The six-day-old rat air pouch model of inflammation: characterization of the inflammatory response to carrageenan.

Inflammation was induced in the 6-day-old rat air pouch by injection of carrageenan. The model was characterized in terms of exudate volume, leucocyte influx, cell free protein, prostaglandin E2 levels, and granuloma formation. The time course of all these inflammatory markers, except prostaglandin E2, showed a 3-hr lag followed by a rapid increase to 8 hr. Thereafter, the rate of increase was much slower to 48 hr. Differential cell counts indicated a predominantly polymorphonuclear cell response (75%) during the first 48 hr. Prostaglandin E2 levels increased rapidly after a 3-hr lag, to a maximum of 440 +/- 140 ng/mL at 15 hr and thereafter quickly declined to 140 +/- 60 ng/mL at 21 hr. Prostaglandin E2 levels were the most sensitive inflammatory marker to (S+)-ibuprofen and were reduced dose dependently in the range 0.05 to 1 mg/kg. We have demonstrated the time course for duration of NSAID-induced reduction of prostaglandin E2 levels during inflammation in an individual animal. Rac-ibuprofen (0.1-1 mg/kg) reduced leucocyte influx at 3 and 5 hr, after which drug effects gradually diminished by 24 hr. Rac-ibuprofen at 1 mg/kg significantly reduced the volume of air pouch exudate recovered at 24 hr but had no effect on protein levels.

Experimental determination of a drug targeting index for S(+)ibuprofen using the rat air pouch model of inflammation.

We have used the rat air pouch model of inflammation and S(+)ibuprofen as an experimental model system to enable the quantitative assessment of the pharmacokinetic determinants of site specific drug delivery. S(+)ibuprofen (50 & 1mg/kg) was administered directly into six day old air pouches immediately following the injection of the irritant carrageenan. Serial exudate and plasma samples were collected and analysed for ibuprofen by HPLC. The procedure was repeated following administration of S(+)ibuprofen (20 & 5mg/kg) intravenously. The parameters describing events in the air pouch and plasma indicated linear kinetics over the doses employed. The dose normalised AUCs were then used to formulate a quantitative measure of benefit for S(+)ibuprofen delivered directly to the air pouch. A Drug Targeting Index (DTI) was calculated from the ratio of AUC in the air pouch and plasma following direct intrapouch administration divided by the same ratio following intravenous administration and gave a value of 130. This pharmacokinetic measure of benefit represents the maximum advantage afforded by the site specific delivery of S(+)ibuprofen as the whole of the administered dose is delivered directly to the site of action.

Pharmacodynamic comparison of regional drug delivery for non-steroidal anti-inflammatory drugs, using the rat air-pouch model of inflammation.

The inhibition of prostaglandin E2 (PGE2) synthesis by S-(+)-ibuprofen and piroxicam have been assessed following intravenous and regional (intrapouch) drug delivery using the rat air-pouch model of inflammation. Anti-inflammatory response was defined as the decrease in the area under the exudate PGE2 concentration-time curve between 3 and 10 h, following regional administration of the irritant carrageenan. Dose-response studies indicated that bolus regional administration of S-(+)-ibuprofen increased potency 30-fold compared with systemic administration and could be further improved 10-fold by regional infusion, whereas regional administration of piroxicam showed no therapeutic advantage. Examination of the concentration-response using AUC revealed that for a given response, average pouch concentrations for S-(+)-ibuprofen during the PGE2 inflammatory response (3 to 10 h) was similar, irrespective of route or mode of administration. In contrast, an advantage following systemic rather than regional administration was revealed for piroxicam, based on plasma concentration-response data, indicating a major systemic anti-inflammatory component for piroxicam but not for S-(+)-ibuprofen. These observations stress the need to take account of both pharmacodynamics and pharmacokinetics when considering the potential advantage of regional administration.

Uptake of teicoplanin by isolated rat hepatocytes: comparison with in vivo hepatic distribution.

