Subcutaneous administration of benzathine benzylpenicillin G has favourable pharmacokinetic characteristics for the prevention of rheumatic heart disease compared with intramuscular injection: a randomized, crossover, population pharmacokinetic study in healthy adult volunteers

Population pharmacokinetics of penicillin G: insights into increased clearance at low concentrations to guide development of improved long-acting formulations for syphilis and prevention of rheumatic fever

Although benzylpenicillin (penicillin G) is listed by the World Health Organization as an Essential Medicine, dose optimization is a persistent challenge, especially for long-acting intramuscular formulations. Maintaining sustained antibiotic exposure at target concentrations is crucial for secondary chemoprophylaxis of rheumatic heart disease and treatment of syphilis. This study compared the pharmacokinetic profile of continuous low-dose benzylpenicillin infusions with a standard-dose bolus and evaluated which renal function marker (serum creatinine, cystatin C, or combined e-glomerular filtration rate [eGFR]) best predicted clearance. Healthy adult volunteers received a single 600 mg IV benzylpenicillin bolus followed by randomization to continuous infusions targeting steady-state concentrations of 3, 6, 9, 12, or 20 ng/mL. Plasma benzylpenicillin concentrations were measured by liquid chromatography-mass spectrometry. Population pharmacokinetic analysis was performed using NONMEM by incorporating both bolus and infusion data, and various GFR estimations were evaluated as covariates for clearance. Data from 72 participants were analyzed, including 504 bolus and 389 continuous infusion samples. A two-compartment model improved fit when the ratio of central volume of distribution between bolus and low-dose infusion was incorporated, and clearance differences at steady state plasma concentration of 3 ng/mL were accounted for. Of the GFR estimations, cystatin C-based eGFR significantly enhanced model fit compared with creatinine-based equations. Benzylpenicillin pharmacokinetics at very low concentrations demonstrated both a higher volume of distribution and increased clearance. Cystatin C-based eGFR may more accurately predict benzylpenicillin clearance, enabling precision dosing for long-acting preparations used for treatment of syphilis and prevention of rheumatic fever.

High dose, subcutaneous injections of benzathine penicillin G (SCIP) to prevent rheumatic fever: A single arm, phase IIa trial of safety and pharmacokinetics

OBJECTIVES

This Phase-IIa trial evaluates the safety and pharmacokinetics of high-dose, 10 weekly subcutaneous injections of penicillin (SCIP) in young people with a history of acute rheumatic fever (ARF).

METHODS

Participants received 7.2-10.8 MU (13.8-20.7 mL) of Bicillin-LA® via subcutaneous injection in Wellington, New Zealand. A subset underwent intensive safety monitoring and serial dried blood spot collection for penicillin assay. Penicillin concentrations informed a population pharmacokinetic model based on 169 data points from 31 participants. The proportion of time penicillin concentrations remained above a range of plausible pharmacological correlates of protection was estimated for SCIP and compared with estimates for intramuscular benzathine penicillin G (BPG).

RESULTS

Fifty-five participants received SCIP at least once, totalling 182 doses. No recurrent ARF or breakthrough streptococcal throat infections were reported. Model-based simulations indicated that SCIP outperformed intramuscular BPG in maintaining protective concentrations across nearly all plausible pharmacological target correlates of protection (10-20 ng/mL). SCIP performed even more favourably when considering modified weight-based dosing or missed BPG injections.

CONCLUSIONS

SCIP is safe, well tolerated and demonstrates favourable penicillin exposure for most individuals. Future research should explore the effectiveness of SCIP over longer periods and in diverse populations and settings.

Establishing the lowest penicillin concentration to prevent pharyngitis due to Streptococcus pyogenes using a human challenge model (CHIPS): a randomised, double-blind, placebo-controlled trial

BACKGROUND

The in-vivo plasma concentration of penicillin needed to prevent Streptococcus pyogenes pharyngitis, recurrent acute rheumatic fever, and progressive rheumatic heart disease is not known. We used a human challenge model to assess the minimum penicillin concentration required to prevent streptococcal pharyngitis.

