The Pulmonary Absorption of Aerosolized and Intratracheally Instilled rhG-CSF and monoPEGylated rhG-CSF

Purpose. The objective of this study was to highlight differences in the pulmonary absorption of a monoPEGylated rhG-CSF and rhG-CSF after intratracheal instillation and aerosol delivery. Methods. Male Sprague Dawley rats (250 g) were anesthetized and intratracheally instilled (IT) with protein solution or were endotracheally intubated and administered aerosol for 20 min via a Harvard small animal ventilator. A DeVilbiss Aerosonic nebulizer containing 5 ml of protein solution at 3 mg/ml was used to generate aerosol. The volume of protein solution deposited in the lung lobes was estimated to be 13 µl after delivery of Tc-99m HSA solutions. The PEGylated proteins consisted of a 6 kDa (P6) or 12 kDa PEG (PI2) linked to the N-terminus of rhG-CSF. rhG-CSF also was administered IT in buffers at pH 4 and pH 7 and in dosing volumes ranging from 100 to 400 µl. Blood samples were removed at intervals after dosing and the total white blood cell counts (WBC) were determined. Plasma was assayed for proteins by an enzyme immuno assay. Results. The plasma protein concentration v. time profiles were strikingly different for aerosol v. IT delivery. The C _max values for rhG-CSF and P12 after aerosol delivery were greater than found after IT (Aerosol: 598 ± 135 (ng/ml) rhG-CSF; 182 ± 14 P12 v. IT: 105 ± 12 rhG-CSF; 65.9 ± 5 P12). Similarly, T_max was reached much earlier after aerosol administration (Aerosol: 21.7 ± 4.8 (min) rhG-CSF; 168 ± 31 P12 v. IT: 100 ± 17 rhG-CSF; 310 ± 121 P12). Estimated bioavailabilities (F_lung %) were significantly greater via aerosol delivery than those obtained after IT (Aerosol: 66 ± 14 rhG-CSF; 12.3 ± 1.9 P12 v. IT: 11.9 ± 1.5 rhG-CSF; 1.6 ± 0.1 P12). An increase in circulating WBC counts was induced by all proteins delivered to the lungs. The rate and extent of absorption of rhG-CSF was not influenced by the pH employed nor the instilled volume. Conclusions. Estimates of bioavailability are dependent upon the technique employed to administer drug to the lungs. Aerosol administration provides a better estimate of the systemic absorption of macromolecules.     

Pulmonary Delivery of Powders and Solutions Containing Recombinant Human Granulocyte Colony-Stimulating Factor (rhG-CSF) to the Rabbit

Two powder formulations (MMAD <4 µm) containing rhG-CSF were insufflated (IF) via an endotracheal tube at doses of 5, 75 or 500 µg/kg to New Zealand white rabbits. Doses of 5 and 500 µg/kg of solutions were administered by intratracheal instillation (IT), subcutaneous (SC) injection in the thigh and intravenous injection (IV) via the marginal ear vein. Blood samples were removed at regular intervals from an indwelling jugular catheter. Blood was analyzed directly for total white blood cell counts (WBC). Plasma was assayed for rhG-CSF by a specific ELISA. The distribution of radioactive dose in lung tissue was found after administering Tc99m HSA in solution or when incorporated into powders. The pharmacokinetics and pharmacodynamics were determined for all routes of administration. High dose IV concentration vs. time profiles declined biexponentially (t_1/2 = 0.6 ± 0.2 hrs, t_1/2 = 4.6 ± 0.2 hrs, n = 8). Clearance was dose dependent (11.6 ± 2.6 [500 µg/kg, n = 8] vs. 21.8 ± 3.3 ml/hr/kg [5 µg/kg, n = 5]). A normal systemic response was obtained after IF, indicating that rhG-CSF retains activity in the solid state. Dissolution and absorption of rhG-CSF from the powders were not rate limiting. The plasma concentration vs. time profiles peaked at similar times to those after IT (T_max 1 -2 hrs) but were earlier than obtained after SC (T_max 6-10 hrs). Powders were less efficiently dosed to the lung lobes after insufflation compared with instillates (14.7 ± 10.5 vs. 60.1 ± 10.6%), resulting in bioavailabilities ranging from 5 to 33%. Bioavailability after SC was 11.0 ± 7.0% and 95.3 ± 7.9% (n = 6) for the low and high doses, respectively.     

