Diabetes Insipidus

Diabetes insipidus (DI) is a disorder of water balance, not glucose metabolism — despite the shared name, it has nothing to do with diabetes mellitus. It is caused by a defect somewhere along the arginine vasopressin (AVP, also called antidiuretic hormone/ADH) axis, producing the excretion of abnormally large volumes of inappropriately dilute (hypotonic) urine, with compensatory thirst and polydipsia.^[1]

Normally, AVP is synthesized in magnocellular neurons of the supraoptic and paraventricular nuclei of the hypothalamus, transported along their axons through the pituitary stalk, and stored in and released from the posterior pituitary (neurohypophysis) — triggered chiefly by a rise in plasma osmolality sensed by hypothalamic osmoreceptors, and to a lesser extent by a fall in blood volume or pressure sensed by baroreceptors. Circulating AVP binds V2 receptors on the basolateral membrane of collecting-duct principal cells, activating a cAMP-protein kinase A pathway that inserts aquaporin-2 (AQP2) water channels into the apical membrane, allowing water reabsorption and concentrating the urine.^[1][2]

Vasopressin (AVP) is synthesized in the paraventricular and supraoptic nuclei of the hypothalamus and transported to the posterior pituitary for release — the exact axis interrupted in central diabetes insipidus. (Aspé-Sánchez M, Moreno M, Rivera MI, Rossi A, Ewer J, CC BY 4.0, Wikimedia Commons)

Two mechanistically distinct defects produce the same clinical picture: central DI, from insufficient AVP synthesis or secretion (a hypothalamic-pituitary problem), and nephrogenic DI, from renal collecting-duct resistance to AVP's action despite normal or even elevated circulating AVP (a kidney problem). A third condition, primary polydipsia, produces an identical polyuria/polydipsia picture through the opposite direction of causation — excessive fluid intake physiologically suppresses AVP, and the resulting polyuria is an entirely appropriate renal response to overhydration rather than any defect of the AVP axis itself. Correctly telling these three apart, especially partial central DI from primary polydipsia, is genuinely the hardest and most consequential step in this chapter.^[1][3]

Central DI is the more common form, with an estimated overall prevalence of roughly 1 in 25,000.^[1] Nephrogenic DI is most often acquired, and lithium is by far its leading cause — a genuinely pharmacist-relevant fact, since lithium produces some degree of concentrating defect in a substantial minority of patients on long-term therapy and is one of the few causes of DI where a pharmacist's medication review and counseling directly change the outcome.^[2]

The core presentation

The defining triad is polyuria (persistently high-volume, dilute urine output — conventionally more than 3 L/day or roughly 50 mL/kg/24h in an adult, occasionally reaching 15-20 L/day in complete central DI), polydipsia (a genuinely intense, often specific craving for cold water), and nocturia, which is frequently the presenting complaint that actually brings the patient in, since it disrupts sleep more than daytime urination does.^[1]

As long as the patient has an intact thirst mechanism and unrestricted access to water, serum sodium and plasma osmolality typically stay normal or only mildly elevated despite the large urine losses — the polydipsia is doing its job. Hypernatremia only develops when free water intake cannot keep pace with urinary losses: impaired thirst, restricted access to water, altered consciousness, or an inability to communicate thirst (infants, postoperative or critically ill patients, some older adults). See Red Flags & Referral.

Clues to the underlying cause

Central DI

• Pituitary or hypothalamic tumours — craniopharyngioma and germinoma in particular, and large pituitary macroadenomas with suprasellar extension compressing or infiltrating the hypothalamic-neurohypophyseal axis.^[1]
• Traumatic brain injury, particularly with a skull-base fracture disrupting the pituitary stalk.^[1]
• Neurosurgery — most often transsphenoidal pituitary surgery; this is common enough, and important enough, to warrant its own monitoring pathway — see Special Populations.^[4]
• Infiltrative and autoimmune disease: Langerhans cell histiocytosis (a classic pediatric cause), neurosarcoidosis, and lymphocytic infundibulo-neurohypophysitis (an autoimmune process, sometimes associated with anti-AVP-cell antibodies).^[1]
• Immune checkpoint inhibitor-induced hypophysitis — an increasingly recognized cause as these cancer therapies become more widely used.
• Familial neurohypophyseal DI — autosomal dominant AVP gene mutations, rare, with progressive childhood onset.^[1]
• Wolfram syndrome (DIDMOAD: DI, diabetes mellitus, optic atrophy, deafness) — rare, autosomal recessive.^[1]
• Idiopathic — a genuine diagnosis of exclusion; a meaningful minority later reveal an underlying lesion on serial imaging, which is why ongoing MRI surveillance matters (see Assessment & Diagnosis and Monitoring & Follow-Up).^[5]