METHODS

In CHIPS, a randomised, double-blind, placebo-controlled, human challenge trial, healthy adult volunteers were randomly assigned by a computer-generated random sequence to target steady-state penicillin plasma concentrations (placebo, 3, 6, 9, 12, or 20 ng/mL). The study was a single-centre trial held in Perth, WA, Australia. Participants had to be healthy adults, aged 18-40 years, at low risk of complicated S pyogenes disease, and without high type-specific IgG antibodies against the emm75 S pyogenes challenge strain. Participants and staff involved in clinical care remained masked to treatment allocation for the duration of the study. Individualised 5-day continuous intravenous infusions of penicillin were commenced 12 h before direct pharyngeal application of the emm75 challenge strain. The primary endpoint was clinical pharyngitis. This trial is registered on the Australian New Zealand Clinical Trials Registry, ACTRN12621000751875, and is completed.

FINDINGS

Between Aug 23, 2022, and July 31, 2023, 60 participants were randomly assigned (35 [58%] were female and 25 [42%] were male), with 57 included in the analysis. The clinical pharyngitis endpoint was met in eight (57%) of 14 in the placebo group, four (44%) of nine in the 3 ng/mL target steady-state penicillin plasma concentration group, four (44%) of nine in the 6 ng/mL group, none of eight in the 9 ng/mL group, none of eight in the 12 ng/mL group, and none of nine in the 20 ng/mL group. No severe or serious adverse events occurred. Using Bayesian concentration-response modelling, the minimum steady-state plasma concentration of penicillin for which 90% of participants would avoid clinical pharyngitis was 8·1 ng/mL (95% credible interval 6·1-10·9).

INTERPRETATION

When steady-state penicillin concentrations are greater than 9 ng/mL, few people will develop experimental emm75 S pyogenes pharyngitis. These data will inform efforts to improve long-acting penicillin preparations and dosage regimens to prevent recurrent rheumatic fever and rheumatic heart disease.

FUNDING

The National Health and Medical Research Council of Australia.

Acceptability and Implementation Challenges of Benzathine Penicillin G Secondary Prophylaxis for Rheumatic Heart Disease in Ethiopia: A Qualitative Study

Background

Monthly intramuscular injections of benzathine penicillin G (BPG) remain the cornerstone of secondary prophylaxis for acute rheumatic fever and rheumatic heart disease (RHD). The barriers to successful delivery of BPG may be patient- or service-delivery-dependent.

Objective

The aim of the present study was to explore the perceived acceptability and implementation challenges of BPG treatment for RHD, from the perspective of healthcare providers (HCPs).

Methodology

A descriptive qualitative study using semi-structured interview guides was conducted in four public hospitals in Ethiopia. Physicians and nurses who had at least 1 year of experience in delivering RHD secondary prophylaxis were recruited. The interviews were audio recorded, transcribed verbatim, and translated into English for analysis using framework method thematic analysis. Identified behavioral factors were mapped onto a theoretical framework of acceptability (TFA), and the Capability, Opportunity, Motivation-Behavior (COM-B) model.

Result

Twenty-two interviews were conducted with HCPs (mean age 39 years, 55% nurses). Insights into BPG use and acceptability were categorized into four major themes related to: (1) individual factors (e.g., fear of anaphylactic reaction), (2) health system barriers (e.g., BPG shortage), (3) patient/caregiver perceptions (e.g., reliance on injectables, over expectation of treatment outcomes), and (4) product (e.g., injection pain, needle blockage).

Conclusions

HCPs identified facilitators and barriers which highlight the complexities associated with BPG as secondary prophylaxis for RHD in Ethiopia. Based on these data, we suggest RHD control programs should (1) provide cross-disciplinary training and education programs to support safe and context-appropriate delivery of BPG (2) improve resourcing of health facilities to facilitate safe drug delivery, (3) establish a comprehensive system for auditing severe adverse reactions post-BPG injection to generate robust pharmacovigilance data, and consider alternative approaches to BPG delivery including access to improved formulations (e.g., BPG suspension formulations in pre-filled syringes).

Highlights

- Key barriers included (a) resistance from healthcare providers to administer benzathine penicillin G (BPG) due to their concerns about injection-related severe adverse events, and potential repercussions should an event occur, (b) poor community and healthcare provider awareness of the disease and its treatment, (c) lack of resources to manage adverse events, and (d) injection pain.- Key enablers included (a) perceived superior treatment benefits of BPG and (b) co-administration of lidocaine/analgesics to reduce injection pain.- Recommendations to address identified challenges include (a) improved training/education on RHD diagnosis, disease progression, and treatment, (b) improved access to supportive resources, (c) active adverse reaction monitoring and reporting, and (d) encouraging the provision/access of globally subsidized BPG suspension formulations in pre-filled syringes.

