Pharmacological Aspects of Over-the-Counter Opioid Drugs Misuse

Several over-the-counter (OTC) drugs are known to be misused. Among them are opioids such as codeine, dihydrocodeine, and loperamide. This work elucidates their pharmacology, interactions, safety profiles, and how pharmacology is being manipulated to misuse these common medications, with the aim to expand on the subject outlined by the authors focusing on abuse prevention and prevalence rates. The reviewed literature was identified in several online databases through searches conducted with phrases created by combining the international non-proprietary names of the drugs with terms related to drug misuse. The results show that OTC opioids are misused as an alternative for illicit narcotics, or prescription-only opioids. The potency of codeine and loperamide is strongly dependent on the individual enzymatic activity of CYP2D6 and CYP3A4, as well as P-glycoprotein function. Codeine can also be utilized as a substrate for clandestine syntheses of more potent drugs of abuse, namely desomorphine (“Krokodil”), and morphine. The dangerous methods used to prepare these substances can result in poisoning from toxic chemicals and impurities originating from the synthesis procedure. OTC opioids are generally safe when consumed in accordance with medical guidelines. However, the intake of supratherapeutic amounts of these substances may reveal surprising traits of common medications.

[Message from the President of the Japanese Society for the Study of Xenobiotics]

The Japanese Society for the Study of Xenobiotics has focused on drug development and clinical pharmacotherapy by applying cutting-edge technology and reviewing drugs. One specific area of focus has been the reverse-translational approach. This approach uses data from the investigation of clinical problems and from the detailed revisiting of preclinical studies to discover new pharmacotherapies and new methods to prevent drug-induced side effects. In 2017, the U.S. Food and Drug Administration restricted the use of prescription codeine cough-and-cold medicines in children. This decision was based on concerns about the effects of the extensive metabolite morphine in cytochrome P450 2D6 ultra-rapid metabolizers. However, there are few reports on the side effects of dihydrocodeine in Japanese children. Our laboratory measured serum concentrations of dihydrocodeine in a 1-month-old infant with respiratory depression who was given dihydrocodeine phosphate in a suspected case of overdosing. Levels of dihydrocodeine and its primary metabolite, dihydromorphine, were high in this infant. However, the molar ratios of glucuronide conjugates of dihydrocodeine and dihydromorphine were lower than those found in a 3-year-old and a 6-year-old child used as references. To support and facilitate reverse-translational research, the elimination of regional differences in the methodologies used for liquid chromatography to measure drug concentrations and for the genotyping of drug-metabolizing enzymes should become the focus in hospitals, laboratories, and doctoral programs.

Dihydrocodeine: safety concerns

Dihydrocodeine (DHC) is a semi-synthetic analogue of codeine, which was formed by the hydrogenation of the double tie in the main chain of the codeine molecule - instead of a double bond between carbons 7 and 8 DHC possesses a single bond. DHC is used as an analgesic and antitussive agent and for the management of dyspnea and opioid addiction. Limited data is available on the potency of DHC to other opioids. The analgesic effect of DHC is similar to codeine and approximately twice as potent as tramadol for an oral route. In contrast to codeine and tramadol, DHC analgesia seem to be irrespective of CYP2D6 activity due to parent compound analgesic effects, multiple metabolic pathways and limited role of dihydromorphine in DHC analgesia. As the drug is commonly available appropriate titration and dosing and knowledge of its metabolism and possible adverse effects are important for safe prescription of DHC.

Dihydrocodeine/Agonists for alcohol dependents

OBJECTIVE

Alcohol addiction too often remains insufficiently treated. It shows the same profile as severe chronic diseases, but no comparable, effective basic treatment has been established up to now. Especially patients with repeated relapses, despite all therapeutic approaches, and patients who are not able to attain an essential abstinence to alcohol, need a basic medication. It seems necessary to acknowledge that parts of them need any agonistic substance, for years, possibly lifelong. For >14 years, we have prescribed such substances with own addictive character for these patients.

METHODS

We present a documented best possible practice, no designed study. Since 1997, we prescribed Dihydrocodeine (DHC) to 102 heavily alcohol addicted patients, later, also Buprenorphine, Clomethiazole (>6 weeks), Baclofen, and in one case Amphetamine, each on individual indication. This paper focuses on the data with DHC, especially. The Clomethiazole-data has been submitted to a German journal. The number of treatments with the other substances is still low.

