Intratumoral delivery of TransCon™ TLR7/8 Agonist promotes sustained anti-tumor activity and local immune cell activation while minimizing systemic cytokine induction

Background

Intratumoral (IT) delivery of toll-like receptor (TLR) agonists has shown encouraging anti-tumor benefit in preclinical and early clinical studies. However, IT delivery of TLR agonists may lead to rapid effusion from the tumor microenvironment (TME), potentially limiting the duration of local inflammation and increasing the risk of systemic adverse events.

Methods

To address these limitations, TransCon^™ TLR7/8 Agonist—an investigational sustained-release prodrug of resiquimod that uses a TransCon linker and hydrogel technology to achieve sustained and predictable IT release of resiquimod—was developed. TransCon TLR7/8 Agonist was characterized for resiquimod release in vitro and in vivo, in mice and rats, and was assessed for anti-tumor efficacy and pharmacodynamic activity in mice.

Results

Following a single IT dose, TransCon TLR7/8 Agonist mediated potent tumor growth inhibition which was associated with sustained resiquimod release over several weeks with minimal induction of systemic cytokines. TransCon TLR7/8 Agonist monotherapy promoted activation of antigen-presenting cells in the TME and tumor-draining lymph nodes, with evidence of activation and expansion of CD8⁺ T cells in the tumor-draining lymph node and TME. Combination of TransCon TLR7/8 Agonist with systemic immunotherapy further promoted anti-tumor activity in TransCon TLR7/8 Agonist-treated tumors. In a bilateral tumor setting, combination of TransCon TLR7/8 Agonist with systemic IL-2 potentiated tumor growth inhibition in both injected and non-injected tumors and conferred protection against tumor rechallenge following complete regressions.

Conclusions

Our findings show that a single dose of TransCon TLR7/8 Agonist can mediate sustained local release of resiquimod in the TME and promote potent anti-tumor effects as monotherapy and in combination with systemic immunotherapy, supporting TransCon TLR7/8 Agonist as a novel intratumoral TLR agonist for cancer therapy. A clinical trial to evaluate the safety and efficacy of TransCon TLR7/8 Agonist, as monotherapy and in combination with pembrolizumab, in cancer patients is currently ongoing (transcendIT-101; NCT04799054).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-022-02708-6.

Design and Preclinical Development of TransCon PTH, an Investigational Sustained-Release PTH Replacement Therapy for Hypoparathyroidism

Hypoparathyroidism (HP) is a condition of parathyroid hormone (PTH) deficiency leading to abnormal calcium and phosphate metabolism. The mainstay of therapy consists of vitamin D and calcium supplements, as well as adjunct Natpara (PTH(1-84)). However, neither therapy optimally controls urinary calcium (uCa) or significantly reduces the incidence of hypercalcemia and hypocalcemia. TransCon PTH, a sustained-release prodrug of PTH(1-34) in development for the treatment of HP, was designed to overcome these limitations. To determine the pharmacokinetics and pharmacodynamics of TransCon PTH, single and repeat s.c. dose studies were performed in rats and monkeys. TransCon PTH demonstrated a half-life of 28 and 34 hours in rats and monkeys, respectively. After repeated dosing, an infusion-like profile of the released PTH, characterized by low peak-to-trough levels, was obtained in both species. In intact rats and monkeys, daily subcutaneous administration of TransCon PTH was associated with increases in serum calcium (sCa) levels and decreases in serum phosphate levels (sP). In monkeys, at a single dose of TransCon PTH that increased sCa levels within the normal range, a concurrent decrease in uCa excretion was observed. In 4-week repeat-dose studies in intact rats and monkeys, uCa excretion was comparable to controls across all dose levels despite increases in sCa levels. Further, in a rat model of HP, TransCon PTH normalized sCa and sP levels 24 hours per day. This was in contrast to only transient trends toward normalization of sCa and sP levels with an up to 6-fold higher molar dose of PTH(1-84). After repeated dosing to HP rats, uCa excretion transiently increased, corresponding to increases in sCa above normal range, but at the end of the treatment period, uCa excretion was generally comparable to sham controls. TransCon PTH was well tolerated and the observed pharmacokinetics and pharmacodynamics were in line with the expected action of physiological replacement of PTH. © 2019 American Society for Bone and Mineral Research.

