Severe Falciparum and Vivax Malaria on the Thailand-Myanmar Border: A Review of 1503 Cases

BACKGROUND

The northwestern border of Thailand is an area of low seasonal malaria transmission. Until recent successful malaria elimination activities, malaria was a major cause of disease and death. Historically the incidences of symptomatic Plasmodium falciparum and Plasmodium vivax malaria were approximately similar.

METHODS

All malaria cases managed in the Shoklo Malaria Research Unit along the Thailand-Myanmar border between 2000 and 2016 were reviewed.

RESULTS

There were 80 841 consultations for symptomatic P. vivax and 94 467 for symptomatic P. falciparum malaria. Overall, 4844 (5.1%) patients with P. falciparum malaria were admitted to field hospitals, of whom 66 died, compared with 278 (0.34%) with P. vivax malaria, of whom 4 died (3 had diagnoses of sepsis, so the contribution of malaria to their fatal outcomes is uncertain). Applying the 2015 World Health Organization severe malaria criteria, 68 of 80 841 P. vivax admissions (0.08%) and 1482 of 94 467 P. falciparum admissions (1.6%) were classified as severe. Overall, patients with P. falciparum malaria were 15 (95% confidence interval, 13.2-16.8) times more likely than those with P. vivax malaria to require hospital admission, 19 (14.6-23.8) times more likely to develop severe malaria, and ≥14 (5.1-38.7) times more likely to die.

CONCLUSIONS

In this area, both P. falciparum and P. vivax infections were important causes of hospitalization, but life-threatening P. vivax illness was rare.

Malaria patient spectrum representation in therapeutic clinical trials of uncomplicated malaria: a scoping review of the literature

BACKGROUND

For the results of clinical trials to have external validity, the patients included in the study must be representative of the population presenting in the general clinical settings. A scoping literature review was performed to evaluate how the eligibility criteria used in anti-malarial efficacy and safety trials translate into patient selection.

METHODS

A search of the WorldWide Antimalarial Resistance Network (WWARN) Clinical Trials Publication Library, MEDLINE, The Cochrane Library, and clinicaltrials.gov was conducted to identify trials investigating anti-malarial efficacy and safety, published between 14th April 2001 and 31st December 2017. An updated search using the WWARN Clinical Trial Publication Library was undertaken to identify eligible publications from 1st January 2018 to 31st July 2021. The review included studies in patients of any age with uncomplicated malaria and any pharmaceutical therapeutic intervention administered. The proportion of trials with malaria-positive patients excluded was calculated and linked to the reported reason for exclusion. A subgroup analysis on eligibility criteria and trial baseline demographics was conducted to assess whether criteria are complied with when recruiting patients.

RESULTS

Out of 847 studies, 176 (21%) trials were included in the final synthesis, screening a total of 157,516 malaria-positive patients, of whom 56,293 (36%) were enrolled and treated. Across the 176 studies included, 84 different inclusion and exclusion criteria were identified. The reason for exclusion of patients who tested positive for malaria was reported in 144 (82%) studies. Three criteria account for about 70% of malaria-positive patients excluded: mixed-species malaria infections or other specific Plasmodium species, parasite counts outside the set study ranges, and refusal of consent.

CONCLUSIONS

Nearly two-thirds of the malaria-positive subjects who present to health facilities are systematically excluded from anti-malarial treatment trials. Reasons for exclusions are largely under-reported. Anti-malarial treatment in the general population is informed by studies on a narrow selection of patients who do not fully represent the totality of those seeking antimalarial treatment in routine practice. While entry criteria ensure consistency across trials, pragmatic trials are also necessary to supplement the information currently available and improve the external validity of the findings of malaria clinical trials.

Leveraging human resources for outbreak analysis: lessons from an international collaboration to support the sub-Saharan African COVID-19 response