RESULTS

The 102 patients with the DHC treatment had 1367 medically assisted detoxifications and specialized therapies before! The 4 years-retention rate was 26.4%, including 2.8% successfully terminated treatments. In our 12-steps scale on clinical impression, we noticed a significant improvement from mean 3.7 to 8.4 after 2 years. The demand for medically assisted detoxifications in the 2 years remaining patients was reduced by 65.5%. Mean GGT improved from 206.6 U/l at baseline to 66.8 U/l after 2 years. Experiences with the other substances are similar but different in details.

CONCLUSION

Similar to the Italian studies with GHB and Baclofen, we present a new approach, not only with new substances, but also with a new setting and much more trusting attitude. We observe a huge improvement, reaching an almost optimal, stable, long term status in around 1/4 of the patients already. Many further optimizations are possible.

Deaths of opiate/opioid misusers involving dihydrocodeine, UK, 1997-2007

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Dihydrocodeine (DHC) is an opioid analgesic sometimes prescribed as an alternative to other medications (e.g. methadone and buprenorphine) for opioid misuse. Its effectiveness is, however, still controversial. DHC prescription rates seem to be related to levels of DHC fatalities, possibly in relation to levels of disregard of the availability of supervised or interval dispensing of opioids, but no large-scale analysis of DHC fatalities has been carried out. We analysed here involvement of DHC in fatalities that occurred between 1997 and 2007 among individuals with a history of opiate/opioid misuse reported to the National Programme on Substance Abuse Deaths (np-SAD).

WHAT THIS STUDY ADDS

DHC, either alone or in combination, was identified in 584 fatalities. Typical cases identified were males in their early thirties. In accidental overdoses, DHC, which had been prescribed to 45% of the victims, was typically identified in combination with other drugs, such as heroin/morphine, methadone and hypnotics/sedatives. Both paracetamol and antidepressants were more typically identified in combination with DHC in suicides. Opiate/opioid misusers should be educated about risks associated with polydrug intake and prescribers should carefully consider a pharmacological intervention alternative to DHC (e.g. methadone, buprenorphine) when managing and treating opiate addiction.

AIMS

Although its effectiveness is somewhat controversial, it appears that dihydrocodeine (DHC) is still prescribed in the UK as an alternative to both methadone and buprenorphine for the treatment of opiate addiction.

METHODS

Data covering the period 1997-2007 voluntarily supplied by coroners were analysed. All cases pertaining to victims with a clear history of opiate/opioid misuse and in which DHC, either on its own or in combination, was identified at post-mortem toxicology and/or implicated in death, were extracted from the database.

RESULTS

Dihydrocodeine, either alone or in combination, was identified in 584 fatalities meeting the selection criteria. In 44% of cases it was directly implicated in the cause of death. These cases represented about 6.8% of all opiate/opioid-related deaths during this period. Typical DHC cases identified were White males in their early thirties. Accidental deaths (96%) were likely to involve DHC in combination with other psychoactives, mainly heroin/morphine, hypnotics/sedatives and methadone. Both paracetamol and antidepressants were found in proportionately more suicide cases than in accidental overdoses. DHC had been prescribed to the decedent in at least 45% of cases.

CONCLUSIONS

Opiate/opioid misusers should be educated about risks associated with polydrug intake. More in particular, co-administration of DHC with heroin, methadone and benzodiazepines may increase the risk of accidental fatal overdose. Prescribers should carefully consider pharmacological intervention alternative to DHC (e.g. methadone, buprenorphine) when managing and treating opiate addiction. More resources are required to do prospective research in this area.

Mass Spectra and Cross-Contribution of Ion Intensity Between Drug Analytes and Their Isotopically Labelled Analogs - Common Opioids and Their Derivatives

