Clinical Pharmacology for Xaracoll
Mechanism Of Action
Bupivacaine blocks the generation and the conduction of nerve impulses, presumably by increasing the threshold for electrical excitation in the nerve, by slowing the propagation of the nerve impulse, and by reducing the rate of rise of the action potential. Clinically, the order of loss of nerve function is (1) pain, (2) temperature, (3) touch, (4) proprioception, and (5) skeletal muscle tone.
Pharmacodynamics
Systemic absorption of bupivacaine produces effects on the cardiovascular system and CNS. At blood concentrations achieved with normal therapeutic doses, changes in cardiac conduction, excitability, refractoriness, contractility, and peripheral vascular resistance are minimal. However, toxic blood concentrations depress cardiac conduction and excitability, which may lead to atrioventricular block, ventricular arrhythmias, and cardiac arrest, sometimes resulting in fatalities. In addition, myocardial contractility is depressed and peripheral vasodilation occurs, leading to decreased cardiac output and arterial blood pressure. These cardiovascular changes are more likely to occur after unintended intravascular injection of liquid formulations of bupivacaine.
Following systemic absorption, bupivacaine can produce CNS stimulation, CNS depression, or both. Apparent central stimulation is manifested as restlessness, tremors, and shivering progressing to convulsions, followed by depression and coma progressing ultimately to respiratory arrest. However, bupivacaine has a primary depressant effect on the medulla and on higher centers. The depressed stage may occur without a prior excited state.
Pharmacokinetics
Local placement of XARACOLL within the surgical site during open inguinal hernia repair resulted in detectable plasma levels of bupivacaine at the first measured time point (0.5 hours) and throughout the 96-hour observation period [see WARNINGS AND PRECAUTIONS]. Systemic plasma levels of bupivacaine following application of XARACOLL do not correlate with local efficacy.
Absorption
The rate of systemic absorption of bupivacaine is dependent on the total dose administered, the route of administration, and the vascularity of the administration site.
Pharmacokinetic parameters for XARACOLL following placement in the surgical site during hernioplasty are presented in Table 2.
Table 2: Pharmacokinetic Parameters for Bupivacaine After Placement of XARACOLL in the Surgical Site During Open Inguinal Hernia Repair
| Parameter | XARACOLL 300 mg N=34 |
Cmax (ng/mL)1 [minimum, maximum] | 663 (264) [274, 1230] |
| Tmax (hours)2 [minimum, maximum] | 3 [1.5, 24] |
| AUC0-last (h•ng/mL)1 | 19493 (7564) |
| AUC0-∞, (h•ng/mL)1 | 20368 (7912) |
| 1½ (hours)1 | 19 (6) |
1 Arithmetic mean (SD) 2 Median |
The highest individual bupivacaine plasma concentration observed in the XARACOLL clinical program was 1230 ng/mL, which occurred 2 hours after placement of the three XARACOLL 100 mg implants (total bupivacaine HCl dose 300 mg) in the surgical site of one patient.
Distribution
After bupivacaine is released from XARACOLL it is absorbed systemically. Local anesthetics including bupivacaine are distributed to some extent to all body tissues, with higher concentrations found in highly perfused organs such as the liver, lungs, heart, and brain.
Local anesthetics including bupivacaine appear to cross the placenta by passive diffusion. The rate and degree of diffusion is governed by (1) the degree of plasma protein binding, (2) the degree of ionization, and (3) the degree of lipid solubility. Fetal/maternal ratios of local anesthetics appear to be inversely related to the degree of plasma protein binding, because only the free, unbound drug is available for placental transfer. Bupivacaine with a high protein binding capacity (95%) has a low fetal/maternal ratio (0.2 to 0.4). The extent of placental transfer is also determined by the degree of ionization and lipid solubility of the drug. Lipid soluble, non-ionized drugs such as bupivacaine readily enter the fetal blood from the maternal circulation.
Elimination
Metabolism
Amide-type local anesthetics such as bupivacaine are metabolized primarily in the liver via conjugation with glucuronic acid. Pipecoloxylidine is the major metabolite of bupivacaine. The elimination of drug from tissue distribution depends largely upon the availability of binding sites in the circulation to carry it to the liver where it is metabolized.
Excretion
After bupivacaine has been released from XARACOLL and is absorbed systemically, bupivacaine excretion is expected to be the same as for other bupivacaine formulations.
