ORPHENADRINE CITRATE, ASPIRIN, AND CAFFEINE
Clinical safety rating: safe
Animal studies have demonstrated safety
Orphenadrine citrate is a centrally acting muscle relaxant with anticholinergic properties; aspirin is a nonsteroidal anti-inflammatory drug (NSAID) that inhibits cyclooxygenase (COX) enzymes, reducing prostaglandin synthesis; caffeine is a central nervous system stimulant that antagonizes adenosine receptors.
| Metabolism | Orphenadrine: hepatic N-demethylation and hydroxylation via CYP450 enzymes; Aspirin: hydrolysis to salicylate and conjugation with glycine and glucuronic acid; Caffeine: hepatic metabolism via CYP1A2. |
| Excretion | Orphenadrine: ~60% renal (metabolites, <8% unchanged), ~20% biliary/fecal; Aspirin: ~80-100% renal (salicylates, dose-dependent; alkaline urine increases excretion); Caffeine: ~1-3% renal (unchanged), main metabolites renal. |
| Half-life | Orphenadrine: ~14 hours (range 12-16 h); Aspirin: 2-3 h for low doses, 15-30 h for high/anti-inflammatory doses due to saturable metabolism; Caffeine: 3-6 h in adults, prolonged in liver disease. |
| Protein binding | Orphenadrine: ~30% (albumin); Aspirin: 80-90% (albumin, saturable); Caffeine: 25-36% (albumin). |
| Volume of Distribution | Orphenadrine: ~2.5 L/kg (widespread, CNS penetration); Aspirin: 0.15-0.2 L/kg (low, primarily extracellular); Caffeine: 0.6-0.8 L/kg. |
| Bioavailability | Oral: Orphenadrine ~90%; Aspirin 40-50% (first-pass hydrolysis to salicylate); Caffeine ~100%. |
| Onset of Action | Oral: Orphenadrine 30-60 min; Aspirin 5-30 min (analgesic); Caffeine 15-45 min. |
| Duration of Action | Orphenadrine 4-6 h; Aspirin 3-6 h (analgesic), up to 8 h (anti-inflammatory); Caffeine 3-5 h (stimulant). |
1-2 tablets (orphenadrine citrate 50 mg, aspirin 770 mg, caffeine 60 mg per tablet) orally every 8-12 hours as needed; maximum 4 tablets per day.
| Dosage form | TABLET |
| Renal impairment | Contraindicated in severe renal impairment (CrCl <30 mL/min). For moderate impairment (CrCl 30-59 mL/min), extend dosing interval to every 12-24 hours. No adjustment for mild impairment (CrCl 60-89 mL/min). |
| Liver impairment | Contraindicated in Child-Pugh class C. For Child-Pugh class B, reduce dose by 50% or extend interval to every 12-24 hours. Use with caution in Child-Pugh class A. |
| Pediatric use | Not recommended for pediatric use due to aspirin's association with Reye's syndrome and lack of safety data for orphenadrine in children. |
| Geriatric use | Use lower end of dosing range (e.g., 1 tablet every 12 hours) due to increased sensitivity to anticholinergic effects and risk of aspirin-induced gastrointestinal bleeding. Avoid use in patients >80 years if possible. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Other anticholinergic drugs can have additive effects Can cause drowsiness and dry mouth.
| Breastfeeding | Aspirin and its metabolites are excreted into breast milk (M/P ratio ~0.04-0.27 for salicylate); orphenadrine is not known to be excreted; caffeine is excreted (M/P ratio ~0.5-0.76). Theoretical risk of Reye's syndrome with aspirin, and irritability in infant with caffeine. Use caution, avoid high doses. |
| Teratogenic Risk | First trimester: Aspirin is associated with increased risk of gastroschisis (ORS 1.5-2.0) and possibly cardiac defects; orphenadrine and caffeine have limited data but caffeine may increase miscarriage risk. Second trimester: Aspirin at high doses may impair fetal renal function; orphenadrine and caffeine effects are not well-studied. Third trimester: Aspirin use after 30 weeks gestation increases risk of premature closure of ductus arteriosus and oligohydramnios; orphenadrine may cause neonatal withdrawal; caffeine may accumulate. |
■ FDA Black Box Warning
No FDA black box warning.
| Common Effects | Dry mouth |
| Serious Effects |
Hypersensitivity to any component; patients with angle-closure glaucoma, pyloric or duodenal obstruction, stenosing peptic ulcer, prostatic hypertrophy, or bladder neck obstruction; severe renal or hepatic impairment; bleeding disorders; concurrent use of anticoagulants.
| Precautions | Avoid in patients with glaucoma, prostatic hypertrophy, or urinary retention due to anticholinergic effects; caution in elderly and those with cardiovascular disease; risk of GI bleeding with aspirin; limit caffeine intake to avoid excessive stimulation. |
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| Fetal Monitoring | Monitor fetal growth and amniotic fluid volume with serial ultrasound if aspirin used in third trimester. Assess ductus arteriosus patency if near term. Monitor maternal bleeding time and platelet function if high-dose aspirin. Observe neonate for signs of withdrawal (orphenadrine) and caffeine-related irritability. |
| Fertility Effects | Aspirin may interfere with implantation via prostaglandin inhibition; high doses may impair ovulation. Orphenadrine has anticholinergic effects that may reduce cervical mucus quality. Caffeine consumption >300 mg/day may delay time to conception and increase risk of infertility. |