Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
FLEXERIL vs INCRELEX
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Cyclobenzaprine is a centrally acting muscle relaxant that acts primarily at the brainstem, reducing tonic somatic motor activity via inhibition of descending serotonergic pathways. It is structurally related to tricyclic antidepressants and exhibits anticholinergic, sedative, and analgesic effects.
Insulin-like growth factor 1 receptor agonist; promotes linear growth by stimulating chondrocyte proliferation at epiphyseal plates and exerts anabolic effects on muscle, bone, and other tissues.
Adjunct to rest and physical therapy for relief of muscle spasm associated with acute, painful musculoskeletal conditions (FDA-approved),Off-label: Fibromyalgia, chronic muscle spasm, tension headaches, and as a sleep aid
Treatment of growth failure in children with severe primary IGF-1 deficiency (primary IGFD) or with growth hormone (GH) gene deletion who have developed neutralizing antibodies to GH
10 mg to 15 mg orally three times a day; maximum daily dose: 30 mg.
Intravenous bolus of 0.1 mg/kg given over 1 minute, followed by continuous intravenous infusion of 0.6 mg/kg/min for 30 minutes. Alternatively, a single intravenous bolus dose of 0.3 mg/kg.
Terminal elimination half-life is 18 hours (range 8–37 hours) with clinical context: requires dose adjustment in hepatic impairment; steady-state reached in ~3–5 days.
Terminal elimination half-life is approximately 8-10 hours in adults; clinically, steady-state is achieved within 2-3 days.
Primarily hepatic via CYP3A4, CYP1A2, and CYP2D6; undergoes N-demethylation and glucuronidation. Active metabolite: norcyclobenzaprine.
Primarily metabolized by proteolysis into smaller peptides and amino acids; not significantly metabolized by CYP enzymes.
Primarily hepatic; approximately 50% excreted in urine as metabolites, less than 1% unchanged; 40% excreted in feces via bile.
Renal: ~95% of absorbed dose as unchanged drug and metabolites; fecal: <5%.
~93% bound to plasma proteins, primarily albumin.
Approximately 90% bound to insulin-like growth factor binding proteins (IGFBPs).
~14 L/kg (range 10–20 L/kg), indicating extensive tissue distribution.
Vd ~0.3-0.5 L/kg, indicating distribution primarily into extracellular fluid.
Oral: ~33% due to extensive first-pass metabolism.
Subcutaneous: 80-100% (high bioavailability).
No specific dosage adjustment guidelines; use with caution in renal impairment due to potential for increased side effects.
No specific dose adjustment recommended for renal impairment; use with caution in patients with severe renal impairment (e GFR < 30 m L/min/1.73 m²) due to limited data.
Contraindicated in hepatic impairment; Child-Pugh class A, B, C: no safe dosage established.
No specific dose adjustment recommended for hepatic impairment; use with caution in patients with Child-Pugh class C cirrhosis due to potential risk of hypoglycemia.
Not recommended for use in children under 15 years old; safety and efficacy not established.
Not approved for use in pediatric patients. Safety and efficacy in children have not been established.
Use lower starting dose (e.g., 5 mg) and titrate slowly; increased risk of sedation and anticholinergic effects. May not be well tolerated; consider alternative therapy.
No specific dose adjustment recommended; elderly patients may be more sensitive to hypoglycemic effects; monitor blood glucose closely.
None
Increased risk of neoplasms; do not use in patients with active or suspected malignancy. Monitor for progression of pre-existing nevi.
Should not be used for longer than 2-3 weeks (acute use only),May impair mental or physical abilities required for driving or operating machinery,Central nervous system depression additive with alcohol and other CNS depressants,Anticholinergic effects: caution in patients with angle-closure glaucoma, urinary retention, or prostatic hypertrophy,Cardiovascular effects: risk of arrhythmias, especially in patients with preexisting cardiac disease (tachycardia, QT prolongation),Serotonin syndrome risk when used with MAOIs, SSRIs, SNRIs, or other serotonergic drugs,Hepatic impairment: lower doses recommended
Risk of malignancy (including intracranial tumors),Lymphoproliferative disorders,Intracranial hypertension (pseudotumor cerebri),Slipped capital femoral epiphysis,Progression of scoliosis,Pancreatitis,Hypoglycemia (especially with fasting or missed meals),Fluid retention (edema, pericardial effusion),Hypersensitivity reactions including anaphylaxis,Thymic hypertrophy
Concurrent use of MAOIs or within 14 days of MAOI therapy,Acute recovery phase of myocardial infarction,Arrhythmias, heart block, or congestive heart failure,Hyperthyroidism
Active or suspected malignancy (including intracranial tumors),Closed epiphyses (skeletal maturity),Acute critical illness (due to increased mortality with ICU use),Hypersensitivity to mecasermin or any component
Alcohol should be avoided due to additive CNS depression. No specific food interactions; take with or without food. Grapefruit juice does not significantly interact, but caution with high-fat meals may alter absorption slightly.
Must be administered within 20 minutes of a meal or snack containing carbohydrates to reduce risk of hypoglycemia. Avoid fasting or skipping meals. Grapefruit/grapefruit juice may alter CYP3A4 metabolism; avoid concurrent use. Alcohol can increase hypoglycemia risk; limit or avoid.