Population pharmacokinetics of cabotegravir following intramuscular thigh injections in adults with and without HIV

Cabotegravir intramuscular gluteal injection is approved for HIV treatment (with rilpivirine) and prevention. Thigh muscle is a potential alternative injection site. We aim to characterize cabotegravir pharmacokinetics and its association with demographics following intramuscular thigh injection in comparison with gluteal injection using population pharmacokinetic (PPK) analysis. Fourteen HIV-negative participants received 600 mg single thigh injection in phase 1 study 208832 and 118 participants with HIV received thigh injections 400 mg monthly 4× or 600 mg once-every-2-months 2× after ≥3 years of gluteal injections in phase 3b study ATLAS-2M provided 1,249 cabotegravir concentrations from 366 thigh injections and 1,998 concentrations from 1,618 gluteal injections. The established gluteal PPK model was modified by adding thigh injection compartment and fit to pharmacokinetic data following both gluteal and thigh injections, enabling within-person comparison in ATLAS-2M. Gluteal parameters were fixed. Similar to the gluteal absorption rate constant (KAgluteal), the thigh absorption rate constant (KAthigh) was slower in females than males and in participants with higher BMI. KAthigh was strongly correlated with KAgluteal (correlation coefficient 0.766), best described by the additive linear relationship KAthigh = KAgluteal + 0.0002527 h-1. Terminal half-life of thigh injection was 26% (male) and 39% (female) shorter than gluteal injection. Relative bioavailability of thigh to gluteal was estimated to be 89.9%. The impact of covariates on cabotegravir exposure following thigh injections was ≤35%. In conclusion, cabotegravir absorption following thigh injection was correlated with, faster than, and 10% less bioavailable than gluteal injection, and correlated with sex and BMI. The cabotegravir thigh PPK model can inform dosing strategies and future study design.

Patient preferences for prophylactic regimens requiring regular injections in children and adolescents: a systematic review and thematic analysis

BACKGROUND

At present, limited literature exists exploring patient preferences for prophylactic treatment of acute rheumatic fever (ARF) and rheumatic heart disease (RHD). Given low treatment completion rates to this treatment in Australia, where the burden of disease predominantly affects Aboriginal and Torres Strait Islander people, an improved understanding of factors driving patient preference is required to improve outcomes. Due to limited available literature, this review sought to explore treatment preferences for conditions for which the findings might be generalisable to the ARF/RHD context.

OBJECTIVE

Explore treatment preferences of patients, parents/caregivers and healthcare providers towards regular injection regimens in paediatric and adolescent populations for any chronic condition. Findings will be applied to the development of benzathine penicillin G (BPG) prophylactic regimens that are informed by treatment preferences of patients and their caregivers. This in turn should contribute to optimisation of successful BPG delivery.

METHODS

A systematic review of databases (Medline, Embase and Global Health) was conducted using a search strategy developed with expert librarian input. Studies were selected using a two-stage process: (1) title and abstract screen and (2) full text review. Data were extracted using a reviewer-developed template and appraised using the JBI Critical Appraisal tool. Data were synthesised according to a thematic analytical framework.

RESULTS

1725 papers were identified by the database search, conducted between 12 February 2022 and 8 April 2022, and 25 were included in the review. Line-by-line coding to search for concepts generated 20 descriptive themes. From these, five overarching analytical themes were derived inductively: (1) ease of use, (2) tolerability of injection, (3) impact on daily life, (4) patient/caregiver agency and (5) home/healthcare interface.

CONCLUSIONS

The findings of this review may be used to inform the development of preference-led regular injection regimens for paediatric and adolescent patient cohorts-specifically for BPG administration in ARF/RHD secondary prophylaxis.

TRIAL REGISTRATION NUMBER

Patient, parent and health personnel preferences towards regular injection regimes in paediatric and adolescent populations-a protocol for a systematic review. PROSPERO 2021 CRD42021284375. Available from: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021284375.