Phase I study of paclitaxel (taxol) and granulocyte colony stimulating factor (G-CSF) in patients with unresectable malignancy

A phase I trial of a 24-hour infusion of paclitaxel was conducted to identify the maximum tolerated dose of paclitaxel with granulocyte colony-stimulating factor (G-CSF) in patients with unresectable malignancy previously untreated with chemotherapy. Nineteen patients with metastatic melanoma or non-small cell lung cancer were treated with paclitaxel administered at 250, 300, 400 mg/m² every 3 weeks. G-CSF, 5 µg/kg was given as a daily subcutaneous injection 24 hours after the completion of the infusion. Dose limiting myelosuppression and peripheral neuropathy was observed at 400 mg/m² and 350 mg/m². Paclitaxel can be safely administered as a 24-hour infusion at 300 mg/m² with G-CSF. Further studies of paclitaxel and G-CSF are recommended to determine a dose–response relationship in sensitive tumors.     

Liquid Dose Pulmonary Instillation of Gentamicin PulmoSpheres® Formulations: Tissue Distribution and Pharmacokinetics in Rabbits

Purpose. To assess the pharmacokinetics and biodistribution of gentamicin, delivered as PulmoSpheres® formulations in rabbit serum and lung tissue following intratracheal instillation in a perflubron vehicle. Methods. Rabbits were anesthetized, intubated, and mechanically ventilated with O₂(FiO₂ = 0.50). Animals were then given 5 mg/kg gentamicin either intravenously, intramuscularly (IM), or intratracheally (IT) gentamicin PulmoSpheres® formulation, instilled in 1.8 ml/kg of liquid perflubron vehicle. Serum and lung lobe sections were collected at multiple time points and assayed for gentamicin content. Results. Serum gentamicin levels peaked at 64.7 g/ml, 11.2 g/ml, and 5.0 g/ml following intravenous, IM, and IT administration, respectively. Absolute bioavailability at 8 h for IM administration was 76.8% and 57.0% when delivered IT. Although peak lung levels of drug were reached within 1 h, total lung gentamicin concentration after IT administration was more than two orders of magnitude greater than that achieved following IM administration (680,540 vs. 4,985 g min, respectively) with significant levels of the antibiotic remaining in the lung even after 1 week. Conclusions. High levels of gentamicin in lung tissue can be achieved by instillation of a gentamicin PulmoSpheres® formulation in a perflubron vehicle, termed liquid dose installation, without reaching toxic systemic levels allowing for increased local delivery of agents such as gentamicin at the site of the infection.     

Extensive Absorption of 2′,3′-Dideoxyinosine by Intratracheal Administration in Rats

Purpose. To evaluate the intratracheal route of administration as an alternative to oral administration for 2,3-dideoxyinosine (ddI). Methods. A ddI dose (40 mg/kg/300 µl or 6.5 mg/kg/50 µl) was instilled into the trachea in female Fisher rats and an intravenous tracer dose (9 µg/kg) of ³H-ddI was administered concomitantly to determine the drug clearance. Plasma concentrations were analyzed for the rate and extent of absorption. Results. ddI was rapidly absorbed from the lungs, with a bioavailability of 63% at 40 mg/kg and 101% at 6.5 mg/kg. By comparison, our previous data showed an oral bioavailability of about 15% (Pharm Res., 9:822, 1992). The distribution of a dye solution instilled intratracheally showed that a fraction of the 300 µL dose spilled over to the gastrointestinal tract, where the entire 50 µL dose was retained in the lungs. The different distribution of the two doses/volumes likely contributed to the different bioavailability, with a fraction of the higher dose/volume degraded in the gastrointestinal tract after the spillover. Absorption of ddI from the airspace of the lung was biexponential, suggesting two absorption processes. Conclusions. These data indicate significantly higher and less variable bioavailability of ddI by the intratracheal route of delivery compared to the oral route. Furthermore, the complete bioavailability at the lower dose/volume indicates no significant pulmonary first pass elimination for ddI.     

