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. |
| Molecular Weight | 668.77 |
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 | Associated with increased risk of congenital malformations, particularly neural tube defects and inguinal hernia, although data are limited. Use only if benefit outweighs risk. |
| 2nd trimester | May cause fetal dependence and respiratory depression at delivery. Use with caution; consider lowest effective dose for shortest duration. |
| 3rd trimester | Chronic use can lead to neonatal abstinence syndrome (NAS). Avoid in late pregnancy, especially near term unless indicated. |
Clinical note
CNS depressants including alcohol and benzodiazepines increase sedation risk Life-threatening respiratory depression may occur.
| FDA category | Positive |
| Placental transfer | Readily crosses the placenta; fetal concentrations can be equal to maternal levels. Chronic use leads to fetal dependence. |
■ 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 |
Severe respiratory depressionAcute or severe bronchial asthmaParalytic ileusKnown hypersensitivity to morphine sulfateConcurrent use of MAO inhibitors 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. |
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| Breastfeeding |
| Morphine is excreted in breast milk in low concentrations. Short-term use is considered compatible with breastfeeding, but monitor infant for drowsiness, respiratory depression, and constipation. Avoid if infant is premature or has respiratory issues. For chronic use, consider alternative analgesics. |
| Lactation Rating | L2 (Safer if infant factors considered) |
| Teratogenic Risk | 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. |
| Food/Dietary | Avoid alcohol; may increase CNS depression. Grapefruit juice may theoretically alter morphine metabolism via CYP3A4 inhibition, but clinical significance is minimal; no strict avoidance required. High-fat meals may delay absorption but do not affect overall bioavailability. Maintain adequate fluid and fiber intake to prevent constipation. |
| Clinical Pearls | For opioid-naïve patients, start with immediate-release formulation; use equianalgesic dosing when converting routes (oral to parenteral ratio 3:1 for chronic dosing). Always co-prescribe a bowel regimen (e.g., senna + docusate) due to opioid-induced constipation. Monitor respiratory rate closely, especially in elderly, COPD, or sleep apnea patients. Naloxone is the reversal agent; consider prescribing naloxone for patients on high doses or concomitant benzodiazepines. Morphine is contraindicated in patients with MAOI use within 14 days. |
| Patient Advice | Take exactly as prescribed; do not crush or chew extended-release capsules. · Avoid alcohol and other CNS depressants (e.g., benzodiazepines, sedatives) as they increase risk of respiratory depression. · Morphine may cause drowsiness; avoid driving or operating heavy machinery until you know how it affects you. · Constipation is a common side effect; increase fluid and fiber intake, and use a stool softener or laxative as recommended. · Do not stop taking suddenly; withdrawal symptoms may occur. Taper under medical supervision. · Store securely out of reach of children and pets; dispose of unused medication via a take-back program. |