Morphine formation from ethylmorphine: implications for drugs-of-abuse testing in urine

In drugs-of-abuse testing, opiates constitute a delicate and controversial task because morphine may occur in urine for several reasons. Ethylmorphine (EtM), which is used as an antitussive drug in many countries, is metabolically converted to morphine. The present study was performed in order to document intra- and interindividual differences in morphine formation after single-dose intake of EtM at two different doses (25 and 50 mg). The urinary excretion of opiates was measured during 48 h with EMIT and gas chromatography-mass spectrometry in 10 healthy volunteers. The mean values of totally recovered EtM and morphine in hydrolyzed urine during 48 h were 42 and 47% of the given dose at high and low dose level, respectively. The ratio between total recovered morphine and EtM ranged from 19 to 131% with a mean value of 48%. The rate of positive outcome in the EMIT opiate-screening assay was 100% during the first 24 h for both doses, and it was still high (> or = 67%) in the 24-48 h time interval. It was found that the decline in urinary EtM is more rapid than for morphine, which leads to an increasing morphine/EtM ratio in urine over time. THe mean value of the morphine/EtM ratio was found to be greater than 1 during the 12-24 h interval and finally increased to greater than 10. There was an intra-individual concordance in morphine/EtM ratio between doses, but there was marked interindividual variation. Morphine/EtM ratios that were greater than 1 were only seen when the concentration of morphine was below 300 micrograms/mmol creatinine. Our results demonstrate that morphine is formed from EtM at a high and variable rate and may be present in urine in concentrations greater than those of EtM even shortly after drug intake.

Biotransformation and pharmacokinetics of ethylmorphine after a single oral dose

1. The pharmacokinetics of ethylmorphine after administration of a single dose of the cough mixture Cosylan were investigated in 10 healthy subjects. 2. The median urinary recovery of ethylmorphine and measured metabolites was 77% over 48 h. The median tmax of unchanged ethylmorphine was 45 min, and the terminal elimination t1/2 was 2 h. Ethylmorphine-6-glucuronide was found to be the major metabolite. 3. Two subjects had significantly lower urinary recovery (0.48 h) of morphine and morphine-glucuronides than the remainder. Furthermore, these two had urinary metabolic ratios (MRO) and partial metabolic clearances (CLmO) for O-deethylation of ethylmorphine tentatively classifying them phenotypically as poor metabolisers of the debrisoquine/sparteine type. 4. Genotyping for cytochrome P450 (CYP) 2D6 alleles revealed five homozygote (wt/wt) and five heterozygote subjects. Two subjects phenotypically classified as poor metabolisers were genotypically CYP2D6A/wt and CYP2D6D/wt, respectively. 5. Serum and urine samples taken more than 8 and 24 h after administration of ethyl-morphine respectively, contained morphine and morphine-glucuronides, but no ethylmorphine, ethylmorphine-6-glucuronide or (serum only) norethylmorphine. Norethylmorphine could be detected after hydrolysis of urine samples in all subjects. The urinary recovery of the active metabolites morphine and morphine-6-glucuronide after administration of ethylmorphine varied by a factor of 9 between individuals. 6. The wide variation in recovery of morphine and morphine-glucuronides after oral administration of ethylmorphine could not be explained simply by a difference in CYP2D6 genotype. Constitutional variation in other enzymatic pathways involved in ethylmorphine metabolism is probably crucial. Ratios of morphine to parent drug cannot be used to distinguish the source of morphine after administration of ethylmorphine. Norethylmorphine should be included in urine assays for opiates in forensic toxicology, and no firm conclusions about the source of morphine are possible based on serum samples obtained more than 24 h after drug administration.

Evidence for a role of cytochrome P450 2D6 and 3A4 in ethylmorphine metabolism

Ethylmorphine is metabolised by N-demethylation (to norethylmorphine) and by O-deethylation (to morphine). The O-deethylation reaction was previously shown in vivo to co-segregate with the O-demethylation of dextromethorphan indicating that ethylmorphine is a substrate of polymorphic cytochrome P450(CYP)2D6. To study further the features of ethylmorphine metabolism we investigated its N-demethylation and O-deethylation in human liver microsomes from eight extensive (EM) and one poor metaboliser (PM) of dextromethorphan. Whereas N-demethylation varied only two-fold there was a 4.3-fold variation in the O-deethylation of ethylmorphine, the lowest rate being observed in the PM. Quinidine, at a concentration of 1 microM, inhibited O-deethylation in microsomes from an EM, but was unable to do so in microsomes from the PM. The immunoidentified CYP2D6 and CYP3A4 correlated with the rates of O-deethylation (r = 0.972) and N-demethylation (r = 0.969), respectively. We conclude that the O-deethylation of ethylmorphine is catalysed by the CYP2D6 in human liver microsomes consistent with previous findings in healthy volunteers.