Subjective and behavioral responses to intravenous fentanyl in healthy volunteers

Fentanyl is a mu opiate agonist which is occasionally abused by medical personnel who have ready access to the drug. We examined in healthy volunteers (N=13) the subjective and psychomotor-impairing effects of intravenous fentanyl (0–100 µg/70 kg). A randomized, placebo-controlled, crossover design was used in which subjects were injected with 0, 25 (N=6), 50 and 100 µg/70 kg fentanyl in a double-blind fashion. Subjects completed several questionnaires commonly used in abuse liability testing studies before drug injection and at periodic intervals for up to 3 h after drug injection. Subjects also completed several psychomotor tests at these times. Some aspects of psychomotor functioning (e.g., eye-hand coordination) were impaired by fentanyl. Fentanyl produced dose-related increases in ratings of high and sedated, but also tended to produce dysphoria and somatic symptomatology. Most subjects reported liking the effects of the two higher doses of fentanyl for at least a brief time after injection, but they varied widely in their liking ratings across the 3-h post-drug injection period. Despite the transient increases in liking ratings, fentanyl did not increase scores on a widely-used measure of drug-induced euphoria (morphine-benzedrine group scale of the Addiction Research Center Inventory). The present results suggest that some medical personnel who experiment with fentanyl may like it, and thus be at increased risk for abusing the drug in the future.     

Phase II trial of edatrexate in patients with advanced pancreatic adenocarcinoma

We conducted a phase II evaluation of edatrexate in 17 previously untreated patients with advanced adenocarcinoma of the pancreas; 14 patients had at least one month of therapy. The initial dose was 80 mg/m²iv. Treatment was administered weekly for 5 weeks, then every other week. Toxicity was generally mild. The median WBC nadir was 5.4 (range 0.6–7.4)×10³/l, and the median platelet nadir was 164.0 (range 62.0–341.0)×10³/l. One patient died with sepsis and gastrointestinal bleeding associated with pancytopenia. Five patients had a mild rash. Nausea occurred in 6 patients, including 3 who had vomiting. In addition, 11 patients complained of vague malaise which seemed to begin within 24–48 hours after administration of edatrexate, and lasted for 2 to 3 days, resolving within 6 days of drug administration. Median survival was 85 days. Although 5 patients had stable disease, including one with relief of pain, no major responses were seen, excluding, with 95% confidence, a response rate in excess of 20%.     

Influence of histamine depletion on learning and memory recollection in rats

To clarify the role of endogenous histamine in learning and memory, the effect of -fluoromethylhistidine on active avoidance response in rats was studied. -Fluoromethylhistidine (20–100 mg/kg or 10–50 µg) significantly (P<0.05 orP<0.01) prolonged the response latency in active avoidance response when administered by either intraperitoneal or intracerebroventricular injection. These effects were dose-related and long lasting. A prolongation of the response latency induced by an intraperitoneal injection of -fluoromethylhistidine (100 mg/kg) was antagonized by intracerebroventricular injection of histamine (10 and 20 ng) in a dose-dependent manner. In addition, the acquisition of this response was retarded by a consecutive intracerebroventricular injection of -fluoromethylhistidine (50 µg), whereas histamine (100 ng) facilitated the response acquisition when administered by the same route. Both intraperitoneal (100 mg/kg) and intracerebroventricular injection of -fluoromethylhistidine (50 µg) significantly (P<0.05 orP<0.01) decreased the brain histamine content, especially in the hippocampus and hypothalamus. When -fluoromethylhistidine (50 µg) was injected intracerebroventricularly, there is a high correlation between a prolongation of the response latency and a decrease in histamine content of these brain areas. Based on these findings, it was concluded that an intimate relation may exist between a prolongation of response latency in the active avoidance response and a decrease in the brain histamine content; endogenous histamine may play an important role in learning and memory recollection in rats.     

