Phenindione

A 'resistant' patient may need 200 mg/day or more; a 'sensitive' patient may need less than 50 mg/day. Concomitant heparin therapy affects INR control tests — heparin should be discontinued at least 6 hours before the first INR control test. Control tests must be undertaken at regular intervals and the dose adjusted according to the results. Monitoring (§4.4): when started using a standard dosing regimen, determine the INR daily or on alternate days in the early days of treatment; once stabilised in the target range the INR can be determined at longer intervals; monitor more frequently in patients at increased risk of over-anticoagulation (e.g. severe hypertension, liver or renal disease) and where adherence may be difficult. Thrombophilia: in patients with protein C deficiency, therapy should be introduced WITHOUT a loading dose (risk of skin necrosis) even if heparin is given; patients with protein S deficiency may also be at risk and therapy should be introduced slowly. Factors that exaggerate the effect and require dose reduction: weight loss, elderly patients, acute illnesses, deficient renal function, decreased dietary vitamin K intake, and certain drugs. Factors that reduce the effect and may require dose increase: weight gain, diarrhoea and vomiting, increased intake of vitamin K, fats or oils, and certain drugs. Review the need for therapy regularly and discontinue when no longer required; issue a patient-held anticoagulant card. Rare cases of calciphylaxis have been reported with vitamin K antagonists — consider stopping treatment if diagnosed. Metabolites often colour the urine pink or orange. Paediatric use: the fetched SPC sections contain no paediatric posology — no paediatric dose is given; verify any paediatric use against a children's formulary and specialist haematology advice. Section 4.5 was not captured in the source bundle; the interactions listed here are drawn from the §4.3 and §4.4 text that was retrieved.