Bull. Org. mond. Sante 1 1962, 26, 51-66 Bull. Wld Hlth Org. The Biological Disposition of Morphine and its Surrogates--2 * E. LEONG WAY, Ph.D.' & T. K. ADLER, Ph.D.' CONTENTS DERIVATIVES OF MORPHINE . 51 Codeine. ................ 51 Heroin. ................ 59 Dihydro-derivatives ............... 62 Nalorphine ................. 63 REFERENCES................. 65 DERIVATIVES OF MORPHINE CODEINE various solvents which have been used to extrac the alkaloid from biological media include a chloro Small concentrations of codeine are found in opium form-ethanol mixture (Oberst, 1941), benzene but commercial supplies are commonly obtained (Adler & Latham, 1950), a chloroform/isoamyl- by chemical conversion of the more abundant alcohol mixture (Axelrod, 1955) and ethylene morphine. Although codeine has been widely used dichloride (Woods, Muehlenbeck & Mellett, 1956). in therapeutics for many years, it is only compara- None of these solvents is specific for codeine tively recently that there has been any elucidation since they all extract alkaloid metabolites as well as of its biological disposition. other interfering substances normally found in Methods of estimation biological material. Consequently, the validity of codeine estimation depends on one of two ap- Codeine (3-methylmorphine) is a strong mono- proaches: (a) effecting a chemical reaction which is acid base (pka = 8.22 or 8.55) (Farmilo, Oestreicher specific for codeine in the presence of extracted & Levi, 1954; Beckett, 1956) which is sparingly contaminating substances, or (b) producing condi- soluble in water and easily extracted from alkaline tions which segregate codeine prior to reaction with aqueous solutions by many organic solvents. The a non-specific reagent. The former approach has had limited use and has consisted in the formation * This study on the biological disposition of morphine of either the insoluble codeine silicotungstate, which and its surrogates is being published in the Bulletin of the has been measured gravimetrically (Oberst, 1940), World Health Organization in four instalments. The first or instalment was devoted to morphine per se (Bull. Wld Hlth the equally insoluble silicomolybdate, which Org., 1961, 25, 227). This-the second-deals with deriva- has been measured nephelometrically (Adler & tives of morphine. The third will deal with synthetic surro- Shaw, 1952). The disadvantage of this approach gates of morphine and the final instalment will discuss general considerations. The four instalments will eventually lies in the fact that considerable coprecipitation be available as a joint reprint. with the normally soluble morphine complex 1 Department of Pharmacology, University of California occurs in the presence of large amounts of codeine Medical Center, San Francisco, Calif., USA. The authors were aided in their preparation of this report respectively (Adler & Shaw, 1952). by Grant RG-1839 from the National Institutes of Health It is the second of these approaches that has been and by Senior Research Fellowship SF 271 from the Public Health Service, US Department of Health, Education and used by most workers, and methods for the separa- Welfare. tion of codeine include column adsorption (Stol- 1085 -51- 52 E. LEONG WAY & T. K. ADLER man & Stewart, 1949), paper partition chromato- Absorption graphy (Latham & Elliott, 1950; Mannering, Dixon, Data on the relative effectiveness of codeine when Baker & Asami, 1954; Takemori & Mannering, administered by different routes do not necessarily 1958), differential extraction of extraneous com- supply a valid basis for interpretation in terms of pounds by a series of buffer washes of the alkaline absorption, since by these tests poor absorption solvent (Adler & Latham, 1950; Latham & Elliott, cannot be distinguished from good absorption 1950; Woods, Muehlenbeck & Mellett, 1956) and coupled with rapid metabolic inactivation. The counter-current distribution (Adler, 1952; Miller quantitative studies of the absorption of codeine & Elliott, 1955; Adler, Fujimoto, Way & Baker, suggest that it is absorbed as well as, and in some 1955). The use of an alkaloid reagent spray (Manner- instances better than, morphine. The diminished ing, Dixon, Baker & Asami, 1954) or of tracer polarity at the 3-position may favour absorption methods (with 14C-labelled codeine) (Latham & when the drug is given by mouth. In man, after a Elliott, 1950) in conjunction with paper chromato- single oral dose of 22 mg the 24-hour urinary graphy has provided semiquantitative information. excretion of codeine and metabolites ranged bet- Quantitative results have been obtained by tracer ween 63% and 86% of the dose and was not methods in conjunction with counter-current distri- much different from that observed after intra- bution (Miller & Elliott, 1955). However, the most muscular injection of the same dose (Adler, Fuji- popular method for quantitative estimation involves moto, Way & Baker, 1955). Oral absorption of the formation of a codeine-dimethylaminoazo- larger or subsequent doses, however, may be poor. benzenesulfonic-acid complex which is readily Thus, in the same