Quantitative determination by HPLC of urinary 6β-hydroxycortisol,an indicator of enzyme induction by rifampicin and antiepileptic drugs

Summary A method for determination of 6-hydroxycortisol in urine by means of high performance liquid chromatography is described. After extraction of 10–30 ml aliquots of urine with ethylacetate, separation is accomplished on a silica gel column (30 cm, Lichrosorb Si 100) with a special two-phase four-component eluent of methylene chloride, n-hexane, ethanol and water. Complete separation of - and-isomers requires 15 to 20 min. For routine determinations precolumn cleaning by backflush permits injections of samples at minimum time intervals. For quantitative determinations, each injection should contain at least 0.05–0.5 µg of 6-hydroxycortisol, depending on the detector employed. The mean excretion rate in healthy male adults (26–40 years) was 273 µg/day (SD=74.5; n=12). In patients on long term mono-therapy with rifampicin, 6-hydroxycortisol excretion had risen fourfold (1166 µg/d; SEM=248; n=7), paralleling the known enzyme-inducing effect of rifampicin. The relatively smaller increase to 498 µg/d observed in patients receiving triple therapy with rifampicin, isoniazid and ethambutol points to possible inhibition by isoniazid. The greatest stimulation of 6-hydroxycortisol excretion (2352 µg/d) was found in patients receiving antiepileptic therapy (phenytoin and/or carbamazepine and other drugs). The HPLC technique for 6-hydroxycortisol proved to be a tool routinely applicable to non-invasive evaluation of drug metabolizing enzyme activity in man.     

Racial Differences in Drug Response: Isoproterenol Effects on Heart Rate in Healthy Males

It was the purpose of this study to investigate racial alterations in -adrenoceptor response. Two groups of healthy, male volunteers gave their consent. There were eight black Americans (mean age, 26.1 ± 2.5 years) and eight white/Caucasian Americans (mean age, 24.4 ± 1.8 years). Each subject underwent an isoproterenol sensitivity test. There was a significant (P < 0.05) decrease in the ratio of E _max to ED50 in the white group (25.3 ± 6.4) compared with the black group (37.1 ± 12.4). Over the dose range of 0.1 to 1.0 µg there was a significant increase in response at both the 0.25- and the 0.5-µg dose (P < 0.05), with the black American group appearing to respond with a greater rate of rise in heart rate following the initial doses.     

Phase I clinical and pharmacokinetic trial of the podophyllotoxin derivative NK611 administered as intravenous short infusion

Background: NK611 is a novel podophyllotoxin derivative. Compared with etoposide, NK611 carries a dimethyl-amino group at the D-glucose moiety. The antitumor activity of NK611 showed to be equal or superior to etoposide in a variety of in vitro and in vivo tumor models. The aim of our present study was to determine the maximum tolerated dose and the dose-limiting toxicities of NK611 administered as intravenous infusion over 30 min every 28 days.Patients and methods: 45 patients (7 female, 38 male; median age 54 [range 37–73]) were enrolled. In a first stage, NK611 was administered without hematopoietic growth factor support; in a second stage, G-CSF was used for further dose escalation. Toxicities were assessed using WHO-criteria.Results: Initially, the dose was escalated from 60 mg/m² to 120 mg/m². In a second patient cohort, doses were further escalated with G-CSF support with doses ranging from 140 mg/m² to 250 mg/m². Dose-limiting toxicities were granulocytopenia and thrombocytopenia. Non-hematologic toxicities consisted of alopecia, mild nausea, and infection. Four partial responses were observed: two at 200 mg/m² (pleural mesothelioma, response duration 7 months, and non-small cell lung cancer, response duration 13 months), and two at 250 mg/m² (hepatocellular carcinoma, response duration 7 months, and non-small cell lung cancer, response duration 2 months). Pharmacokinetic analyses were performed in all patients. Using an open 3-compartment model, the terminal half-life (t_1/2) was 14.7 ± 3.7 h. The AUC at 250 mg/m² was determined to be 330 ± 147 g/mlh, the plasma clearance of NK611 was 16.2 ± 8.2 ml/min · m² and the V_ss was 16.8 ± 3.3 l/m². Protein binding of NK611 was 98.7%.Conclusion: the recommended dose for clinical Phase II studies is 120 mg/m² without G-CSF support and 200 mg/m² with G-CSF support.     

