ADH disorders Flashcards
what is diabetes inspidius
○ Rare condition
○ Characterised by excessive urination and often feeling thirsty
○ Not related to diabetes mellitus
main symptoms of diabetes insidious
§ extreme thirst (polydipsia)
§ excessive urination and at night (polyuria)
cause of diabetes insipidus
○ Problems with a hormone called vasopressin (AVP), aka ADH
what is role of ADH
○ Plays a key role in regulating the amount of fluid in the body
○ Produced by nerve cells in the hypothalamus
○ AVP from the hypothalamus travels to pituitary gland, where it is stored until needed
○ Pituitary gland releases AVP when fluid in the body is low
○ Helps retain water in the body by reducing amount of water lost through kidneys, making the kidneys produce more concentrated urine
what happens in diabetes insipidus re ADH
lack of ADH = kidneys cannot make enough concentrated urine = too much water passes from the body
nephrogenic diabetes inspipidus
○ Rare cases: kidneys do not respond to ADH, causing nephrogenic diabetes insipidus
2 types of diabetes insipidious
cranial
nephrogenic
what is cranial DI
not enough ADH in body to regulate urine production
§ Most common type
§ May be caused by damage to hypothalamus or pituitary gland e.g. post infection, post op, brain tumour, head injury
what is nephrogenic DI
§ Sufficient ADH in body but kidneys do not respond to it
§ May be caused by kidney damage or may be inherited
May be caused by some medications - particularly lithium
which medicine is known to cause nephrogenic DI
lithium
use of the drug desmopressin
analogue of vasopressin = desmopressin
used in the treatment of cranial DI
dose tailored to produce slight diuresis every 24h to avoid water intoxication
when may desmopressin only be required for short period
only in diabetes insipidus following trauma or pituitary surgery
which one has longer duration of action and potency - desmipressin or vasopressin
desmopressin
compare desmopressin and vasopressin
- Desmopressin is more potent and has longer duration of action than vasopressin
- Also has no vasoconstrictor effect, unlike vasopressin - this means it will not increase BP
- Given PO or intranasally for maintenance therapy
- Given by injection in postop period or in unconscious pt
explain use of desmopressin in differential diagnosis of DI - e.g. is it cranial or nephrogenic??
- Water deprivation (this should stimulate normal ADH release in a normal person)
- IM or intranasal dose of desmopression
- If pt is able to produce concentrated urine and reduce urine output after water deprivation and admin of desmopression = cranial DI
- Failure to respond (i.e. still producing dilute urine) = nephrogenic DI
In nephrogenic and partial pituitary diabetes insipidus, benefit may be gain from the paradoxical antidiuretic effect of which drugs
partial pituitary DI = subtype of cranial DI where the patient still produces some ADH but insufficient amounts.
complete pituitary DI = no production of ADH
thiazides e.g. bendro
this AED drug may be useful sometimes in partial pituitary diabetes insidious (unlicensed)
discuss its use
Carbamazepine
May act by sensitising the renal tubules to the action of remaining endogenous vasopressin
Other uses of desmopressin - 3
- Also used to boost factor VIII conc in mild to moderate haemophilia and inn von Willebrand’s disease
- Also used to test fibrinolytic response
- May also have a role in nocturnal enuresis (bed wetting)
other use of vasopressin infusion
used to control variceal bleeding in portal hypertension, before more definitive treatment and with variable results
what is terlipressin
- Derivative of vasopressin (ADH) with less pressor and antidiuretic activity
- Also used in a similar way to vasopressin infusion i.e. for variceal bleeding
less pressor activity = less effect on raising BP
what is oxytocin
- Another posterior pituitary hormone
Indicated in obstetrics
name an ADH antagonist
hint - abx
- Demeclocycline HCl:
- Can be used in treatment of hyponatraemia resulting from inappropriate secretion of ADH, if fluid restriction alone doesn’t restore sodium concentration or is not tolerable
- Thought to act by directly blocking renal tubular effect of ADH
in SIADH, too much ADH = more water reabsorbed = dilutes sodium in the blood = low sodium levels
demecleocycline blocks this and helps the kidneys get rid of excess water and thus allows sodium levels to increase to normal
name the other ADH antagonist (hint not the abx)
and discuss its use
- Tolvaptan
○ Vasopressin V2-receptro antagonist
○ Licensed for treatment of hyponatraemia secondary to syndrome of inappropriate ADH secretion
○ Treatment duration with tolvaptan is determined by the underlying disease and its treatment
○ Rapid correction of hyponatraemia during tolvaptan therapy can cause osmotic demyelination
§ Leads to serious neurological events
§ Close monitoring of serum sodium conc and fluid balance essential!!
interactions with desmopressin are to do with this electrolyte imbalance
hyponatreaemia
e..g diuretics, antipsychotics. antidepressants, NSAIDs, AEDs
Water reabsoption can result in dilution of sodium = hyponatraemia, even if levels in body are normal
A patient has come into the out-patient clinic as they recently experienced urinary retention. They had their blood tests screened which showed an increase in antidiuretic hormone. Which electrolyte imbalance results would also be seen on the patient’s blood test results?
Increased antidiuretic hormone leads to more water being stored in the body. This then dilutes the salt concentration in the blood, resulting in hyponatraemia.
pituitary DI aka
cranial
partial diabetes inspidius is when…
cranial/pituitary
its when you have some ADH, but insufficient
so still have polydipsia and polyuria because there is not enough ADH to effectively control water levels in body
If a patient has untreated DI, what electrolyte imbalance would you exepct?
HYPERnatraemia
This is because there is too much water loss from the body and not enough reabsorption
Body is dehydrated
Thus sodium in body rises
How would you manage nephrogenic diabetes inspididus
Since nephrogenic diabetes insipidus does not respond to desmopressin, treatment typically involves using thiazide diuretics (despite the paradox of diuretic use) and managing electrolyte imbalances. It can also include increasing fluid intake to prevent dehydration.
Desmopressin - what do you need to counsel pt on re water intake?
Have to ensure you are restricting fluid intake otherwise it can lead to fluid retention and/or hyponatraemia
Desmopressin increases water reabsorption in the kidneys, and without appropriate fluid restriction, this can lead to excessive water retention and dilution of sodium levels in the blood. Proper patient education about fluid intake and regular monitoring of electrolyte levels are essential components of safe desmopressin therapy.
Desmopressin what do you need to counsel re nocturnal enuresis
Hyponatraemic convulsions
Patients being treated for primary nocturnal enuresis should be warned to avoid fluid overload (including during swimming) and to stop taking desmopressin during an episode of vomiting or diarrhoea (until fluid balance normal).