Pregnancy Category B. Animal studies have not demonstrated fetal risk, but no adequate human studies in pregnant women. Use only if clearly needed. First trimester: no known risk. Second trimester: no known risk. Third trimester: potential for neonatal adverse effects such as respiratory depression and withdrawal if used near term.
INCRELEX (mecasermin) is an IGF-1 analog. In animal studies, there is no evidence of teratogenicity; however, data in pregnant women are insufficient. First trimester: No known malformation risk. Second/third trimesters: Fetal overgrowth (macrosomia) may occur if maternal IGF-1 levels are elevated. Caution advised.
Excreted in breast milk in small amounts (M/P ratio not established). Clinical relevance uncertain; however, due to potential for adverse effects in nursing infants, caution is advised. Alternative therapies preferred, especially when nursing a premature or low-birth-weight infant.
Excretion into human milk unknown; molecular weight (7.5 k Da) suggests minimal transfer. M/P ratio not established. Caution recommended; alternative feeding may be considered until more data available.
No specific dosing adjustments recommended for pregnancy. Use lowest effective dose and shortest duration due to potential neonatal effects. Pharmacokinetics may be altered in pregnancy; however, no dose adjustment guidelines exist.
No established dose adjustments. Physiologic changes in pregnancy (increased renal clearance, plasma volume) may reduce drug levels; however, safety and efficacy data are lacking. Use only if clearly needed with careful monitoring.
Flexeril (cyclobenzaprine) is structurally related to tricyclic antidepressants (TCAs) and shares similar anticholinergic and sedative properties. It should not be used longer than 2-3 weeks due to lack of evidence for efficacy beyond that duration. Avoid in patients with hyperthyroidism, heart block, or recent MI. Concomitant use with MAOIs can cause hypertensive crisis. Onset of muscle relaxation is delayed; therapeutic effect may not be apparent until after 2-4 days. Sedation is the most common side effect and can be used to aid sleep.
INCRELEX (mecasermin) is recombinant human insulin-like growth factor-1 (IGF-1) used for growth failure in severe primary IGF-1 deficiency. Monitor blood glucose closely due to risk of hypoglycemia; administer within 20 minutes of a meal or snack. Do not use in patients with closed epiphyses, active malignancy, or history of malignancy. Can cause intracranial hypertension (pseudotumor cerebri); monitor for headache, visual disturbances. Injection site reactions common.
Do not take for longer than 3 weeks unless directed by your doctor.,This medication may cause drowsiness or dizziness; avoid driving or operating heavy machinery until you know how it affects you.,Avoid alcohol and other CNS depressants (e.g., benzodiazepines, opioids) as they may increase sedation.,Do not stop suddenly if taken regularly; taper dose to avoid withdrawal symptoms like headache or nausea.,Inform your doctor if you have glaucoma, urinary retention, or are taking MAO inhibitors (e.g., phenelzine, tranylcypromine).,Take exactly as prescribed; do not increase dose or frequency.,May cause dry mouth; use sugar-free gum or candy for relief.
Do not use INCRELEX if you have cancer or a history of cancer.,Take exactly as prescribed; inject within 20 minutes after a meal or snack to prevent low blood sugar.,Do not inject into the same site repeatedly; rotate injection sites.,Watch for signs of low blood sugar (shakiness, sweating, confusion) and have fast-acting sugar (e.g., juice, glucose tablets) available.,Report severe headache, vision changes, or nausea immediately (possible increased pressure in the skull).,Inform all healthcare providers you are using this medication.
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about FLEXERIL vs INCRELEX, answered by our medical review team.
FLEXERIL is a Muscle Relaxant that works by Cyclobenzaprine is a centrally acting muscle relaxant that acts primarily at the brainstem, reducing tonic somatic motor activity via inhibition of descending serotonergic pathways. It is structurally related to tricyclic antidepressants and exhibits anticholinergic, sedative, and analgesic effects.. INCRELEX is a Growth Factor that works by Insulin-like growth factor 1 receptor agonist; promotes linear growth by stimulating chondrocyte proliferation at epiphyseal plates and exerts anabolic effects on muscle, bone, and other tissues.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between FLEXERIL and INCRELEX depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of FLEXERIL is: 10 mg to 15 mg orally three times a day; maximum daily dose: 30 mg.. The standard adult dose of INCRELEX is: Intravenous bolus of 0.1 mg/kg given over 1 minute, followed by continuous intravenous infusion of 0.6 mg/kg/min for 30 minutes. Alternatively, a single intravenous bolus dose of 0.3 mg/kg.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between FLEXERIL and INCRELEX in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. FLEXERIL is classified as Category C. Pregnancy Category B. Animal studies have not demonstrated fetal risk, but no adequate human studies in pregnant women. Use only if clearly needed. First trimester: no known risk. . INCRELEX is classified as Category C. INCRELEX (mecasermin) is an IGF-1 analog. In animal studies, there is no evidence of teratogenicity; however, data in pregnant women are insufficient. First trimester: No known mal. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.