Influence of training dose on nicotine discrimination in humans

Non-human research indicates that drug discrimination results may depend largely on the specific training conditions, including initial training dose. It has recently been shown that humans can discriminate among different doses of nicotine delivered by nasal spray. In this study, we examined the influence of training dose on subsequent behavioral discrimination of a range of nicotine doses. Male (n=17) and female smokers (n=16) were randomly assigned to low (10 µg/kg) versus high (30 µg/kg) nicotine training dose groups and trained reliably to discriminate this dose from placebo (0) on day 1 (80% correct identification). All but six subjects (four in low, two in high) learned this discrimination and continued on to day 2, in which both groups received 0, 5, 10, 20, and 30 µg/kg in ascending order (30 min between dosings) and were tested for generalization with their training dose using quantal and quantitative behavioral discrimination tasks. Subjective responses via traditional self-report measures were also assessed. Nicotine-appropriate responding on day 2 was significantly greater in low- versus high-dose groups, especially at 5 µg/kg. However, this difference due to training dose was seen more in women than in men. Discrimination behavior was associated with subjective effects of head rush in males, and with head rush and decline in urge to smoke in females. These results show that discriminative stimulus effects of nicotine are not fixed properties of the drug, but can be influenced by training conditions, and that effects associated with this discrimination may differ between men and women.     

Solute Absorption from the Airways of the Isolated Rat Lung. IV. Mechanisms of Absorption of Fluorophore-Labeled Poly-α,β-[N(2-Hydroxyethyl)-DL-Aspartamide]

The pulmonary absorption kinetics of a single molecular weight distribution (MWD) of fluorophore-labeled poly-,-[N(2-hydroxyethyl)-DL-aspartamide] (F-PHEA), a hydrophilic and biocompatible synthetic polypeptide, were studied in the isolated, perfused rat lung (iprl) as functions of administered polymer concentration, dose, vehicle, and presence and absence of fluorophore. The MWD was characterized before and after absorption by measurement of weight- and number-averaged molecular weights (M _wand M _n, respectively) using high-performance gel-permeation chromatography. Values for M _w and M _n were 8.6 and 5.3 kD before, and 6.7 and 4.7 kD after, absorption into the perfusate; there was no significant metabolism and the MWD of the absorbed polymer was independent of both dose and sampling time over a 3-hr period. F-PHEA failed to show any evidence of aggregation in solution or changes in dose distribution within the airways as functions of increasing polymer concentration and dose. A concentration ranging study indicated the presence of a saturable, carrier-mediated transport process for F-PHEA with a maximum absorption rate, V _max, of approximately 180 µg or 0.027 µmol/hr. Coadministration of fluorophore-free PHEA was capable of depressing the absorption of F-PHEA. The transport process for F-PHEA appeared to have a molecular weight limit of about 7 kD for this hydrophilic polymer.     

Systemic Absorption and Activity of Recombinant Consensus Interferons After Intratracheal Instillation and Aerosol Administration

Purpose. The pulmonary pharmacokinetics and bioactivity of E. coli derived recombinant consensus interferon (CIFN) and a modified lactose-conjugated consensus interferon (LacCIFN) were evaluated in animals. Methods. Estimated doses of 20 and 100 µg/kg of the interferons were administered to anesthetized rats by aerosol via ultrasonic nebulizer as well as intravenous injection. Rats also received nominal doses of 50 and 200 µg/kg via intratracheal instillation (IT). Hamsters were treated with interferon via various routes including IT. The effectiveness of treatment was assessed by the resistance to development of hind leg paralysis following infection with encephalomyocarditis virus. Results. Significant amounts of CIFN and LacCIFN were found in rat plasma after aerosol administration. Peak plasma levels occurred 25–30 minutes with estimated bioavailabilities approaching 70%. Absorption of CIFN was rate limiting and plasma levels were detectable 12 hr post-dose. The CIFN at IT doses as low as 5 µg/kg was effective at reducing paralysis in hamsters but protection was variable and doses of up to 100 µg/kg were not 100% effective. Conclusions. Despite the incomplete protection, the results demonstrate the feasibility of treating systemic viral infections with interferon administered directly to the lungs.     

