FINASTERIDE AND TADALAFIL
Clinical safety rating: safe
Nitrates can cause severe hypotension Can cause priapism and back pain.
Finasteride is a 5α-reductase inhibitor that inhibits conversion of testosterone to dihydrotestosterone (DHT). Tadalafil is a phosphodiesterase-5 (PDE5) inhibitor that enhances nitric oxide-mediated vasodilation by increasing cyclic guanosine monophosphate (cGMP) in smooth muscle.
| Metabolism | Finasteride is extensively metabolized in the liver via CYP3A4; tadalafil is primarily metabolized by CYP3A4. |
| Excretion | Finasteride: 57% feces, 39% urine (metabolites); Tadalafil: 36% urine, 61% feces (mostly metabolites). |
| Half-life | Finasteride: 6-8 hours (elderly ~8 hours); Tadalafil: 17.5 hours (enables once-daily dosing). |
| Protein binding | Finasteride: 90% bound to albumin and alpha-1-acid glycoprotein; Tadalafil: 94% bound to albumin. |
| Volume of Distribution | Finasteride: 76 L/kg (1.1 L/kg in elderly); Tadalafil: 63-77 L/kg (extensive tissue distribution). |
| Bioavailability | Finasteride: 63% oral (80% relative to IV); Tadalafil: 80% oral (bioavailability unaffected by food). |
| Onset of Action | Finasteride: 3-6 months for BPH symptom improvement; Tadalafil: 30-60 min for erectile dysfunction. |
| Duration of Action | Finasteride: continuous effect with daily dosing (maximal at 6-12 months); Tadalafil: up to 36 hours for erectile function. |
One capsule containing finasteride 5 mg and tadalafil 5 mg orally once daily.
| Dosage form | CAPSULE |
| Renal impairment | No adjustment for mild-moderate renal impairment (CrCl ≥30 mL/min). Avoid in severe renal impairment (CrCl <30 mL/min) or on dialysis due to increased tadalafil exposure. |
| Liver impairment | Child-Pugh A: no adjustment. Child-Pugh B: limit tadalafil dose to 5 mg (same as given); use caution. Child-Pugh C: avoid use. |
| Pediatric use | Not indicated in pediatric patients; safety and efficacy not established. |
| Geriatric use | No dose adjustment required; monitor for orthostatic hypotension and dizziness, as elderly may be more sensitive to vasodilatory effects. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Nitrates can cause severe hypotension Can cause priapism and back pain.
| FDA category | Animal |
| Breastfeeding | Finasteride: Excreted in breast milk (M/P ratio unknown); not recommended. Tadalafil: Presence in breast milk unknown; avoid due to potential adverse effects. |
| Teratogenic Risk | Finasteride: Contraindicated in pregnancy due to risk of hypospadias in male fetuses (Category X). Tadalafil: Category B; no fetal harm in animal studies, but insufficient human data. Avoid combination in pregnant women. |
■ FDA Black Box Warning
There is no FDA black box warning for the combination product. Individual components have warnings: Finasteride exposure during pregnancy may cause abnormalities of male external genitalia; Tadalafil is contraindicated in patients taking guanylate cyclase stimulators (e.g., riociguat) and nitrates.
| Common Effects | BPH |
| Serious Effects |
Hypersensitivity to finasteride or tadalafil; concurrent use of nitrates or guanylate cyclase stimulators (e.g., riociguat); women who are or may become pregnant (finasteride teratogenicity).
| Precautions | Risk of priapism (tadalafil); sudden hearing loss (tadalafil); orthostatic hypotension with concomitant antihypertensives; prostate-specific antigen (PSA) level reduction (finasteride); risk of high-grade prostate cancer (finasteride); use in women of childbearing potential (finasteride teratogenicity). |
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| Fetal Monitoring | If inadvertent exposure in pregnancy, perform fetal ultrasound for external genitalia abnormalities (finasteride). No specific monitoring for tadalafil. |
| Fertility Effects | Finasteride: May reduce sperm count and motility; effect reversible. Tadalafil: No adverse effects on spermatogenesis. Combination effect not studied. |