Efficacy of chlorthalidone and hydrochlorothiazide in combination with amiloride in multiple doses on blood pressure in patients with primary hypertension: a protocol for a factorial randomized controlled trial

To compare CTD 25 mg with amiloride 20 mg versus other combinations of thiazide with amiloride, with respect to BP-lowering efficacy, in subjects with primary hypertension.

To compare, in subjects with primary hypertension, CTD 25 mg with amiloride 20 mg versus other combinations of thiazide with amiloride, with respect to the incidence of adverse events, variation of laboratory parameters, and proportion of patients who achieved BP control.

This is a randomized double-blind single-center superiority trial, controlled by active treatment, with factorial design (2 × 2), with a 1:1:1:1 allocation ratio, follow-up period of 12 weeks, and a primary endpoint of mean change from baseline in 24-h systolic and diastolic BP measured by ABPM. Eligible participants will be randomized to receive two simultaneous interventions: a thiazide diuretic (CTD 25 mg/day or HCTZ 50 mg/day) and a potassium-sparing diuretic (amiloride 10 mg/day or amiloride 20 mg/day).

The study will be conducted in the Center for Clinical Research of Hospital de Clínicas de Porto Alegre (HCPA), which aims to establish guidelines and policies regarding the conduct of clinical research as a whole. In this sense, it provides adequate infrastructure for the development of all stages of clinical and epidemiological studies, in line with the public health needs of Brazil.

Inclusion criteria:

If the patient is on antihypertensive monotherapy prior to randomization and has BP below 160/100 mmHg (as measured by office BP), he may have his medication suspended for 2 weeks to confirm the inclusion criteria (washout phase).

Exclusion criteria:

The trial has a factorial design, where participants will receive two simultaneous interventions: a thiazide diuretic (CTD 25 mg or HCTZ 50 mg) and a potassium-sparing diuretic (amiloride 10 mg or amiloride 20 mg). Participants will be randomly assigned to four parallel groups:

The thiazide diuretic and amiloride will be combined in a single capsule, which will be provided by a compounding pharmacy. The medication will be administered as fixed-dose combinations. Patients will be instructed to take the medication orally in the morning upon waking. Adherence to trial medication will be assessed by means of pill count.

See Additional file 1 for the Template for Intervention Description and Replication (TIDieR) checklist.

Primary outcomes:

Secondary outcomes:

Participants will be recruited from outpatient clinics and from Basic Health Units (public health system) in Porto Alegre, Brazil, and then invited to participate in the study.

The first visit will consist of (1) informed consent signing, (2) eligibility assessment, and (3) sociodemographic and clinic data collection. If the patient is taking an antihypertensive drug and has BP below 160/100 mmHg (as measured by office BP), he will have his medication suspended for 2 weeks to confirm the eligibility criteria (washout phase, which allows most of the effects of the BP drug to vanish). If no antihypertensive medication is being used, BP measurements will be carried out in the office (average of three measurements) and ABPM will be placed. Then, participants will be instructed to return the next day after fasting (12 h) for laboratory tests.

The next visit will consist of removal of ABPM, confirmation of primary hypertension through ABPM (mean 24-h systolic BP ≥ 130 mmHg or mean 24-h diastolic BP ≥ 80 mmHg), office BP measurement (average of three measurements), anthropometric evaluation, and laboratory tests. After confirming the eligibility criteria, randomization and delivery of the study drug will be performed.

The intermediate visit (week 6) will consist of office BP measurement (average of three measurements), evaluation of adherence to treatment, investigation of adverse events, and delivery of study medication. Participants will be instructed to return in 6 weeks after fasting (12 h) for laboratory tests.

The close-out visit (week 12) will consist of office BP measurement (average of three measurements), anthropometric evaluation, evaluation of adherence to treatment, investigation of adverse events, laboratory tests, and placement of ABPM. Participants will be instructed to return the next day for removal of ABPM, verification of laboratory test results, and termination of study participation.

The schedule of enrollment, interventions, and assessments is presented in Fig. 1. The allocation of participants and timeline are presented in Fig. 2.