Effect of Dose and Release Rate on Pulmonary Targeting of Liposomal Triamcinolone Acetonide Phosphate

Purpose. To demonstrate the importance of dose and drug release rate for pulmonary targeting of inhaled glucocorticoids using an animal model of intrapulmonary drug deposition. Methods. Liposomes composed of 1,2-distearoyl phosphatidylcholine (DSPC), 1,2-distearoyl phosphatidylglycerol (DSPG) and triamcinolone acetonide phosphate (TAP) or liposomes containing triamcinolone acetonide (TA) were prepared by a mechanical dispersion method followed by extrusion through polycarbonate membranes. Encapsulation efficiency was assessed after size exclusion gel chromatography by reverse phase HPLC. The effect of liposome size (200 nm and 800 nm) on the release kinetics of water-soluble encapsulated material was determined in vitro at 37°C using 6-carboxyfluorescein as a marker and Triton X-100 (0.03%) as a leakage inducer. To investigate the relationship between drug release and pulmonary targeting, 100 g/kg of TAP in 800 nm liposomes was delivered to male rats by intratracheal instillation (IT) and the results compared to data for 100 g/kg TA liposomes (recently shown to exhibit a rapid drug release under sink conditions) and to previous studies reported for an equal dose of TAP in solution and TAP in 200 nm (1). Pulmonary targeting was assessed by simultaneously monitoring glucocorticoid receptor occupancy over time in lung and liver using an ex vivo receptor binding assay as a pharmacodynamic measure of glucocorticoid action. To assess the effect of dose on pulmonary targeting experiments were performed using 2.5, 7.5, 25, 100, and 450 g/kg of TAP in 800 nm liposomes. Results. The in vitro efflux of 6-carboxyfluorescein from (DSPC:DSPG) liposomes after exposure to Triton-X was biexponential. The terminal half-lives of 3.7 h and 9.0 h for the 200 nm and 800 nm liposomes, respectively, demonstrated that larger liposomes promote slower release of encapsulated water-soluble solute while previous results already indicated that encapsulation of lipophilic TA does not result in sustained release. Pulmonary targeting, defined as the difference between cumulative lung and liver receptor occupancies was most pronounced for the 800 nm liposomes (370%*h), followed by the 200 nm preparation (150%*h). No targeting was observed for TAP in solution (30%*h) or the rapid releasing TA liposome preparation. Correspondingly, the mean pulmonary effect time (MET) increased from 2.4–3.0 hr for TA liposomes or TAP in solution to 5.7 h and >6.2 h for TAP in 200 nm and in 800 nm liposomes, respectively. Escalating doses of TAP encapsulated in 800 nm liposomes revealed a distinct bell shaped relationship between the TAP dose and pulmonary targeting with a maximum occurring at 100 g/kg (370%*h). Conclusions. The in vivo data presented here confirm that pulmonary residence time and dose affect the extent of lung targeting of glucocorticoids delivered via the lung.     

Experimental Combination Chemotherapy with Thymidylate Synthetase and Ribonucleotide Reductase Inhibitors

The synergistic cytotoxic effects on exponentially growing 9L rat brain tumor cells of several inhibitors of thymidylate synthetase (TS) and ribonucleotide reductase (RNR) used in combination were investigated using a colony forming efficiency assay as the experimental endpoint. A 24 h treatment with nontoxic (0.1 µg/ml) or low (1.0 µg/ml) doses of 5-fluorouracil (FUra), 5-fluorodeoxyuridine, 5,8-dideazaisofolic acid, or 2-deoxy-2-fluoro-ara-uracil markedly enhanced cell kill caused by subsequent administration of 100 µg/ml hydroxyurea (HU) for 6 h. When a similar dose of HU or 1-formylisoquinoline thiosemicarbazone was administered for 6 h immediately after a 24 h treatment with either a 0.1 µg/ml or 1.0 µg/ml of FUra, a cell kill of approximately 1 log in addition to that caused by each drug alone was obtained. Thus a synergistic cell kill was consistently obtained when a low dose of TS inhibitors was administered 24 h before a 6 h treatment with another low dose of agents that act as RNR inhibitors. This synergism was not observed when FUra-treated cells were treated with methotrexate, 6-mercaptopurine, vincristine, or l,3-bis(2-chloroethyl)-1-nitrosourea. Similarly, a 6 h treatment with 1 µg/ml of FUra of cells that had been treated for various periods with 100 µg/ml of HU did not increase cell kill more than that obtained with HU alone (30% cell kill).     

