Liquid Chromatographic Determination of Levodopa and Levodopa-Carbidopa in Solid Dosage Forms: Collaborative Study

Abstract

A liquid chromatographic method for the determination of levodopa in tablets and capsules and levodopa-carbidopa in tablets was collaboratively studied by 6 laboratories. Collaborators were supplied with duplicate powdered composites of levodopa (1 synthetic formulation, 1 commercial tablet, and 1 commercial capsule) and levodopa- carbidopa (1 synthetic formulation and 2 commercial tablets), along with individual levodopa-carbidopa tablets for content uniformity determinations. The repeatability coefficient of variation (CV„) and reproducibility coefficient of variation (CV„) for levodopa single component were 0.48 and 0.87%; for levodopa in combination, 0.50 and 0.90%; and for carbidopa, 0.77 and 1.20%, respectively. Overall, the recovery values for levodopa and carbidopa from synthetic formulations simulating tablets were 100.4 and 99.5%, respectively .The pooled CVD„ and CVDX values for the individual tablet assays were 2.07 and 2.30% for levodopa, and 1.80 and 2.24% for carbidopa, respectively. The method has been adopted official first action for determination of the active ingredients in levodopa tablets and capsules and in levodopa-carbidopa tablets and for content uniformity testing in the combination dosage form.

Spectrophotometric Method for the Determination of Carbidopa Using Neotetrazolium Chloride

“…The results obtained from the determination of carbidopa using both the described procedure and the corresponding USP. XXII and BP 1988 official methods were statistically compared by means of Student's t-test as well as by the variance ratio F-test, and no significant difference was observed.For the analytical estimation of carbidopa, besides the official compendia which specify HPLC (US Pharmacopeia XXII, 1990) and potentiometry (British Pharmacopoeia, 1988), various methods have been reported (Steup et a1 1986;Ting 1986Ting , 1987 Foerster et a1 1988), including three spectrophotometric procedures from our laboratories (Issopoulos 1989a(Issopoulos , b, 1990. This paper describes the use of neotetrazolium chloride (NTZC) to determine carbidopa.…”

“…For the analytical estimation of carbidopa, besides the official compendia which specify HPLC (US Pharmacopeia XXII, 1990) and potentiometry (British Pharmacopoeia, 1988), various methods have been reported (Steup et a1 1986;Ting 1986Ting , 1987 Foerster et a1 1988), including three spectrophotometric procedures from our laboratories (Issopoulos 1989a(Issopoulos , b, 1990. This paper describes the use of neotetrazolium chloride (NTZC) to determine carbidopa.…”