SYNALGOS-DC
Clinical safety rating: caution
Comprehensive clinical and safety monograph for SYNALGOS-DC (SYNALGOS-DC).
Dihydrocodeine is a semisynthetic opioid agonist that binds to mu-opioid receptors in the central nervous system, inhibiting ascending pain pathways and altering pain perception. Aspirin inhibits cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis, thereby providing analgesic and anti-inflammatory effects. Caffeine is a central nervous system stimulant that may enhance analgesia by reducing pain perception and increasing the efficacy of other analgesics.
| Metabolism | Dihydrocodeine is metabolized primarily via O-demethylation and N-demethylation in the liver, mediated by CYP2D6 and CYP3A4, to active metabolites including dihydromorphine. Aspirin is hydrolyzed to salicylic acid, which undergoes conjugation with glycine and glucuronic acid, and oxidative metabolism. Caffeine is metabolized by CYP1A2 to paraxanthine, theobromine, and theophylline. |
| Excretion | Renal: ~90% (dihydrocodeine, as metabolites, primarily glucuronides); biliary/fecal: ~10%. |
| Half-life | Dihydrocodeine: 3.5-4.5 hours; aspirin: 15-20 minutes; caffeine: 3-6 hours. Context: Dihydrocodeine half-life supports q4-6h dosing; aspirin short half-life limits analgesia duration. |
| Protein binding | Dihydrocodeine: ~20-30% (albumin); aspirin: ~50-80% (albumin, saturable); caffeine: ~25-36% (albumin). |
| Volume of Distribution | Dihydrocodeine: 1.2-1.7 L/kg; clinical meaning: distributes extensively into tissues, including CNS. |
| Bioavailability | Oral: Dihydrocodeine ~70-80% (first-pass metabolism); aspirin: 40-50% (due to hydrolysis in gut wall/liver); caffeine: nearly 100%. |
| Onset of Action | Oral: 30-45 minutes (dihydrocodeine); aspirin: 20-30 minutes; caffeine: 30-45 minutes. |
| Duration of Action | Dihydrocodeine: 4-6 hours; aspirin: 3-4 hours; caffeine: 4-6 hours. Note: Fixed-dose combination (dihydrocodeine 16 mg, aspirin 356.4 mg, caffeine 30 mg) provides analgesia limited by aspirin content. |
1-2 capsules orally every 4 hours as needed for pain; each capsule contains dihydrocodeine bitartrate 16 mg, acetaminophen 356.4 mg, and caffeine 30 mg. Maximum: 8 capsules per day.
| Dosage form | CAPSULE |
| Renal impairment | Avoid use if CrCl < 30 mL/min due to accumulation of dihydrocodeine and acetaminophen. For CrCl 30-60 mL/min, extend dosing interval to every 6 hours and monitor closely. For CrCl > 60 mL/min, no adjustment needed. |
| Liver impairment | Contraindicated in severe hepatic impairment (Child-Pugh C). In moderate impairment (Child-Pugh B), reduce dose by 50% and monitor for hepatotoxicity. In mild impairment (Child-Pugh A), no adjustment but caution. |
| Pediatric use | Not recommended for pediatric patients due to variable metabolism of dihydrocodeine and risk of respiratory depression. Specific weight-based dosing not established; alternative agents preferred. |
| Geriatric use | Start at lowest effective dose (1 capsule every 6 hours). Monitor for CNS depression, falls, and constipation. Avoid in frail elderly due to increased sensitivity and risk of toxicity from acetaminophen accumulation. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for SYNALGOS-DC (SYNALGOS-DC).
| Breastfeeding | Dihydrocodeine and paracetamol are excreted into breast milk. Milk-to-plasma ratio (M/P) for dihydrocodeine is approximately 2.4; for paracetamol, M/P ~1.0 (but clinically negligible). Aspirin (as present in some formulations) is excreted with M/P 0.01–0.1; risk of Reye syndrome in infants. Caffeine M/P ~0.5–0.8. Use caution; benefit-risk evaluation required. |
| Teratogenic Risk | First trimester: Association with neural tube defects and congenital heart defects with opioid use. Second/third trimesters: Risk of miscarriage, preterm birth, fetal growth restriction, and neonatal abstinence syndrome with chronic use. No specific data on dihydrocodeine combination; teratogenic risk considered low from oral contraceptives, but paracetamol/aspirin/caffeine components may contribute. |
■ FDA Black Box Warning
WARNING: ADDICTION, ABUSE, AND MISUSE; LIFE-THREATENING RESPIRATORY DEPRESSION; ACCIDENTAL INGESTION; NEONATAL OPIOID WITHDRAWAL SYNDROME; CYTOCHROME P450 3A4 INTERACTION; CONCOMITANT USE OF BENZODIAZEPINES OR OTHER CNS DEPRESSANTS; and RISKS FROM CONCOMITANT USE WITH ALCOHOL. See full prescribing information.
| Serious Effects |
["Hypersensitivity to dihydrocodeine, aspirin, caffeine, or any component","Significant respiratory depression","Acute or severe bronchial asthma in an unmonitored setting or without resuscitative equipment","Known or suspected gastrointestinal obstruction, including paralytic ileus","Severe bleeding disorders (aspirin)","Children and teenagers with viral infections (risk of Reye's syndrome)","Concomitant use of monoamine oxidase inhibitors (MAOIs) or within 14 days of such therapy","Severe hepatic impairment","Severe renal impairment"]
| Precautions | ["Addiction, abuse, and misuse","Life-threatening respiratory depression","Accidental ingestion (especially in children)","Neonatal opioid withdrawal syndrome","CYP3A4 interaction (potent inhibitors or inducers)","Concomitant use with benzodiazepines or other CNS depressants","Risk of bleeding (aspirin)","Reye's syndrome (aspirin use in viral infections in children)","Serotonin syndrome (with serotonergic drugs)","Adrenal insufficiency","Hypotension, including orthostatic hypotension","Seizures","Increased intracranial pressure","Gastrointestinal adverse effects (aspirin)","Renal impairment","Hepatic impairment"] |
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| Fetal Monitoring | During pregnancy: Serial fetal growth ultrasounds, amniotic fluid volume assessment, and nonstress tests in third trimester for chronic use. Monitor for neonatal withdrawal signs (e.g., tremors, irritability) postpartum. In lactation: Infant monitoring for sedation, respiratory depression, and poor feeding. |
| Fertility Effects | Opioid use may cause menstrual irregularities and anovulation. No specific studies on dihydrocodeine; aspirin may impair implantation, caffeine in high doses may delay conception. The combination may reduce fertility; reversible upon discontinuation. |