Initial and long-term outpatient experience with pirmenol for control of ventricular arrhythmias

Summary Pirmenol, a new class IA antiarrhythmic agent, has shown promise in short-term trials, but long-term efficacy has not been documented. We thus evaluated 11 patients with frequent (60/h) premature ventricular complexes (PVC) given oral pirmenol for 25–727 days. Ten of 11 patients entering the long-term open trial had shown 70% (mean 83%) PVC suppression during in-hospital pirmenol dose ranging. Long-term pirmenol was given in divided doses of 100–600 mg/day. Mean PVC frequency during baseline was 13,078/24h (range, 3,218–32,718); couplets averaged 481/24h (1–2,829) and runs 45/24h (0–334). Ambulatory monitoring was performed at 1, 3, 6, and 12 months, then semiannually. Mean absolute PVC suppression at 1 month averaged 75% (p0.02). Median individual percentage PVC suppression was 94%. During the first 3 months, 8 patients (73%) continued to show a favorable response (70% suppression), and 3 had arrhythmia recurrence and were dropped. One responder was withdrawn after the onset of paroxysmal atrial fibrillation, and another early responder was withdrawn after 3 months because of arrhythmia relapse. Six patients have been treated for over 1 year, with 99% mean PVC suppression. Mean couplet and run frequencies at 1 month decreased by means of 76% (p0.05) and 92% (p=0.001) respectively. At 1 year, couplets were suppressed 99.8% and runs by 99.7% in the 6 patients remaining on pirmenol. Mean QT interval increased slightly (7.1%,p<0.05); mean PR and QRS intervals were unchanged. Plasma pirmenol concentrations averaged 1.49 µg/ml at clinic evaluations, 1.72 µg/ml in responders vs 1.08 µg/ml in nonresponders. Inade-quate plasma drug concentrations may be one cause for arrhythmia recurrence. Adverse effects were minimal. Thus, oral pirmenol is a safe and effective agent for long-term outpatient management of complex ventricular arrhythmias in selected patients.At the time this trial was conducted, Dr. Hampton was the American Society of Hospital Pharmacists postdoctoral fellow in cardiovascular pharmacotherapeutics     

Interaction between clonidine and physostigmine in normal rats and in rats after sinoaortic denervation

Summary Clonidine (3–30 g · kg^–1, i.v.) induced a fall in mean arterial pressure in rats after sinoaortic denervation but not in sham-operated animals. Moreover, sinoaortic denervation reduced the bradycardic action of this antihypertensive drug. Pressor and tachycardic response to physostigmine (60 g · kg^–1, i.v.) were greater in denervated than in sham-operated rats. The increase of mean arterial pressure was 26.2 ± 2.2 mm Hg in sham-operated rats (n = 12) and 53.8 ± 2.0 mm Hg in denervated rats (n = 12, P < 0.005).Pretreatment with 3 g · kg^–1 (i. v.) of clonidine did not alter the pressor response to physostigmine (60 g · kg^–1) in either of the two groups; 10 and 30 g · kg^–1 of clonidine reduced the physostigmine-induced increase of mean arterial pressure in sham-operated rats but enhanced the pressor response in denervated animals. Furthermore, an ineffective dose of physostigmine (30 g - kg^–1 i.v.) induced a pressor response after pretreatment with clonidine (10 gg · kg^–1) in denervated rats.Clonidine (10 g · kg^–1) did not affect the pressor effect of 1,1 dimethyl-4-phenylpiperazinium iodide (DMPP: 50 g · kg^–1 i.v.) or phenylephrine (4 g · kg ^–1, i.v.) in either group.The anticholinergic effect of clonidine in sham-operated rats may be explained by an inhibitory action on the release of acetylcholine in several brain structures but the facilitatory effect of clonidine observed in denervated animals is not clear. The results did not suggest a peripheral involvement in this facilitatory effect. Send offprint requests to M. A. Enero at the above address     