Emerging infectious diseases are a growing threat in sub-Saharan African countries, but the human and technical capacity to quickly respond to outbreaks remains limited. Here, we describe the experience and lessons learned from a joint project with the WHO Regional Office for Africa (WHO AFRO) to support the sub-Saharan African COVID-19 response.In June 2020, WHO AFRO contracted a number of consultants to reinforce the COVID-19 response in member states by providing actionable epidemiological analysis. Given the urgency of the situation and the magnitude of work required, we recruited a worldwide network of field experts, academics and students in the areas of public health, data science and social science to support the effort. Most analyses were performed on a merged line list of COVID-19 cases using a reverse engineering model (line listing built using data extracted from national situation reports shared by countries with the Regional Office for Africa as per the IHR (2005) obligations). The data analysis platform The Renku Project ( https://renkulab.io ) provided secure data storage and permitted collaborative coding.Over a period of 6 months, 63 contributors from 32 nations (including 17 African countries) participated in the project. A total of 45 in-depth country-specific epidemiological reports and data quality reports were prepared for 28 countries. Spatial transmission and mortality risk indices were developed for 23 countries. Text and video-based training modules were developed to integrate and mentor new members. The team also began to develop EpiGraph Hub, a web application that automates the generation of reports similar to those we created, and includes more advanced data analyses features (e.g. mathematical models, geospatial analyses) to deliver real-time, actionable results to decision-makers.Within a short period, we implemented a global collaborative approach to health data management and analyses to advance national responses to health emergencies and outbreaks. The interdisciplinary team, the hands-on training and mentoring, and the participation of local researchers were key to the success of this initiative.

Cross-sectional study of nutritional intake among patients undergoing tuberculosis treatment along the Myanmar-Thailand border

OBJECTIVE

This study summarises nutritional intake among patients with tuberculosis (TB) along the Myanmar-Thailand border according to the local diet.

SETTING

TB clinic along the Myanmar-Thailand border.

PARTICIPANTS

Cross-sectional surveys of 24-hour food recall were conducted with participants receiving anti-TB treatment. Participants were purposively selected to reflect proportion of age, sex and HIV co-infection based on historical patient records. Out of a total of 28 participants, 20 (71.4%) were men and 5 (17.9%) were co-infected with HIV.

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary outcome compared actual recorded intake to recommended intake. Secondary outcomes compared weight gain and body mass index (BMI) from diagnosis to time of survey.

RESULTS

There were no significant differences in macronutrient or micronutrient intake by sex or for patients supplementing their rations. Mean treatment length at time of survey was 20.7 weeks (95% CI: 16.5 to 24.8). A significantly higher proportion of women (8/8, 100%) met caloric requirements compared with men (9/20, 45.0%, p=0.010), but few participants met other macronutrient or micronutrient requirements, with no significant differences by sex or for patients supplementing their rations. From diagnosis to the time of the survey, participants averaged significant weight gain of 6.48 kg (95% CI: 3.87 to 9.10) and increased BMI of 2.47 kg/m² (95% CI: 1.45 to 3.49; p=0.0001 for both). However, 50% (14/28) still had mild or more severe forms of malnutrition.

CONCLUSIONS

This cross-sectional survey of nutritional intake in patients undergoing TB treatment in a sanatorium setting demonstrates the difficulty in sufficiently meeting nutritional demands, even when providing nutritional support.

Prevention of mother-to-child transmission of hepatitis B virus: protocol for a one-arm, open-label intervention study to estimate the optimal timing of tenofovir in pregnancy

INTRODUCTION

Hepatitis B virus (HBV) remains a public health threat and the main route of transmission is from mother to child (MTCT). Tenofovir disoproxil fumarate (TDF) treatment can reduce MTCT of HBV although the optimal timing to attain undetectable HBV DNA concentrations at delivery is unknown. This protocol describes the procedures following early initiation of maternal TDF prior to 20 weeks gestation to determine efficacy, safety and feasibility of this approach in a limited-resource setting.

METHODS AND ANALYSES

One hundred and seventy pregnant women from the Thailand-Myanmar border between 12 and <20 weeks gestational age will be enrolled into a one-arm, open-label, TDF treatment study with cessation of TDF 1 month after delivery. Sampling occurs monthly prenatal, at birth and at 1, 2, 4 and 6 months post partum. Measurement of tenofovir concentrations in maternal and cord plasma is anticipated in 10-15 women who have detectable HBV DNA at delivery and matched to 20-30 women with no detectable HBV DNA. Infant HBsAg status will be determined at 2 months of age and HBV DNA confirmed in HBsAg positive cases. Adverse events including risk of flare and adherence, based on pill count and questionnaire, will be monitored. Infants will receive HBV vaccinations at birth, 2, 4 and 6 months and hepatitis B immunoglobulin at birth if the mother is hepatitis B e antigen positive. Infant growth and neurodevelopment at 6 months will be compared with established local norms.

ETHICS AND DISSEMINATION

This study has ethical approval by the Ethics Committee of the Faculty of Tropical Medicine, Mahidol University (FTM ECF-019-06), Johns Hopkins University (IRB no: 00007432), Chiang Mai University (FAM-2559-04227), Oxford Tropical Research Ethics Committee (OxTREC Reference: 49-16) and by the local Tak Community Advisory Board (TCAB-02/REV/2016). The article will be published as an open-access publication.

