MINIRIN MELT TABLETS 120MCG

Indications

• Diabetes insipidus
• Nocturnal enuresis
• Postoperative polyuria or polydipsia
• Mild to moderate hemophilia A
• von Willebrand disease
• Fibrinolytic response testing
• Renal function testing

Dosage

Adults: Doses are adjusted according to urine osmol

Mechanism of action

Desmopressin binds to G-protein-coupled V2 receptors on the basolateral membrane of renal distal convoluted tubules and collecting ducts. This interaction activates adenylate cyclase, raising intracellular cyclic AMP levels and promoting the translocation of aquaporin-2 (AQP2) water channels to the apical membrane, facilitating water reabsorption. In vascular endothelium, it stimulates V2 receptors, leading to the release of von Willebrand factor, which stabilizes Factor VIII, enhancing hemostatic function.

Pharmacodynamics

Desmopressin is a selective V2 receptor agonist that increases renal collecting duct permeability to water, reducing urine volume and increasing urine osmolality. Its effects on coagulation include raising plasma levels of Factor VIII and von Willebrand factor, which aids hemostasis. Unlike vasopressin, desmopressin has minimal effects on blood pressure and gastrointestinal motility, and its action can last between 6 to 20 hours depending on the administration route.

Pharmacokinetics

Desmopressin is absorbed well following sublingual or intranasal administration. It has a long duration of action compared to natural vasopressin, and its effects can diminish with repeated dosing due to tachyphylaxis. The drug has a narrow therapeutic index, necessitating careful monitoring of fluid intake to avoid water overload and hyponatremia. The elimination half-life varies based on the route and formulation used.

Contra-indications

• Hypersensitivity to desmopressin or any of its excipients
• Severe renal impairment
• Hyponatraemia
• Fluid retention or conditions associated with fluid overload

Adverse effects

• Headache
• Nausea
• Abdominal cramps
• Flushing
• Hyponatraemia
• Water intoxication
• Dizziness
• Nasal congestion (inhalation form)

Interactions

• Lamotrigine (increases risk of hyponatraemia)
• Antiepileptics (increases risk of hyponatraemia)
• Chlorpromazine (increases risk of hyponatraemia)

Precautions

• Monitor fluid intake and serum sodium levels to prevent hyponatraemia
• Caution in patients with a history of cardiovascular disease or renal impairment
• Use with caution in the elderly or those with conditions predisposing to fluid overload

Pregnancy

Desmopressin should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus, as safety in human pregnancy has not been established.

Breast-feeding

Caution should be exercised when administering desmopressin to breastfeeding women, as it is not known whether it is excreted in human milk.

Storage

Store at room temperature, away from moisture and heat. Protect from light. Keep out of reach of children.

Formulations

• Sublingual tablet (e.g., 100 micrograms)
• Intranasal spray (e.g., 10 micrograms per spray)
• Intravenous injection solution
• Subcutaneous injection solution

Mechanism of action

Desmopressin exerts its effects at the molecular level by binding to G-protein-coupled V2 receptors located on the basolateral membrane of the distal convoluted tubules and collecting ducts of the kidney. Upon binding to the V2 receptor, desmopressin stimulates the enzyme adenylate cyclase, which increases intracellular levels of cyclic AMP (cAMP). This signaling cascade triggers the phosphorylation and translocation of aquaporin-2 (AQP2) water channels from intracellular vesicles to the apical (luminal) cell membrane. These channels allow water to flow passively from the renal tubule back into the systemic circulation, thereby concentrating the urine and maintaining fluid homeostasis. In the vascular endothelium, desmopressin stimulates V2 receptors that trigger the release of von Willebrand factor (vWF) from the Weibel-Palade bodies of endothelial cells. The released vWF subsequently stabilizes and protects Factor VIII in the plasma, effectively increasing the available pool of clotting factors required for primary hemostasis. In the context of primary nocturnal enuresis, desmopressin's action is primarily peripheral (renal); however, research has explored its ability to influence the circadian rhythm of AVP secretion in the central nervous system to help normalize nighttime urine production.

Pharmacodynamics

Desmopressin acts as a selective V2 receptor agonist that systemically regulates water reabsorption and blood coagulation. Its primary action is to increase the permeability of the renal collecting ducts to water, which results in reduced urine volume and increased urine osmolality. Unlike the natural hormone vasopressin, desmopressin has a high degree of selectivity for the V2 receptor over the V1 receptor, meaning it does not cause a significant increase in blood pressure or gastrointestinal smooth muscle contraction. In patients with hemophilia A or von Willebrand disease, desmopressin administration leads to a 2- to 20-fold increase in plasma levels of Factor VIII and von Willebrand factor, though this effect is transient and can diminish with repeated doses due to tachyphylaxis. The duration of action for desmopressin is significantly longer than that of natural vasopressin, typically lasting 6 to 20 hours depending on the route of administration. It has a narrow therapeutic index regarding fluid balance; excessive dosing or failure to restrict fluid intake can rapidly lead to water intoxication and hyponatremia. Systemic physiological changes include a measurable decrease in plasma osmolality and a corresponding increase in urine concentration.