Validation and Uncertainty Estimation of an Ecofriendly and Stability-Indicating HPLC Method for Determination of Diltiazem in Pharmaceutical Preparations

A green, simple, and stability-indicating RP-HPLC method was developed for the determination of diltiazem in topical preparations. The separation was based on a C18 analytical column using a mobile phase consisted of ethanol: phosphoric acid solution (pH = 2.5) (35？:？65, v/v). Column temperature was set at 50°C and quantitation was achieved with UV detection at 240？nm. In forced degradation studies, the drug was subjected to oxidation, hydrolysis, photolysis, and heat. The method was validated for specificity, selectivity, linearity, precision, accuracy, and robustness. The applied procedure was found to be linear in diltiazem concentration range of 0.5–50？μg/mL ( ). Precision was evaluated by replicate analysis in which % relative standard deviation (RSD) values for areas were found below 2.0. The recoveries obtained (99.25%–101.66%) ensured the accuracy of the developed method. The degradation products as well as the pharmaceutical excipients were well resolved from the pure drug. The expanded uncertainty (5.63%) of the method was also estimated from method validation data. Accordingly, the proposed validated and sustainable procedure was proved to be suitable for routine analyzing and stability studies of diltiazem in pharmaceutical preparations. 1. Introduction Anal fissure is one of the most common and painful proctologic diseases that is effectively treated and prevented with conservative measures in its acute form, whereas chronic fissures may require medical or surgical therapy. Because of the disability associated with surgery for anal fissure and the risk of incontinence, medical alternatives for surgery have been sought. Most recently, pharmacologic approaches that relax the anal smooth muscle, to accomplish reversibly what occurs in surgery, have been used to obtain fissure healing [1–3]. Glyceryl trinitrate ointment (0.2%) has an efficacy of up to 68% in healing chronic anal fissure, but it is associated with headache as the major and most common side effect. Diltiazem, a calcium channel antagonist used in the treatment of angina, hypertension, and arrhythmias, achieved healing of chronic anal fissure comparable to 0.2% Glyceryl trinitrate ointment but caused fewer side effects [4]. Therefore, it is preferred to use diltiazem to treat this chronic disease [5]. The structures of diltiazem and its main impurity are presented in Figure 1. Figure 1: Molecular structures of diltiazem (a) and desacetyl diltiazem (b). Concerning new therapeutic application of diltiazem, validated and stability-indicating methods should be available to determine