TransCon CNP, a Sustained-Release C-Type Natriuretic Peptide Prodrug, a Potentially Safe and Efficacious New Therapeutic Modality for the Treatment of Comorbidities Associated with Fibroblast Growth Factor Receptor 3-Related Skeletal Dysplasias

TransCon CNP is a C-type natriuretic peptide (CNP-38) conjugated via a cleavable linker to a polyethylene glycol carrier molecule, designed to provide sustained systemic CNP levels upon weekly subcutaneous administration. TransCon CNP is in clinical development for the treatment of comorbidities associated with achondroplasia. In both mice and cynomolgus monkeys, sustained exposure to CNP via TransCon CNP was more efficacious in stimulating bone growth than intermittent CNP exposure. TransCon CNP was well tolerated with no adverse cardiovascular effects observed at exposure levels exceeding the expected clinical therapeutic exposure. At equivalent dose levels, reductions in blood pressure and/or an increase in heart rate were seen following single subcutaneous injections of the unconjugated CNP-38 molecule or a daily CNP-39 molecule (same amino acid sequence as Vosoritide, USAN:INN). The half-life of the daily CNP-39 molecule in cynomolgus monkey was estimated to be 20 minutes, compared with 90 hours for CNP-38, released from TransCon CNP. C _max for the CNP-39 molecule (20 µg/kg) was approximately 100-fold higher, compared with the peak CNP level associated with administration of 100 µg/kg CNP as TransCon CNP. Furthermore, CNP exposure for the daily CNP-39 molecule was only evident for up to 2 hours postdose (lower limit of quantification 37 pmol/l), whereas TransCon CNP gave rise to systemic exposure to CNP-38 for at least 7 days postdose. The prolonged CNP exposure and associated hemodynamically safe peak serum concentrations associated with TransCon CNP administration are suggested to improve efficacy, compared with short-lived CNP molecules, due to better therapeutic drug coverage and decreased risk of hypotension. SIGNIFICANCE STATEMENT: The hormone C-type natriuretic peptide (CNP) is in clinical development for the treatment of comorbidities associated with achondroplasia, the most common form of human dwarfism. The TransCon Technology was used to design TransCon CNP, a prodrug that slowly releases active CNP in the body over several days. Preclinical data show great promise for TransCon CNP to be an effective and well-tolerated drug that provides sustained levels of CNP in a convenient once-weekly dose, while avoiding high systemic CNP bolus concentrations that can induce cardiovascular side effects.

Evaluation of Nonacog Beta Pegol Long-term Safety in the Immune-deficient Rowett Nude Rat (Crl:NIH-Foxn1rnu)

Nonacog beta pegol is a 40-kDa polyethylene glycosylated (PEGylated) human recombinant coagulation factor IX, intended for the treatment of hemophilia B. Human coagulation factors are immunogenic in animals; therefore, to evaluate the long-term toxicity of nonacog beta pegol, an immune-deficient, athymic rat (Rowett nude; Crl:NIH-Foxn1(rnu)) was used. Rats (n = 216) were given intravenous nonacog beta pegol 0, 40, 150, 600, or 1,200 IU/kg every 5th day for 26 weeks. To avoid infections, the animals were housed in a full-barrier environment with sterilized food and bedding. Standard toxicity end points were unaffected by treatment. All treated animals were exposed to nonacog beta pegol throughout the study, and no animals developed antidrug antibodies. Immunohistochemical staining revealed PEG in choroid plexus epithelial cells in a dose-dependent manner. Transmission electron microscopy showed that PEG was distributed in cytoplasmic vesicles of these cells, with no apparent effect on cellular organelle structures. Fourteen (6.5%) animals were euthanized or died prematurely due to nontreatment-related infections in the urogenital system and skin. In conclusion, the athymic rat is a suitable model for testing chronic toxicity of human proteins that are immunogenic in animals. Nonacog beta pegol was generally well tolerated, with no adverse effect of PEG on choroid plexus epithelial cells.

Matrix metalloproteinases (MMPs), tissue inhibitors of metalloproteinases (TIMPs) and transforming growth factor-β (TGF-β) in advanced canine myxomatous mitral valve disease

This study investigated mitral valve and myocardial protein and gene expression of matrix metalloproteinases (MMPs), their tissue inhibitors (TIMPs) and transforming growth factor-β (TGF-β) and plasma MMP and TGF-β concentrations in age-matched dog groups euthanized due to either advanced myxomatous mitral valve disease (MMVD) or other reasons. Furthermore, echocardiographic data and lumen/area ratio were correlated with tissue and plasma levels of MMPs, TIMPs and TGF-βs. Mitral valve and myocardial gene expression of MMP2, MMP14, TGF-β1 and TGF-β2 were increased and plasma MMP9 was decreased in advanced MMVD dogs. Myocardial gene expression of TIMP2 and TIMP3 were increased in advanced MMVD. All affected markers correlated to echocardiographic parameters. Significantly narrowed lumen/area ratio was associated with increased myocardial expression of MMP2, MMP14, TIMP2 and TIMP3. No differences in tissue protein expression were recorded. MMP2, MMP14, TIMP2, TIMP3, TGF-β1 and TGF-β2 appear to play a local role in the development of advanced MMVD.