The kidney is the main excretory organ for most local anesthetics and their metabolites. Only 6% of bupivacaine is excreted unchanged in the urine.
Specific Populations
Age
Various pharmacokinetic parameters of the local anesthetics such as bupivacaine can be significantly altered by the age of the patient [see Geriatric Use].
Hepatic Impairment
Various pharmacokinetic parameters of the local anesthetics can be significantly altered by the presence of hepatic disease. Patients with hepatic disease, especially those with severe hepatic disease, may be more susceptible to the potential toxicities of the amide-type local anesthetics [see Use In Specific Populations].
Renal Impairment
Various pharmacokinetic parameters of the local anesthetics can be significantly altered by the presence of renal disease, factors affecting urinary pH, and renal blood flow [see WARNINGS AND PRECAUTIONS, Use In Specific Populations, Geriatric Use].
Animal Toxicology And/Or Pharmacology
Bupivacaine collage-matrix implants delayed bone healing in a rat osteotomy model compared to saline, bupivacaine, or placebo collagen implant alone. The clinical significance of these delays is not known.
Clinical Studies
The efficacy and safety of XARACOLL were evaluated in two randomized, multi-center, double-blind, placebo-controlled Phase 3 trials in patients undergoing open inguinal repair under general anesthesia.
In Study 1, 298 patients were enrolled. The mean age was 53.2 years (range 19 to 86) and patients were predominantly male (96%). In Study 2, 312 patients were enrolled. The mean age was 49.7 years (range 18 to 85) and patients were predominantly male (98%). In each study, three XARACOLL implants, containing 100 mg bupivacaine HCl each, were cut in half. Three halves were placed into the hernia repair site below the site of mesh placement. The muscle/fascial layer was closed and the remaining three halves were placed between the fascia/muscle closure and the skin closure. The placebo consisted of three implants without bupivacaine HCl, similarly prepared and placed. Use of low-dose lidocaine, administered topically or subcutaneously for intravenous catheter placement, or administered intravenously during the induction of general anesthesia prior to surgery and placement of XARACOLL, was reported.
Pain intensity was rated by the patients using a 0 to 10 numerical rating scale at multiple time points up to 72 hours. Immediately postoperatively, patients were allowed parenteral morphine rescue medication as needed. Once tolerating oral intake, patients received a standard acetaminophen regimen (650 mg orally three times daily) and immediate-release oral morphine (15 mg) was available as needed.
The primary outcome measure was the time-weighted sum of pain intensity from Time 0 through 24 hours (SPI24). The secondary endpoints were total use of opioid analgesia from Time 0 through 24 hours (TOpA24), time-weighted sum of pain intensity from Time 0 through 48 hours (SPI48), total use of opioid analgesia from Time 0 through 48 hours (TOpA48), time-weighted sum of pain intensity from Time 0 through 72 hours (SPI72), and total use of opioid analgesia from Time 0 through 72 hours (TOpA72).
In both Study 1 and Study 2, there was a statistically significant treatment effect for XARACOLL compared to placebo in SPI24 and TOpA24. There was no statistically significant treatment effect for XARACOLL compared to placebo in SPI72 and TOpA72. Table 3 shows the mean sum of pain intensity over the first 24 hours after surgery.
Table 3: Mean Sum of Pain Intensity Over the First 24 Hours After Surgery (Primary Endpoint)
| Study 1 | Study 2 |
XARACOLL N=197 | Placebo1 N=101 | XARACOLL N=207 | Placebo1 N=105 |
| SPI242 Mean (SD) | 85.9 (47.2) | 106.8 (48.2) | 88.3 (47.0) | 116.2 (44.0) |
| Difference3 95% CI | -20.8 (-32.2, -9.4) | | -27.8 (-38.6, -17.1) | |
1 Placebo consisted of three collagen implants. 2 Primary endpoint 3 Treatment compared with placebo SD=standard deviation; CI=confidence interval; SPI (sum of pain intensity): |
The proportion of patients who did not receive opioid rescue analgesia through 72 hours in the XARACOLL and placebo treatment groups was 36% and 22%, respectively, in Study 1, and 28% and 12%, respectively, in Study 2. The median time to first opioid rescue analgesia in the XARACOLL and placebo treatment groups was 11 hours and 1 hour, respectively, in Study 1, and 6 hours and 1 hour, respectively in Study 2.