Nephrogenic DI

• Lithium — the leading cause of acquired nephrogenic DI, producing some degree of concentrating defect in a substantial proportion of patients on long-term therapy; risk rises with cumulative dose and duration, and the defect can persist even after lithium is stopped once collecting-duct principal cells have been chronically injured.^[2]
• Hypercalcemia and hypokalemia — both impair AQP2 trafficking and collecting-duct concentrating ability, and both are reversible once corrected.^[2]
• Other drugs: demeclocycline, foscarnet, cidofovir, amphotericin B, and certain fluoroquinolones — less common culprits than lithium, but worth screening for on medication review.
• Chronic kidney disease, relief of chronic urinary tract obstruction (post-obstructive diuresis), and sickle cell disease or trait — chronic tubulointerstitial mechanisms.
• Congenital nephrogenic DI — X-linked AVPR2 mutations account for roughly 90% of congenital cases (affecting males, with carrier females sometimes mildly affected); autosomal AQP2 mutations account for most of the remainder.^[2][6]

Primary polydipsia — not a cause of DI, but the key differential

• Psychiatric illness, particularly schizophrenia and other psychotic disorders.
• Medications with anticholinergic or dry-mouth effects that drive compulsive drinking.
• Habitual high fluid intake pursued for a perceived health benefit.

Confirm true hypotonic polyuria first

Before pursuing a DI-specific workup, confirm the pattern actually fits: urine output persistently above roughly 3 L/day (or 50 mL/kg/24h) in an adult, with urine osmolality below 300 mOsm/kg (or specific gravity below 1.005) in the setting of a normal-to-high plasma osmolality.^[1] Check a serum glucose at the same time — osmotic diuresis from uncontrolled diabetes mellitus is a far more common cause of polyuria and must be excluded before assuming a vasopressin-axis problem. Baseline labs should also include serum sodium, calcium, and potassium, and renal function.

The three-way differential

^[7][3]

Diagnostic testing — two acceptable pathways

The classic indirect water deprivation test (fluid restriction under close supervision, with hourly weight and 2-hourly urine osmolality, continued until 5% of body weight is lost or urine osmolality plateaus, followed by a desmopressin challenge with repeat urine osmolality) remains the practical default where copeptin testing is unavailable, but has a real, well-documented weak point: it correctly separates primary polydipsia from partial central DI in only about 3 of 4 patients, precisely the distinction that matters most clinically.^[3][7] It also requires an experienced centre to interpret safely, since over-restricting fluid in a patient who in fact has severe DI risks dangerous hypernatremic dehydration during the test itself.^[7]

The newer, preferred approach where available is a hypertonic saline-stimulated copeptin test: copeptin is a stable, easily-measured surrogate co-secreted with AVP in equimolar amounts, and a randomized comparison found it correctly distinguished primary polydipsia from partial central DI in over 95% of patients, versus roughly 73% for the water deprivation test.^[3] A single basal (unrestricted) copeptin level above 21.4 pmol/L is high enough, on its own, to diagnose nephrogenic DI without any provocative testing at all — only significant renal AVP resistance produces a copeptin that high in a genuinely polyuric patient.^[3] Copeptin assay availability varies between Canadian centres; where it is not available, the water deprivation/desmopressin protocol remains the practical standard, ideally performed somewhere experienced with it.^[7]

Imaging and cause-finding

Once central DI is confirmed or strongly suspected, obtain pituitary/hypothalamic MRI. Loss of the normal posterior pituitary "bright spot" on T1-weighted imaging supports the diagnosis, but is not standalone diagnostic — it is also absent in up to a quarter of normal individuals. Stalk thickening or a mass lesion points toward the underlying cause.^[5][1] A genuine minority of adults labelled "idiopathic" central DI at diagnosis go on to show an evolving mass or infiltrative lesion on serial imaging over subsequent years — this is why scheduled follow-up MRI (for example, at around 6 months, then periodically) is recommended rather than a single scan at diagnosis being considered definitive.^[5]

For suspected nephrogenic DI, direct the workup at the specific cause: confirm current or recent lithium exposure and duration, calcium, potassium, and renal imaging if obstruction is suspected. A congenital pattern (onset in infancy, X-linked family history) warrants AVPR2/AQP2 genetic testing and referral to a centre experienced with congenital NDI.^[6]