Holter monitoring of small breed dogs with advanced myxomatous mitral valve disease with and without a history of syncope

Background

Syncope is a transient loss of consciousness occasionally occurring in dogs with advanced myxomatous mitral valve disease (MMVD).

Objective

(1) To study ECG changes during syncopal episodes in dogs with advanced MMVD and (2) to compare the occurrence of arrhythmias and changes in heart rate variability (HRV) between dogs with advanced MMVD with and without a history of syncope.

Animals

Forty‐three privately owned dogs (<15 kg) with advanced MMVD: 21 with and 22 without a history of syncope.

Methods

Prospective study with dogs recruited for an evaluation including history, physical examination, echocardiography, and arrhythmia and HRV analysis performed on 24‐hour Holter recordings.

Results

A syncopal episode was observed during Holter monitoring in 4 dogs: 3 dogs had sinus rhythm and 1 dog had sinus arrest followed by escape rhythm. An arrhythmia variable representing sinus arrhythmia was significantly lower in dogs with a history of syncope than in those without (P = .008). Eight of 26 HRV variables were significantly different between dogs with and without a history of syncope.

Conclusions and Clinical Importance

Compared with dogs without a history of syncope, dogs with advanced MMVD and a history of syncope did not have a higher occurrence of arrhythmias, but had less sinus arrhythmia, and had changes in HRV variables representing decreased overall HRV, decreased parasympathetic, and increased sympathetic modulation of heart rate.

Left ventricular twist and circumferential strain in dogs with myxomatous mitral valve disease

BACKGROUND

During the cardiac cycle, the ventricle undergoes a twisting motion because of the oblique orientation of the left ventricular (LV) myofibers. This can be quantified by speckle-tracking echocardiography (STE). In mitral regurgitation (MR) in humans, the short axis deformation has been suggested as being pivotal to LV function. Decreased and delayed LV twist has been described in experimental MR, but has not been studied in myxomatous mitral valve disease (MMVD).

HYPOTHESES

(1) Magnitude (CSt) and rate (CSRs) of systolic circumferential deformation decrease before the onset of congestive heart failure (CHF); (2) magnitude and rate of LV twist decrease, and onset of untwist is delayed, with increasing MMVD severity.

ANIMALS

A total of 97 privately owned small- to medium-sized dogs.

METHODS

Severity of MMVD was assessed by echocardiography and presence of clinical signs of CHF. Magnitude and rate of LV twist and circumferential deformation were evaluated by STE.

RESULTS

Dogs with CHF receiving treatment had increased CSt, CSRs, early diastolic untwisting rate, and delayed onset of untwist compared to dogs with minimal MMVD and increased systolic twist compared to dogs with mild MMVD (all P < .01). CSt and time to onset of untwist increased with echocardiographic variables of MR severity (all P < .002). CSRs and several LV twist variables decreased with increasing systolic LV internal diameter (all P < .01).

CONCLUSIONS AND CLINICAL IMPORTANCE

No STE-derived variable was decreased before onset of CHF. In dogs with CHF receiving treatment, the delayed onset of relaxation might indicate LV dysfunction and the hyperdynamic CSt and LV twist reflect compensatory mechanisms.

Radial and longitudinal strain and strain rate assessed by speckle-tracking echocardiography in dogs with myxomatous mitral valve disease

BACKGROUND

Assessment of left ventricular (LV) function using conventional echocardiographic methods is difficult in mitral regurgitation (MR) owing to altered hemodynamic loading conditions. Newer methods such as speckle-tracking echocardiography (STE) provide assessment of LV strain (St) and strain rates (SR).

HYPOTHESES

Global St and SR are 1) decreased in dogs with clinical signs of congestive heart failure (CHF) due to myxomatous mitral valve disease (MMVD) compared with clinically healthy dogs, and are 2) associated with conventional echocardiographic indices of MMVD severity.

ANIMALS

The study subjects were 93 privately owned dogs with different MMVD severities.