Tissue distribution of teicoplanin, a large glycopeptide antibiotic, is slow but at equilibrium its whole body distribution volume is relatively large (Vss = 1.18-2.78 liter/kg), despite a high binding to plasma albumin. In vivo distribution into liver is extensive. Previous in vitro homogenate studies suggest that teicoplanin binds to cell membranes but only enters some cells. This possibility was investigated with isolated hepatocytes incubated for 4 h with [14C]teicoplanin alone and in the presence of additional teicoplanin (1 and 100 microg/ml). Uptake was determined after separating the cells by rapid centrifugation through a dibutyl phthalate layer and assessing viability by the trypan blue exclusion test. Teicoplanin cell uptake curves, initially rapid followed by slower distribution (which agrees with in vivo findings), were adequately described by a closed two-compartment model. Whereas entry into hepatocytes was independent of drug concentration, binding to the cell exterior membrane was concentration-dependent. The equilibrium distribution ratio (Kpu(c) +/- S.D.; 42 +/- 10) was somewhat smaller than estimated in vivo (106 +/- 9), but similar to that reported previously in vitro using liver homogenates (54 +/- 11). Also, the estimated membrane permeability-surface area product was larger in vitro than in vivo (PSu +/- S.D.; 5.5 +/- 2.9 versus 0.74 +/- 0.10 ml/min per whole liver). The most likely explanation for this difference is that in vivo only a small fraction of the total cell surface area is exposed to the perisinusoidal space, where exchange occurs.

Regional drug delivery II: relationship between drug targeting index and pharmacokinetic parameters for three non-steroidal anti-inflammatory drugs using the rat air pouch model of inflammation.

PURPOSE: To quantify the advantage gained by direct administration to a target site for two non-steroidal anti-inflammatory drugs (NSAIDs) piroxicam and diclofenac in the rat air pouch model of inflammation. To derive a model relating drug targeting index (DTI) to the pharmacokinetic parameters of the target and systemic sites, and to compare predictions with observations. METHODS: DTI was calculated based on area under the concentration time curve at target (pouch) and systemic site (venous blood) following administration into and sampling from both sites. A model was derived relating DTI to systemic clearance, target permeability, plasma protein binding and fraction of the targeted dose that is systemically available. RESULTS: Both NSAIDs exhibited linear pharmacokinetics over the dose ranges studies. They differed primarily in total body clearance which was approximately 16 fold greater for diclofenac (213 ml hr-1 per 250 g) than piroxicam (13 ml hr-1 per 250 g). Observed DTIs (11, 114 and 276 for piroxicam, S[+]ibuprofen [studied previously] and diclofenac) were ranked in order of total body clearance but were approximately 7.5 fold lower than predicted (101, 700 and 2214 respectively). CONCLUSIONS: The discrepancy was explained by the influx of the plasma binding protein, albumin, into the target site due to increased vascular permeability associated with the inflammatory response. The originally derived equation for DTI, which assumed only unbound drug diffuses across the target site, was modified to take into account the simultaneous flux of bound drug.

Regional drug delivery I: permeability characteristics of the rat 6-day-old air pouch model of inflammation.

PURPOSE: To determine the permeability characteristics of the rat air pouch model of inflammation using permeability extremes within which the NSAIDs S[+] ibuprofen, piroxicam and diclofenac could be evaluated. METHODS: Permeability was calculated using concentration data obtained following intrapouch and intravenous administration of [3H]-water, [14C]-urea, [14C]-inulin and [125I]-albumin and compared to similar data obtained for the three NSAIDs. RESULTS: Similar permeability values (5-6.5 ml hr-1) were obtained for the three NSAIDS which fell between the permeability extremes of the molecular weight markers [3H]-water (9.7 ml hr-1), [14C]-urea (6.8 ml hr-1), [14C]-inulin (1.0 ml hr-1) and [125I]-albumin (0.6 ml hr-1). Coadministration of equipotent anti-inflammatory doses of the NSAIDs did not affect local blood flow to the air pouch (as assessed by urea kinetics) but did reduced vascular permeability (as assessed by albumin flux into the pouch). CONCLUSIONS: Comparison of the NSAIDs with the permeabilities of the molecular weight markers indicates that a perfusion rate limitation probably exists. Systemic absorption is complete over the first two hours following intrapouch administration of the NSAIDs, therefore albumin flux into the pouch is insufficient to materially affect the permeability of the NSAIDs. However, subsequently (post 5hr) albumin concentration in the pouch rises sufficiently to lower the effective flux of the NSAIDs.