"Hurts less, lasts longer"; a qualitative study on experiences of young people receiving high-dose subcutaneous injections of benzathine penicillin G to prevent rheumatic heart disease in New Zealand

BACKGROUND

Four-weekly intramuscular (IM) benzathine penicillin G (BPG) injections to prevent acute rheumatic fever (ARF) progression have remained unchanged since 1955. A Phase-I trial in healthy volunteers demonstrated the safety and tolerability of high-dose subcutaneous infusions of BPG which resulted in a much longer effective penicillin exposure, and fewer injections. Here we describe the experiences of young people living with ARF participating in a Phase-II trial of SubCutaneous Injections of BPG (SCIP).

METHODOLOGY

Participants (n = 20) attended a clinic in Wellington, New Zealand (NZ). After a physical examination, participants received 2% lignocaine followed by 13.8mL to 20.7mL of BPG (Bicillin-LA®; determined by weight), into the abdominal subcutaneous tissue. A Kaupapa Māori consistent methodology was used to explore experiences of SCIP, through semi-structured interviews and observations taken during/after the injection, and on days 28 and 70. All interviews were recorded, transcribed verbatim, and thematically analysed.

PRINCIPAL FINDINGS

Low levels of pain were reported on needle insertion, during and following the injection. Some participants experienced discomfort and bruising on days one and two post dose; however, the pain was reported to be less severe than their usual IM BPG. Participants were 'relieved' to only need injections quarterly and the majority (95%) reported a preference for SCIP over IM BPG.

CONCLUSIONS

Participants preferred SCIP over their usual regimen, reporting less pain and a preference for the longer time gap between treatments. Recommending SCIP as standard of care for most patients needing long-term prophylaxis has the potential to transform secondary prophylaxis of ARF/RHD in NZ and globally.

Lack of awareness of secondary rheumatic prevention in preoperative candidates for mitral valve surgery - alarming situation

BACKGROUND

We conducted this study to assess the compliance with secondary rheumatic prophylaxis among preoperative patients with rheumatic mitral valve disease undergoing valvular heart surgery at a tertiary care cardiac hospital in a developing country.

METHODS

This is a descriptive cross-sectional study conducted at a tertiary care cardiac hospital in Karachi, Pakistan. The inclusion criteria encompassed patients of any sex, aged between 18 and 80 years, who had been diagnosed with rheumatic mitral valve disease through transthoracic echocardiography and had undergone valvular heart surgery. The level of compliance with secondary rheumatic prophylaxis and barriers toward noncompliance was assessed during routine preoperative interview session. This preventive measure plays a crucial role in reducing the progression of the disease and improving patient outcomes.

RESULTS

Out of the 239 patients included in the study, 125 (52.3%) were females, with a mean age of 38.8 ± 11.8 years. The majority of patients (88.7%) came from rural areas. Among the patients, 79 (33.1%) received rheumatic prophylaxis, while 160 (66.9%) did not adhere to it regularly. The common barriers for receiving rheumatic prophylaxis were non availability (41.0%) and nonaffordability (40.6%). Additionally, 28.0% of patients had lacked awareness of the importance of rheumatic prophylaxis, and 2.5% expressed fear of injection site pain and subsequent symptoms.

CONCLUSIONS

A concerning level of noncompliance with secondary rheumatic prophylaxis was observed. The barriers identified in patients who did not receive rheumatic prophylaxis were primarily related to affordability, availability, lack of awareness, and fear of injection site pain and subsequent symptoms.

The roles of immuno-modulator treatment and echocardiographic screening in rheumatic fever and rheumatic heart disease control: research from Aotearoa, New Zealand

This review summarises advances in research from Aotearoa, New Zealand (NZ) that have potential to reduce the inequitable distribution of acute rheumatic fever (ARF) and rheumatic heart disease (RHD). ARF incidence and RHD prevalence are unacceptably inequitable for Māori and Pacifica. Recent qualitative research has demonstrated mismatches between the lived experience of those with ARF/RHD and health service experience they encounter. NZ-led research has contributed knowledge to all stages of disease prevention (primordial, primary and secondary) and for tertiary management. Modifiable risk factors for ARF are racism across health sectors, household crowding, barriers to accessing primary health care, a high intake of sugar-sweetened beverages and preceding sore throat and skin infections. NZ research has evaluated the impact of a large-scale sore throat management programme and Streptococcal A vaccine development. This review highlights two programme domains of research by the authors that have the potential to reduce the burden of chronic RHD: firstly, effective immunomodulation of ARF to reduce the severity of carditis, with current clinical trials of hydroxychloroquine in NZ; secondly, the development of echocardiographic screening of previously undetected RHD. This now meets criteria for an effective screening test and has potential translation for disease control of RHD.