METHODS

Prospectively recruited dogs were grouped according to MMVD severity based on echocardiographic evaluation of MR and presence of clinical signs. Global radial and longitudinal St, SR, and indices of LV dyssynchrony were assessed.

RESULTS

On group-wise comparisons, dogs with CHF had increased global longitudinal St, global longitudinal and radial SR in systole (SRs), and early diastole (SRe) compared with dogs with no or minimal MR (all P < .04). On multiple regression analyses, these global STE variables increased with degree of MR, but associations with left atrial-to-aortic root ratio (LA/Ao) were best described by second-order polynomial equations. Thus, curvilinear relationships were found for LA/Ao and longitudinal St, SRs, and SRe (all P < .002) and radial St and SRe (all P < .001).

CONCLUSIONS AND CLINICAL IMPORTANCE

Assessed by STE, LV function appeared to be augmented in moderate-to-severe disease. However, at CHF stages with greatly enlarged atria, a decrease to levels comparable to dogs with no or minimal MR was observed.

Advanced electrocardiographic parameters change with severity of mitral regurgitation in Cavalier King Charles Spaniels in sinus rhythm

BACKGROUND

Multiple advanced resting ECG (A-ECG) techniques have improved the diagnostic or prognostic value of ECG in detecting human cardiac diseases even before onset of clinical signs or changes in conventional ECG.

OBJECTIVE

To determine which A-ECG parameters, derived from 12-lead A-ECG recordings, change with severity of mitral regurgitation (MR) caused by myxomatous mitral valve disease (MMVD) in Cavalier King Charles Spaniels (CKCSs) in sinus rhythm.

ANIMALS

Seventy-six privately owned CKCSs.

METHODS

Dogs were prospectively divided into 5 groups according to the degree of MR (estimated by color Doppler mapping as the percentage of the left atrial area affected by the MR jet) and presence of clinical signs. High fidelity approximately 5-minute 12-lead ECG recordings were evaluated using custom software to calculate multiple conventional and A-ECG parameters.

RESULTS

Nineteen of 76 ECG parameters were significantly different (P < .05) across the 5 dog groups. A 4-parameter model that incorporated results from 1 parameter of heart rate variability, 2 parameters of QT variability, and 1 parameter of QRS amplitude was identified that explained 82.4% of the variance with a correlation coefficient (R) of 0.60 (P < .01). When age or murmur grade was included in the statistical model the prediction value further increased the R to 0.74 and 0.85 (P < .01), respectively.

CONCLUSION

In CKCSs with sinus rhythm, 4 selected A-ECG parameters further improve prediction of MR jet severity beyond age and murmur grade, although the predictive increment in this study probably is not sufficient to warrant utilization in clinical veterinary practice.

Heart rate, heart rate variability, and arrhythmias in dogs with myxomatous mitral valve disease

BACKGROUND

Autonomic modulation of heart rhythm is thought to influence the pathophysiology of myxomatous mitral valve disease (MMVD).

HYPOTHESES

(1) Holter-derived variables reflecting autonomic modulation of heart rhythm change with MMVD severity in Cavalier King Charles Spaniels (CKCS); (2) Holter-derived variables can identify MMVD severity in CKCS; and (3) Holter-derived variables in CKCS in congestive heart failure (CHF) secondary to MMVD differ from those in dogs of other breeds in CHF.

ANIMALS

Ninety privately owned dogs: 70 CKCS with variable MMVD severity and 20 non-CKCS in CHF secondary to MMVD.

METHODS

Dogs were prospectively recruited and divided into 5 MMVD severity groups based on history, breed, and physical and echocardiographic examination findings. Holter-derived variables included heart rate variability (HRV), heart rate (HR), and arrhythmia evaluated from 24-hour Holter recordings.

RESULTS

In CKCS, 18 of 26 HRV (all P < .0002) and 3 of 9 arrhythmia (all P < .0004) variables decreased with increasing MMVD, whereas minimum and mean HR (all P < .0001) increased with increasing MMVD severity. An arrhythmia variable representing sinus arrhythmia ("premature normals") (P < .0001) and the HRV variable triangular index (TI) (P < .0001) could distinguish CKCS with moderate or severe mitral regurgitation from CKCS in CHF in specific intervals. Among dogs in CHF, Holter-derived variables did not differ among breeds.

CONCLUSIONS AND CLINICAL IMPORTANCE

In CKCS, Holter-derived variables changed with MMVD severity. "Premature normals" and TI showed diagnostic potential. Breed differences were not seen among dogs in CHF secondary to MMVD.

