Formulary Monographs [BLOOD FORMATION AND COAGULATION, 2000]
BLOOD FORMATION AND COAGULATION
2000
BLOOD FORMATION, COAGULATION AND THROMBOSIS
Before treatment is commenced the cause of blood loss must be diagnosed. Iron may be given orally or parenterally. The rate of haemoglobin response is not faster when iron is given parenterally and therefore the rapid cure of the anaemia is not met. Iron dextran can be given as a course of intramuscular injections or in selected cases as a total dose infusion given intravenously over 6 - 8 hours.

Indications for parenteral therapy:

(1) Malabsorption

(2) Genuine intolerance to oral therapy

(3) Uncooperative patient

Oral iron therapy involves use of simple iron salts which are the most economical and contain the highest dosages of iron. Maximum iron absorption occurs in the duodenum and prolonged release p rep arations often deliver iron to parts of the small intestine where absorption is poor. These preparations have no therapeutic advantage to justify their cost. Iron should be prescribed three (3) times daily after meals to (avoid gastric intolerance). The need is to supply 150 - 200 mg of elemental iron daily .


20:12 ANTITHROMBOTIC AGENTS

These are used to prevent thrombus formation or the extension of an existing thrombus. Heparin combines with antithrombin and is an immediate acting inhibitor of the thrombin/fibrinogen reaction. Heparin can be given s.c. (prophylaxis), i.m. (not recommended) or i.v. Effects are short lived and therefore continuous i.v. infusion seems to be associated with better results and fewer complications, under carefully controlled conditions, e.g. in an Intensive Care Unit or with an infusion pump . Hemorrhage can be treated with protamine sulphate. One mg neutralizes 100 units of heparin.

Oral anticoagulants act by inhibiting the hepatic synthesis of the vitamin K dependent clotting factors. It makes 36 - 48 hours for the anticoagulant effect to develop and so if immediate effect is required then hep arin must be started simultaneously and given 2 - 5 days. Laboratory control of prothrombin time is essential.

Drugs such as phenyl-butazone, indomethacin, salicylates and clofibrate increase the effect of oral anti- coagulants while barbiturates diminish its effect.

Hemorrhage should be treated by omission of the drug (if mild) or with i.m. or i.v. vitamin K.

Sensitivity is rare with warfarin but more common with phenindione.

Dose Range

Loading doses are no longer recommended. Start patient on expected daily dose or as a compromise give four (4) times exp ected daily dose on day one and the daily dose on each subsequent day (the latter regime takes into account the half-time of warfarin). The daily dose varies depending on body weight, sex, age, diseases and other drugs. Thus a 90 kg six foot tall man of fifty may require 12.5 mg per day while a five foot, 50 kg elderly lady may require only 2 mg.