SUBSYS
Clinical safety rating: caution
Comprehensive clinical and safety monograph for SUBSYS (SUBSYS).
SUBSYS (fentanyl) is a mu-opioid receptor agonist that produces analgesia by mimicking endogenous opioids, increasing potassium efflux and reducing calcium influx, thereby inhibiting neuronal transmission of pain signals.
| Metabolism | Primarily hepatic via CYP3A4 isoenzyme; major metabolites include norfentanyl (inactive), hydroxyfentanyl, and others. |
| Excretion | Primarily renal (~75% as metabolites, <10% unchanged); biliary/fecal excretion of conjugates; ~9% in feces. |
| Half-life | Terminal half-life 2–4 hours (single dose); prolonged to 7–15 hours in hepatic/renal impairment; clinical context: necessitates q4–6h dosing for chronic pain. |
| Protein binding | 80–90% bound to albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | 3–4 L/kg (wide distribution, high tissue affinity; indicates extensive partitioning into lipid-rich tissues). |
| Bioavailability | Sublingual/transmucosal: 50–70% (SUBSYS system); buccal: 75%; intravenous: 100%. |
| Onset of Action | Sublingual/transmucosal: 5–15 minutes (fastest); intravenous: 1–2 minutes; buccal: 10–20 minutes. |
| Duration of Action | 2–4 hours (immediate-release); note: rapid absorption leads to short analgesic window; titration may require frequent dosing. |
SUBSYS (fentanyl buccal soluble film) is indicated for breakthrough pain in opioid-tolerant patients. Initial dose: 100 mcg (one 100 mcg film) placed on the inner cheek, allowed to dissolve over 15-25 minutes; may repeat once after 30 minutes if pain not relieved. Titrate to effective dose (200, 400, 600, 800, 1200, 1600 mcg). Maximum: 4 doses per day. No more than 2 doses per breakthrough pain episode. Wait at least 2 hours before treating next episode.
| Dosage form | SPRAY |
| Renal impairment | No specific dosing adjustment is recommended for renal impairment, but use with caution due to potential accumulation of fentanyl metabolites. For GFR < 30 mL/min, consider dose reduction and monitor for respiratory depression. |
| Liver impairment | Child-Pugh Class A or B: No adjustment necessary. Child-Pugh Class C: Consider dose reduction (e.g., start at 50% of usual initial dose) and monitor carefully due to reduced clearance. |
| Pediatric use | Safety and efficacy in pediatric patients (aged <18 years) have not been established. Not recommended for use in pediatric patients. |
| Geriatric use | In patients aged ≥65 years, start at the lowest available dose (100 mcg) and titrate slowly. Monitor for increased sensitivity and respiratory depression. Dose selection should be cautious, reflecting greater frequency of decreased hepatic, renal, or cardiac function. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for SUBSYS (SUBSYS).
| Breastfeeding | Fentanyl is excreted in breast milk with a milk-to-plasma ratio (M/P) of approximately 0.3-0.8, depending on the study. After a single dose, the relative infant dose is estimated at 0.5-2.5% of the weight-adjusted maternal dose. Chronic use may lead to accumulation in breastfed infants, with potential for sedation, apnea, and withdrawal. Use only if clearly needed, with caution. Monitor infant for drowsiness, difficulty feeding, and respiratory depression. The CDC recommends avoiding opioids during breastfeeding when possible; if used, limit to the lowest effective dose for the shortest duration. |
| Teratogenic Risk | Pregnancy Category D. Use of SUBSYS (fentanyl buccal tablet) during pregnancy may cause neonatal opioid withdrawal syndrome (NOWS) and respiratory depression at birth if used near term. Fentanyl is associated with reduced fetal growth, preterm birth, and stillbirth, particularly with chronic use. First trimester exposure has limited data; however, opioid use is generally not associated with major malformations. Risk increases with prolonged or high-dose use, especially in the third trimester. Avoid use unless benefit outweighs risk. |
■ FDA Black Box Warning
Risk of respiratory depression, addiction, abuse, and misuse; life-threatening respiratory depression can occur even at recommended doses. Accidental ingestion can cause fatal overdose. Concomitant use of CNS depressants increases risk. Neonatal opioid withdrawal syndrome with prolonged use during pregnancy. Concomitant use with CYP3A4 inhibitors may increase fentanyl exposure.
| Serious Effects |
Hypersensitivity to fentanyl or any component; opioid-non-tolerant patients; acute or postoperative pain; significant respiratory depression; acute or severe asthma; paralytic ileus; MAO inhibitor use within 14 days.
| Precautions | Respiratory depression, abuse potential, interactions with CNS depressants, hypoventilation, hypotension, bradycardia, and opioid-induced hyperalgesia. Use with caution in patients with head injuries, pulmonary disease, hepatic or renal impairment, and elderly or debilitated patients. |
Loading safety data…
| Fetal Monitoring | Monitor maternal vital signs, sedation level, and respiratory rate before and during use. For pregnant patients, fetal heart rate monitoring should be considered during labor and delivery due to risk of neonatal respiratory depression. Assess for signs of opioid withdrawal in both mother and neonate, especially with chronic use. Regular growth ultrasounds may be indicated for prolonged use. After birth, monitor neonate for NOWS using standardized assessment tools (e.g., Finnegan score) for at least 48-72 hours. Avoid abrupt discontinuation; taper if chronic use. |
| Fertility Effects | Long-term opioid use may cause hypothalamic-pituitary-gonadal axis suppression, leading to reduced gonadotropin release, hypogonadism, and sexual dysfunction. Reversible decreases in sperm count and motility have been reported in males; females may experience menstrual irregularities, anovulation, and reduced fertility. In vitro studies suggest no direct impairment of sperm or oocyte function at therapeutic levels. Infertility typically resolves upon opioid discontinuation. Advise patients planning pregnancy about potential effects on fertility. |