Tamoxifen pharmacokinetics and pharmacodynamics in older patients with non-metastatic breast cancer

BACKGROUND

We aimed to study the pharmacokinetics and -dynamics of tamoxifen in older women with non-metastatic breast cancer.

METHODS

Data for this analysis were derived from the CYPTAM study (NTR1509) database. Patients were stratified by age (age groups < 65 and 65 and older). Steady-state trough concentrations were measured of tamoxifen, N-desmethyltamoxifen, 4-hydroxy-tamoxifen, and endoxifen. CYP2D6 and CYP3A4 phenotypes were assessed for all patients by genotyping. Multiple linear regression models were used to analyze tamoxifen and endoxifen variability. Outcome data included recurrence-free survival at time of tamoxifen discontinuation (RFSt) and overall survival (OS).

RESULTS

668 patients were included, 141 (21%) were 65 and older. Demographics and treatment duration were similar across age groups. Older patients had significantly higher concentrations of tamoxifen 129.4 ng/ml (SD 53.7) versus 112.2 ng/ml (SD 42.0) and endoxifen 12.1 ng/ml (SD 6.6) versus 10.7 ng/ml (SD 5.7, p all < 0.05), independently of CYP2D6 and CYP3A4 gene polymorphisms. Age independently explained 5% of the variability of tamoxifen (b = 0.95, p < 0.001, R² = 0.051) and 0.1% of the variability in endoxifen concentrations (b = 0.45, p = 0.12, R² = 0.007). Older patients had worse RFSt (5.8 versus 7.3 years, p = 0.01) and worse OS (7.8 years versus 8.7 years, p = 0.01). This was not related to differences in endoxifen concentration (HR 1.0, 95% CI 0.96-1.04, p = 0.84) or CYP polymorphisms.

CONCLUSION

Serum concentrations of tamoxifen and its demethylated metabolites are higher in older patients, independent of CYP2D6 or CYP3A4 gene polymorphisms. A higher bioavailability of tamoxifen in older patients may explain the observed differences. However, clinical relevance of these findings is limited and should not lead to a different tamoxifen dose in older patients.

Genetic variants found in paediatric oncology patients with severe chemotherapy-induced toxicity: A case series

Paediatric oncology patients who develop severe chemotherapy-induced toxicity that requires dose reduction, delay or termination of treatment are at risk of decreased treatment efficacy. Previous research has provided evidence that genetic variants in TPMT, NUDT15, UGT1A1 and DPYD are associated with toxicity of anticancer drugs. This led to pharmacogenetic guidelines that are integrated into clinical practice in paediatric oncology. Recently, novel genetic variants have been associated with a higher risk of developing chemotherapy-induced toxicity. In this case series, we selected 21 novel variants and genotyped these in nine patients with excessive chemotherapy-induced toxicity using whole exome sequencing or micro-array data. We observed that six out of nine patients carried at least one variant that, according to recent studies, potentially increased the risk of developing methotrexate- or vincristine-induced toxicity. As patient-derived genetic data are becoming widely accessible in paediatric oncology, these variants could potentially enter clinical practice to mitigate chemotherapy-induced toxicity.

Effect of CYP2C19 genotypes on tamoxifen metabolism and early-breast cancer relapse

CYP2C19*2 and CYP2C19*17 might influence tamoxifen metabolism and clinical outcome. Our aim was to investigate the effect of CYP2C19 genotypes on tamoxifen concentrations and metabolic ratios (MRs) and breast cancer recurrence in a large cohort of Caucasian women. Genetic variants (CYP2D6 and CYP2C19 genotypes), tamoxifen and metabolites concentrations, baseline characteristics, and breast cancer recurrence from the CYPTAM study (NTR1509) were used. CYP2C19*2 and CYP2C19*17 genotypes were evaluated as alleles and as groups based on CYP2D6 genotypes (high, intermediate and low activity). Log-rank test and Kaplan–Meier analysis were used to evaluate differences in recurrence defined as relapse-free survival (RFS). Classification tree analyses (CTAs) were conducted to assess the levels of interactions per polymorphism (CYP2D6 and CYP2C19 genotypes) on endoxifen concentrations. No differences in mean concentrations and MRs were observed when comparing CYP2C19 genotypes (CYP2C19*1/*1; CYP2C19*1/*2; CYP2C19*2/*2; CYP2C19*1/*17; CYP2C19*17/*17; CYP2C19*2/*17). Only significant differences (p value < 0.05) in mean concentrations and MRs were observed when comparing tamoxifen activity groups (high, intermediate and low activity). A log-rank test did not find an association across CYP2C19 genotypes (p value 0.898). CTAs showed a significant relationship between CYP2D6 and endoxifen (p value < 0.0001), but no association with CYP2C19 genotypes was found. CYP2C19 polymorphisms do not have a significant impact on tamoxifen metabolism or breast cancer relapse.

Identification of pharmacogenetic biomarkers for efficacy of cytoreductive surgery plus hyperthermic intraperitoneal mitomycin C in patients with colorectal peritoneal metastases

INTRODUCTION

Mitomycin C (MMC) is commonly used in patients with colorectal peritoneal metastases (CPM) treated with cytoreductive surgery plus hyperthermic intraperitoneal chemotherapy (CRS + HIPEC). MMC requires metabolic activation prior to exert its cytotoxic effect of which the main activating enzymes are NQO1 and POR. However, not all patients are able to activate MMC for example due to polymorphisms in the genes encoding these enzymes. The aim of this study was to investigate the association of NQO1∗2, NQO1∗3, and POR∗28 with the efficacy of CRS + HIPEC with MMC in patients with CPM.