• Restore normal, thirst-guided fluid balance and relieve the polyuria, nocturia, and quality-of-life burden of untreated DI.
• Prevent hypernatremia — the dominant risk of undertreated DI or of any situation where free water access is impaired.
• Prevent hyponatremia and water intoxication — the dominant risk of over-replacement with desmopressin, especially if fluid intake is not also moderated; this "goldilocks" balance, unusual among the conditions in this library, runs through nearly every section of this chapter.
• Identify and correct reversible contributors wherever they exist: reduce or change lithium where psychiatrically feasible, correct hypercalcemia or hypokalemia, relieve urinary tract obstruction.
• In central DI caused by a mass lesion, coordinate antidiuretic therapy with definitive management of the lesion itself, without either delaying necessary desmopressin or over-treating during a period of genuine physiologic flux (for example, the perioperative triphasic response).
• For nephrogenic DI, set a realistic target — most acquired non-lithium and all congenital cases will not "normalize" the way central DI does with desmopressin; a meaningful reduction in urine volume (commonly in the order of 20-50%) plus protection from dehydration is the genuine, achievable goal.
• Equip every patient (and caregivers, where relevant) to recognize and respond to both under- and over-replacement between visits — safe long-term management here depends heavily on the patient's own self-monitoring.

Central DI — desmopressin

Desmopressin (DDAVP) is a synthetic AVP analogue with a longer half-life, minimal pressor activity, and — importantly for pregnancy — resistance to degradation by placental vasopressinase (see Special Populations). It is available as an intranasal spray, an oral tablet, a sublingual/orally-disintegrating tablet, and a subcutaneous/IV formulation for acute or perioperative use.^[5] Bioavailability differs substantially by route: the oral dose needed for an equivalent effect is roughly 10 times the intranasal dose, and the subcutaneous/IV dose is roughly 10 times more potent than the intranasal dose — combined with real inter-individual variability in sensitivity, this is why dosing must always be individualized rather than started at a fixed "standard" dose.^[5] General approach start low, titrate the dose and frequency upward over days to weeks to the lowest amount that controls symptoms (reduced urine volume, resolved nocturia), rather than aiming to eliminate urine output entirely.

Practical prevention build in a deliberate weekly delayed or skipped dose ("drug holiday") to allow a period of free-water clearance (aquaresis) before dilutional hyponatremia can accumulate, and have the patient track daily body weight as a simple home marker of fluid retention.^[8] Avoid unrestricted ad-lib fluid intake alongside a fixed desmopressin dose in any patient who has lost the normal thirst-driven safety valve — adipsic DI, altered consciousness, infants — this specific combination is the classic setup for water intoxication; use a fixed, individualized fluid prescription instead in these patients.

Nephrogenic DI — the paradoxical regimen

1st line, all causes a thiazide diuretic (hydrochlorothiazide) combined with dietary sodium and protein restriction. The mechanism is genuinely counterintuitive: mild thiazide-induced volume depletion activates the renin-angiotensin-aldosterone system, which increases proximal tubule sodium and water reabsorption — leaving less volume delivered to the resistant distal nephron, and therefore less obligate free-water loss despite the underlying AQP2/V2-receptor defect being completely unchanged. Sodium and protein restriction reduce the solute load that must be excreted through the same mechanism, further shrinking obligate urine volume.^[2]

Adjunct, insufficient response add an NSAID (indomethacin, or ibuprofen as a more practical alternative) — NSAIDs inhibit renal prostaglandin synthesis, which normally blunts AVP's action, so removing that brake augments whatever concentrating capacity remains; monitor renal function closely, especially alongside a thiazide, given the additive renal risk.^[2]

Lithium-induced nephrogenic DI — a specific, mechanism-targeted option

Lithium-induced NDI specifically add amiloride to the thiazide-and-diet regimen (or use a combination amiloride-hydrochlorothiazide product for convenience). Amiloride blocks the epithelial sodium channel (ENaC) on the apical membrane of collecting-duct principal cells — which is the exact route lithium itself uses to enter those cells — so amiloride both contributes its own paradoxical antidiuretic effect and limits ongoing lithium-induced cellular injury.^[9][2] A randomized, placebo-controlled crossover trial in lithium-treated patients found that 6 weeks of amiloride 10 mg daily measurably improved desmopressin-stimulated urinary concentrating ability and increased urinary AQP2 excretion.^[9]