The Subcutaneous Administration of Beta-Lactams: A Case Report and Literary Review-To Do Small Things in a Great Way

The subcutaneous (s.c.) route is a commonly used method for delivering various drugs, although its application in the administration of antibiotics is relatively uncommon. In this case, we report a successful treatment of nosocomial pneumonia using piperacillin/tazobactam via continuous subcutaneous administration. Furthermore, this article provides an overview of the current literature regarding the s.c. administration of beta-lactam antibiotics. Based on our analysis, we identified only 15 studies that described the s.c. use of beta-lactam antibiotics in human subjects. Among these studies, cephalosporins were the most extensively investigated antibiotic class, with 10 available studies. According to the study findings, all three antibiotic classes (cephalosporins, penicillins, and carbapenems) demonstrated a similar pharmacokinetic profile when administered via the subcutaneous route. The subcutaneous route appears to be associated with a lower peak serum concentration (Cmax) but a comparable minimum blood concentration (Cmin) and an extended half-life (t1/2) when compared to conventional routes of antibiotic administration. Further research is necessary to determine whether subcutaneously administered beta-lactam antibiotics in human subjects achieve pharmacodynamic targets and demonstrate clinical efficacy.

Subcutaneous infusion of high-dose benzathine penicillin G is safe, tolerable, and suitable for less-frequent dosing for rheumatic heart disease secondary prophylaxis: a phase 1 open-label population pharmacokinetic study

Since 1955, the recommended strategy for rheumatic heart disease (RHD) secondary prophylaxis has been benzathine penicillin G [BPG; 1.2 MU (900 mg)] injections administered intramuscularly every 4 weeks. Due to dosing frequency, pain, and programmatic challenges, adherence is suboptimal. It has previously been demonstrated that BPG delivered subcutaneously at a standard dose is safe and tolerable and has favorable pharmacokinetics, setting the scene for improved regimens with less frequent administration. The safety, tolerability, and pharmacokinetics of subcutaneous infusions of high-dose BPG were assessed in 24 healthy adult volunteers assigned to receive either 3.6, 7.2, or 10.8 MU (three, six, and nine times the standard dose, respectively) as a single subcutaneous infusion. The delivery of the BPG to the subcutaneous tissue was confirmed with ultrasonography. Safety assessments, pain scores, and penicillin concentrations were measured for 16 weeks post-dose. Subcutaneous infusion of penicillin (SCIP) was generally well tolerated with all participants experiencing transient, mild infusion-site reactions. Prolonged elevated penicillin concentrations were described using a combined zero-order (44 days) and first-order (t1/2 = 12 days) absorption pharmacokinetic model. In simulations, time above the conventionally accepted target concentration of 20 ng/mL (0.02 µg/mL) was 57 days for 10.8 MU delivered by subcutaneous infusion every 13 weeks compared with 9 days of every 4-weekly dosing interval for the standard 1.2 MU intramuscular dose (i.e., 63% and 32% of the dosing interval, respectively). High-dose SCIP (BPG) is safe, has acceptable tolerability, and may be suitable for up to 3 monthly dosing intervals for secondary prophylaxis of RHD.

Development of a sustained release implant of benzathine penicillin G for secondary prophylaxis of rheumatic heart disease

BACKGROUND

Regular intramuscular (i.m.) benzathine penicillin G (BPG) injections have been the cornerstone of rheumatic heart disease (RHD) secondary prophylaxis since the 1950s. Patient adherence to IM BPG is poor, largely due to pain, the need for regular injections every 3-4 weeks and health sector delivery challenges in resource-limited settings. There is an urgent need for new approaches for secondary prophylaxis, such as an implant which could provide sustained penicillin concentrations for more than 6 months.

