Antidiuretic hormone disorders Flashcards
What is diabetes insipidus?
Large amount of dilute urine produced causing extreme thirst
What are the two types of DI and what are their causes?
> Pituitary (cranial): hypothalamus does not create enough ADH
Nephrogenic: kidneys do not respond to ADH
How can nephrogenic DI be treated?
Thiazide diuretics- due to paradoxical effect on kidneys
What are the two meds used for treatment of pituitary DI?
Vasopressin and its analogue Desmopressin.
Doses adjusted to produce slight diuresis every 24 hours to avoid water intoxication
Which is more potent vasopressin or desmopressin?
Desmopressin- it also has a longer duration of action and has no vasoconstrictor effects
When is desmopressin used?
In the differential diagnosis of pituitary diabetes insipidus- failure to respond indicates nephrogenic diabetes insipidus
What is the use of carbamazepine in diabetes insipidus?
It is sometimes useful in sensitising renal tubules to the action of remaining vasopressin
What are some other uses for desmopressin?
> In haemophilia and Von Willebrands disease to boost factor VIII (8) concentration.
Nocturnal enuresis.
What advice should be given to patients about fluid intake when on desmopressin?
Limit fluid intake to a minimum from 1 hour before dose until 8 hours afterwards.
Why should intranasal desmopressin not be given in nocturnal enuresis?
Due to increased risk of hyponatraemic convulsions
What are the common side effects of desmopressin?
-Fluid retention
-Hyponatraemia on administration without restricting fluid intake (in more serious cases
with convulsions)
-Stomach pain
-Headache
-Nausea and vomiting
What is the major side effect that should be considered with desmopressin?
- Increased risk of hyponatraemic convulsions when
taking desmopressin for nocturnal enuresis.
How can the risk of hyponatraemic convulsions be reduced?
- Avoiding fluid overload
- Stopping the medication during an episode of vomiting or diarrhoea (until fluid balance normal).
- Keeping to the recommended doses and by avoiding concomitant use of drugs which increase secretion of vasopressin (e.g. paracetamol, nicotine, and tricyclic
antidepressants) .
Which group are more at risk of hyponatraemic convulsions and how should this be managed?
Increased risk in elderly patients — measure baseline
serum sodium concentration, then monitor regularly
during treatment; discontinue treatment if levels fall
below baseline.
What are the risks of desmopressin in pregnancy?
Small oxytocic effect in third trimester; increased risk
of pre-eclampsia