Amiloride does not interfere with lithium's therapeutic mood-stabilizing effect, so it is specifically valuable when lithium remains psychiatrically necessary and cannot simply be stopped.^[2] Watch closely both thiazides and amiloride reduce lithium clearance and can raise serum lithium concentration — arrange closer lithium-level monitoring, and coordinate any lithium dose adjustment with the prescriber, whenever either diuretic is started or adjusted.^[2] Where lithium can be discontinued or switched without destabilizing the patient's psychiatric condition, that is generally preferable — but this decision belongs with the prescriber/psychiatry team, not a unilateral pharmacist recommendation to stop.

Congenital nephrogenic DI

The same general paradoxical approach (thiazide plus low-solute diet, with an NSAID or amiloride added as needed) applies lifelong in congenital AVPR2/AQP2-related NDI, with genotype- and age-specific detail beyond this chapter's scope; refer to a centre experienced with the condition, per the current international expert consensus.^[6]

Primary polydipsia

Do not treat with desmopressin or any antidiuretic agent — the correct management is gradual, supervised reduction of fluid intake and addressing the underlying psychiatric or behavioural driver (see Non-Pharmacologic Treatment), not pharmacologic antidiuresis.

• Free access to water at all times is itself core therapy in untreated or newly diagnosed DI — never restrict fluids as home management. Fluid restriction has exactly one legitimate use in this condition: the closely supervised diagnostic water deprivation test, never a routine treatment step.
• Dietary sodium and protein restriction is core therapy for nephrogenic DI, not an optional adjunct to the thiazide — both act through the same reduced-solute-load mechanism described in Choose Initial Treatment, and the regimen predictably underperforms if dietary adherence is poor.^[2]
• A medical alert bracelet or wallet card documenting the DI diagnosis and desmopressin dependence is genuinely important for central DI patients, given the real risk of rapid, severe hypernatremic dehydration if a treating team unfamiliar with the diagnosis withholds or delays desmopressin while the patient cannot advocate for themselves (unconscious, post-trauma, postoperative).
• Daily home self-monitoring — body weight, and where practical, urine frequency/volume and thirst level — gives both the patient and the care team an early warning of under- or over-treatment between visits.
• For adipsic patients, or anyone with impaired consciousness or cognition, use a fixed, prescribed daily fluid volume rather than thirst-guided intake, with caregiver education, since the normal safety net of thirst is absent.
• Work with the prescriber toward the lowest effective lithium dose, or an alternative mood stabilizer where psychiatrically appropriate, rather than a pharmacist independently recommending discontinuation.
• Correct hypercalcemia or hypokalemia directly, and relieve urinary tract obstruction where present — both are genuinely reversible causes of nephrogenic DI.
• For primary polydipsia, a gradual, supervised reduction in fluid intake — not an abrupt cutoff — plus psychiatric or behavioural support where a psychiatric driver is identified.
• Offer genetic counselling for congenital nephrogenic DI and familial neurohypophyseal DI, given the hereditary pattern and its implications for family planning.^[6]

Pregnancy

DI in pregnancy is uncommon, affecting roughly 2-4 per 100,000 gestations, but genuinely distinct in mechanism and management.^[10] The placenta produces vasopressinase (a cysteine aminopeptidase from the trophoblast) that degrades native circulating AVP — this can unmask or worsen central DI as pregnancy progresses, and can also produce a transient, gestation-limited DI in women with no prior history, through excessive placental vasopressinase activity alone.^[10] Treatment of choice, any DI in pregnancy desmopressin — unlike native vasopressin, it is structurally resistant to degradation by placental vasopressinase, so it remains fully effective throughout gestation.^[10] Women with pre-existing central DI typically need their desmopressin dose titrated upward during pregnancy (increased vasopressinase activity plus expanded plasma volume and GFR), and back down again after delivery.^[10][1]

Transient gestational DI clusters with preeclampsia, HELLP syndrome, and acute fatty liver of pregnancy — impaired hepatic clearance of vasopressinase in these conditions is thought to contribute — so new polyuria/polydipsia later in pregnancy, especially alongside hypertension or liver dysfunction, should prompt evaluation for both.^[10] Gestational DI typically resolves within 4-6 weeks postpartum as placental vasopressinase clears; persistence beyond this window suggests unmasking of pre-existing, previously subclinical central or nephrogenic DI rather than a truly transient process.^[10] Arrange pre-pregnancy counselling for women with known DI, and closer-than-usual monitoring through gestation given the likelihood of a changing dose requirement.^[10] For any pregnancy-associated nephrogenic component, involve obstetrics before starting a thiazide, given the generally more cautious approach to diuretics in pregnancy.