Selective changes in oxidative xenobiotic metabolism in vivo and in vitro after parenteral administration of recombinant bovine somatotrophin to rats

Effects of recombinant bovine somatotrophin (rBST) on in vivo and in vitro oxidative drug metabolism were studied in male rats. rBST was given subcutaneously at a dose of 250 or 500 micrograms 100 g-1 bodyweight 24 h-1 in different dosage patterns. Sulphadimidine (SDD) plasma clearance, urinary excretion of 6-hydroxy-SDD and the in vitro microsomal SDD-hydroxylations were only inhibited when rBST was given in three injections per 24 hours. The hepatic microsomal ethylmorphine N-demethylation rate and the testosterone hydroxylation rate at the 6 beta position were significantly reduced after one rBST injection per 24 hours. Microsomal testosterone hydroxylation rates at the 16 alpha and 2 alpha-positions were reduced depending on the frequency of rBST administration. It is concluded that the inhibition of in vivo and in vitro drug oxidation in rats by rBST is associated with selective changes in activity of cytochrome P450 enzymes in the liver.

Depression of hepatic glutathione by opioid analgesic drugs in mice

The ability of morphine and other opioid analgesic drugs to diminish hepatocellular glutathione (GSH) concentrations was examined in ICR mice. When administered intraperitoneally, morphine, hydromorphone, ethylmorphine, l-alpha-acetylmethadol (LAAM), and meperidine all caused a significant decrease in hepatic GSH concentrations in male mice while codeine, methadone, butorphanol, nalbuphine, and pentazocine were without effect even at doses up to those approaching acute lethality. Depression of hepatic GSH equivalent to that observed after ip administration could be elicited by icv administration of small doses of morphine, ethylmorphine, and hydromorphone. LAAM and meperidine were ineffective following icv administration in these experiments. The discrepancy between results following ip versus icv administration of LAAM and meperidine suggests that hepatic metabolism of some opioids may be important for their activity in the CNS, as both norLAAM and normeperidine diminished hepatic GSH when administered by the icv route. The opioid-induced lowering of hepatic GSH does not appear to be sex-dependent since morphine and LAAM produced qualitatively and quantitatively similar effects on hepatic GSH in female mice. Morphine administered icv produced a substantial increase in the hepatotoxicity of two compounds dependent upon GSH for detoxification, acetaminophen and cocaine, as measured by serum alanine aminotransferase activities. These observations indicate that a number of opioid analgesic drugs have the potential to diminish hepatic GSH. Further, these results support earlier studies which indicate that central opioid effects on hepatic GSH are mediated through mu-opioid receptor stimulation. Last, these studies suggest that a centrally initiated opioid action on hepatic GSH may significantly influence the susceptibility of the liver to the effects of some hepatotoxic agents.

Analgesic efficacy and tolerability of diflunisal in oral surgery

A double-blind, completely randomized study was carried out on 169 patients to compare the analgesic efficacy and tolerability of diflunisal with that of Veralgin after surgical removal of impacted third molars. One group received 1000 mg diflunisal (Donobid, MSD) 2 h preoperatively and then 500 mg twice daily for 2.5 days, and the other group Veralgin (aminophenazon. 286 mg, barbital. 114 mg, aethylmorph. hydrochlorid. 20 mg, Orion), a fixed combination widely used in Finland, 1 tablet twice daily beginning 2 h prior to operation. Visual analogue scales were used to estimate pain. Diflunisal was found to be superior in relieving pain in the early postoperative period, the associated frequency of adverse clinical experiences was lower and the final evaluation of analgesic efficacy by both the patients and the investigators, was in its favour. The study confirms that postoperative pain after third molar surgery can be controlled well without the use of mainly centrally acting combination analgesics.