be given 2-4 h after uneventful spinal or epidural block (see ASRA guidelines).

Question 20

Regarding low-molecular-weight heparin:

It must be given before surgery to provide effective thromboprophylaxis

Answer 20

False. Postoperative dosing regimens have been shown to be equally effective in providing thromboprophylaxis.

Question 21

With regard to coagulation studies:

You would expect a normal bleeding time in von Willebrand’s disease

Answer 21

False. You would expect a prolonged bleeding time due to the impaired platelet function.

Question 22

With regard to coagulation studies:

The INR is the ratio of patient’s APPT to control using international reference preparation

Answer 22

False. It is the ratio of patient’s PT to control using international reference preparation.

Question 23

With regard to coagulation studies:

Factor V abnormalities can result in a prolonged APTT

Answer 23

True. Factor V abnormalities can result in a prolonged APTT and PT.

Question 24

With regard to coagulation studies:

Factor V abnormalities can result in a prolonged PT

Answer 24

True

Question 25

With regard to coagulation studies:

Haemophilia is a cause of an elevated APTT

Answer 25

True. Both low factor VIII (haemophilia A) or IX (haemophilia B) would result in an elevated APTT.