A study of the in vitro interaction between lidocaine and premedications using human liver microsomes*

Comparative evaluation of the efficacy of two anesthetic gels (2% lignocaine and 20% benzocaine) in reducing pain during administration of local anesthesia - A randomized controlled trial

Background and Aims

Topical anesthetic agents are widely used in the field of pediatric dentistry to reduce pain and apprehension during administration of local anesthesia. Various topical anesthetic agents are available, among which the most commonly used ones are lignocaine and benzocaine. Hence we planned this study to compare and evaluate the effectiveness of topical anesthesia on needle insertion pain during administration of inferior alveolar nerve block.

Material and Methods

This double blind clinical study included 30 children of 4-8 years of age who were divided equally into two groups: Group A-2% lignocaine hydrochloride gel (Lox 2%) and Group B-20% benzocaine gel (ProGel-B). The intervention involved assessment of pain perception by the child during administration of inferior alveolar nerve block. The child's pain assessment was done using modified Wong-Baker pain rating scale. The ratings were subjected to statistical analysis.

Results

In Group A, 6.7% (N = 1) showed slight pain, 66.7% (N = 10) showed moderate pain, and 26.7% (N = 4) showed severe pain. In Group B, 46.7% (N = 7) showed no pain, 46% (N = 7) showed slight pain, and 6.7% (N = 1) showed moderate pain on needle insertion. (P value -0.000).

Conclusion

This study demonstrates that there is a highly significant difference between the topical anesthetic effectiveness of 2% lignocaine and 20% benzocaine on needle insertion pain in inferior alveolar nerve block. Twenty percent benzocaine showed better results than 2% lignocaine in reducing the needle insertion pain.

Absorption characteristics of epidural levobupivacaine with adrenaline and clonidine in children

AIM

To determine if the addition of adrenaline, clonidine, or their combination altered the pharmacokinetic profile of levobupivacaine administered via the caudal epidural route in children.

METHODS

Children aged <18 years old scheduled to undergo sub-umbilical surgery were administered caudal levobupivacaine plain 2.5 mg · ml(-1) or with adjuvants adrenaline 5 mcg · ml(-1) or clonidine 2 mcg · ml(-1) or their combination. Covariate analysis included weight and postnatal age (PNA). Time-concentration profile analysis was undertaken using nonlinear mixed effects models. A one-compartment linear disposition model with first-order input and first-order elimination was used to describe the data. The effect of either clonidine or adrenaline on absorption was investigated using a scaling parameter (Fabs(CLON), Fabs(ADR)) applied to the absorption half-life (Tabs).

RESULTS

There were 240 children (median weight 11.0, range 1.9-56.1 kg; median postnatal age 16.7, range 0.6-167.6 months). Absorption of levobupivacaine was faster when mixed with clonidine (Fabs(CLON) 0.60; 95%CI 0.44, 0.83) but slower when mixed with adrenaline (Fabs(ADR) 2.12; 95%CI 1.45, 3.08). The addition of adrenaline to levobupivacaine resulted in a bifid absorption pattern. While initial absorption was unchanged (Tabs 0.15 h 95%CI 0.12, 0.18 h), there was a late absorption peak characterized by a Tabs(LATE) 2.34 h (95%CI 1.44, 4.97 h). The additional use of clonidine with adrenaline had minimal effect on the bifid absorption profile observed with adrenaline alone. Neither clonidine nor adrenaline had any effect on clearance. The population parameter estimate for volume of distribution was 157 l 70 kg(-1). Clearance was 6.5 l · h(-1) 70 kg(-1) at 1-month PNA and increased with a maturation half-time of 1.6 months to reach 90% of the mature value (18.5 l · h(-1) 70 kg(-1)) by 5 months PNA.

CONCLUSIONS

The addition of adrenaline decreases the rate of levobupivacaine systemic absorption, reducing peak concentration by half. Levobupivacaine concentrations with adrenaline adjuvant were reduced compared to plain levobupivacaine for up to 3.5 hours. Clonidine as an adjuvant results in faster systemic absorption of levobupivacaine and similar concentration time profile to levobupivacaine alone. Adding adrenaline with clonidine does not alter the concentration profile observed with adrenaline alone.

Pharmacokinetic modeling of absorption behavior of 9-aminocamptothecin (9-AC) released from colon-specific HPMA copolymer-9-AC conjugate in rats

PURPOSE

To quantitate and predict colon-specific 9-aminocamptothecin (9-AC) release from the N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-9-AC conjugate and its absorption behavior after oral administration in rats.

METHODS

Drug distribution in the gastrointestinal (GI) tract and the plasma concentration-time profile of 9-AC released from the HPMA copolymer conjugate were predicted using the degradation, transit, and absorption rate constants in cecum. The fate of 9-AC in cecum and liver was measured by in-situ cecum absorption and liver perfusion.

RESULTS

Following oral administration of the conjugate, 9-AC was released rapidly in cecum. Based on the pharmacokinetic model, up to 60% of the dose was in the cecum at ~6 h, and 7% of the dose still remained there at 24 h. The predicted plasma concentration curve for released 9-AC after an oral dose of 3 mg/kg of 9-AC equivalent increased gradually and reached a peak of 98 nM at 7 h, then started decreasing slowly to 16 nM at 24 h. The bioavailability value was estimated as 0.31 after the first-pass elimination.

CONCLUSIONS

A pharmacokinetic model delineated the impact of GI transit, drug absorption rate, and first-pass metabolism on drug disposition following oral administration of HPMA copolymer-9-AC conjugate in rats.

Effects of Premedication Medicines on the Formation of the CYP3A4-Dependent Metabolite of Ropivacaine, 2', 6'-Pipecoloxylidide, on Human Liver Microsomes in vitro

Ropivacaine is a relatively new amide-type local anaesthetic, mainly used for surgery and postoperative pain relief. In this study we have investigated the interaction between the CYP3A4 metabolite of ropivacaine, 2',6'-pipecoloxylidide (PPX), and premedication with, i.e., psychotropic and antianxiety agents (diazepam, midazolam), hypnotics (thiamylal), local anaesthetics (lidocaine), depolarizing muscular relaxants (vecuronium), antihypertensive (clonidine) and H(2)-receptor antagonist (cimetidine) using human liver microsomes in vitro. The effects of the interaction between PPX and premedications were examined using a human liver microsomal preparation in vitro. The concentrations of ropivacaine and PPX were determined by HPLC with UV detection. The apparent Michaelis-Menten constant (Km) and the maximal velocity of total metabolic formation (V(max)) of PPX, the main metabolite of ropivacaine in human liver microsomes, were 17.7 (microM, mean) and 711 (nmol/min./mg protein, mean), respectively. Five premedications (diazepam, lidocaine, cimetidine, vecuronium and clonidine) did not inhibit ropivacaine metabolism in human liver microsomes at concentrations within the therapeutic range. However, midazolam and thiamylal weakly inhibited ropivacaine metabolism in competitive manner (IC(50) 7.8 microM and 250 microM, respectively). The results show lack of interaction between ropivacaine and seven premedication medicines within the therapeutic range of ropivacaine using human liver microsomes in vitro.