To perform a prospective randomized double-blind clinical trial we evaluated the sample size of 100 people for each group. This study was approved by Ethics Committee of “Tabriz University of Medical Sciences”. The trial was registered in “IRCT”. Additionally, all aspects of the present study plan were explained to patients and written informed consents were obtained consequently.

Considering pain incidence ratios of 29.3 % and 12 % for the control and intervention groups respectively, confidence interval of 0.05, power of 20 % and loss probability of 20 % throughout the follow-up period using the following formula, a sample size of 100 people were calculated

N = 2 z 1 − α / 2 * z β 2 * P * 1 − P / p1 – p 2 2 (1)

P = p1 + p 2 / 2 (2)

N = 86 + 15 ≠ 100 (3)

As the number of the patients with renal colic referring to the emergency department of Imam Reza Hospital is abundant [5], the sample size was considered as 120 people for both groups and a total number of 240.

Using the website of http://www.randomization.com 240 letters of A and B were evenly (120) produced and patients were allocated to one of the two groups of A (Group I) and B (Group II), in the order provided by the site.

Patients were evenly divided into two groups of I, receiving intravenous lidocaine (n = 120), and II, receiving intravenous morphine (n = 120). As previously mentioned the study was double-blind and the executive of the research project was unaware of the obtained figures using online software from http://www.randomization.com. Firstly, patients entering emergency department with complaint of flank pain were identified, interviewed and examined. Later, patients with pain radiating to genitalia and groin, nausea, vomiting, urinary irritation symptoms and tenderness in costovertebral angle were selected.

To provide the patients with required analgesia and to avoid any inconvenience regarding pain management, initial diagnosis was made based on clinical findings (unilateral abdominal pain radiating to the genitalia) associated with a positive urine analysis for hematuria. However diagnosis was later confirmed using Kidney, Ureter, and Bladder (KUB) radiographies and sonography studies. Since all patients experienced unilateral abdominal pain and their urine analyses were positive for hematuria, no further diagnostic criteria for renal colic were set throughout the study [1].

All patients aged 18 to 65 years, and did not have history of renal, hepatic or cardiac disease (Ischemic Heart Disease).

Patients with history of allergy to lidocaine and morphine, an inability or unwillingness to provide written informed consent and pregnant females were excluded from the study as well. Patients whose pain did not relieve using lidocaine or morphine were administered supplementary drugs. Then, method of drug administration, the reason for prescription and possible complications were explained to the patients and it was emphasized that using either lidocaine or morphine is safe.

After explaining method of treatment and obtaining informed written consent, 12 lead electrocardiograms were taken from all patients to make sure no history of heart diseases existed. Later, patients were monitored by an emergency medicine specialist throughout the procedure. Additionally patients were asked to identify the degree of their pain using Visual Analogue Pain Scale (VAS), zero represented painless and 10 was the worst experienced pain. Vital signs and other symptoms of patients including nausea, vomiting, dysuria, hematuria, and etc. were recorded. Firstly, all the enrolled patients received intravenous metoclopramide (0.15 mg/kg). Later, to reduce pain in patients suffering from renal colic in group I lidocaine solution (1.5 mg/kg) and in group II morphine solution (0.1 mg/kg) were administered intravenously slowly (Each syringe contained 10 mL of solution, either 10 mg of morphine or 200 mg of lidocaine %2 (1 mL = 20 mg)). The trial was considered accomplished when either the patient had a pain score of less than 3 for 30 minutes after the last analgesic dose or the 10 mL of solution in the syringe was used up.

As fluid therapy is not commonly used in our center to treat patients with renal colic and it is restored only for patients who are dehydrated or have sepsis, our patients received very little amount of fluid, (10 mL) administered only by injection [6].

Notice

All the processes of injection and filling in the questionnaires were performed by another person who was a specialist (not involved in research project) and blinded to the injected drug as well as the patients groupings. Patients were blinded to the injected medications as well. The doses required for the administered medication were calculated by another colleague. Hence; neither the patients nor the administrator were aware of the medications used.

Consequently, 5, 10, 15 and 30 minutes after injection, incidence of pain in patients was recorded based on Visual Analog Scale (VAS). Statistical data and results were expressed using descriptive statistics as percentage and Mean ± SD. To compare the response to treatment, statistical Mann–Whitney U-test was performed in two groups. Kolmogroff Smirnov test was used for normality of variables and QQ plot test was used in cases of necessity. The data were analyzed using the SPSS16 software.