Antidiuretic hormone, or ADH for short, is the primary hormone that regulates fluid balance in the body, and is normally produced by the hypothalamus and stored in the posterior pituitary, which are both located within the brain.
Now, ADH disorders arise when the pituitary releases too much or too little of it. These disorders include diabetes insipidus, which results from a decrease in ADH; and syndrome of inappropriate ADH secretion, or SIADH for short, which results from an increased secretion of ADH.
Okay, so on one end of the spectrum, there’s ADH deficiency, which causes diabetes insipidus. This disorder is treated with ADH replacement therapy, which involves medications like vasopressin, which is a synthetic form of ADH, and desmopressin, which is a vasopressin analogue.
Both medications can be administered subcutaneously. In addition, vasopressin can be administered intramuscularly, and desmopressin can be administered orally, intranasally, or intravenously.
Once administered, these medications act on the kidneys by mimicking the actions of ADH, ultimately promoting the reabsorption of water at the distal convoluted tubule and collecting duct.
Now, these medications may cause side effects like headache, lethargy, and flushing. Other important side effects include nausea, vomiting, heartburn, and abdominal cramps.
In addition, clients who take vasopressin may present with urticaria and vertigo. These medications also cause vasoconstriction, resulting in cardiovascular side effects. Clients on vasopressin may experience chest pain, and even myocardial infarction.
On the other hand, clients taking desmopressin may develop hypertension, tachycardia, and palpitations. In addition, desmopressin may cause anaphylactic reactions. Finally, desmopressin can lead to water intoxication and hyponatremia, which can cause seizures and fatal brain dysfunction.
Alright, now these medications are contraindicated in hyponatremia, and that’s a boxed warning, since it can lead to seizures! In addition, they should be used with caution in clients with severe renal disease, and those with coronary artery disease, since they may cause vasoconstriction.
In addition, vasopressin should be used with caution in clients who experience migraines, seizures, or asthma. On the other hand, desmopressin is also used with caution in those with nephrogenic diabetes insipidus, as well as in clients with cystic fibrosis, hypertension, and electrolyte imbalances.
On the opposite end of the spectrum, there’s ADH excess, which causes syndrome of inappropriate antidiuretic hormone secretion, or SIADH for short.
This disorder is treated with vasopressin receptor antagonists, such as conivaptan, which is administered intravenously, and tolvaptan, which is given orally. Once administered, these medications inhibit the action of ADH, ultimately promoting water excretion in urine.
Side effects of vasopressin receptor antagonists include nausea, vomiting, constipation, as well as polyuria and dehydration. In addition, clients taking conivaptan may experience headache, confusion, insomnia, and increased thirst.
Some clients may also develop injection site reactions, orthostatic hypotension, and electrolyte abnormalities, such as hypokalemia, hypomagnesemia, and hyponatremia.
On the other hand, clients taking tolvaptan may present with dizziness and fever, as well as electrolyte abnormalities like hyperkalemia and hypernatremia, and may develop hyperglycemia.
Finally, tolvaptan may cause strokes, ventricular fibrillation, disseminated intravascular coagulation or DIC, and bleeding, as well as pulmonary embolism, respiratory depression, and rhabdomyolysis.
Lastly, tolvaptan has a boxed warning for hepatotoxicity and for osmotic demyelination syndrome, especially if the hyponatremia from SIADH is corrected too quickly.
Finally, vasopressin receptor antagonists are contraindicated in clients presenting with hypovolemia, and should be used with caution during pregnancy and breastfeeding. Additional precautions for conivaptan include orthostatic hypertension, heart failure, and renal disease.
On the other hand, tolvaptan is also contraindicated in clients with anuria or autosomal dominant polycystic kidney disease, and should be used with caution also in children and elderly clients.
In addition, tolvaptan should be administered in specialized care settings, where blood sodium levels can be carefully monitored during treatment. Finally, caution should be taken in clients with dehydration, hyperkalemia, malnutrition, alcoholism, or hepatic disease.