Quantitative determination of piritramide in human serum applying liquid chromatography-two-stage mass spectrometry

Quantification of piritramide in human colostrum

WHAT IS KNOWN AND OBJECTIVE

In our university hospital (UZBrussel), one of the options to control post-operative pain after a Caesarean section under general anaesthesia is to administer piritramide by patient-controlled intravenous analgesia (PCIA). As no information is available about the possible transfer of this synthetic narcotic analgesic into breastmilk, women are frequently advised not to breastfeed their newborn. A sensitive liquid chromatographic (LC) method coupled with UV detection will therefore be developed and validated for the quantification of piritramide in colostrum samples to evaluate the presence of the analgesic in the first milk.

METHODS

The method included the isolation and concentration of piritramide from colostrum using protein precipitation and solid-phase extraction (SPE) using a mixed-mode cation exchange sorbent. Subsequently, the extracted samples were analysed on a microbore C₁₈ column (1 mm id) and a mobile phase consisting of 15 mm ammonium hydroxide in methanol/tetrahydrofuran/water 50 : 10 : 40 V/V/V.

RESULTS AND DISCUSSION

As colostrum contains a high amount of proteins, mixed-mode cation exchange SPE was preceded by a 1 : 2 dilution and protein precipitation with phosphoric acid followed by double centrifugation of the samples. The reversed-phase LC-UV method used a mobile phase at alkaline pH to obtain a selective method for piritramide and the internal standard pipamperone. After investigating the validation characteristics (linearity, accuracy, precision and stability), samples from ten patients who had received piritramide via PCIA during the first 48 h post-partum were analysed.

WHAT IS NEW AND CONCLUSION

To the best of our knowledge, this is the first method described for the quantification of the synthetic narcotic analgesic piritramide in colostrum samples. The obtained results suggest that after the administration of this opioid by PCIA to nursing mothers low concentrations of piritramide can be found in the first milk, but are mostly below the limit of quantification of 30 ng/mL.

Stability of analytes in biosamples - an important issue in clinical and forensic toxicology?

Knowledge of the stability of drugs in biological samples is important for the interpretation of toxicological findings. This paper reviews data on the stability of drugs in blood, plasma, or serum. Since such data have already been reviewed for classic drugs of abuse, the focus here is on newer drugs of abuse and on therapeutic drugs. Key information about the conditions of the stability experiments will be provided and the following drugs or drug classes are covered: amphetamines, amphetamine-derived, piperazine-derived, and phenethylamine-derived designer drugs, antidepressants, neuroleptics, anti-HIV drugs, antiepileptics, cardiovascular drugs, and others. In addition, aspects of stability experiments and their evaluations are discussed. The data presented show that the majority of drugs are stable in blood, plasma, or serum samples under the conditions usually encountered in a clinical or forensic toxicology laboratory. Instability usually only occurs for drugs carrying ester moieties, sulfur atoms, or other easily oxidized or reduced structures. Nevertheless, clinical or forensic specimens should always be stored at least in the refrigerator and preferably at -20 degrees C or lower to avoid any degradation. Finally, results obtained from biosamples that have been stored at room temperature for a longer time should be interpreted with great care and partial degradation should always be considered.

An automated and fully validated LC-MS/MS procedure for the simultaneous determination of 11 opioids used in palliative care, with 5 of their metabolites

A fully validated liquid chromatographic procedure coupled with electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) is presented for quantitative determination of the opioids buprenorphine, codeine, fentanyl, hydromorphone, methadone, morphine, oxycodone, oxymorphone, piritramide, tilidine, and tramadol together with their metabolites bisnortilidine, morphine-glucuronides, norfentanyl, and nortilidine in blood plasma after an automatically performed solid-phase extraction (SPE). Separation was achieved in 35 min on a Phenomenex C12 MAX-RP column (4 microm, 150 x 2 mm) using a gradient of ammonium formiate buffer (pH 3.5) and acetonitrile. The validation data were within the required limits. The assay was successfully applied to authentic plasma samples, allowing confirmation of the diagnosis of overdose situations as well as monitoring of patients' compliance, especially in patients under palliative care.

Pharmacokinetics of piritramide in newborns, infants and young children in intensive care units

