Organic Modifier Case Study

3. Results and discussion 3.1. Optimization of chromatographic conditions
A rapid, simple, reproducible and accurate RP-HPLC method was developed for simultaneous determination of pregabalin and atenolol in dosage forms, spiked and volunteer human urine.
To optimize the proposed HPLC method; several parameters such as effect of organic modifier, pH of buffer and flow rate were studied.
The effect of organic modifier:
The percentage of organic modifier (methanol) has a critical effect on separation of pregabalin and atenolol. It was found that increasing the proportion of methanol than 10% led to interference between pregabalin peak and urine matrix and inadequate resolution between atenolol and pregabalin. While decreasing the proportion

Therefore we decided to determine the urinary excretion pattern of these two drugs after single oral administration and by which we can determine the concentration of atenolol and pregabalin at any time during 24 hours after oral administration.
The urinary excretion pattern of pregabalin and atenolol were investigated in healthy volunteers after a single oral administration of 75 mg of Lyrica® tablet and 50 mg of Ateno® tablet. Pregabalin is well absorbed after oral administration. It undergoes negligible metabolism in humans and is eliminated from the systemic circulation primarily by renal excretion as unchanged drug. Atenolol is incompletely absorbed (about 50%), but most of the absorbed dose reaches the systemic circulation. It undergoes little or no metabolism by the liver and the absorbed portion is eliminated by renal

The drugs were stable for at least three freeze-thaw cycles. No considerable changes were observed for the stability of the spiked urine samples after 2 weeks of storage at -20˚C.
4.8. System suitability test
Resolution (Rs) is a measure of the degree of separation between two adjacent peaks. A value of 1.5 for resolution implies a complete separation of the two compounds [50].
Resolutions and other system suitability parameters (capacity factor (k/), selectivity factor (α), number of theortical plates and RSD% of retention time were calculated for atenolol and pregabalin. Their values were found to be acceptable (Table 12).
5. Conclusion
The proposed HPLC method provides simple, accurate and reproducible quantitative analysis for simultaneous determination of atenolol and pregabalin in dosage forms, spiked and human urine.
The cumulative excretion patterns of atenolol and pregabalin have a valuable clinical application by detecting the concentration of the two drugs in urine at any time during 24 hours after oral