1. Antidiuretic hormone disorders Flashcards
What is diabetes insipidus
Diabetes Insipidus is characterised by polyuria (excessive urine that is dilute) and polydipsia (excessive thirst). This is caused by insufficient ADH or vasopressin.
The two types of diabetes insipidus and its management
Cranial: Hypothalamus/pituitary glands do not make enough ADH. Desmopressin usually treats this
Nephrogenic: The kidneys do not respond to ADH. This is treated with thiazide diuretics through a paradoxical side effect by urinary retention
Desmopressin mechansim of action & compare it to vasopressin
A potent synthetic analogue of vasopressin (ADH), causing the urine to become more concentrated and less in volume. It has a longer duration of action than VASOpressin and has NO vasoconstrictor effects, so will not raise blood pressure
Desmopressin indications and administration
Diabetes insipidus and nocturnal enuresis (bedwetting in children).
It comes as nasal sprays, drops, sublingual tablets.
Desmopressin side effects
Hyponatraemia - low sodium as electrolytes such as sodium become diluted in the blood.
This may induce hyponatraemic convulsions resulting from a depletion of sodium in the brain causing a disruption in brain electrical activity. CAUTION in epileptic patients and elderely, as they are at an increased risk of hyponatraemia
Oedema - excessive conservation of water. CAUTION in heart failure and hypertension, as excessive fluid can also raise blood pressure. Also caution in migraine.
Desmopressin Interactions
Interacts with drugs that increase vasopressin (ADH) secretion, such as tricyclic antidipressants.
Interacts with drugs that cause hyponatraemia, such as NSAIDs, SSRI’s, diuretics.
What is Syndrome of inappropriate antidiuretic hormone secretion (SIADH)
Characterised as hyponatraemia caused by inapropriate ADH secretion as too much water is conserved therefore blood sodium levels are diluted. Resulting in hyponatraemia.
SIADH treatment
- Restrict fluid intake
- Democlocyline (tetracycline - this drug blocks renal effects of ADH in the kidneys)
or Tolvaptan (vasopressin/ADH receptor antagonist).
However if the sodium balance is corrected too quickly it causes a rapid shift of water in cells, damaging the myelin sheath of neurones and can cause serious CNS effects.
