Journal of Pharmaceutical and Biomedical Analysis 61 (2012) 78–85 Contents lists available at SciVerse ScienceDirect Journal of Pharmaceutical and Biomedical Analysis j ourna l ho me p a ge: www.elsevier.com/locate/jpba Bioavailability study of triamterene and xipamide using urinary pharmacokinetic data following single oral dose of each drug or their combination Hadir M. Maher a,b,∗ , Rasha M. Youssef a , Eman I. El-Kimary a , Ekram M. Hassan a,c , Magda A. Barary a a Faculty of Pharmacy, Department of Pharmaceutical Analytical Chemistry, University of Alexandria, El-Messalah, Alexandria 21521, Egypt b College of Pharmacy, Department of Pharmaceutical Chemistry, King Saud University, Riyadh 11495, P.O. Box 22452, Saudi Arabia c Faculty of Pharmacy, Department of Pharmaceutical Analytical Chemistry, Beirut Arab University, Beirut, Lebanon a r t i c l e i n f o Article history: Received 3 October 2011 Received in revised form 26 November 2011 Accepted 28 November 2011 Available online 6 December 2011 Keywords: Triamterene Xipamide Urine analysis Pharmacokinetics HPLC–DAD a b s t r a c t An efficient chromatographic method for the simultaneous determination of triamterene (TRI) and xipamide (XIP) in urine samples, based on high performance liquid chromatography with photodi- ode array detector (HPLC–DAD) has been developed. The HPLC separation was performed on a RP stainless-steel C-18 analytical column (250 mm × 4.6 mm, 5 m) with a gradient elution system of 0.05 M phosphate buffer adjusted to pH 4.0 and methanol as the mobile phase. The method was used to determine the urinary excretion profile and to calculate different urinary pharmacokinetic parameters following oral dose of their combination compared with single oral doses of each drug and hence comparing their bioavailability. Quantitation was performed using chlorthalidone as internal standard. The calibration graphs of each drug were rectilinear in the range of 0.2–40 g/mL urine for TRI and 0.2–15 g/mL urine for XIP. An HPLC–DAD method was also successfully developed for the simultaneous determination of the investigated drugs in pharmaceutical preparations. The methods were validated in terms of linear- ity, accuracy, precision, selectivity, limits of detection and quantitation and other aspects of analytical validation. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Triamterene (TRI) is a mild diuretic belonging to the potassium-sparing family. TRI alone is relatively inefficient as an antihypertensive drug. Thus it is usually co-administered with some other, more potent diuretics (e.g. a thiazide or anthranilic acid derivative). This combination has a synergistic effect. When TRI is given alone in the treatment of edema, the oral dosage range is 150–250 mg daily. After oral administration, about 30–70% of the dose is excreted in urine, mainly as the sulfate conjugate of p- hydroxytriamterene, with about 5–10% of the dose as unchanged drug [1]. In urine, TRI has been determined using different tech- niques [2–9]. Only few of the previously published reports [3,8,9] describe the urinary excretion profile of TRI of which, no suitable HPLC method with photodiode array detection was reported for studying the urinary excretion profile of TRI either alone or in com- bination with xipamide. Xipamide (XIP) is a sulfonamide diuretic drug used for the treat- ment of high blood pressure and edema [10]. The common dose of ∗ Corresponding author at: Faculty of Pharmacy, Department of Pharmaceuti- cal Analytical Chemistry, University of Alexandria, El-Messalah, Alexandria 21521, Egypt. Tel.: +20 3 4871317; fax: +20 3 4873273. E-mail address: hadirrona@yahoo.com (H.M. Maher). xipamide is 20–40 mg day -1 with a maximum dose of 80 mg day -1 and the maximum diuresis is between 3 and 4.5 h. About 88% of a dose is excreted in the urine with about 50% as unchanged drug and 30% as xipamide-O-glucuronide [1]. XIP has been determined in urine using different methods [11–20]. Only one report [11] illus- trates its urinary excretion till 6 h, but no reports, to our knowledge, have been reported for studying its urinary excretion profile up to 24 h either alone or in combination with triamterene diuretic. The toxicity of TRI/XIP combination is less than that reported for the individual constituents [21]. Literature review revealed that only one report is available for the determination of mixed tablets of TRI and XIP which comprises spectrophotometric and densito- metric methods [22]. Recently, diuretics have been abused in sports with weight classes, such as weightlifting, wrestling and boxing when ath- letes try to reduce their body weight in order to qualify for lower weight classes. It is also reported that athletes use diuretics to avoid detection of doping agents by reducing their urine concentration. Accordingly, the determination of diuretics in biological samples is a very important issue in doping control. The analysis of these drugs in physiological samples usually requires some form of prepara- tion. Liquid–liquid [11] and solid phase [14,15] extractions are extensively used to separate the diuretics from the protein matrix and endogenous compounds. These procedures are however time- consuming and frequently incomplete recoveries are attained. 0731-7085/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jpba.2011.11.032