METHODS

In this study we developed and evaluated a slow release implant with potential for substantially extended treatment. The side wall of a solid drug rich core was coated with polycaprolactone which acts as an impermeable barrier. The exposed surfaces at the ends of the implant defined the release surface area, and the in vitro release rate of drug was proportional to the exposed surface area across implants of differing diameter. The in vivo pharmacokinetics and tolerability of the implants were evaluated in a sheep model over 9 weeks after subcutaneous implantation.

RESULTS

The absolute release rates obtained for the poorly water-soluble benzathine salt were dependent on the exposed surface area demonstrating the impermeability of the wall of the implant. The implants were well-tolerated after subcutaneous implantation in a sheep model, without adverse effects at the implantation site. Gross structural integrity was maintained over the course of the study, with erosion limited to the dual-exposed ends. Steady release of penicillin G was observed over the 9 weeks and resulted in approximately constant plasma concentrations close to accepted target concentrations.

CONCLUSION

In principle, a long acting BPG implant is feasible as an alternative to IM injections for secondary prophylaxis of RHD. However, large implant size is currently a significant impediment to clinical utility and acceptability.

Evaluation of a Community-Led Program for Primordial and Primary Prevention of Rheumatic Fever in Remote Northern Australia

Environmental factors including household crowding and inadequate washing facilities underpin recurrent streptococcal infections in childhood that cause acute rheumatic fever (ARF) and subsequent rheumatic heart disease (RHD). No community-based 'primordial'-level interventions to reduce streptococcal infection and ARF rates have been reported from Australia previously. We conducted a study at three Australian Aboriginal communities aiming to reduce infections including skin sores and sore throats, usually caused by Group A Streptococci, and ARF. Data were collected for primary care diagnoses consistent with likely or potential streptococcal infection, relating to ARF or RHD or related to environmental living conditions. Rates of these diagnoses during a one-year Baseline Phase were compared with a three-year Activity Phase. Participants were children or adults receiving penicillin prophylaxis for ARF. Aboriginal community members were trained and employed to share knowledge about ARF prevention, support reporting and repairs of faulty health-hardware including showers and provide healthcare navigation for families focusing on skin sores, sore throat and ARF. We hypothesized that infection-related diagnoses would increase through greater recognition, then decrease. We enrolled 29 participants and their families. Overall infection-related diagnosis rates increased from Baseline (mean rate per-person-year 1.69 [95% CI 1.10-2.28]) to Year One (2.12 [95% CI 1.17-3.07]) then decreased (Year Three: 0.72 [95% CI 0.29-1.15]) but this was not statistically significant (p = 0.064). Annual numbers of first-known ARF decreased, but numbers were small: there were six cases of first-known ARF during Baseline, then five, 1, 0 over the next three years respectively. There was a relationship between household occupancy and numbers (p = 0.018), but not rates (p = 0.447) of infections. This first Australian ARF primordial prevention study provides a feasible model with encouraging findings.

Smart design of patient centric long-acting products: from preclinical to marketed pipeline trends and opportunities

INTRODUCTION

We see a development in the field of long-acting products to serve patients with chronic diseases by providing benefits in adherence, efficacy and safety of the treatment. This review investigates features of long-acting products on the market/pipeline to understand which drug substance (DS) and drug product (DP) characteristics likely enable a successful patient-centric, low-dosing frequency product.

AREAS COVERED

This review evaluates marketed/pipeline long-acting products with greater than one week release of small molecules and peptides by oral and injectable route of administration (RoA), with particular focus on patient centricity, adherence impact, health outcomes, market trends, and the match of DS/DP technologies which lead to market success.

EXPERT OPINION

Emerging trends are expected to change the field of long-acting products in the upcoming years by increasing capability in engineered molecules (low solubility, long half-life, high potency, etc.), directly developing DP as long-acting oral/injectable, increasing the proportion of products for local drug delivery, and a direction towards more subcutaneous, self-administered products. Among long-acting injectable products, nanosuspensions show a superiority in dose per administration and dosing interval, overwhelming the field of infectious diseases with the recently marketed products.

