Adult: As monotherapy or in combination with α-1 adrenergic antagonist: 0.5 mg once daily. Assess treatment after at least 6 months; treatment duration depends on patient’s clinical response.
Hepatic Impairment
Severe: Contraindicated.
Administration
May be taken with or without food.
Contraindications
Severe hepatic impairment. Women, children and adolescents. Pregnancy and lactation.
Special Precautions
Patient with large post-void residual urine volume or severely reduced urinary flow. Mild to moderate hepatic impairment. Not indicated for the prevention of prostate cancer.
Adverse Reactions
Significant: Cardiac failure; reduction in total sperm count, semen volume, and sperm motility. Rarely, breast cancer. Immune system disorders: Allergic reactions (e.g. rash, pruritus, urticaria, localised oedema, angioedema). Investigations: Increased LH, testosterone, TSH. Nervous system disorders: Dizziness. Psychiatric disorders: Depression. Reproductive system and breast disorders: Testicular pain and swelling, impotence, decreased libido, ejaculation disorders, breast disorders (e.g. tenderness, enlargement). Skin and subcutaneous tissue disorders: Alopecia (primarily body hair loss), hypertrichosis.
Avoid donating blood during treatment and for at least 6 months following treatment cessation. Women of child-bearing potential or who are pregnant should not handle crushed or broken tab. Excreted in semen therefore use of condom is recommended.
Monitoring Parameters
Evaluate patients for prostate cancer (e.g. digital rectal examinations) prior to treatment and periodically thereafter. Monitor prostate-specific antigen (PSA) levels (new baseline after 6 months from treatment initiation then regularly thereafter); urinalysis (baseline). Assess for signs and symptoms of changes in breast tissue (e.g. pain, nipple discharge, lumps).
Drug Interactions
Increased serum concentrations with moderate CYP3A4 inhibitors (e.g. verapamil, diltiazem), or potent CYP3A4 inhibitors (e.g. ritonavir, indinavir, nefazodone, itraconazole, ketoconazole).
Lab Interference
Decrease PSA level by approx 50% within 3-6 months of use.
Action
Description: Mechanism of Action: Dutasteride, a 4-azo analog of testosterone, is a competitive, selective inhibitor of both type 1 (skin and liver) and type 2 (reproductive tissues) 5α-reductase, resulting in the inhibition of the conversion of testosterone to dihydrotestosterone thus reducing levels of circulating dihydrotestosterone. Pharmacokinetics: Absorption: Absorbed from the gastrointestinal tract. Bioavailability: Approx 60%. Time to peak plasma concentration: 1-3 hours. Distribution: Volume of distribution: 300-500 L. Plasma protein binding: 99% to albumin. Metabolism: Extensively metabolised in the liver by CYP3A4 and CYP3A5 isoenzymes into 6-hydroxydutasteride (same activity with dutasteride); 4′-hydroxydutasteride and 1,2-dihydrodutasteride (less potent than dutasteride). Excretion: Via faeces (40% as metabolites, approx 5% as unchanged drug); urine (<1% as unchanged drug). Elimination half-life: Approx 3-5 weeks.
Chemical Structure
Dutasteride Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 6918296, Dutasteride. https://pubchem.ncbi.nlm.nih.gov/compound/Dutasteride. Accessed Nov. 22, 2023.
Storage
Store between 15-30°C. Follow applicable procedures for receiving, handling, administration, and disposal.
G04CB02 - dutasteride ; Belongs to the class of testosterone-5-alpha reductase inhibitors. Used in the treatment of benign prostatic hypertrophy.
References
Anon. Dutasteride. AHFS Clinical Drug Information [online]. Bethesda, MD. American Society of Health-System Pharmacists, Inc. https://www.ahfscdi.com. Accessed 25/09/2023.Anon. Dutasteride. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 25/09/2023.Avodart 0.5 mg Capsule (GlaxoSmithKline Pharmaceutical Sdn. Bhd.). National Pharmaceutical Regulatory Agency - Ministry of Health Malaysia. https://www.npra.gov.my. Accessed 25/09/2023.Avodart Capsule, Liquid Filled (Woodward Pharma Services LLC). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 25/09/2023.Buckingham R (ed). Dutasteride. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 25/09/2023.Dutasteride 0.5 mg Soft Capsules (Ennogen IP Ltd,). MHRA. https://products.mhra.gov.uk. Accessed 25/09/2023.Joint Formulary Committee. Dutasteride. British National Formulary [online]. London. BMJ Group and Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 25/09/2023.
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