For the quantitation of most drugs and their metabolites, GC-MS is currently the preferred method and isotopically labeled analogs of the analytes are the internal standards (ISs) of choice. Under this analytical setting, chemical derivatization (CD) plays a critical role in the sample preparation process. In addition to meeting the conventional objectives of CD, products derived from the selected CD method must generate ions suitable for designating the analyte and the IS; these ions cannot have significant cross-contribution (CC), i.e., contribution to the intensity of the ions designating the analyte by the IS, and vice versa. With this in mind, the authors have reviewed literature and information provided by manufacturers, searching for suitable CD reagents, CD methods, and isotopically labeled analogs of the analytes related to the following 11 opioids: heroin, 6-acetylmorphine, morphine, hydromorphone, oxymorphone, 6-acetylcodeine, codeine, hydrocodone, dihydrocodeine, oxycodone, and noroxycodone. These analytes and ISs were derivatized with various derivatization groups, followed by GCMS analysis. The resulting MS data are systematically presented in two forms: (a) full-scan mass spectra; and (b) CC data of ion-pairs with potential for designating the analytes and their respective ISs. Many (if not most) of these full-scan mass spectra are not yet available in the literature and should be of reference value to laboratories engaged in the analysis of these drugs/metabolites. Full-scan MS data were further used to select ion-pairs with potential for designating the analytes and ISs in quantitative analysis protocols. The CC data of these ion-pairs were evaluated using data collected in selected ion monitoring mode and systematically tabulated, readily available for analysts searching for this important analytical parameter.

Contribution of dihydrocodeine and dihydromorphine to analgesia following dihydrocodeine administration in man: a PK-PD modelling analysis

AIMS

It is not clear whether the analgesic effect following dihydrocodeine (DHC) administration is due to either DHC itself or its metabolite, dihydromorphine (DHM). We examined the relative contribution of DHC and DHM to analgesia following DHC administration in a group of healthy volunteers using a PK-PD link modelling approach.

METHODS

A single oral dose of DHC (90 mg) was administered to 10 healthy volunteers in a randomised, double-blind, placebo-controlled study. A computerized cold pressor test (CPT) was used to measure analgesia. On each study day, the volunteers performed the CPT before study medication and at 1.25, 2.75, 4.25 and 5.75 h postdose. Blood samples were taken at 0.25 h (predose) and then at half hourly intervals for 5.75 h postdose. PK-PD link modelling was used to describe the relationships between DHC, DHM and analgesic effect.

RESULTS

Mean pain AUCs following DHC administration were significantly different to those following placebo administration (P = 0.001). Mean pain AUC changes were 91 score x s(-1) for DHC and -17 score x s(-1) for placebo (95% CI = +/- 36.5 for both treatments). The assumption of a simple linear relationship between DHC concentration and effect provided a significantly better fit than the model containing DHM as the active moiety (AIC = 4.431 vs 4.668, respectively). The more complex models did not improve the likelihood of model fits significantly.

CONCLUSIONS

The findings suggest that the analgesic effect following DHC ingestion is mainly attributed to the parent drug rather than its DHM metabolite. It can thus be inferred that polymorphic differences in DHC metabolism to DHM have little or no effect on the analgesic affect.

Pharmacokinetics of dihydrocodeine and its active metabolite after single and multiple oral dosing

AIMS

The pharmacokinetics of dihydrocodeine (DHC) and its active metabolite dihydromorphine (DHM) were assessed after a single oral dose of DHC and after increasing doses of DHC at steady-state. Methods Twelve healthy male volunteers (18-45 years, CYP2D6 extensive metabolizers (EMs), MR<1 took a single oral dose (s.d.) of DHC 60 mg after breakfast. After 60 h DHC 60 mg was administered twice daily for 3 days, the dose was increased to 90 mg twice daily for 3 days, the final dose of 120 mg was administered twice daily for 3 days (multiple dose: m.d.). Blood sampling and urine collection: during 60 h after s.d. and during 12 h after m.d. Results No significant differences in the area under the curve (AUC) of both, DHC and DHM could be detected after a single oral dose of 60 mg DHC (AUC (0,infinity)) and during steady-state doses of 60 mg DHC (AUC(0,12 h)). During increasing steady-state doses of DHC, the data showed a dose linearity of AUC, maximal serum concentration (Cmax ) and minimal steady-state serum levels (Cssmin) of both, DHC and DHM (P<0.0001), point estimates of DHC dose corrected AUCs were well within the bioequivalence range (60 mg: 0.989; 90%CI 0.951-1. 028, 90 mg: 0.997; 90%CI 0.959-1.036, 120 mg: 0.977; 90%CI 0.940-1. 016). O-demethylation from DHC to DHM remained constant within the increasing steady-state doses of DHC in the 12 extensive metabolizers of CYP2D6.

