Sunday, 19 August 2007

MRCOG Phenytoin


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).

[3] Clinical Pharmacology,9th edition, P.N.Bennet & M.J.Brown
[5] BNF 53 section 4.8.2
[7],9,Slide 9

Wednesday, 8 August 2007

MRCOG Achondroplasia


This is the most common non lethal skeletal dysplasia.
The clinical characteristics are: short stature (proximal shortening of limbs), large head, and hypoplastic mid face.

Large head with frontal bossing is a common feature but hydrocephalus can also occur(1)

I.Q is usually normal.(2)

Mode of inheritance is autosomal dominant.

Prenatal testing
(a) High risk pregnancy-This is where one or both parents having achondroplasia. It can be done by analysing the cells from chorionic villus sampling or amniocentesis. The objective is identify the fatal homozygous (both genes are defective) achondroplasia from heterozygous (one gene is defective).

(b) Low risk pregnancy: ultrasound done at 22 weeks may detect short foetal limbs.(3)

The children with achondroplasia can also have normal limb lengths at birth

Achondroplasia is also associated with polyhydramnios.(4)