For an absolute difference of 6 mmHg in systolic BP on 24-h ABPM, with an alpha of 0.05, power of 80%, and standard deviation of 9 mmHg, it will be necessary to study 76 patients in total. The sample size will be increased by 10% to account for possible losses in follow-up, resulting in 84 patients being randomized (42 for each arm).

Participants will be recruited from outpatient clinics in HCPA and Instituto de Cardiologia do Rio Grande do Sul, Brazil, and from Basic Health Units (public health system). Patients potentially eligible for the study will be contacted by telephone by the trial investigator, who will explain the study and ascertain the patient’s interest. If interested, the patient will be seen in the Center for Clinical Research of HCPA, where the study consultations will be made. The enrollment period is expected to extend over 24 months.

A computer-generated sequence created by the Random Allocation Software [35] will be used to randomly assign patients to the four interventions, stratified by 24-h systolic BP on ABPM (< 140 or ≥ 140 mmHg), with a 1:1:1:1 allocation using random block sizes to generate equal allocation ratio and parallel groups. The block sizes will not be disclosed, to ensure concealment. The randomization process will be performed before the beginning of the trial, with the random allocation sequence registered in Research Electronic Data Capture (REDCap) [36]. To guarantee concealment of the allocation list, randomization will be implemented through a web-based automated system. All patients who give consent for participation and who fulfill the inclusion criteria will be randomized. An independent researcher not involved in the enrolment will produce the randomization sequence. The research team will be blinded to the randomization sequence and it will be concealed from the researchers enrolling and assessing participants. The interventions will be delivered by researchers with extensive knowledge of the study medication.

The study medication in all groups will have the same color, taste, consistency, odor, and appearance. In this way, patients, care providers, outcome assessors, and the entire research team will be blinded regarding the allocation to treatment groups throughout the study. Unblinding will occur only when knowledge of the actual treatment is absolutely essential for further management of the patient, particularly in the occurrence of serious adverse events.

The research team will be trained to perform anthropometric and BP measurements as well as the application of questionnaires. A laboratory technician will collect blood samples after 12-h fasting. These samples will be forwarded for analysis and discarded shortly after. No biological specimens will be stored for future studies. Study data will be collected and managed using REDCap tools hosted at HCPA.

Study data will be collected and managed using REDCap tools hosted at HCPA. REDCap is a secure, web-based application designed to support data capture for research studies, providing: 1) an intuitive interface for validated data entry; 2) audit trails for tracking data manipulation and export procedures; 3) automated export procedures for seamless data downloads to common statistical packages; and 4) procedures for importing data from external sources. An eCRF will be constructed for data registration. Data integrity will be enforced through valid values and range checks. For data analysis, subject-related data from REDCap will be exported and analyzed in statistics software (IBM SPSS). Before data export, all patient identifiers will be removed.

Each participant will be given an identification number at enrolment, and each identification number will have an eCRF. The list over identification codes will be deleted at the end of the study. All trial data, including Trial Master File, eCRF, the source datasheet of the eCRF, and the list of identification codes will be stored in the external server of REDCap with continuous backup. REDCap data are kept for 10 years. Study-related patient documentation and the signed informed consent form will be stored in a patient-specific folder.

Assuming there will be no interaction between thiazides and amiloride, we intend to carry out pooled analysis of the differences between CTD (CTD 25 mg with amiloride 10 mg and CTD 25 mg with amiloride 20 mg) versus HCTZ (HCTZ 50 mg with amiloride 10 mg and HCTZ 50 mg with amiloride 20 mg) and the differences between amiloride in a lower dose (amiloride 10 mg with CTD 25 mg and amiloride 10 mg with HCTZ 50 mg) versus amiloride in a higher dose (amiloride 20 mg with CTD 25 mg and amiloride 20 mg with HCTZ 50 mg).

Due to the short duration of the trial and minimal risks associated with the interventions, a Data Monitoring Committee will not be established, and interim analyses will not be performed. Committees involved in trial coordination and conduct are to be decided elsewhere and will be described in amendments or in the final text.