CONCLUSIONS

In the studied dose range (60-120 mg) the pharmacokinetics of DHC and its active metabolite DHM are linear in EMs of CYP2D6.

The visceral and somatic antinociceptive effects of dihydrocodeine and its metabolite, dihydromorphine. A cross-over study with extensive and quinidine-induced poor metabolizers

AIMS

Dihydrocodeine is metabolized to dihydromorphine via the isoenzyme cytochrome P450 2D6, whose activity is determined by genetic polymorphism. The importance of the dihydromorphine metabolites for analgesia in poor metabolizers is unclear. The aim of this study was to assess the importance of the dihydromorphine metabolites of dihydrocodeine in analgesia by investigating the effects of dihydrocodeine on somatic and visceral pain thresholds in extensive and quinidine-induced poor metabolizers.

METHODS

Eleven healthy subjects participated in a double-blind, randomized, placebo-controlled, four-way cross-over study comparing the effects of single doses of placebo and slow-release dihydrocodeine 60 mg with and without premedication with quinidine sulphate 50 mg on electrical, heat and rectal distension pain tolerance thresholds. Plasma concentrations and urinary excretion of dihydrocodeine and dihydromorphine were measured.

RESULTS

In quinidine-induced poor metabolizers the plasma concentrations of dihydromorphine were reduced between 3 and 4 fold from 1.5 h to 13.5 h after dosing (P < 0.005) and urinary excretion of dihydromorphine in the first 12 h was decreased from 0.91% to 0.28% of the dihydrocodeine dose (P < 0.001). Dihydrocodeine significantly raised the heat pain tolerance thresholds (at 3.3 h and 5 h postdosing, P < 0.05) and the rectal distension defaecatory urge (at 3.3 h and 10 h postdosing, P < 0.02) and pain tolerance thresholds (at 3.3 h and 5 h postdosing, P < 0.05) compared with placebo. Premedication with quinidine did not change the effects of dihydrocodeine on pain thresholds, but decreased the effect of dihydrocodeine on defaecatory urge thresholds (at 1.5 h, 3.3 h and 10 h postdosing, P < 0.05).

CONCLUSIONS

In quinidine-induced poor metabolizers significant reduction in dihydromorphine metabolite production did not result in diminished analgesic effects of a single dose of dihydrocodeine. The metabolism of dihydrocodeine to dihydromorphine may therefore not be of clinical importance for analgesia. This conclusion must however, be confirmed with repeated dosing in patients with pain.

Characterization of the human cytochrome P450 enzymes involved in the metabolism of dihydrocodeine

AIMS

Using human liver microsomes from donors of the CYP2D6 poor and extensive metabolizer genotypes, the role of individual cytochromes P-450 in the oxidative metabolism of dihydrocodeine was investigated.

METHODS

The kinetics of formation of N- and O-demethylated metabolites, nordihydrocodeine and dihydromorphine, were determined using microsomes from six extensive and one poor metabolizer and the effects of chemical inhibitors selective for individual P-450 enzymes of the 1A, 2A, 2C, 2D, 2E and 3A families and of LKM1 (anti-CYP2D6) antibodies were studied.

RESULTS

Nordihydrocodeine was the major metabolite in both poor and extensive metabolizers. Kinetic constants for N-demethylation derived from the single enzyme Michaelis-Menten model did not differ between the two groups. Troleandomycin and erythromycin selectively inhibited N-demethylation in both extensive and poor metabolizers. The CYP3A inducer, alpha-naphthoflavone, increased N-demethylation rates. The kinetics of formation of dihydromorphine in both groups were best described by a single enzyme Michaelis-Menten model although inhibition studies in extensive metabolizers suggested involvement of two enzymes with similar Km values. The kinetic constants for O-demethylation were significantly different in extensive and poor metabolizers. The extensive metabolizers had a mean intrinsic clearance to dihydromorphine more than ten times greater than the poor metabolizer. The CYP2D6 chemical inhibitors, quinidine and quinine, and LKM1 antibodies inhibited O-demethylation in extensive metabolizers; no effect was observed in microsomes from a poor metabolizer.

CONCLUSIONS

CYP2D6 is the major enzyme mediating O-demethylation of dihydrocodeine to dihydromorphine. In contrast, nordihydrocodeine formation is predominantly catalysed by CYP3A.