Sunday, 19 August 2007

MRCOG Phenytoin

Phenytoin
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Pharmacokinetics
Phenytoin is poorly absorbed from the intestine.[1]
It is metabolised in the liver.[2]


The half life of phenytoin at low doses (giving subtheraputic concentrations) is 6-24 hours.[3]It increases to 20-60 hours at higher doses.


Phenytoin is administered orally or by intravenous injection.[4]
Phenytoin sodium may be given by slow intravenous injection, with ECG monitoring, followed by the maintenance dosage. Intramuscular use of phenytoin is not recommended (absorption is slow and erratic).[5]
Fosphenytoin is a water soluble pro-drug of phenytoin which can be administered by intramuscular injection.


Magnesium sulphate is superior to phenytoin for the prevention of eclampsia in hypertensive pregnant women.[6]


Phenytoin can cause fetal hydantoin syndrome. The following are the features of fetal hydantoin syndrome[7]

(a) mild to moderate growth deficiency
(b) mild mental deficiency
(c) craniofacial abnormalities 


(i) ocular hypertelorism
(
ii)broad nasal bridge
(iii) low set abnormal ears
(
iv)cleft lip and palate
(v) hypoplasia of distal phalanges
(
vi)micro - brachycephaly

Hirsutism is side effect of phenytoin. Phenytoin could also cause folate deficiency and this is why epileptic patients needs folic acid in a higher dose(5 mg).

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[1] http://www.emedicine.com/emerg/topic421.htm
[2] http://www.emedicine.com/emerg/topic421.htm
[3] Clinical Pharmacology,9th edition, P.N.Bennet & M.J.Brown
[4] http://findarticles.com/p/articles/mi_m0FSS/is_6_14/ai_n17211622/pg_3
[5] BNF 53 section 4.8.2
[6] http://content.nejm.org/cgi/content/abstract/333/4/201
[7] http://www.ulg.upol.cz/www/lectures/Teratogen%ED%20faktoryAng.ppt#262,9,Slide 9