MORPHINE SULFATE
Clinical safety rating: avoid
CNS depressants including alcohol and benzodiazepines increase sedation risk Life-threatening respiratory depression may occur.
Agonist at mu, kappa, and delta opioid receptors in the central nervous system, mimicking endogenous endorphins. Primarily mu-receptor activation leads to analgesia by inhibiting adenylate cyclase, decreasing cAMP, and modulating ion channels (e.g., opening GIRK channels, closing voltage-gated calcium channels), reducing neurotransmitter release.
| Metabolism | Primarily hepatic via glucuronidation (UGT2B7) to morphine-3-glucuronide (M3G, inactive) and morphine-6-glucuronide (M6G, active with greater analgesic potency); minor pathways include N-demethylation to normorphine. Excretion mainly renal. |
| Excretion | Renal: 90% (primarily as morphine-3-glucuronide and morphine-6-glucuronide, with 10% unchanged); Biliary/Fecal: 7-10%. |
| Half-life | Terminal elimination half-life: 2-4 hours in adults; prolonged in neonates (6-8 hours), elderly, and renal impairment (up to 15 hours). |
| Protein binding | 30-35%, primarily to albumin. |
| Volume of Distribution | 3-5 L/kg; large Vd indicates extensive tissue distribution, including skeletal muscle and adipose tissue. |
| Bioavailability | Oral: 20-40% (first-pass metabolism); IM/SC: 80-100%; Rectal: 30-50%; Intranasal: 50-60% (variable); IV: 100%. |
| Onset of Action | IV: 5-10 minutes; IM: 10-30 minutes; Oral: 30-60 minutes (immediate-release); Intrathecal/Epidural: 15-30 minutes. |
| Duration of Action | IV/IM: 3-5 hours (analgesic); Oral immediate-release: 3-6 hours; Extended-release: 8-24 hours; Neuraxial: up to 24 hours. |
5-10 mg intravenously every 4 hours as needed; 10-30 mg orally every 4 hours as needed; 0.1-0.2 mg/kg intramuscularly every 4 hours as needed.
| Dosage form | CAPSULE, EXTENDED RELEASE |
| Renal impairment | GFR 30-50 mL/min: administer 75% of normal dose; GFR 10-29 mL/min: administer 50% of normal dose; GFR <10 mL/min: administer 25% of normal dose. |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50%; Child-Pugh C: avoid use or use with extreme caution at 25% of normal dose. |
| Pediatric use | 0.1-0.2 mg/kg intravenously or intramuscularly every 4 hours as needed; maximum single dose 15 mg. |
| Geriatric use | Start at 25-50% of the usual adult dose; titrate cautiously; monitor for respiratory depression and constipation. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
CNS depressants including alcohol and benzodiazepines increase sedation risk Life-threatening respiratory depression may occur.
| FDA category | Positive |
| Breastfeeding | Morphine is excreted into breast milk. M/P ratio approximately 1.1. In therapeutic doses, amounts are low (<10% of maternal weight-adjusted dose) and unlikely to cause adverse effects in healthy term infants. Caution in preterm infants or those with respiratory compromise. |
| Teratogenic Risk |
■ FDA Black Box Warning
Addiction, abuse, and misuse; life-threatening respiratory depression; accidental ingestion (especially in children); neonatal opioid withdrawal syndrome (prolonged use in pregnancy); risks with concomitant use of benzodiazepines or other CNS depressants (may cause profound sedation, respiratory depression, coma, death).
| Common Effects | Constipation |
| Serious Effects |
Significant respiratory depression; acute or severe bronchial asthma; known or suspected gastrointestinal obstruction (including paralytic ileus); hypersensitivity to morphine or any component; concurrent use of monoamine oxidase inhibitors (MAOIs) or within 14 days of such therapy.
| Precautions | Risk of respiratory depression (especially in elderly, cachectic, debilitated); risk of opioid-induced hyperalgesia; risk of hypotension (especially in hypovolemic patients); risk of seizures; risk of serotonin syndrome with serotonergic drugs; adrenal insufficiency; androgen deficiency; severe hypotension; gastrointestinal obstruction; impaired consciousness; head injury; increased intracranial pressure; acute abdominal conditions; biliary tract disease; acute pancreatitis; use in pregnancy (neonatal withdrawal); breastfeeding (withdrawal in infant); use with MAOIs; severe renal or hepatic impairment. |
Loading safety data…
| First trimester: Limited data; no major malformations reported at therapeutic doses. Second and third trimesters: Chronic use may lead to fetal opioid dependence and neonatal opioid withdrawal syndrome (NOWS) after birth. High doses near term may cause neonatal respiratory depression. |
| Fetal Monitoring | Monitor maternal vital signs, pain scores, and sedation. Assess fetal heart rate patterns if chronic use. Monitor neonate for signs of respiratory depression and NOWS for at least 48 hours after birth if maternal use in late pregnancy. |
| Fertility Effects | Opioids may cause hypothalamic-pituitary-gonadal axis suppression, potentially leading to decreased libido, erectile dysfunction, or anovulation. Reversible upon discontinuation. |