TRIAL REGISTRATION NUMBER

NCT02995005, Pre-results.

Early life risk factors of motor, cognitive and language development: a pooled analysis of studies from low/middle-income countries

OBJECTIVE

To determine the magnitude of relationships of early life factors with child development in low/middle-income countries (LMICs).

DESIGN

Meta-analyses of standardised mean differences (SMDs) estimated from published and unpublished data.

DATA SOURCES

We searched Medline, bibliographies of key articles and reviews, and grey literature to identify studies from LMICs that collected data on early life exposures and child development. The most recent search was done on 4 November 2014. We then invited the first authors of the publications and investigators of unpublished studies to participate in the study.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Studies that assessed at least one domain of child development in at least 100 children under 7 years of age and collected at least one early life factor of interest were included in the study.

ANALYSES

Linear regression models were used to assess SMDs in child development by parental and child factors within each study. We then produced pooled estimates across studies using random effects meta-analyses.

RESULTS

We retrieved data from 21 studies including 20 882 children across 13 LMICs, to assess the associations of exposure to 14 major risk factors with child development. Children of mothers with secondary schooling had 0.14 SD (95% CI 0.05 to 0.25) higher cognitive scores compared with children whose mothers had primary education. Preterm birth was associated with 0.14 SD (-0.24 to -0.05) and 0.23 SD (-0.42 to -0.03) reductions in cognitive and motor scores, respectively. Maternal short stature, anaemia in infancy and lack of access to clean water and sanitation had significant negative associations with cognitive and motor development with effects ranging from -0.18 to -0.10 SDs.

CONCLUSIONS

Differential parental, environmental and nutritional factors contribute to disparities in child development across LMICs. Targeting these factors from prepregnancy through childhood may improve health and development of children.

Migrant perinatal depression study: a prospective cohort study of perinatal depression on the Thai-Myanmar border

PURPOSE

Perinatal depression is a significant contributor to maternal morbidity. Migrant women in resource-poor settings may be at increased risk, yet little research has been conducted in low-income and middle-income settings. This prospective cohort study of migrant women on the Thai-Myanmar border aims to establish prevalence of perinatal depression, identify risk factors for perinatal depression and examine associations with infant outcomes.

PARTICIPANTS

Participating women are labour migrants and refugees living on the Thai-Myanmar border. A total of 568 women were recruited in their first trimester of pregnancy and are being followed up to 1-year postpartum.

FINDINGS TO DATE

At baseline, women in our study had a median age of 25 years, the predominant ethnicity was Sgaw Karen (48.9%), agriculture was the main employment sector (39.2%) and educational attainment was low with a median of 4 years of education. In the first trimester of pregnancy, a quarter (25.8%; 95% CI 22.3 to 29.5) of all women were depressed as diagnosed by the Structured Clinical Interview for the Diagnosis of DSM-IV Disorders.

FUTURE PLANS

Follow-up is ongoing and expected to continue until January 2018. The prevalence of depression at later stages of pregnancy and during the first postpartum year will be identified, and associations between depression status and demographic, social, migration-related, medical, obstetric and infant factors will be quantified.

TRIAL REGISTRATION NUMBER

NCT02790905.

The suitability of laboratory-bred Anopheles cracens for the production of Plasmodium vivax sporozoites

BACKGROUND

A stenogamous colony of Anopheles cracens (A. dirus B) established 20 years ago in a Thai insectary proved susceptible to Plasmodium vivax. However, routine sporozoite production by feeding on field-collected blood samples has not been described. The setting-up of an A. cracens colony in an insectary on the Thai-Myanmar border and the process of using P. vivax field samples for the production of infectious sporozoites are described.

METHODS

The colony was started in 2012 from egg batches that were sent from the Department of Parasitology, Faculty of Medicine, University of Chiang Mai, to the Shoklo Malaria Research Unit (SMRU), on wet filter paper in sealed Petri dishes. From May 2013 to December 2014, P. vivax-infected blood samples collected from patients seeking care at SMRU clinics were used for membrane feeding assays and sporozoite production.

