Fluorescence spectra of chloroquine suspension: A probable tool for quality assessment of the most common antimalarial in a user-friendly manner

Sir,

Chloroquine is a popular drug used in the treatment of malaria. Due to its good safety profile, it can be used in pregnant mothers and children. Furthermore, high elimination time of the drug provides long posttreatment preventive effect.[1] However, the poor or substandard quality of chloroquine is a worldwide concern which imposes life at risk and contributes toward the drug resistance.[2,3] Therefore, quality assessment of chloroquine is of much concern.[4]

In the market, chloroquine is commonly available as a suspension for use in the pediatric population and tablets for use in adults. We feel that strict quality assurance of suspension is warranted as it is used in the pediatric population.

In this context, we have studied the fluorescence emission spectra of chloroquine diphosphate (MP Biomedicals Catalog No. 193919, 10 mg/ml in distilled water) at λEx 300 and found that chloroquine diphosphate in distilled water gives fluorescence emission in the range of 330–400 nm [Figure 1a]. Similarly, the fluorescence emission spectra of chloroquine phosphate suspension containing 10 mg/ml chloroquine (Lariago manufactured by Ipca Laboratories Ltd. Sejavta, Ratlam 457002. Batch No. GFA 018045R) were also studied [Figure 1b]. The spectrum of distilled water is given in Figure 1c. TECAN Infinite 200 Pro M PLEX multimode reader is used throughout the study setting the instrument in default mode. The chloroquine suspension contains sunset yellow, which is a synthetic food color. The sunset yellow is a fluorescent material which, when excited (λEx 310–410 nm), gives emission at 592 nm.[5]

Figure 1.

Fluorescence emission scan of (a) pure chloroquine diphosphate (10 mg/ml), (b) chloroquine suspension (10 mg/ml), and (c) distilled water at λEx 300 nm (Y-axis represents arbitrary fluorescence unit and X-axis represents wavelength in nm). Effect of different concentrations of chloroquine suspension on the fluorescence intensity (d) up to 0.625 mg/ml and (e) up to 1 mg/ml of drug (Y-axis represents arbitrary fluorescence unit and X-axis represents concentration in mg/ml)

We have observed that outside the fluorescence emission range of chloroquine and sunset yellow, the suspension shows a typical pattern of emission when excited at 300 nm [Figure 1b]. However, in pure chloroquine and the suspension when excited at 300 nm, maximum emission is noted at 357 ± 20 nm.

It is interesting to note that at λEx 300 nm/λEm 357 nm, the fluorescent intensity increases linearly with increasing concentration of chloroquine suspension in distilled water (up to 0.625 mg/ml) [Figure 1d]. However, at higher concentration of chloroquine, the fluorescence intensity follows the logarithmic curve pattern [Figure 1e].

We feel that the addition of sunset yellow in the suspension is the causative factor for deviation of the spectra of chloroquine diphosphate and the suspension, although the emission maximum is the same. We recommend more experimental study in the said direction, and by doing so, we feel that algorithm can be developed for quality control of chloroquine suspension by studying its fluorescence spectra without estimating chloroquine by tedious extraction–purification steps.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.