At all follow-up visits, adverse events will be investigated by spontaneous reporting and by a directed questionnaire. An adverse event is considered to be any undesired medical occurrence in a clinical trial participant who has received a pharmaceutical product, even if it does not necessarily have a causal relationship to that treatment. A severe adverse event is considered to be any unfavorable medical occurrence that results in death, threat to life, hospitalization or its prolongation, or persistent or significant disability. The causal relationship to the study drug and the intensity of adverse events will be evaluated by the investigators. The communication of adverse events classified as severe or unexpected will be reported to the Ethics Committee. SAE must be reported by the principal investigator within 24-h after the SAE becomes known. The participant who presents with a severe adverse event will be withdrawn from the study. Withdrawal may also occur in the event of intolerance of the participant to non-severe adverse events. In this case, the procedures for the last visit will be carried out. Laboratory adverse events, such as hypokalemia, hyperuricemia, and hyperglycemia, will be investigated at the final visit. All adverse events and withdrawals due to adverse events will be reported, irrespective of severity, with no frequency threshold.

A quality assurance audit/inspection of this study may be conducted by the competent authority. The quality assurance auditor/inspector will have access to all medical records, the investigator’s study related files and correspondence, and the informed consent documentation that is relevant to this clinical study. The investigator will allow the persons being responsible for the audit or the inspection to have access to the source data/documents and to answer any questions arising. All involved parties will keep the patient data strictly confidential.

This article followed the Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT) 2013 statement on the writing of a study protocol for a clinical trial [38]. The filled SPIRIT checklist can be found in Additional file 2. The World Health Organization Trial Registration Data Set is provided in Additional file 3.

Any modifications to the protocol which may impact on the conduct of the study or potential benefit to the patient or may affect patient safety, including changes of study objectives, study design, patient population, sample sizes, study procedures, or significant administrative aspects, will require a formal amendment to the protocol. Such amendments will be approved by the Ethics Committee of HCPA prior to implementation. Amendments will be disclosed in the new version of the protocol with reasons.

Trained physicians responsible for eligibility will supply informed consent forms to patients willing to participate in the trial. The consent form includes institutional affiliation, the objectives of the study, a description of the testing procedures, explanation about interventions and its randomized allocation nature, information about expected length of time for participation, the potential risks and benefits involved in the study, the costs to the participants, information on anonymized data sharing, and an explanation of the patient’s right to refuse participation or to withdraw consent at any time. A copy of the consent form is given to the participant, and this fact is documented in the subject’s record. The investigator in charge of providing clarification on the study and seeking the participant’s ethical consent must allow the subject sufficient time to decide whether or not to participate in the trial. Once a subject decides to participate, a signed and personally dated informed consent form is obtained from the subject before any trial-related procedure. As there are no plans for use of data from this trial in ancillary studies, no additional consent will be required.

Study data will be collected and managed using REDCap tools. All laboratory specimens, reports, data collection, processes, and administrative forms will be identified by a coded identification number to maintain participant confidentiality. After full data analysis, all subject identifiers will be erased. The principal investigator will grant the relevant personnel user rights to view, edit, or overwrite data entries by password as applicable. All edits will be automatically documented in the change history log. Direct access to source data may be granted in the case of monitoring, audit, or inspections. All personnel must treat patient data as confidential. As far as possible, encoded data will be used.

All trial investigators will be given access to the cleaned data sets. Project data sets will be stored in the external server of REDCap hosted at HCPA, and all data sets will be password protected. To ensure confidentiality, data dispersed to project team members will be blinded of any identifying participant information.

The study drugs have been used for a long time to treat hypertension and are considered safe. The risks of the study are mainly due to the possibility of adverse effects with the drugs. The most frequent adverse effects are anorexia, dyspepsia, dizziness, headache, cramps, and increased urine volume, and usually do not require discontinuation of treatment. In case of adverse effects or problems related to participation in the study that require medical treatment, the investigators will be responsible for the care such that participant do not incur costs.