Clinical Pharmacology for Posimir
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. In general, the progression of anesthesia is related to the diameter, myelination and conduction velocity of affected nerve fibers. Clinically, the order of loss of nerve function is as follows: (1) pain, (2) temperature, (3) touch, (4) proprioception, and (5) skeletal muscle tone.
Pharmacodynamics
Systemic absorption of bupivacaine produces effects on the cardiovascular and central nervous systems. At blood concentrations achieved with 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 to 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, local anesthetics can produce central nervous system stimulation, depression or both. Apparent central stimulation is usually manifested as restlessness, tremors and shivering, progressing to convulsions, followed by depression and coma, progressing ultimately to respiratory arrest. However, the local anesthetics have a primary depressant effect on the medulla and on higher centers. The depressed stage may occur without a prior excited stage.
Pharmacokinetics
Infiltration of POSIMIR into the surgical wound results in plasma levels of bupivacaine that can persist for 168 hours. Systemic plasma levels of bupivacaine following administration of POSIMIR are not correlated with local efficacy.
Absorption
The rate of systemic absorption of bupivacaine is dependent upon the total dose of drug administered, the route of administration, and the vascularity of the administration site.
Pharmacokinetic parameters of bupivacaine are shown in Table 10 after single-dose infiltration of POSIMIR in arthroscopic subacromial decompression surgical procedure.
Table 10. Summary of Pharmacokinetic Parameters for Bupivacaine after Administration of a Single Dose of POSIMIR 5 mL (660 mg)
| Surgical Procedure |
|
Cmax
(ng/mL) |
AUC0-t# (h·ng/mL) |
Tmax
(h) |
T1/2
(h) |
| Arthroscopic subacromial decompression Study 1* |
N |
36 |
36 |
36 |
36 |
| Mean |
593 |
19395 |
5.9^ |
16.4 |
| SD |
299 |
12056 |
1.0-24.0^ |
5.1 |
| Arthroscopic subacromial decompression |
N |
18 |
18 |
18 |
18 |
| Mean |
1006 |
47015 |
8.0^ |
26.1 |
| SD |
454 |
20040 |
2.1-26.9^ |
8.2 |
#t = last sampling time
^ Median / Range (min-max)
* Drug leakage from the surgical site was suspected. |
Distribution
Depending upon the route of administration, bupivacaine is distributed to some extent to all body tissues, with high concentrations found in highly perfused organs such as the liver, lungs, heart, and brain.
Bupivacaine appears 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
The mean half-life of bupivacaine after POSIMIR administration in adults who underwent arthroscopic subacromial decompression range from 16.4 to 26.1 hours.
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
The kidney is the main excretory organ for most local anesthetics and their metabolites. Urinary excretion is affected by urinary perfusion and factors affecting urinary pH. Only 6% of bupivacaine is excreted unchanged in the urine.
Specific Populations
Hepatic Impairment
Pharmacokinetics of POSIMIR have not been evaluated in patients with hepatic impairment. [see WARNINGS AND PRECAUTIONS and Use In Specific Populations].
Renal Impairment
Pharmacokinetics of POSIMIR have not been evaluated in patients with renal impairment. [see Use In Specific Populations].
Geriatric Patients
Pharmacokinetics of POSIMIR have not been evaluated in geriatric patients.
Elderly patients have exhibited higher peak plasma concentrations than younger patients following administration of bupivacaine HCl. The total plasma clearance was decreased in these patients [see Use In Specific Populations].
Animal Toxicology And/Or Pharmacology
Necrosis of the joint cartilage was observed following intra-articular injection of a single dose of POSIMIR or POSIMIR vehicle in the dog model.
Clinical Studies
The effectiveness of POSIMIR was evaluated in ten adequate and well-controlled studies in patients undergoing open and laparoscopic abdominal procedures, abdominal hysterectomy, inguinal hernia repair, and open and arthroscopic shoulder procedures. Adequate evidence of effectiveness was demonstrated in one of three studies conducted in patients undergoing shoulder surgery (described in detail below) and was not demonstrated in any soft tissue procedure evaluated.
Study 1
Study 1 was a randomized, multicenter, assessor blinded, placebo-controlled (vehicle) clinical trial in 107 patients undergoing arthroscopic subacromial decompression surgery with an intact rotator cuff. Associated procedures included inspection of the glenohumeral joint, distal clavicle excision, bursectomy, synovectomy, removal of loose body, resection of coracoacromial ligament and subacromial spurs, rotator cuff debridement, and minor debridement of articular cartilage. There were no open surgical procedures performed during this study. The mean age was 50 years (range 21 to 70 years), 60% of treated patients were female, 96% were White, 2% were Hispanic, 1% were Asian, and 1% were Other.