Toremifene and its metabolites enhance doxorubicin accumulation in estrogen receptor negative multidrug resistant human breast cancer cells

The enhanced accumulation of doxorubicin by agents known to reverse multidrug resistance provides a good functional test for evaluating modulating activity. In the present study, the non-steroidal triphenylethylene toremifene selectively increased doxorubicin accumulation in multidrug resistant estrogen receptor negative MDA A-1 human breast cells compared to the MDA 231 wild type cells. MDA A-1 cells were noted to be 1,000 fold resistant to doxorubicin (IC 50=< 0.1g/ml MDA 231; IC 50=100g/ml MDA A-1). Total accumulation of doxorubicin, expressed as area under the time concentration curve (AUC), was increased significantly in doxorubicin resistant cells (156% increase) versus wild type MDA 231 cells (6% increase). Correction of the accumulation defect to doxorubicin in drug resistant cells required a 18–20 hour pre-incubation with toremifene. The effects of toremifene on cell cycle in MDA A-1 cells was analyzed by flow cytometric techniques. Toremifene had a dose response relationship in blocking cells in G0–G1 reducing the number of cells entering S phase of the cell cycle. This effect was maximal at concentrations which increased the accumulation of doxorubicin in MDA A-1 cells. Several metabolites of toremifene were also noted to increase doxorubicin accumulation in MDA A-1 doxorubicin resistant cells. Tore XVIII (deaminocarboxytoremifene), Tore IV (4-hydroxy-N-desmethyltoremifene) and N-desmethyltoremifene all increased the accumulation of doxorubicin significantly (114%, 128% and 42% respectively). Finally, we show evidence that toremifene and its active metabolites are present in high concentrations in human plasma following a single 200 mg oral dose. Toremifene remains a very promising agent for modulating doxorubicin cytotoxicity in multidrug resistance.     

Evidence for an A2 adenosine receptor in guinea pig lung

Summary Adenosine receptors in guinea pig lung were characterized by measurement of cyclic AMP formation and radioligand binding. 5-N-Ethylcarboxamidoadenosine (NECA) increased cyclic AMP levels in lung slices about 4-fold over basal values with an EC₅₀ of 0.32 mol/l. N⁶-R-(–)-Phenylisopropyladenosine (R-PIA) was 5-fold less potent than NECA. 5-N-Methylcarboxamidoadenosine (MECA) and 2-chloroadenosine had EC₅₀-values of 0.29 and 2.6 mol/l, whereas adenosine and inosine had no effect. The adenosine receptors in guinea pig lung can therefore be classified as A₂ receptors. Several xanthine derivatives antagonized the NECA-induced increase in cyclic AMP levels. 1,3-Diethyl-8-phenylxanthine (DPX; K _i 0.14 mol/l) was the most potent analogue, followed by 8-phenyltheophylline (K _i 0.55 mol/l), 3-isobutyl-1-methylxanthine (IBMX; K _i 2.9 mol/l) and theophylline (K _i 8.1 mol/l). In contrast, enprofylline (1 mmol/l) enhanced basal and NECA-stimulated cyclic AMP formation. In addition, we attempted to characterize these receptors in binding studies with [³H]NECA. The K _D for [³H]NECA was 0.25 mol/l and the maximal number of binding sites was 12 pmol/mg protein. In competition experiments MECA (K _i 0.14 mol/l) was the most potent inhibitor of [³H]NECA binding, followed by NECA (K _i 0.19 mol/l) and 2-chloroadenosine (K _i 1.4 mol/l). These results correlate well with the EC₅₀-values for cyclic AMP formation in lung slices. However, the K _i-values of R-PIA and theophylline were 240 and 270 mol/l, and DPX and 8-phenyltheophylline did not compete for [³H]NECA binding sites. Therefore, a complete characterization of A₂ adenosine receptors by [³H]NECA binding was not achieved. In conclusion, our results show the presence of adenylate cyclase-coupled A₂ adenosine receptors in lung tissue which are antagonized by several xanthines.