Clinical Update

What Did My Patient Actually Take? Codeine Results Interpretation

Codeine is an all-natural opioid that is found in opium and is used pharmaceutically to treat mild to moderately severe pain. The interpretation of codeine and other drugs in drug testing can be complicated due to the many variables that can affect the presence of metabolites. Codeine can be metabolized to norcodeine, morphine, hydrocodone, norhydrocodone, hydromorphone, and dihydrocodeine. Furthermore, the metabolites morphine, hydrocodone, and hydromorphone are also drugs that can be prescribed (Figure 1).1 Please note that the interpretation of results differs when using presumptive vs. definitive testing methods and may also differ among laboratories. The information provided here is intended to assist providers with deciphering positive codeine results reported by Aegis, which have undergone definitive testing by liquid chromatography/tandem mass spectrometry.

Codeine Metabolism

Norcodeine, the normetabolite of codeine, is a unique biomarker that results from the CYP 3A4 metabolism of  codeine after ingestion.2 Although norcodeine possesses weak opioid activity, it is not likely to contribute to the overall analgesic effect.3-5 CYP3A4 metabolism is subject to induction and inhibition by many drug-drug and drug-food interactions, potentially altering opioid normetabolite concentrations.6-10  Drugs that inhibit or induce the CYP3A4 route of metabolism can modify the effect of opioids by increasing or decreasing analgesic effects or causing adverse drug effects such as sedation, respiratory depression, and/or death.

Morphine, hydrocodone, and hydromorphone are pharmacologically active metabolites of codeine and are products of CYP2D6 metabolism.8-11 Although CYP2D6 cannot be induced, it is subject to inhibition by a host of medications and may also become saturated. CYP2D6 also exhibits a tremendous amount of genetic variability.8,12 The clinical significance of CYP2D6 inhibition is variable and can bring about either an increase in active parent drug causing adverse drug effects such as sedation, respiratory depression, and/or death or it can lead to a decrease in active metabolite, resulting in decreased analgesic effects.

Figure 1. Opioid Metabolism

The period of detection for codeine is based on pharmacokinetic data and drug concentrations found in controlled administration studies, when available. Codeine, and most opioids, typically have a period of detection up to about 5 days in urine and up to about 48 hours in oral fluid. Typically, in oral fluid, parent drug concentrations exceed metabolite concentrations (Figure 2), whereas the reverse is true for urine. However, this is not always the case (Figure 3). Therefore, metabolite ratios should not be used to establish codeine compliance. Concentrations yielded in urine are typically ten times higher than in oral fluid.13

There is no validated algorithm that substantiates a correlation between the amount of drug ingested and the amount found in a urine drug screen. Due to the number of factors that can influence the amount of drug eliminated, there can be significant fluctuations in concentrations from test to test in the same patient, and from patient to patient on similar dosages of the same drug.  This includes, but is not limited to, concentration of the urine specimen, timing of last dose in relation to collection, frequency of dosing, amount ingested, chronicity of ingestion, extent of drug absorption, liver/kidney function, drug-drug interactions, genetic differences, etc.14,15

Codeine Minor Metabolism 

Metabolites may be present in the absence of parent drug. For example, a patient who ingests codeine could have only detectable morphine in the urine.2 Though it would be helpful for interpretation, parent to metabolite ratios do not allow for the identification of the initial opioid ingested. There is, however, one notable exception for codeine: the metabolism of codeine to hydrocodone, which will typically have a concentration of less than 5% of the codeine concentration16 and should not exceed parent drug concentrations.2 The enzymes responsible for these metabolic pathways have not been identified, and metabolism may not occur in all patients. The laboratory report example in Figure 4 demonstrates a hydrocodone metabolite concentration of 1.5% of the total codeine concentration in urine.