RESULTS

Mosquitoes were fed on blood samples from 55 patients, and for 38 (69 %) this led to the production sporozoites. The average number of sporozoites obtained per mosquito was 26,112 (range 328-79,310). Gametocytaemia was not correlated with mosquito infectiousness (p = 0.82), or with the number of the sporozoites produced (Spearman's ρ = -0.016, p = 0.905). Infectiousness did not vary with the date of collection or the age of the patient. Mosquito survival was not correlated with sporozoite load (Spearman's ρ = 0.179, p = 0.282).

CONCLUSION

Consistent and routine P. vivax sporozoites production confirms that A. cracens is highly susceptible to P. vivax infection. Laboratory-bred colonies of this vector are suitable for experimental transmission protocols and thus constitute a valuable resource.

The role of point-of-care tests in antibiotic stewardship for urinary tract infections in a resource-limited setting on the Thailand-Myanmar border

Objective

Published literature from resource‐limited settings is infrequent, although urinary tract infections (UTI) are a common cause of outpatient presentation and antibiotic use. Point‐of‐care test (POCT) interpretation relates to antibiotic use and antibiotic resistance. We aimed to assess the diagnostic accuracy of POCT and their role in UTI antibiotic stewardship.

Methods

One‐year retrospective analysis in three clinics on the Thailand–Myanmar border of non‐pregnant adults presenting with urinary symptoms. POCT (urine dipstick and microscopy) were compared to culture with significant growth classified as pure growth of a single organism >10⁵ CFU/ml.

Results

In 247 patients, 82.6% female, the most common symptoms were dysuria (81.2%), suprapubic pain (67.8%) and urinary frequency (53.7%). After excluding contaminated samples, UTI was diagnosed in 52.4% (97/185); 71.1% (69/97) had a significant growth on culture, and >80% of these were Escherichia coli (20.9% produced extended‐spectrum β‐lactamase (ESBL)). Positive urine dipstick (leucocyte esterase ≥1 and/or nitrate positive) compared against positive microscopy (white blood cell >10/HPF, bacteria ≥1/HPF, epithelial cells <5/HPF) had a higher sensitivity (99% vs. 57%) but a lower specificity (47% vs. 89%), respectively. Combined POCT resulted in the best sensitivity (98%) and specificity (81%). Nearly one in ten patients received an antimicrobial to which the organism was not fully sensitive.

Conclusion

One rapid, cost‐effective POCT was too inaccurate to be used alone by healthcare workers, impeding antibiotic stewardship in a high ESBL setting. Appropriate prescribing is improved with concurrent use and concordant results of urine dipstick and microscopy.

Respiratory virus surveillance in hospitalised pneumonia patients on the Thailand-Myanmar border

Background

Pneumonia is a significant cause of morbidity and mortality in the developing world. Viruses contribute significantly to pneumonia burden, although data for low-income and tropical countries are scarce. The aim of this laboratory-enhanced, hospital-based surveillance was to characterise the epidemiology of respiratory virus infections among refugees living on the Thailand-Myanmar border.

Methods

Maela camp provides shelter for ~45,000 refugees. Inside the camp, a humanitarian organisation provides free hospital care in a 158-bed inpatient department (IPD). Between 1st April 2009 and 30th September 2011, all patients admitted to the IPD with a clinical diagnosis of pneumonia were invited to participate. Clinical symptoms and signs were recorded and a nasopharyngeal aspirate (NPA) collected. NPAs were tested for adenoviruses, human metapneumovirus (hMPV), influenza A & B, and RSV by PCR.

Results

Seven hundred eight patient episodes (698 patients) diagnosed as pneumonia during the enhanced surveillance period were included in this analysis. The median patient age was 1 year (range: < 1-70), and 90.4% were aged < 5 years. At least one virus was detected in 53.7% (380/708) of episodes. Virus detection was more common in children aged < 5 years old (<1 year: OR 2.0, 95% CI 1.2-3.4, p = 0.01; 1-4 years: OR 1.4, 95% CI 0.8-2.3, p = 0.2). RSV was detected in 176/708 (24.9%); an adenovirus in 133/708 (18.8%); an influenza virus in 68/708 (9.6%); and hMPV in 33/708 (4.7%). Twenty-eight episodes of multiple viral infections were identified, most commonly adenovirus plus another virus. RSV was more likely to be detected in children <5 years (OR 12.3, 95% CI 3.0-50.8, p = 0.001) and influenza viruses in patients ≥5 years (OR 2.8, 95% CI 1.5-5.4, p = 0.002). IPD treatment was documented in 702/708 cases; all but one patient received antimicrobials, most commonly a beta-lactam (amoxicillin/ampicillin +/−gentamicin in 664/701, 94.7%).