Holter monitoring in clinically healthy Cavalier King Charles Spaniels, Wire-haired Dachshunds, and Cairn Terriers

BACKGROUND

Few reported studies describe normal values from 24-hour ECG (Holter) recordings of small breed dogs.

OBJECTIVES

To investigate influence of breed, age, sex, body weight, degree of recording artifact, and mitral valve prolapse (MVP) on Holter recordings of 3 breeds of small dogs that have differing predispositions for myxomatous mitral valve disease. The study also assessed if heart rate (HR) at clinical examination (HRex) was associated with HR during Holter monitoring and evaluated the reproducibility of Holter variables.

ANIMALS

Fifty clinically healthy, privately owned dogs of the breeds Cavalier King Charles Spaniel (CKCS), Wire-haired Dachshund (wD), or Cairn Terrier (CT).

METHODS

Prospective, longitudinal observational study. Dogs were recruited for clinical examination, echocardiography, and Holter monitoring. In 8 CKCS, Holter recordings were performed twice with a 7-day interval. Arrhythmia and heart rate variability (HRV) analysis (time and frequency domain analysis) were performed on Holter recordings.

RESULTS

Fifteen out of 27 Holter derived variables were significantly associated with breed (P < .03), but not with age (P > .7), sex (P > .2), body weight (P > .7), degree of recording artifact (P > .4), or MVP (P > .6). During Holter recording, minimum (P = .0001) and mean HR (P = .0001) were higher in CKCS compared with wD. CKCS had significantly lower values than wD, CT, or both in 10 out of 13 HRV variables (P < .03). Minimum and mean HR during Holter recording were correlated with HRex (r = 0.55, P = .0003). HR and time domain variables had a coefficient of variation <10%.

CONCLUSIONS AND CLINICAL IMPORTANCE

There is an influence of breed on Holter-derived variables in 3 breeds of small dogs. Arrhythmia and HRV analysis can be performed on 24-hour ambulatory ECG (Holter) recordings. Arrhythmia analysis includes HR measurements and identification of arrhythmias.

Brain-natriuretic peptide and cyclic guanosine monophosphate as biomarkers of myxomatous mitral valve disease in dogs

Elevations in the plasma concentrations of natriuretic peptides correlate with increased severity of myxomatous mitral valve disease (MMVD) in dogs. This study correlates the severity of MMVD with the plasma concentrations of the biomarkers N-terminal fragment of the pro-brain-natriuretic peptide (NT-proBNP) and its second messenger, cyclic guanosine monophosphate (cGMP). Furthermore, the L-arginine:asymmetric dimethylarginine (ADMA) ratio was measured as an index of nitric oxide availability. The study included 75 dogs sub-divided into five groups based on severity of MMVD as assessed by clinical examination and echocardiography. Plasma NT-proBNP and cGMP concentrations increased with increasing valve dysfunction and were significantly elevated in dogs with heart failure. The cGMP:NT-proBNP ratio decreased significantly in dogs with heart failure, suggesting the development of natriuretic peptide resistance. Although the l-arginine:ADMA ratio decreased with increasingly severe MMVD, this was largely due to the older age of the dogs with heart failure.

Clustering protein sequence and structure space with infinite Gaussian mixture models

We describe a novel approach to the problem of automatically clustering protein sequences and discovering protein families, subfamilies etc., based on the theory of infinite Gaussian mixtures models. This method allows the data itself to dictate how many mixture components are required to model it, and provides a measure of the probability that two proteins belong to the same cluster. We illustrate our methods with application to three data sets: globin sequences, globin sequences with known three-dimensional structures and G-protein coupled receptor sequences. The consistency of the clusters indicate that our method is producing biologically meaningful results, which provide a very good indication of the underlying families and subfamilies. With the inclusion of secondary structure and residue solvent accessibility information, we obtain a classification of sequences of known structure which both reflects and extends their SCOP classifications. A supplementray web site containing larger versions of the figures is available at http://public.kgi.edu/approximately wid/PSB04/index.html

Perfusion quantification using Gaussian process deconvolution

The quantification of perfusion using dynamic susceptibility contrast MRI (DSC-MRI) requires deconvolution to obtain the residual impulse response function (IRF). In this work, a method using the Gaussian process for deconvolution (GPD) is proposed. The fact that the IRF is smooth is incorporated as a constraint in the method. The GPD method, which automatically estimates the noise level in each voxel, has the advantage that model parameters are optimized automatically. The GPD is compared to singular value decomposition (SVD) using a common threshold for the singular values, and to SVD using a threshold optimized according to the noise level in each voxel. The comparison is carried out using artificial data as well as data from healthy volunteers. It is shown that GPD is comparable to SVD with a variable optimized threshold when determining the maximum of the IRF, which is directly related to the perfusion. GPD provides a better estimate of the entire IRF. As the signal-to-noise ratio (SNR) increases or the time resolution of the measurements increases, GPD is shown to be superior to SVD. This is also found for large distribution volumes.

