Chapter 6: Constant rate regiment

Ex2
For prolonged surgical procedures, succinylcholincheloride is given by i.v. infusion for sustained muscle relaxation. A typical initial dose is 20 mg followed by continuous infusion of 4 mg/min. The infusion must be individualized because of variation in the kinetics of metabolism of succinylcholine. Estimate the elimination half-lives of suc- cinylcholine in patients requiring 0.4 mg/min and 4 mg/min, respectively, to maintain 20 mg in the body

Answer

When reach a steaty state, the elimination rate constant can be calculate using the equation \[A_{ss} = \frac{R_0}{k}\], and we have \[ k = \frac{R_0}{A_{ss}}\] then base on this equation to calculat t half-life \[t_{1/2} = \frac{ln2}{k}\]

options(digits = 2)
ex2_Ass <- 20 # mg
ex2_R01 <- 0.4 #mg/min
ex2_R02 <- 4 # mg/min

# when R0 = 0.4
ex2_k1 <- ex2_R01 / ex2_Ass
ex2_t1 <- log(2)/ ex2_k1

# when R0 = 4
ex2_k2 <- ex2_R02 / ex2_Ass
ex2_t2 <- log(2) / ex2_k2

• when R0 = 0.4 mg/min, t_1/2 = 34.66 min.
  
• when R0 = 4 mg/min, t_1/2 = 3.47 min.