Population pharmacokinetic study of benzathine penicillin G administration in Indigenous children and young adults with rheumatic heart disease in the Northern Territory, Australia

BACKGROUND

Benzathine penicillin G (BPG) is the cornerstone of secondary prophylaxis to prevent Streptococcus pyogenes infections, which precede acute rheumatic fever (ARF). The paucity of pharmacokinetic (PK) data from children and adolescents from populations at the highest risk of ARF and rheumatic heart disease (RHD) poses a challenge for determining the optimal dosing and frequency of injections and undermines efforts to develop improved regimens.

METHODS

We conducted a 6 month longitudinal PK study of young people receiving BPG for secondary prophylaxis. Throat and skin swabs were collected for microbiological culture along with dried blood spot (DBS) samples for penicillin concentrations. DBSs were assayed using LC-MS/MS. Penicillin concentration datasets were analysed using non-linear mixed-effects modelling and simulations performed using published BMI-for-age and weight-for-age data.

RESULTS

Nineteen participants provided 75 throat swabs, 3 skin swabs and 216 penicillin samples. Throat cultures grew group C and G Streptococcus. Despite no participant maintaining penicillin concentration >20 ng/mL between doses, there were no S. pyogenes throat infections and no ARF. The median (range) observed durations >20 ng/mL for the low- and high-BMI groups were 14.5 (11.0-24.25) and 15.0 (7.5-18.25) days, respectively.

CONCLUSIONS

Few patients at highest risk of ARF/RHD receiving BPG for secondary prophylaxis maintain penicillin concentrations above the target of 20 ng/mL beyond 2 weeks during each monthly dosing interval. These PK data suggest that some high-risk individuals may get inadequate protection from every 4 week dosing. Future research should explore this gap in knowledge and PK differences between different populations to inform future dosing schedules.

High risk of early sub-therapeutic penicillin concentrations after intramuscular benzathine penicillin G injections in Ethiopian children and adults with rheumatic heart disease

Introduction

Intramuscular benzathine penicillin G (BPG) injections are a cornerstone of secondary prophylaxis to prevent acute rheumatic fever (ARF) and rheumatic heart disease (RHD). Uncertainties regarding inter-ethnic and preparation variability, and target exposure profiles of BPG injection are key knowledge gaps for RHD control.

Methods

To evaluate BPG pharmacokinetics (PK) in patients receiving 4-weekly doses in Ethiopia, we conducted a prospective cohort study of ARF/RHD patients attending cardiology outpatient clinics. Serum samples were collected weekly for one month after injection and assayed with a liquid chromatography-mass spectroscopy assay. Concentration-time datasets for BPG were analyzed by nonlinear mixed effects modelling using NONMEM.

Results

A total of 190 penicillin concentration samples from 74 patients were included in the final PK model. The median age, weight, BMI was 21 years, 47 kg and 18 kg/m², respectively. When compared with estimates derived from Indigenous Australian patients, the estimate for median (95% confidence interval) volume of distribution (V/F) was lower (54.8 [43.9–66.3] l.70kg^-1) whilst the absorption half-life (t_1/2-abs2) was longer (12.0 [8.75–17.7] days). The median (IQR) percentage of time where the concentrations remained above 20 ng/mL and 10 ng/mL within the 28-day treatment cycle was 42.5% (27.5–60) and 73% (58.5–99), respectively.

Conclusions

The majority of Ethiopian patients receiving BPG as secondary prophylaxis to prevent RHD do not attain target concentrations for more than two weeks during each 4-weekly injection cycle, highlighting the limitations of current BPG strategies. Between-population variation, together with PK differences between different preparations may be important considerations for ARF/RHD control programs.

Rheumatic heart disease (RHD) is the most common form of acquired heart disease in Ethiopia across all age groups. Monthly benzathine penicillin G (BPG) injections remains the cornerstone of secondary prophylaxis to prevent recurrent acute rheumatic fever (ARF) and progression to RHD, but data supporting the optimal dose and timing of BPG injections is a major knowledge gap for National RHD control programs, particularly amongst the highest risk groups. In this study we measured penicillin concentrations in Ethiopian patients receiving regular BPG injections. It demonstrates that that most Ethiopian patients receiving BPG as secondary prophylaxis to prevent RHD do not maintain target concentrations for more than two weeks during each 4-weekly injection cycle. This study highlights the limitation of the current BPG dosing recommendations and underpin global calls for improved penicillin formulations and better dosing and delivery strategies.