The mean (CV%) Cmax and AUC of methylene blue 2,917 ng/mL (39%) and 13977 ng.hr/mL (21%) following a 2 mg/kg dose administered as a 5-minute intravenous infusion.
Distribution
The mean± standard deviation steady state volume of distribution of a 2 mg/kg dose of methylene blue injection was 255 L ± 58. The mean plasma protein binding of methylene blue is approximately 94% in vitro. Methylene blue exhibits concentration-dependent partitioning into blood cells in vitro. The blood-to-plasma ratio was 5.1±2.8 at 5 minutes from the start of a 2 mg/kg dose administered as a 5-minute intravenous infusion and reached a plateau of 0.6 at 4 hours in a clinical study. Methylene Blue is a substrate for the P- glycoprotein (P-gp, ABCB1) transporter, but not for BCRP or OCT2 in vitro.
Elimination
Methylene blue has a half-life of approximately 24 hours in humans.
Metabolism
Methylene blue is metabolized by CYPs 1A2, 2C19 and 2D6 in vitro; however, the predominant in vitro pathway appears to be UGT-mediated conjugation by multiple UGT enzymes, including UGT1A4 and UGT1A9.
Azure B, which is a minor impurity in methylene blue, is also formed in humans as a metabolite of methylene blue, with an overall drug/metabolite AUC ratio of greater than 6:1. Azure B has 8-fold lower potency than methylene blue.
Excretion
Approximately 40% of methylene blue is excreted into the urine unchanged.
Specific Populations
Renal Impairment
After a single 1 mg/kg dose of methylene blue injection, AUC0-96h increased by 52%, 116%, and 192% in subjects with mild (estimated glomerular filtration rate (eGFR) 60–89 mL/min/1.73 m2), moderate (eGFR 30-59 mL/min/1.73m2), and severe (eGFR 15-29 mL/min/1.732m2) renal impairment, respectively. Cmax increased by 42%, 34%, and 15% in subjects with mild, moderate, and severe renal impairment respectively [see Dosage and Administration (2.2) and Use in Specific Populations (8.6)]. The half-life was unchanged in patients with mild to moderate renal impairment.
The AUC0-96h of Azure B after a single 1 mg/kg dose increased by 29%, 94%, and 339% in subjects with mild (estimated glomerular filtration rate (eGFR) 60–89 mL/min/1.73 m2), moderate (eGFR 30-59 mL/min/1.73m2), and severe (eGFR 15-29 mL/min/1.732m2) renal impairment, respectively. Cmax increased by 23%, 13%, and 65% in subjects with mild, moderate, and severe renal impairment, respectively [see Dosage and Administration (2.2) and Use in Specific Populations (8.6)]
Drug Interactions Studies
Clinical Studies:
The coadministration of 2 mg/kg dose of methylene blue injection with midazolam (a CYP3A4 substrate), caffeine (a CYP1A2 substrate), warfarin (a CYP2C9 substrate), and dextromethorphan (a CYP2D6 substrate) in a cocktail study did not affect the exposure of these substrates compared to their exposure without methylene blue injection administration.
In Vitro Studies:
Cytochrome P450 (CYP450) Enzymes:
Methylene blue inhibits CYP isozymes 1A2, 2B6, 2C8, 2C9, 2C19, 2D6 and 3A4/5. Possible time-dependent inhibition of CYP2C9, CYP2D6 and CYP3A4/5 (testosterone as substrate) was also observed. Methylene blue induces CYP1A2 but does not induce CYP2B6 or CYP3A4.
UDP-Glucuronosyltransferase (UGT):
Methylene blue inhibits UGT1A9 and UGT1A4, but did not significantly inhibit UGTs 1A1, 1A3, 1A6, 2B7 or 2B15.
Transporter:
Methylene blue is both a substrate for and an inhibitor of P-gp but is not a substrate for BCRP or OCT2 in vitro. Methylene blue is not a significant inhibitor of BCRP, OAT1, OAT3, OAT1B1 or OAT1B3. Methylene blue inhibits OCT2, MATE1 and MATE2-K.