study, only 48% of the dose was soluble in organic solvents and easily determined recovered from the urine of a subject receiving by spectrophotometric means. This " methyl 70.5 mg every 4 hours for a period of 12 hours. orange method ", first suggested by Brodie and Rapid mobilization of the drug from the intra- Udenfriend (Brodie & Udenfriend, 1945; Brodie, muscular site in man is evidenced by the appearence Udenfriend & Dill, 1947) as a non-specific basic of 14CO2 in the breath within 15 minutes after amine reaction, has yielded quantitative results injection of 22 mg of either codeine-N-14CH3 or following isolation of codeine either by counter- codeine-04CH3 (Adler, Fujimoto, Way & Baker, current distribution (Adler, 1954; Adler, Fujimoto, 1955). With the former the general pattern of Way & Baker, 1955), buffer-wash procedure (Adler pulmonary 14CO2 resembles that seen after intra- & Latham, 1950; Latham & Elliott, 1950; Woods, muscular injection of 8 mg of morphine-N-14CH3 Muehlenbeck & Mellett, 1956) or elution from a (Elliott, Tolbert, Adler & Anderson, 1954). paper chromatogram (Takemori & Mannering, In the monkey, after subcutaneous injection of 1958). 20 mg/kg codeine maximum plasma levels of The methyl orange method is also useful for 3 ,ug/ml free codeine and 15-18 ,tg/ml bound codeine determining norcodeine concentrations, provided are found about one hour after injection (Woods, that the organic solvent is not ethylene dichloride, Muehlenbeck & Mellett, 1956). An additional in which the norcodeine-methyl-orange complex 5 ,tg/ml are found in the plasma at this time as free is relatively poorly soluble (Adler, Fujimoto, Way and bound morphine, thus bringing the total & Baker, 1955). alkaloid concentration to 23-26 ,ug/ml-or about Tracer methods involving codeine-3-04CH3 and the same concentration of alkaloids as is found in codeine-N-14CH3 have been important in establish- monkey plasma after injection of a larger (30 mg/kg) ing carbon dioxide as a metabolic product of dose of morphine (Mellett & Woods, 1956). codeine and in indicating that the carbon may In the dog peak levels of free codeine are reached originate from either the 3-methoxy (Adler & earlier and are higher than in the monkey on the Latham, 1950) or the N-methyl group (Adler, 1952). same dose, but peak levels of bound codeine are Measurement of radioactivity per se has been lower and are found later. Thus, after subcutaneous useful in tracing the distribution and routes of injection of 20 mg/kg, dog plasma rapidly attains excretion of codeine together with its metabolites a maximum concentration of 7 ,ug/ml free codeine (Latham & Elliott, 1950), but definitive information at 45 minutes; the concentration of bound codeine of codeine metabolism is provided only when tracer is about 2 ,tg/ml at this time and slowly reaches the techniques are combined with other physico- maximum of 14 ,ug/ml at 120 minutes after injection chemical methods (Adler, 1958). (Woods, Muehlenbeck & Mellett, 1956). In the dog BIOLOGICAL DISPOSITION OF MORPHINE AND ITS SURROGATES. 2 53 sublingual application of codeine required a dose N-14CH3 or codeine-04CH3 the 14C levels in the of 27-54 mg/kg to be as effective as 1 mg/kg given brain were approximately the same as those in subcutaneously (Walton & Lacey, 1935b). plasma and muscle. This contrasts sharply with The difficulties mentioned above are encountered the finding that after injection of morphine-N-14CH3 in drawing conclusions as to the absorption of the plasma and muscle 14C levels are 10-20 times codeine in the rat from the excellent study by Ercoli higher than the brain levels. Miller & Elliott (1955) & Lewis (1945) on the effectiveness of the drug when found that after 1 hour a rapid decline in 14C levels administered by subcutaneous, intraperitoneal, occurs which parallels the pharmacological activity, intravenous and oral routes. However, quantitative as measured by reaction time to a thermal stimulus. data on the absorption of that subcutaneous dose Characterization by counter-current distribution of found by Ercoli & Lewis to be effective within 30 mi- the radioactivity present in the brain 30 minutes nutes in 40-60% of their rats are provided by the after injection indicated that 99.6% of the 14C could study of Latham & Elliott (1950) on the distribution be ascribed to unaltered codeine. In these experi- of 14C after injection of 40 mg of codeine-3-O4CH3 ments peak concentrations of 14C equal to approxi- per kg in male Slonaker-Wistar rats. Recalculation mately 20 ,ug/g were reached also at 60 minutes of the figures to take into account sample size and in the liver and adrenals, the levels declining to half the contribution of blood-borne "IC taken up at the this value at 150 minutes. The kidney continued to injection site (additional data furnished by personal show a marked increase in 14C concentration with communication with the authors) shows that 73 % of time. Latham & Elliott (1950) found no decline the dose of 14C had been absorbed by 60 minutes in 14C concentration after 60 minutes when Slonaker- and 84.6% by 120 minutes after injection.