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. |
| Molecular Weight | Finasteride: 372.55 Da; Tadalafil: 389.45 Da |
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 | Contraindicated. Finasteride is a 5α-reductase inhibitor that can inhibit conversion of testosterone to DHT, potentially interfering with male fetal genital development. Tadalafil is a PDE5 inhibitor with limited human data, but animal studies show no teratogenicity. Combined use lacks safety data. |
| 2nd trimester | Contraindicated. Potential risk of finasteride-induced hypospadias and other genital anomalies in male fetuses. Tadalafil use not recommended due to unknown fetal effects. |
| 3rd trimester | Contraindicated. Finasteride exposure in late pregnancy may still affect fetal genital development. Tadalafil may cause uterine relaxation and affect labor. |
Clinical note
Nitrates can cause severe hypotension Can cause priapism and back pain.
| FDA category | Animal |
| Placental transfer | Both finasteride and tadalafil cross the human placenta. Finasteride: extensive transfer in animal models, likely crosses based on molecular weight and lipophilicity. Tadalafil: limited human data but molecular weight (389.45 Da) suggests possible transfer. Combined transfer not well studied. |
■ 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 |
Pregnancy or suspected pregnancyWomen of childbearing potential without reliable contraception (finasteride component)Hypersensitivity to finasteride, tadalafil, or any componentConcurrent use of organic nitrates (tadalafil contraindication)Severe hepatic impairment (Child-Pugh class C)Severe renal impairment (CrCl <30 mL/min) if used for BPH
| 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). |
Loading safety data…
| Breastfeeding | Finasteride is excreted in breast milk in animal studies; human data unavailable. Tadalafil is excreted in breast milk in small amounts. Avoid breastfeeding due to potential adverse effects on infant development, particularly with finasteride's antiandrogenic activity. |
| Lactation Rating | L5 - Avoid |
| 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. |
| 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. |
| Food/Dietary | Avoid grapefruit and grapefruit juice as they increase tadalafil plasma concentrations. Alcohol may potentiate hypotension and dizziness. High-fat meals may delay tadalafil absorption but do not reduce efficacy. |
| Clinical Pearls | Finasteride and tadalafil combination is used for benign prostatic hyperplasia (BPH). Tadalafil may cause priapism; advise immediate medical attention for erections lasting >4 hours. Finasteride decreases serum PSA by ~50%; double PSA values for interpretation. Avoid coadministration with strong CYP3A4 inhibitors (e.g., ketoconazole) due to increased tadalafil exposure. Tadalafil is contraindicated with nitrates due to severe hypotension. Assess cardiovascular stability before prescribing tadalafil. |
| Patient Advice | Take the medication at the same time daily with or without food. · Seek emergency care for erections lasting longer than 4 hours. · Inform your doctor about all medications, especially nitrates or alpha-blockers. · Finasteride may reduce PSA levels; do not stop taking before PSA testing without consulting your doctor. · Avoid grapefruit juice as it may increase side effects. · Tadalafil may cause dizziness or syncope; avoid driving if affected. |