The study will be done in 2 phases:
Phase I: Development of the SMS text messages
The SMS messages to be used in the trial will be developed and pre-tested in focus group discussions of a convenience sample of subjects similar to the target population for understandability and acceptability.
Phase II: Parallel group, open-label, randomized, controlled trial
Target Population
Hypertensive patients being seen at the General Medicine Outpatient Clinic of a public, tertiary, university hospital in Manila, Philippines
Sampling Method
A criterion sampling strategy will be used in the study. Patients who fulfill the eligibility criteria will be recruited consecutively until the desired sample size is reached.
Randomization and Allocation Concealment
Eligible patients will be randomized to one of two treatment groups using a computer-generated random allocation sequence. Allocation of treatment will be done by a third party using sequential, sealed opaque envelopes.
Blinding
Given the nature of the intervention, patients will not be blinded to the treatment groups. However, measures will be taken to blind the physicians managing the participants at the clinic. Outcome assessors will also be blinded to the participants' treatment groups.
Procedures and Measurements
Written, informed consent will be obtained prior to enrolment in the study. Once an eligible participant has given consent, he will be randomized to either the intervention or control arm of the trial by a third party using sequentially numbered opaque envelopes. At the end of a 12-week follow up period, participants will be asked to return for a final study visit, where blood pressure and medication adherence will be measured. Acceptability of the SMS intervention will also be determined using a structured questionnaire. A period of four weeks from scheduled date of final visit is allowed before a patient is considered to have been lost to follow-up.
Intervention: SMS reminders
Patients in the intervention arm will receive 2 text messages per week delivered via SMS on randomly chosen days and times during the 12-week study period. The aims of the messages are to remind patients to take their blood pressure medications daily, what the target blood pressure is, and the benefits of daily intake of anti-hypertensive medications. Successful contact will be assumed when "Message sent" is seen on the screen. Otherwise, the same text message shall be immediately resent up to a maximum of 3 times. Receipt of the messages will be free to the study participants and independent of their telephone service provider.
Control: Usual Care
Routine or usual care of hypertensive patients at the General Medicine Outpatient clinic is based on the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. This consists of physician visits, advice and medication prescription by the healthcare provider. It does not include sending SMS messages to encourage adherence and provide information regarding hypertension.
Outcome Measurements
Blood Pressure
Blood pressure will be measured using a calibrated digital sphygmomanometer manufactured by Omron after the participant has been seated quietly for five minutes. The average of two readings taken five minutes apart will be recorded.
Medication Adherence
The Adherence Self-Report Questionnaire (ASRQ), a brief, validated, self-administered questionnaire, will be used to measure medication adherence. Participants will be asked to complete the Filipino translation of the ASRQ.
Acceptability of SMS Messages
Acceptability of the SMS messages will be measured using a brief, self-administered questionnaire.
Planned Analysis
Descriptive statistics for baseline characteristics, adherence scores, and adherence rates in both groups (mean, sd, frequency (%), median) will be computed. Between-group comparisons will be done at baseline to check for similarity of baseline characteristics, and at the end of 12 weeks to test the hypothesis of inequality between two populations. All hypothesis tests will be one-sided with a level of significance set at 0.05. Intention-to-treat (ITT) analysis will be done, with possible sensitivity analysis for drop-outs. All statistical computations will be computed using the Stata statistical software.
Sample Size
The NCSS-PASS statistical software was used to compute for the desired sample size.
The sample size required to fulfill the objectives of the study is 286 subjects per group. Allowing for a loss to follow up of approximately 20%, the final sample size is 350 subjects per group (total of 700 subjects).
Ethical Considerations
Ethics approval will be obtained prior to conducting this study. Written informed consent will be obtained from all participants prior to enrolment. Good clinical practice guidelines will be followed during the course of the study.
At the beginning of the trial, it will be emphasised that communication through SMS in this study is one-way (provider to patient), so there will be no reply to any and all text messages received from participants. The participants will also be advised to consult their physicians for any problems they may experience.
