Desmopressin (DDAVP)

Mechanism

Pharmacological Class and Group

Synthetic analogue of the antidiuretic hormone vasopressin (Selective V2 receptor agonist).

Mechanism of Action

Desmopressin results from two major structural modifications of the native arginine vasopressin: the deamination of hemicystin in position 1 and the substitution of L-arginine for D-arginine in position 8. This almost completely eliminates its affinity for the V1a receptor (responsible for the effect of peripheral systemic vasoconstriction and elevation of blood pressure) and exponentially increases its selective antidiuretic potency at the receptor. V2.

Cellular Water Retention Mechanism

1. Basolateral V2 Receptor Binding: Desmopressin selectively binds to Gs protein-coupled vasopressin type 2 receptors (V2R) on the basolateral cell membrane of the principal cells of the cortical and medullary collecting duct of the kidney.

2. Activation of Adenylate Cyclase and PKA: Signaling stimulates the synthesis of cAMP, directly activating protein kinase A (PKA).

3. Translocation of Aquaporin-2 (AQP2) to Apical Membrane: PKA phosphorylates cellular actin-myosin motors promoting exocytosis and translocation of cytoplasmic vesicles containing water channels Aquaporin-2 (AQP2) toward the cellular apical luminal membrane:

Insertion of AQP2 Passage of water from the urinary lumen to the cellular cytosol Exit to the interstitium by AQP3/AQP4

4. Urine Concentration and Decrease in Urinary Flow: Water is passively reabsorbed following the hypertonic medullary osmotic gradient, netly reducing urinary volume and proportionally raising urinary osmolarity.

5. Release of Coagulation Factors (Extra-renal effect mediated by endothelial V2 receptors): Stimulates the release into the capillary circulation of Von Willebrand Factor (vWF) from the endothelial Weibel-Palade bodies and Coagulation Factor VIII, enhancing primary hemostasis.

Pharmacokinetics

High Resolution Pharmacokinetics

• Routes of administration: Oral (tablets), sublingual (oral lyophilized), intranasal (spray) and intravenous/subcutaneous.
• Bioavailability: Extremely low orally (0.08% to 0.16%) due to gastric proteolytic digestion, requiring substantially higher doses than parenteral doses. Intranasal bioavailability of 3-5%; complete parenteral (100%).
• Distribution: Apparent volume of distribution of 0.2-0.5 L/kg. It does not bind to circulating plasma proteins. It does not significantly cross the blood-brain barrier.
• Metabolism: Enzymatic peptide clearance without participation of hepatic cytochrome CYP450.
• Excretion: 65% of the absorbed dose is excreted unchanged in urine in the following 24 hours.
• Half-life (t_1/2): Terminal elimination half-life of approximately 2 to 3 hours, but the local antidiuretic biological effect persists between 6 and 12 hours depending on the formulation.

Indicators and dose

Clinical Indications and Off-Label Uses

• Central Diabetes Insipidus (Neurogenic): Standard first-choice replacement treatment (inadequate pituitary secretion of ADH). Note: It has no efficacy in nephrogenic diabetes insipidus (tubular resistance to the V2 receptor).
• Primary Monosymptomatic Nocturnal Enuresis: In pediatric patients over 5 years of age with adequate prior nocturnal fluid restriction.
• Von Willebrand Disease Type 1 and Mild Hemophilia A: For the control of bleeding or prevention of bleeding prior to minor surgical interventions (such as dental extractions).
• Nocturia associated with idiopathic nocturnal polyuria in adults: Net reduction in nocturnal urine volume.

Dosage and Clinical Adjustment

Central Diabetes Insipidus:

• Oral Formulation: Start with 0.1 mg three times a day orally. Usual therapeutic range of 0.1 mg to 0.8 mg daily divided into 2 or 3 doses, adjusting doses individually according to urinary volume and electrolyte balance.
• Intranasal Formulation (Spray): Start with 10 µg per day intranasally (a single spray shot), which can be administered as a single dose or divided into two doses (usual range of 10-40 µg per day).
• Parenteral formulation (SC / EV): 0.5 to 1 µg every 12 hours.

Von Willebrand Disease / Mild Hemophilia A (Hemostatic Prophylaxis):

• 0.3 µg/kg diluted in 50 mL of physiological solution by slow intravenous route over a period of 20-30 minutes, administered 30 minutes prior to the scheduled surgery.

Adjustment in Renal Failure: Absolutely contraindicated in patients with eGFR < 50 mL/min/1.73 m².

Security

Absolute and Relative Contraindications

Absolute Contraindications

• Hypersensitivity to the drug.
• Established hyponatremia prior to initiation: Serum sodium levels < 135 mEq/L.
• Congestive heart failure or conditions prone to volume overload.
• Psychogenic polydipsia or active dipsomania (extreme risk of induced free water intoxication).
• Syndrome of inappropriate ADH secretion (SIADH).
• Moderate to severe renal failure (eGFR < 50 mL/min/1.73 m²).

Relative Contraindications

• Elderly patients (>65 years), due to a very high intrinsic susceptibility to rapidly develop severe dilutional hyponatremia.
• Von Willebrand disease Type 2B (induced risk of spontaneous intravascular platelet aggregation and secondary consumptive thrombocytopenia).

Adverse Effects (ADR) and Specific Toxicity

• Common (1%-10%): Transient throbbing headache, nausea, mild abdominal cramping pain, xerostomia (dry mouth), congestion or irritation of the nasal mucosa (with chronic use of nasal spray), mild epistaxis.
• Very rare (<0.01%): Severe water intoxication and acute dilutional hyponatremia.

Critical Toxicity: Severe Dilutional Hyponatremia

If desmopressin is administered without rigorous restriction of free water intake, the kidney continues to reabsorb water despite plasma dilution. This decreases the osmolarity of the extracellular fluid and causes the osmotic movement of water into the cells, inducing severe acute cerebral edema.

Desmopressin + Unrestricted Water Intake Hyponatremia (Na⁺ < 120 mEq/L) Cerebral Edema

Initial symptoms include progressive headache, nausea, explosive vomiting, psychomotor agitation, mental confusion, and disorientation. If left uncorrected, it rapidly progresses to massive cerebral edema, generalized tonic-clonic seizures, coma, and death from uncal herniation. It is mandatory to suspend the drug and give priority to 3% hypertonic saline under strict monitoring in the ICU to prevent central pontine myelinolysis.

Drug Interactions of Clinical Relevance

• SIADH-inducing drugs (NSAIDs, Carbamazepine, SSRI Antidepressants, Clofibrate): Powerful pharmacodynamic synergism that massively enhances free water retention and increases the risk of severe acute hyponatremia.
• Loperamide: Increases the plasma concentration of oral desmopressin by up to threefold by increasing transit time and intestinal absorption permeability.

Safety in Pregnancy and Breastfeeding

• Pregnancy: Compatible. It has been used safely and effectively in pregnant patients with central diabetes insipidus without reporting an increase in congenital malformations or uterotonic effects (it does not significantly activate the V1b or oxytocic receptor at therapeutic doses).
• Breastfeeding: Compatible. It is excreted in breast milk in extremely low quantities, insensible to alter the free water balance or the natural antidiuretic function of the infant.