Postoperative and neurosurgical patients — the triphasic response

Postoperative DI is genuinely common after pituitary/hypothalamic surgery — reported in roughly 10-20% of patients after transsphenoidal resection, and considerably higher at some centres — but the large majority is transient, resolving within a week in about half of affected patients and within 3 months in the large majority.^[4] A minority instead follow a distinctive triphasic pattern, which is uncommon overall but is exactly the pattern most likely to produce a missed, clinically significant complication if it is not anticipated:^[4]

^[4]

The practical implication: arrange close inpatient monitoring of fluid balance, urine output, and serum sodium for at least the first one to two weeks after any pituitary or hypothalamic surgery, and reassess the ongoing need for desmopressin regularly rather than continuing a fixed postoperative dose by default — a patient successfully treated for Phase 1 who continues unchanged into Phase 2 is at real risk of significant hyponatremia.^[4] Equally, do not assume early postoperative polyuria means permanent DI — most does not — nor assume it will always resolve on its own; confirm the final status with follow-up testing rather than guessing either way.

Pediatrics

Infants with congenital nephrogenic DI cannot express thirst behaviorally and present instead with unexplained fevers, poor feeding, failure to thrive, and hypernatremic dehydration in the first weeks of life. Early diagnosis and a structured feeding/fluid protocol matter enormously here, since repeated hypernatremic episodes in infancy carry a real risk to neurodevelopment — refer to a paediatric nephrology or endocrinology centre rather than managing this population in a general/adult-oriented pathway.^[6]

Renal impairment

Thiazide efficacy for nephrogenic DI falls away as glomerular filtration declines, roughly below an eGFR in the 30-45 mL/min range depending on the specific agent; a loop diuretic is sometimes substituted in this setting for a broadly similar solute-delivery-reducing effect, though the evidence specific to nephrogenic DI is limited — involve nephrology for this population.

Older adults

Blunted thirst sensation, comorbid cognitive impairment, and polypharmacy all compound the "safety net gone" hypernatremia risk described in Red Flags & Referral — apply a lower threshold for close monitoring and caregiver involvement in this group.

• Central DI on desmopressin: check serum sodium at initiation and with every dose change (for example, within the first 1-2 weeks), then periodically thereafter — more frequently during early titration, during any hospitalization or perioperative period, or in a patient unable to reliably self-monitor. Reinforce the weekly delayed-dose technique and daily weight tracking at every visit.^[8][5]
• Nephrogenic DI on a thiazide and/or amiloride: monitor serum sodium, potassium, and renal function; where lithium continues, check the lithium level specifically after starting or adjusting either diuretic, given the real interaction described in Choose Initial Treatment. Reassess urine volume and symptoms to confirm the regimen is achieving the expected 20-50% reduction rather than assuming full normalization.
• Central DI with no cause identified at diagnosis: schedule surveillance pituitary MRI (for example, at around 6 months, then periodically per specialist judgment) to catch an evolving mass or infiltrative lesion not visible at initial presentation.^[5][1]
• Postoperative patients: daily sodium and fluid-balance monitoring through the anticipated triphasic window, with an explicit plan to reassess and, where appropriate, discontinue desmopressin as the patient transitions between phases rather than continuing a fixed dose indefinitely.^[4]
• Complete medication reconciliation whenever a new diuretic, NSAID, or other nephrotoxic or hyponatremia-risk agent is added for a patient already established on desmopressin, or on amiloride/thiazide therapy for nephrogenic DI.
• In pregnancy, reassess the desmopressin dose requirement at each trimester and again postpartum, anticipating both an increased requirement during gestation and a prompt taper or discontinuation afterward if the DI was gestational.^[10]

