A rapid, specific and sensitive high performance liquid chromatographic method has been developed for the determination of quinidine (Q) and dihydroquinidine (DHQ) in human plasma. Plasma samples are extracted with a benzene-isoamyl alcohol mixture ( 1: 1) followed by separation on a microparticulate reverse-phase column. Quinidine, dihydroquinidine, and their metabolltes are detected by fluorescence In acid medlum using post-column additlon of sulfuric acid. Plasma concentrations as low as 0.05 pg/mL can be measured with a relative standard deviation less than 10%. The complete assay procedure takes about 30 min.Recovery from plasma is at least 95 YO. A linear response is obtained in the concentration range of 0.05 to 10 pg/mL of quinidine in plasma. The minimum detectable quantity is 1 ng on column.To study quinidine pharmacokinetics in human subjects, a specific method for the separation and determination of quinidine, dihydroquinidine, and their metabolites is needed. Quinidine may contain u p to 20% of a natural contaminant, dihydroquinidine, depending on the source ( I ) . Dihydroquinidine is an analogue of quinidine with similar if not greater antiarrhythmic effect ( 2 , 3 ) . Drayer et al. have reported that three metabolites of quinidine found in man are pharmacologically active in mice and rabbits ( 4 ) . Until this activity, or lack thereof, is verified in humans, plasma level determinations of quinidine for the purpose of therapeutic dosage adjustment should be specific with minimal contribution from dihydroquinidine or metabolites. The analytical method commonly used to determine quinidine in plasma is that of Cramer and Isaksson (5). This method is based on extraction of alkalinized plasma samples with benzene, which excludes the more polar metabolites, and then back extraction into H2S04 for fluorimetric quantitation of t h e quinidine.However, Huynh-Ngoc and Sirios (6) have found t h a t some metabolites are being measured along with the quinidine in this method. They recommend washing the benzene layer with NaOH to eliminate interferences from less polar metabolites.Numerous chromatographic procedures have been developed for the determination of quinidine (7-19). Several of them (7-10) are specific but time-consuming TLC procedures which we did not consider suitable for routine clinical monitoring. Some of them (11, 12) have been applied only to pharmaceutical preparations. Several others (13-15) did not separate quinidine from dihydroquinidine. The method presented here provides good separation of quinidine, dihydroquinidine, and their metabolites, is sensitive enough to determine low concentrations of quinidine and dihydroquinidine, and is rapid enough for routine clinical monitoring of plasma levels. EXPERIMENTALApparatus. A Waters Model ALC202 liquid chromatograph fitted with a Model 6000 constant flow pump, a 30 cm X 3.9 mm i.d. pBondapak C18 column (Waters Associates, Milford, Mass.) and a Rheodyne Model 7120 syringe loading sample injector with a 175-pL sample loop was used. A 5 cm X 2 mm ...

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The Flora of Panama is one of the richest in the world (Schultes, 1972) as plants from South and Central America as well as from the Caribbean area can be found here. However, with the exception of research carried out by our group, the Panamanian plants have not been subjected to any form of systematic chemical or pharmacological study. As a part of our continuing interest in the unexplored National Flora, we initiated a screening program to make a preliminary selection of plants for future phytochemical studies, and to uncover new sources of phytoconstituents which may eventually be found to have biological activities. Our initial studies, reported at this time, involve screening the plant extracts for alkaloids. Plant collections were made over a period of about three years, beginning in 1973, from different parts of the country. EXPERIMENTALDrying of Plant Material. -The collected plant material was dried in a ventilated electrically heated drier at approximately 50°C. In some instances, plant material dried at room temperature was also used for making extracts. The taxonomic identity of the plant specimens was established by one of us (Mireya Correa).