Blood flow in muscle groups and drug absorption

Area of Science:

• Physiology
• Pharmacology
• Biomedical Engineering

Background:

• Intramuscular drug administration is a common route for medication delivery.
• Variability in drug absorption can occur due to differences in local physiological conditions at the injection site.
• Muscle blood flow (MBF) is a key factor influencing the pharmacokinetics of intramuscularly administered drugs.

Purpose of the Study:

• To investigate whether variations in resting muscle blood flow (MBF) at common intramuscular injection sites could explain differences in drug absorption.
• To quantify and compare MBF in three distinct muscle groups: gluteus maximus, vastus lateralis, and deltoid.

Main Methods:

• Simultaneous measurement of MBF in paired muscles using dual, matched linear rate meters in 20 adult subjects.
• Calculation of MBF based on the 133xenon washout rate, fitted to a single exponential model.
• Randomized injection order within an incomplete block design to control for potential biases.

Main Results:

• Deltoid MBF (11.6 ml/100 gm/min) was significantly higher (p < 0.05) than gluteus maximus MBF (9.6 ml/100 gm/min).
• Vastus lateralis MBF showed no significant difference compared to gluteus maximus or between sides.
• A consistent 19% difference in resting MBF was observed among the studied muscle groups.

Conclusions:

• Consistent and significant differences in resting MBF exist among specific muscle groups.
• These MBF variations are substantial enough to influence the rate of drug absorption and peak serum concentrations after intramuscular administration.
• Site selection for intramuscular injections should consider MBF to optimize drug bioavailability and therapeutic outcomes.