Conclusions

Viral nucleic acid was identified in the nasopharynx in half the patients admitted with clinically diagnosed pneumonia. Development of immunisations targeting common respiratory viruses is likely to reduce the incidence of pneumonia in children living refugee camps and similar settings.

Neonatal intensive care in a Karen refugee camp: a 4 year descriptive study

Background

A third of all deaths in children aged <5 years occur in the neonatal period. Neonatal intensive care is often considered too complex and expensive to be implemented in resource poor settings. Consequently the reductions that have been made in infant mortality in the poorest countries have not been made in the neonatal period. This manuscript describes the activities surrounding the introduction of special care baby unit (SCBU) in a refugee setting and the resulting population impact.

Methods

A SCBU was developed in Maela refugee camp on the Thailand-Myanmar border. This unit comprised of a dedicated area, basic equipment, drugs and staff training. Training was built around neonatal guidelines, comprising six clinical steps: recognition, resuscitation, examination, supportive medical care, specialised medical care, and counselling of parents with sick newborns.

Results

From January 2008 until December 2011, 952 infants were admitted to SCBU. The main admission diagnoses were early onset neonatal sepsis, jaundice and prematurity. Early prematurity (<34 weeks) carried the highest risk of mortality (OR 9.5, 95% CI 5.4–16.5, p<0.001). There was a significant decrease in mortality from 19.3% (2008) to 4.8% (2011) among the infants admitted for prematurity (p=0.03). The neonatal mortality in Maela camp as a whole declined by 51% from 21.8 to 10.7 deaths per 1000 live births over the corresponding period (p=0.04). Staff expressed more confidence in their ability to take care of neonates and there was a more positive attitude towards premature infants.

Conclusion

Neonatal mortality can be reduced in a resource poor setting by introduction of a simple low cost unit specialising in care of sick neonates and run by local health workers following adequate training. Training in recognition and provision of simple interventions at a high standard can increase staff confidence and reduce fatalistic attitudes towards premature neonates.

Changes in the body weight of term infants, born in the tropics, during the first seven days of life

BACKGROUND

Identifying unwell neonates, particularly in the first week of life, is often subjective. If normal values are known, calculating the weight lost or gained from birth weight can be a useful adjunct in the evaluation of the health of a neonate.

METHODS

Serial body weights of well, term, breast fed infants who were attending for routine follow up, were recorded at the Shoklo Malaria Research Unit clinic in Maela Camp for displaced persons on the Thailand Myanmar border. Newborn examination was routine. Weight loss, expressed as percent weight lost from birth weight, and weight gain, expressed as a velocity (g/kg/day), was calculated for the first seven days of life. The results from normal birth weight infants, low birth weight infants (<2.5 kg) and small for gestational age infants (SGA) were examined.

RESULTS

In the first week of life there were no significant differences in weight gained or lost across the three study groups. The maximum weight lost was 4.4% (95% CI 4.1 - 4.6%), which occurred on day three. Weight gain ranged from 13 g/kg/day [95% CI 10 - 16] on day four to 18 g/kg/day [95% CI 15 - 20] on days six and seven.

CONCLUSIONS

Use of these normal values for weight gain and loss, allows infants falling outside of the expected range (95% CI) to be easily identified and subsequently highlighted as needing further medical review.

High rates of pneumonia in children under two years of age in a South East Asian refugee population

BACKGROUND

There are an estimated 150 million episodes of childhood pneumonia per year, with 11-20 million hospital admissions and 1.575 million deaths. Refugee children are particularly vulnerable, with poorly defined pneumonia epidemiology.

METHODS

We followed a birth cohort of 955 refugee infants, born over a one-year period, until two years of age. Clinical and radiographic pneumonia were diagnosed according to WHO criteria. Detailed characteristics were collected to determine risk factors for clinical, radiological and multiple episodes of pneumonia. Investigations were taken during a pneumonia episode to help determine or to infer an aetiological diagnosis.

FINDINGS

The incidence of clinical pneumonia was 0.73 (95% CI 0.70-0.75) episodes per child year (/CY) and of radiological primary endpoint pneumonia (PEP) was 0.22/CY (95% CI 0.20-0.24). The incidence of pneumonia without severe signs was 0.50/CY (95% CI 0.48-0.53), severe pneumonia 0.15/CY (95% CI 0.13-0.17) and very severe pneumonia 0.06/CY (0.05-0.07). Virus was detected, from a nasopharyngeal aspirate, in 61.3% of episodes. A reduced volume of living space per person (IRR 0.99, 95% CI 0.99-1.0, p = 0.003) and young maternal age (IRR 1.59, 95% CI 1.12-2.27, p = 0.01) were risk factors for developing pneumonia. The risk of a child having >1 episode of pneumonia was increased by having a shorter distance to the next house (IRR 0.86, 95% CI 0.74-1.00, p = 0.04). Infants were at risk of having an episode of PEP if there was a shorter distance from stove to bed (IRR 0.89, 95% CI 0.80-0.99, p = 0.03). Raised CRP and neutrophil values were associated with PEP.