Patients were randomized 2:1:1 to receive POSIMIR, vehicle placebo, or bupivacaine HCl 50 mg, and all patients received general anesthesia. No analgesic pre-medication or local anesthetics were administered. POSIMIR and vehicle placebo were administered under direct arthroscopic visualization as single injections into the subacromial space through one of the arthroscopic portals at the end of the surgery. Bupivacaine HCl 50 mg was administered subacromially as a single dose. Post-operatively, patients received acetaminophen 500 mg or 1000 mg every six hours, depending on body weight, through 72 hours, and were allowed morphine rescue medication as needed, either 2 mg IV or 10 mg orally. Pain intensity was rated by the patients using a 0 to 10 numerical rating scale (NRS) at multiple time points up to72 hours.
The primary outcome measures were the normalized area under the curve (nAUC) of mean pain intensity on movement scores collected at specified intervals over the first 72 hours after surgery and total opioid rescue analgesia (IV morphine-equivalent dose) through 72 hours. In this clinical study, POSIMIR 5 mL demonstrated a significant reduction in mean pain intensity compared with placebo of 1.3 points on a 0 to 10 NRS scale over 72 hours ( Figure 1 ).
Figure 1. Mean Pain Intensity on Movement Through 72 Hours After Surgery, Subacromial Decompression Study 1
The median total use of opioid rescue analgesia (IV morphine equivalent dose) from 0 to 72 hours for the POSIMIR treatment group (4 mg) was statistically lower than for the placebo treatment group (12 mg). The median use of opioid rescue analgesia in the bupivacaine treatment group was 8 mg.
Study 2
Study 2 was a randomized, double-blind, placebo-controlled (vehicle) clinical trial in 60 patients undergoing arthroscopic subacromial decompression, inspection of glenohumeral joint, synovectomy, removal of loose body, minor debridement of articular cartilage, minor debridement or minor repair of rotator cuff, open distal clavicle excision, bursectomy, and resection of coracoacromial ligament and subacromial spurs. The mean age was 48 years (range 27 to 68 years), 55% of treated patients were female, 95% were White, 2% were Asian, and 2% were Other.
Patients were randomized 2:1 to receive POSIMIR or vehicle placebo, and all patients received general anesthesia. Post-operatively, patients were allowed morphine rescue medication as needed, either 3 mg IV or 10 mg to 15 mg orally, or acetaminophen. Pain intensity was rated by the patients using a 0 to 10 numerical rating scale (NRS) at multiple time points up to 72 hours.
The primary outcome measures were mean pain intensity on movement AUC through 72 hours and total opioid rescue analgesia (IV morphine-equivalent dose) through 72 hours. There was no statistically significant difference in either primary endpoint between the POSIMIR and vehicle placebo treatment groups ( Figure 2 ).
Figure 2: Mean Pain Intensity on Movement Through 72 Hours After Surgery, Subacromial Decompression Study 2
Study 3
Study 3 was a randomized, double-blind, placebo-controlled (vehicle) and open-label PK clinical trial in 92 patients undergoing a variety of shoulder surgical procedures, including rotator cuff repair, subacromial decompression, glenoid labrum repair or debridement, and biceps tendon repair. The majority of patients underwent arthroscopic procedures; however, six patients underwent a combination of arthroscopic and open procedures. The mean age was 54 years (range 20 to 82 years), 59% of treated patients were male, 87% were White, 8% were African American, 3% were Other, and 2% were Asian.
An equal number of patients were randomized to two cohorts. The routes of POSIMIR or vehicle placebo administration in Cohort 1 were subacromial or subcutaneous injection or a combination. In Cohort 2, POSIMIR or vehicle placebo was administered via injection under direct arthroscopic visualization into the subacromial space. Surgical procedures were completed either under local or general anesthesia. Post-operatively, patients were allowed morphine IV, oxycodone orally, or acetaminophen orally as needed.
The primary outcome measures were mean pain intensity on movement and at rest through 120 hours and pain control through day seven. There was no statistically significant difference in either primary endpoint between POSIMIR and vehicle placebo treatment groups ( Figure 3 ).
Figure 3: Mean Pain Intensity on Movement Through 120 Hours After Surgery, Subacromial Decompression Study 3