Twelve years' clinical experience with the CarboMedics prosthetic heart valve

BACKGROUND AND AIM OF THE STUDY

The CarboMedics bileaflet prosthetic heart valve was first implanted as part of a prospective clinical study at the authors' institution in November 1987. The patient cohort included was part of a multicenter trial set up by the manufacturer for an FDA application. The present report details findings over a 12-year period, with a continuous follow up on this patient cohort.

METHODS

Between November 1987 and August 1990, 132 patients (68 males, 64 females; median age 56 years; range 12-74 years) received a CarboMedics heart valve prosthesis. All patients were included in the study, whether surgery was elective or emergency, first time or reoperation. There were 69 aortic, 49 mitral and 12 double (aortic + mitral) valve replacements. Two patients had isolated tricuspid valve replacement. Concomitant surgery was performed in 15 patients. Anticoagulation with warfarin was started on postoperative day 1. After discharge, patients were examined regularly as outpatients for up to five years. Subsequent follow up was obtained prospectively by questionnaires to the patients' general practitioner, or by telephone calls. Actuarial estimates of survival and freedom from morbid events were calculated using the Kaplan-Meier method; 95% confidence limits for the distribution function were calculated according to the Greenwood formula.

RESULTS

Complete follow up information was available for 94% of the patients; total follow up was 1,014.3 patient-years (pt-yr). Actuarial survival at 12 years was 62 +/- 0.5% overall (61 +/- 6.5% for aortic; 66 +/- 7.5% for mitral; 65 +/- 14.0% for double valve replacements). Actuarial rates of freedom from complications were: valve thrombosis 100%, embolism 92 +/- 2.8%, and anticoagulant-related bleeding 77 +/- 5.6%. The linearized rates per 100 pt-yr were: embolism 0.89 (aortic 0.74, mitral 1.30); anticoagulant-related bleeding 2.56; paravalvular leakage overall 0.20 (aortic 0.37); prosthetic valve endocarditis overall 0.20 (aortic 0.37). There was no hemolysis, prosthetic valve dysfunction or structural deterioration.

CONCLUSION

Over a 12-year time frame, the CarboMedics prosthetic heart valve has proven to be a highly reliable device with no structural failures, and a low incidence of valve-related complications.

Presynaptic and postsynaptic competition in models for the development of neuromuscular connections

In the establishment of connections between nerve and muscle there is an initial stage when each muscle fibre is innervated by several different motor axons. Withdrawal of connections then takes place until each fibre has contact from just a single axon. The evidence suggests that the withdrawal process involves competition between nerve terminals. We examine in formal models several types of competitive mechanism that have been proposed for this phenomenon. We show that a model which combines competition for a presynaptic resource with competition for a postsynaptic resource is superior to others. This model accounts for many anatomical and physiological findings and has a biologically plausible implementation. Intrinsic withdrawal appears to be a side effect of the competitive mechanism rather than a separate non-competitive feature. The model's capabilities are confirmed by theoretical analysis and full scale computer simulations.

Bioinequivalence of erythromycin ethylsuccinate and enteric-coated erythromycin pellets following multiple oral doses

Bioequivalence comparisons between erythromycin ethylsuccinate and an enteric-coated erythromycin base pellet product were made following multiple-dose, oral administration. Twenty-four volunteers participated in a ten-dose protocol (one dosage unit every six hours) using a complete crossover design. Plasma samples were assayed using a microbiological method specific for erythromycin base in the presence of the ester. Without correcting for the differences in doses administered, the amount of active erythromycin base absorbed from the enteric-coated pellet (250 mg base) was five to seven times that absorbed from the erythromycin ethylsuccinate product (400 mg base equivalent) at steady state. Erythromycin ethylsuccinate is not bioequivalent to an enteric-coated erythromycin base pellet product. The lower bioavailability of the ethylsuccinate may be due to instability in the acidic medium of the stomach.