Desmopressin: diabetes insipidus and low sodium risk

Vasopressin tells the kidneys to hold on to water. In cranial diabetes insipidus the pituitary does not release enough, so large volumes of dilute urine are passed and intense thirst follows. The emc entry describes DDAVP tablets as treatment for vasopressin-sensitive cranial diabetes insipidus and for excess urine output and thirst after pituitary surgery. Desmopressin acts on kidney receptors to reduce urine volume and concentrate it. The condition shares a name with diabetes mellitus but is unrelated to blood sugar. A dedicated NHS patient page was not available when checked.

The SmPC gives a starting dose for adults and children and says maintenance is adjusted to the response, usually within a stated range several times a day. Specialists tailor the dose to urine volume, thirst and blood sodium. Tablet products include 0.1 mg and 0.2 mg DDAVP tablets and sublingual formulations from other suppliers listed on emc, which are not interchangeable milligram for microgram, so always use the product on your label.

Because desmopressin keeps water in, drinking large volumes while on it can dilute the blood. The SmPC says that treatment without a reduction in fluid intake may lead to water retention and hyponatraemia, with headache, nausea, vomiting and weight gain. Follow your specialist's advice on how much to drink, and report persistent headache, nausea, vomiting or sudden weight gain promptly.

• Seek urgent advice: severe headache or repeated vomiting.

• Report sudden weight gain.

The SmPC says it is unsuitable for people with cardiac insufficiency or other conditions needing diuretics. Psychogenic polydipsia and alcohol misuse must be excluded before prescribing.

The SmPC names SSRIs, tricyclic antidepressants, carbamazepine and NSAIDs as medicines that increase hyponatraemia risk. Loperamide can increase desmopressin levels about threefold. Tell your specialist before starting any new prescription or over-the-counter medicine, including painkillers such as ibuprofen.

The SmPC reports limited data from pregnancies with desmopressin exposure, with rare malformations noted, and recommends blood pressure monitoring because of pre-eclampsia risk. Treatment in pregnancy for diabetes insipidus is managed by a specialist team.

Useful topics include how many times a day you pass urine, how thirsty you feel, whether you wake at night to drink or pass urine, any headache or nausea after doses, and which other medicines you take. Your team uses this, with blood sodium results, to decide whether the dose is balanced between controlling the polyuria and avoiding water retention. Bring a short diary of fluid intake and urine output if asked, because it gives the clinic a clearer picture than memory alone, and mention any recent illness, travel or hot weather that may have changed how much you drank.

People on desmopressin often carry a medical alert card, check weight if instructed, and have periodic sodium tests, particularly after a dose change or during illness with vomiting or diarrhoea. If you are unwell and cannot take tablets or keep fluids down, contact your endocrinology team or NHS 111 because both too much and too little desmopressin effect can be hazardous. Desmopressin is prescription only, and suspected side effects can be reported through the Yellow Card scheme.