Piritramide is indicated for treatment of postoperative pain and analgosedation in the intensive care unit (ICU) setting. In an open prospective study the pharmacokinetics of piritramide were investigated in four groups: newborns (NB, age: 1-28 days) (n=8), infants 1 (IF1, age: 2-4 months) (n=7), infants 2 (IF2, age: 5-12 months) (n=14) and young children (YC, age: 2-4 years) (n=10). The recommended paediatric dose range for therapy of postoperative pain is 50-200 microg/kg. Piritramide was administered intravenously as a single dose by bolus injection of 50 microg/kg. Blood samples were collected at 0, 15, 45, 90 min and 3, 6, 9, 12 h after application, and urine samples were collected before application and during the following intervals: 1-2, 2-6, 6-12 h. Piritramide was measured in blood and urine by HPLC-ESI-MS. The following pharmacokinetic parameters: maximum plasma concentration (C(max)), distribution half-life (t 1/2 alpha), elimination half-life (t 1/2 beta), total clearance (Cl(t)) and median volume of distribution at equilibrium (Vd(ss)) were calculated using a non-compartment and a two-compartment model for the disposition of piritramide (TOPFIT and NONMEM-pharmacokinetic analysis). Newborns (NB) showed the highest maximum plasma concentrations (median+/-SD) C(max) (79+/-240 microg/l) compared to the other three groups (IF1 36+/-367, IF2 12+/-81 and YC 16+/-9 microg/l) without statistical significance. The median elimination half-lives (t 1/2 beta) were 702+/-720 min in NB, 157+/-102 min in IF1, 160+/-68 min in IF2 and 166+/-143 min in YC. For t 1/2 beta the difference between NB and the other three groups (IF1, IF2 and YC) was statistically significant (Mann-Whitney-U, P<0.05). Cl(t) was 15.9+/-16.7, 46.6+/-76.9, 235.5+/-454.1 and 338+/-168.1 ml/min in NB, IF1, IF2 and YC respectively. The total clearance increased exponentially with an elimination half-life of 702 min from 15.9 ml/min in NB to 46.6 ml/min in IF2. Differences between the NB/IF1 groups and IF2/YC groups were significantly significant (NB vs. IF2, NB vs. YC, IF1 vs. IF2 and IF1 vs. YC). Vd(ss) was 2.0+/-4.93, 1.7+/-2.5, 7.0+/-5.2 and 6.7+/-2.2 l/kg in NB, IF1, IF2 and YC respectively. In comparison to group IF1 the Vd(ss) was significantly larger in groups IF2 and YC (Mann-Whitney U, P<0.05). Newborns showed a high initial concentration and a distinct prolongation of the elimination half-life of piritramide compared to infants, young children and adults. Therefore, dosage needed to treat postoperative pain should be reduced, and the repetitive doses should be geared to the analgesic effects. In infants and young children the elimination of piritramide is increased compared to adults; therefore the duration of the effects of piritramide will be shortened, and dose intervals ought to be reduced. Subsequent clinical trials for detailed dose adjustment of piritramide in paediatric patients comparing pharmacokinetics and effectiveness are needed.

Quantitative determination of piritramide in human plasma and urine by off- and on-line solid-phase extraction liquid chromatography coupled to tandem mass spectrometry

A method for the liquid chromatography/tandem mass spectrometric (LC/MS/MS) quantification of piritramide, a synthetic opioid, in plasma after conventional off-line solid-phase extraction (SPE) and in urine by on-line SPE-LC/MS/MS in positive electrospray mode was developed and validated. Applicability of the on-line approach for plasma samples was also tested. Deuterated piritramide served as internal standard. For the off-line SPE plasma method mixed cation-exchange SPE cartridges and a 150 x 2 mm C18 column with isocratic elution were used. For the on-line SPE method, a Waters Oasis HLB extraction column and the same C18 analytical column in a column-switching set-up with gradient elution were utilized. All assays were linear within a range of 0.5-100 ng/mL with a limit of detection of 0.05 ng/mL. The intra- and interday coefficients of variance ranged from 1.3 to 6.1% for plasma and 0.5 to 6.4% for urine, respectively. The extraction recovery for the off-line plasma assay was between 90.7 and 100.0%. Influence of matrix effects, and freeze/thaw and long-term stability were validated for both approaches; influence of urine pH additionally for quantification in urine.

Death during patient-controlled analgesia: piritramide overdose and tissue distribution of the drug

We report about a fatality during patient-controlled analgesia (PCA). Piritramide peripheral blood concentration was measured with 0.1 mg/l and exceeded the normal therapeutic range. Therefore, a fatal overdose was considered as the cause of death with respiratory depression as the underlying pathophysiological mechanism. The tissue distribution was studied; highest concentrations of piritramide were measured in kidney, bile and urine. Due to a large volume of distribution a difference in the drug concentration found in heart and peripheral bloods the phenomenon of drug redistribution was observed. Confronted with toxicological results, investigations revealed, that the PCA pump had been changed during a previous servicing from displaying mg/h to ml/h, therefore, the anesthetist had entered "1.5" assuming mg/h, but actually applying 1.5 ml/h (which was therefore equivalent to 2.25 mg/h, given a concentration in the cartridge of 1.5 mg piritramide/ml). In total, 61.5 ml (instead of 61.5 mg) had been infused, equivalent to 92.25 mg piritramide. This case report is a further example that human errors can play a crucial role in the safety of medical equipment. Experts in anesthesia recommended human factors engineering design principles to improve the safety of medical devices.