1. Central DI on desmopressin with persistent polyuria or nocturia despite what seems like an adequate trial: reassess adherence and, for the intranasal route, device/technique and concurrent nasal congestion (which reduces absorption) before titrating the dose further or switching routes, rather than assuming true pharmacologic failure.
2. New hyponatremic symptoms in a desmopressin-treated patient: hold the next dose, check serum sodium urgently, and institute (or reinforce) a scheduled drug holiday rather than simply trimming the dose slightly and continuing unchanged.
3. Suspected nephrogenic DI with minimal response to thiazide plus dietary sodium/protein restriction: confirm dietary adherence first — this regimen fails quickly if sodium restriction is not genuinely followed — then add an NSAID; for a lithium-related cause, add or optimize amiloride specifically and revisit whether a lithium dose reduction is feasible with the prescriber.
4. A patient whose polyuria does not fit its presumed category — for example, apparent nephrogenic DI that unexpectedly responds well to desmopressin, or vice versa — should prompt reconsidering the original classification; a partial defect or an evolving central lesion can be missed on an equivocal initial water deprivation test. Consider repeat testing or a copeptin-based assessment at a specialized centre.
5. Idiopathic central DI with a normal MRI at diagnosis but a changing picture — new anterior pituitary hormone deficits, visual symptoms, or stalk thickening on follow-up imaging — warrants closer-interval repeat imaging and neuro-endocrine referral rather than continuing to label it idiopathic indefinitely.
6. Persistent hypokalemia, or a rising lithium level, after starting a thiazide/amiloride regimen for lithium-induced nephrogenic DI: adjust potassium and lithium monitoring and coordinate a lithium dose reduction with psychiatry, rather than abandoning the antidiuretic regimen outright, unless the interaction genuinely cannot be managed.

• Assuming any polyuria is DI without first checking serum glucose and confirming the urine is truly dilute — osmotic diuresis from uncontrolled diabetes mellitus is a far more common cause.
• Prescribing desmopressin before confirming central (rather than nephrogenic) DI, or in an unrecognized primary polydipsia patient — both scenarios cause genuine harm: ineffective therapy in nephrogenic DI, and a real risk of dangerous hyponatremia in primary polydipsia.
• Allowing unrestricted, ad-lib fluid intake alongside a fixed desmopressin dose in any patient without a reliable, intact thirst mechanism.
• Using fluid restriction as routine home management of DI rather than reserving it for the closely supervised diagnostic water deprivation test alone.
• Treating lithium-induced nephrogenic DI with desmopressin instead of the paradoxical thiazide/amiloride approach that actually addresses a renal-resistance mechanism.
• Stopping lithium abruptly or unilaterally as a "DI treatment" without coordinating with the prescribing psychiatrist — amiloride specifically exists to allow lithium to continue when it is still needed.
• Missing the interaction risk of adding a thiazide or amiloride to a patient on lithium without arranging closer lithium-level monitoring.
• Continuing a fixed postoperative desmopressin dose unchanged through the full triphasic window without daily sodium monitoring, risking a missed transition into the SIADH phase.
• Treating an absent posterior pituitary "bright spot" on MRI as independently diagnostic of central DI — it is also absent in up to a quarter of normal individuals.
• Failing to schedule surveillance MRI in adult idiopathic central DI, and so missing an evolving mass lesion not visible at initial diagnosis.
• Relying on the classic water deprivation test as though it reliably separates partial central DI from primary polydipsia — its accuracy for exactly this distinction is only moderate; a hypertonic-saline copeptin approach, where available, performs substantially better.

How to use this table: Doses are adult doses and require patient-specific confirmation (renal/hepatic function, weight, allergy history). Pediatric dosing is weight-based per the current product monograph unless stated. Drug pricing is intentionally omitted. Select any drug name to open its complete Pharmasist Drug Database page.

Central DI — Desmopressin, by Route

Bioavailability differs substantially by route — the oral dose is roughly 10-fold the intranasal dose, and the SC/IV dose is roughly 10-fold more potent than intranasal. Individualize every dose; start low and titrate to symptom relief.

Nephrogenic DI — The Paradoxical Antidiuretic Regimen

<div data-block="lesson-gallery"><img src="https://upload.wikimedia.org/wikipedia/commons/4/49/2625_Aquaporin_Water_Channel.jpg" alt="Diagram of a water channel (aquaporin) protein embedded in a cell membrane, with water molecules passing through"><div data-block="caption">A water channel (aquaporin) protein embedded in the cell membrane — the same family of channel, aquaporin-2, that vasopressin inserts into the collecting-duct apical membrane, and whose trafficking is disrupted in nephrogenic diabetes insipidus. (OpenStax College, Anatomy & Physiology, CC BY 3.0, Wikimedia Commons)</div></div> Desmopressin has no role here — these agents work by reducing obligate urine volume through renal sodium/solute handling, not by replacing a hormone the kidney cannot respond to.