SLO-PHYLLIN
Clinical safety rating
cautionComprehensive clinical and safety monograph for SLO-PHYLLIN (SLO-PHYLLIN).
SLO-PHYLLIN (theophylline) is a xanthine bronchodilator that relaxes bronchial smooth muscle, likely by inhibiting phosphodiesterase, increasing intracellular cAMP, blocking adenosine receptors, and enhancing endogenous catecholamine release.
| Metabolism | Primarily hepatic via CYP450 enzymes: CYP1A2, CYP2E1, CYP3A4; metabolite: 1,3-dimethyluric acid. Approximately 10% excreted unchanged in urine. |
| Excretion | Renal: ~10% unchanged; hepatic metabolism accounts for ~90% of elimination, with metabolites excreted in urine. Fecal: <5%. |
| Half-life | Terminal elimination half-life is approximately 3-8 hours in adults (non-smokers, healthy), 1-5 hours in smokers, and 20-30 hours in neonates. Clinical context: Half-life is prolonged in hepatic cirrhosis, heart failure, and with certain drug interactions (e.g., cimetidine, ciprofloxacin). |
| Protein binding | Approximately 40% bound to albumin; binding is saturable and decreased in neonates, hepatic disease, and acidosis. |
| Volume of Distribution | 0.45 L/kg (range 0.3-0.7 L/kg). Clinical meaning: Distributes evenly into body water and highly perfused tissues; Vd increased in premature infants and decreased in obesity. |
| Bioavailability | Oral immediate-release: 96-100%; oral sustained-release (Slo-Phyllin): 90-100% relative to immediate-release; rectal: variable (~80-100% for enema); IV: 100%. |
| Onset of Action | Oral immediate-release: 30-60 minutes; IV: immediate (within minutes); oral sustained-release: 1-2 hours. |
| Duration of Action | Immediate-release: 4-6 hours; sustained-release: 8-12 hours (Slo-Phyllin is a sustained-release formulation). Clinical note: Duration is dose-dependent and influenced by metabolic rate; therapeutic levels (5-15 mcg/mL) maintained for 8-12 hours with proper dosing. |
| Molecular Weight | 180.16 |
Theophylline (Slo-Phyllin) immediate-release: 100-200 mg orally every 6 hours; sustained-release: 200-400 mg orally every 12 hours. Dose titrated to serum theophylline concentration of 5-15 mcg/mL.
| Dosage form | CAPSULE, EXTENDED RELEASE |
| Renal impairment | No specific dose adjustment is required for renal impairment. However, monitoring serum concentrations is recommended due to altered clearance in severe renal failure (GFR <10 mL/min). |
| Liver impairment | Child-Pugh Class B or C: Reduce dose by 50% and monitor serum concentrations closely. Avoid use in severe hepatic impairment if possible. |
| Pediatric use | Starting dose: 5 mg/kg/day orally in divided doses every 6 hours (immediate-release) or every 12 hours (sustained-release). Titrate based on serum concentrations, targeting 5-15 mcg/mL. Maximum dose: 24 mg/kg/day or 900 mg/day, whichever is less. |
| Geriatric use | Start at low end of dosing range (e.g., 200-300 mg/day sustained-release). Monitor serum concentrations carefully as clearance is reduced in elderly patients, increasing risk of toxicity. |
| 1st trimester | Limited human data; animal studies show increased risk of fetal malformations at high doses. Use only if clearly needed. |
| 2nd trimester | Monitor maternal serum levels closely; risk of neonatal jitteriness, tachycardia, and vomiting if maternal levels are high. |
| 3rd trimester | May cause neonatal irritability, apnea, and feeding intolerance near term; avoid high doses. |
Clinical note
Comprehensive clinical and safety monograph for SLO-PHYLLIN (SLO-PHYLLIN).
| Placental transfer | Crosses placenta; fetal serum levels approximate maternal levels. |
| Breastfeeding | Theophylline is excreted into breast milk in low concentrations (about 10% of maternal serum level). Occasional irritability and sleep disturbance have been reported in infants. Monitor infant for signs of stimulation. American Academy of Pediatrics considers compatible with breastfeeding. |
| Lactation Rating | L2 (Limited data - compatible) |
| Teratogenic Risk | Theophylline (Slo-Phyllin) is classified as FDA Pregnancy Category C. Animal studies have shown teratogenic effects at high doses, but human data are limited. First trimester exposure is not associated with major congenital malformations. Third trimester use may lead to transient neonatal apnea, jitteriness, or tachycardia due to placental transfer. No increased risk of preterm birth or low birth weight has been consistently demonstrated. |
| Fetal Monitoring | Monitor maternal serum theophylline levels (target 5-15 mcg/mL) every 1-2 months during pregnancy and more frequently if dose adjustments are made. Assess fetal growth by ultrasound if pregnancy is complicated by severe asthma or preeclampsia. Monitor neonatal heart rate and respiratory status for 24-48 hours after delivery if maternal use in third trimester. |
| Fertility Effects | No specific adverse effects on fertility in males or females have been reported. Theophylline does not impair spermatogenesis or ovulation. Asthma control itself is important for fertility; uncontrolled asthma may affect ovulation. |
■ FDA Black Box Warning
No FDA boxed warning.
| Serious Effects |
Hypersensitivity to theophylline or any componentActive seizures not controlled by therapyUncontrolled cardiac arrhythmias
| Precautions | Concurrent illness (fever, influenza), hepatic impairment, elderly, and smoking alter metabolism; narrow therapeutic index (10-20 mcg/mL); monitor serum levels; risk of seizures, arrhythmias, and death with toxicity; reduce dose with CYP1A2 inhibitors (cimetidine, fluoroquinolones, macrolides) or inducers (smoking, rifampin, phenytoin); caution in peptic ulcer disease, seizure disorders, cardiac arrhythmias. |
| Food/Dietary | Avoid high-fat meals as they may alter absorption of sustained-release preparations. Limit caffeine-containing foods and beverages. Avoid charcoal-broiled foods, which can increase metabolism. |
| Clinical Pearls | Monitor serum theophylline levels closely due to narrow therapeutic index (10-20 mcg/mL). Adjust dose in patients with heart failure, liver disease, or on CYP1A2 inhibitors (e.g., ciprofloxacin, fluvoxamine). Do not crush or chew sustained-release tablets. Cigarette smoking induces metabolism, requiring higher doses. |
| Patient Advice | Take this medication exactly as prescribed, usually every 8-12 hours. · Do not crush or chew the tablets; swallow them whole. · Avoid excessive caffeine intake (coffee, tea, chocolate) as it may increase side effects. · Contact your doctor if you experience nausea, vomiting, insomnia, or irregular heartbeat. · Do not change brands or formulations without consulting your doctor. |
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