CONCLUSIONS

There was a high incidence of pneumonia in young children in this SE Asian refugee population. Viral infections were important, however CXR and non-specific marker findings suggested that bacteria may be involved in up to a third of cases.

Operational and economic evaluation of an NGO-led sexually transmitted infections intervention: north-western Cambodia

OBJECTIVE

Sexually transmitted infection (STI) services were offered by the nongovernmental organization Médecins Sans Frontières-Holland in Banteay Meanchey province, Cambodia, between 1997 and 1999. These services targeted female sex workers but were available to the general population. We conducted an evaluation of the operational performance and costs of this real-life project.

METHODS

Effectiveness outcomes (syndromic cure rates of STIs) were obtained by retrospectively analysing patients' records. Annual financial and economic costs were estimated from the provider's perspective. Unit costs for the cost-effectiveness analysis included the cost per visit, per partner treated, and per syndrome treated and cured.

FINDINGS

Over 30 months, 11,330 patients attended the clinics; of these, 7776 (69%) were STI index patients and only 1012 (13%) were female sex workers. A total of 15 269 disease episodes and 30 488 visits were recorded. Syndromic cure rates ranged from 39% among female sex workers with genital ulcers to 74% among men with genital discharge; there were variations over time. Combined rates of syndromes classified as cured or improved were around 84-95% for all syndromes. The total economic costs of the project were US 766,046 dollars. The average cost per visit over 30 months was US 25.12 dollars and the cost per partner treated for an STI was US 50.79 dollars. The average cost per STI syndrome treated was US 48.43 dollars, of which US 4.92 dollars was for drug treatment. The costs per syndrome cured or improved ranged from US 46.95-153.00 dollars for men with genital ulcers to US 57.85-251.98 dollars for female sex workers with genital discharge.

CONCLUSION

This programme was only partly successful in reaching its intended target population of sex workers and their male partners. Decreasing cure rates among sex workers led to relatively poor cost-effectiveness outcomes overall despite decreasing unit costs.

Influence of input rates on (+/-)-isradipine haemodynamics and concentration-effect relationship in healthy volunteers

Since the magnitude of the response to a drug may depend upon the drug input rate, the concentration-effect relationship of the new dihydropyridine (+/-)-isradipine was investigated using different administration modalities. Ten normotensive healthy volunteers were given, double-blind and in a crossover fashion, isradipine as a 1 mg iv infusion, 5 mg oral solution, 5 mg standard tablet, 10 mg slow release formulation, and a placebo. Blood pressure, heart rate, and plasma isradipine concentrations were recorded for 24 h. The maximal fall in diastolic blood pressure was similar after the infusion (-11.40 mmHg), the oral solution (-15.20 mmHg), and the standard tablet (-12.50 mmHg). In healthy volunteers the slow release form had no significant effect on blood pressure. The concentration-effect plots showed an increasing slope in the order infusion, solution, and table, and anticlockwise hysteresis. This was partly due to marked heart rate counter-regulation, the corresponding mean maximal heart rate increases being 24, 19, and 17 beats.min-1. The pronounced counter-regulation of the heart rate implies that a slow isradipine input rate would be more effective in decreasing blood pressure.

[The effect of rate of administration of isradipine on the hemodynamic response]

As the magnitude of drug response may depend on its input rate, we investigated the rate of administration-effect relationship of the new dihydropyridine isradipine. Ten healthy volunteers received (double-blind and cross-over) isradipine 1 mg i.v. (5 min), 5 mg solution, 5 mg tablet, 10 mg sustained release, and placebo. Blood pressure and heart rate were recorded for 24 h. A single dose of slow-release formulation isradipine does not induce significant hemodynamic effects in healthy subjects. The maximal BP fall was comparable with either i.v., solution, and conventional tablet administration. This is due to a stronger heart rate counter-regulation, linked to rapid isradipine administration. These results imply that slow input rates of isradipine are more effective in lowering blood pressure.