Duloxetine Stats & Data
CNCCC(Oc1cccc2ccccc12)c1cccs1ZEUITGRIYCTCEM-KRWDZBQOSA-NPharmacology
DrugBankDescription
Duloxetine is a dual serotonin and norepinephrine reuptake inhibitor. It was originally discovered in 1993 and developed by Eli Lilly and Company as LY248686. Duloxetine first received approval from the FDA in August, 2004 as Cymbalta for the treatment of Major Depressive Disorder. It has since received approval for a variety of indications including the treatment of neuropathic pain, Generalized Anxiety disorder, osteoarthritis, and stress incontinence. Duloxetine continues to be investigated for the treatment of pain in cancer, surgery, and more.
Mechanism of Action
Duloxetine is a potent inhibitor of neuronal serotonin and norepinephrine reuptake and a less potent inhibitor of dopamine reuptake. Duloxetine has no significant affinity for dopaminergic, adrenergic, cholinergic, histaminergic, opioid, glutamate, and GABA receptors. Action on the external urinary sphincter is mediated via duloxetine's CNS effects. Increased serotonin and norepinephrine concentrations in Onuf's nucleus leads to increased activation of 5-HT2, 5-HT3, and α1 adrenergic receptors. 5-HT2 and α1 are both Gq coupled and their activation increases the activity of the inositol trisphosphate/phospholipase C (IP3/PLC) pathway. This pathway leads to release of intracellular calcium stores, increasing intracellular calcium concentrations, and facilitating neuronal excitability. 5-HT3 functions as a ligand-gated sodium channel which allows sodium to flow into the neuron when activated. Increased flow of sodium into the neuron contributes to depolarization and activation of voltage gated channels involved in action potential generation. The combined action of these three receptors contributes to increased excitability of the pudendal motor nerve in response to glutamate. Also related to duloxetine's action at the spinal cord is its modulation of pain.
Pharmacodynamics
Duloxetine, through increasing serotonin and norepinephrine concentrations in Onuf's nucleus, enhances glutamatergic activation of the pudendal motor nerve which innervates the external urethral sphinter. This enhanced signaling allows for stronger contraction. Increased contraction of this sphincter increases the pressure needed to produce an incontinence episode in stress urinary incontinence. Duloxetine has been shown to improve Patient Global Impression of Improvement and Incontinence Quality of Life scores. It has also been shown to reduce the median incontinence episode frequency at doses of 40 and 80 mg. Action at the dorsal horn of the spinal cord allows duloxetine to strengthen the the serotonergic and adrenergic pathways involved in descending inhibition of pain. This results in an increased threshold of activation necessary to transmit painful stimuli to the brain and effective relief of pain, particularly in neuropathic pain. Pain relief has been noted in a variety of painful conditions including diabetic peripheral neuropathy, fibromyalgia, and osteoarthritis using a range of pain assessment surveys. While duloxetine has been shown to be effective in both animal models of mood disorders and in clinical trials for the treatment of these disorders in humans, the broad scope of its pharmacodynamic effects on mood regulation in the brain has yet to be explained.
Metabolism
Duloxetine is extensively metabolized primarily by CYP1A2 and CYP2D6 with the former being the greater contributor. It is hydroxylated at the 4, 5, or 6 positions on the naphthalene ring with the 4-hydroxy metabolite proceeding directly to a glucuronide conjugate while the 5 and 6-hydroxy metabolites proceed through a catechol and a 5-hydroxy, 6-methoxy intermediate before undergoing glucuronide or sulfate conjugation. CYP2C9 is known to be a minor contributor to the 5-hydroxy metabolite. Another uncharacterized metabolite is known to be excreted in the feces but comprises <5% of the total excreted drug. Many other metabolites exist but have not been identified due their low contribution to the overall profile of duloxetine and lack of clinical significance.
Absorption
Duloxetine is incompletely absorbed with a mean bioavailability of 50% although there is wide variability in the range of 30-80%. The population absorption constant (ka) is 0.168 h-1.The molecule is susceptible to hydrolysis in acidic environments necessitating the use of an enteric coating to protect it during transit through the stomach. This creates a 2 hour lag time from administration to the start of absorption. The Tmax is 6 hours including the lag time. Administering duloxetine with food 3 hour delay in Tmax along with an 10% decrease in AUC. Similarly, administering the dose at bedtime produces a 4 hour delay and 18% decrease in AUC with a 29% reduction in Cmax. These are attributed to delayed gastric emptying in both cases but are not expected to impact therapy to a clinically significant degree.
Toxicity
**Overdose** Fatalities have been reported with doses of 1000mg involving both mixed drugs as well as duloxetine alone. Signs and symptoms of overdose include: somnolence, coma, serotonin syndrome, seizure, syncope, hypo- or hypertension, tachycardia, and vomiting. No antidote exists and the drug is unlikely to be cleared by hemodialysis. Supportive care is recommended along with activated charcoal and gastric lavage to reduce absorption. If serotonin syndrome occurs specific treatment such as temperature control or cyproheptadine may be initiated. **Carcinogenicity & Mutagenicity** Increased incidence of hepatocellular carcinomas and adenomas were reported in female mice fed 140 mg/kg/day duloxetine for 2 years, equivalent to 6 times the maximum recommended human dose (MRHD). No effect was reported with doses of 50mg/kg/day (2 time MRHD) in females or 100 mg/kg/day in males (4 times MRHD). Similar investigation in rats produced no carcinogenicity at doses of 27 mg/kg/day (2 times MRHD)in females and 36 mg/kg/day in males (4 times MRHD). No mutagenicity, clastogenicity, induction of sister chromatid exchange, or genotoxicity has been observed in toxicology investigations. **Reproductive Toxicity** Neither male or female rats displayed adverse reproductive effects at doses up to 45 mg/kg/day (4 times MRHD). **Lactation** An estimated 25% of plasma duloxetine appears in breast milk with the estimated daily infant dose being 0.
Indication
**Indicated** for: 1) Management of Major Depressive Disorder. 2) Management of Generalized Anxiety Disorder. 3) Management of diabetic peripheral neuropathy. 4) Management of fibromyalgia. 5) Management of chronic musculoskeletal pain. 6) Management of osteoarthritis of the knee in adults. 7) Management of chronic lower back pain in adults. 8) Management of stress urinary incontinence in adult women. **Off-label** uses include: 1) Management of chemotherapy-induced peripheral neuropathy. 2) Management of stress urinary incontinence in adult men after prostatectomy until recovery is complete.
Protein Binding
Over 90% bound to plasma proteins, primarily albumin and α1 acid-glycoprotein.
Elimination
About 70% of duloxetine is excreted in the urine mainly as conjugated metabolites. Another 20% is present in the feces as the parent drug, 4-hydroxy metabolite, and an uncharacterized metabolite. Biliary secretion is thought to play a role due to timeline of fecal excretion exceeding the time expected of normal GI transit.
Volume of Distribution
Apparent Vd of 1620-1800 L. Duloxetine crosses the blood-brain barrier and collects in the cerebral cortex at a higher concentration than the plasma.
Clearance
There is a large degree of interindividual variation reported in the clearance of duloxetine with values ranging from 57-114 L/h. Steady state concentrations have still been shown to be dose proportional with a doubling of dose from 30 to 60 mg and from 60 to 120 mg producing 2.3 and 2.6 times the Css respectively.
Experience Report Analysis
ErowidDemographics
Gender Distribution
Age Distribution
Reports Over Time
Effect Analysis
ErowidEffects aggregated from 15 experience reports (15 Erowid)
Effect Sentiment Distribution
Confidence Distribution
Positive Effects 5
Adverse Effects 3
Dosage Distribution
Dose distribution from experience reports
Real-World Dose Distribution
62K DosesFrom 20 individual dose entries
Oral (n=20)
Form / Preparation
Most common forms and preparations reported
Redose Patterns
Redosing behavior across 15 reports