METHOD

A retrospective follow-up design was used to study genetic association in patients with histologically proven CPM treated with CRS + HIPEC with MMC with respect to peritoneal recurrence rate after 3 months (primary endpoint), after 6 months, disease-free survival and overall survival. Genetic polymorphisms NQO1∗2, NQO1∗3, and POR∗28 were tested for association.

RESULTS

A total of 253 patients were included. In NQO1∗3 carriers the peritoneal recurrence rate 3 and 6 months after HIPEC was significantly higher than in wild type patients, respectively 30.0% vs 3.8% (p = 0.009) and 40.0% vs 12.1% (p = 0.031). In line with these results, NQO1∗3 was associated with a shorter disease-free survival (HR 2.04, 95% CI [1.03-4.03]). There was no significant association with overall survival (HR 1.42, 95% CI [0.66-3.07]).

CONCLUSION

Carriership of the NQO1∗3 allele is associated with worse peritoneal recurrence rate and disease-free survival. These results suggest that individualization of patients treated with CRS + HIPEC based upon pharmacogenetics may be beneficial.

The pediatric acenocoumarol dosing algorithm: the Children Anticoagulation and Pharmacogenetics Study

Essentials A pediatric pharmacogenetic dosing algorithm for acenocoumarol has not yet been developed. We conducted a multicenter retrospective follow-up study in children in the Netherlands. Body surface area and indication explained 45.0% of the variability in dose requirement. Adding the genotypes of VKORC1, CYP2C9 and CYP2C18 to the algorithm increased this to 61.8%.

SUMMARY

Background The large variability in dose requirement of vitamin K antagonists is well known. For warfarin, pediatric dosing algorithms have been developed to predict the correct dose for a patient; however, this is not the case for acenocoumarol. Objectives To develop dosing algorithms for pediatric patients receiving acenocoumarol with and without genetic information. Methods The Children Anticoagulation and Pharmacogenetics Study was designed as a multicenter retrospective follow-up study in Dutch anticoagulation clinics and children's hospitals. Pediatric patients who used acenocoumarol between 1995 and 2014 were selected for inclusion. Clinical information and saliva samples for genotyping of the genes encoding cytochrome P450 (CYP) 2C9, vitamin K epoxide reductase complex subunit 1 (VKORC1), CYP4F2, CYP2C18 and CYP3A4 were collected. Linear regression was used to analyze their association with the log mean stable dose. A stable period was defined as three or more consecutive International Normalized Ratio measurements within the therapeutic range over a period of ≥ 3 weeks. Results In total, 175 patients were included in the study, of whom 86 had a stable period and no missing clinical information (clinical cohort; median age 8.9 years, and 49% female). For 80 of these 86 patients, genetic information was also available (genetic cohort). The clinical algorithm, containing body surface area and indication, explained 45.0% of the variability in dose requirement of acenocoumarol. After addition of the VKORC1, CYP2C9, and CYP2C18 genotypes to the algorithm, this increased to 61.8%. Conclusions These findings show that clinical factors had the largest impact on the required dose of acenocoumarol in pediatric patients. Nevertheless, genetic factors, and especially VKORC1, also explained a significant part of the variability.

Comparison of the Guidelines of the Clinical Pharmacogenetics Implementation Consortium and the Dutch Pharmacogenetics Working Group

Both the Clinical Pharmacogenetics Implementation Consortium (CPIC) and Dutch Pharmacogenetics Working Group provide therapeutic recommendations for well-known gene-drug pairs. Published recommendations show a high rate of concordance. However, as a result of different guideline development methods used by these two consortia, differences between the published guidelines exist. The aim of this paper is to compare both initiatives and explore these differences, with the objective to achieve harmonization.

Determinants of the Magnitude of Interaction Between Tacrolimus and Voriconazole/Posaconazole in Solid Organ Recipients

Administration of azole antifungals to tacrolimus-treated solid organ recipients results in a major drug-drug interaction characterized by increased exposure to tacrolimus. The magnitude of this interaction is highly variable but cannot currently be predicted. We performed a retrospective analysis of 126 solid organ recipients (95 lung, 31 kidney) co-treated with tacrolimus and voriconazole (n = 100) or posaconazole (n = 26). Predictors of the change in tacrolimus dose-corrected trough concentrations (C/D) between baseline and tacrolimus-azole co-therapy were assessed using linear mixed modeling. Patients were genotyped for relevant polymorphisms in CYP3A4, CYP3A5, MDR1, CYP2C19, POR, and UGT1A4. Tacrolimus C/D increased by a factor 5.0 ± 2.7 (range 1.0-20.2) for voriconazole and 4.4 ± 2.6 (range 0.9-18.0) for posaconazole, suggesting that a 66% dose reduction is insufficient for the majority of patients. Change in C/D was blunted in CYP3A5 expressors (estimated effect: -43%, p = 0.017) and affected by hematocrit (+8% per %, p = 0.004), baseline C/D (-14% per 100% increase, p < 0.001), and age (+1%, p = 0.008). However, the final model explained only 22% of interindividual variability in C/D change. In conclusion, CYP3A5 genotype and several clinical variables were identified as modulators of the tacrolimus-azole interaction, but these did not permit accurate predictions in individual patients.

Effect of CYP3A4*22, CYP3A5*3, and CYP3A combined genotypes on tamoxifen metabolism

Background

Tamoxifen is one of the cornerstones of endocrine therapy for breast cancer. Recently, the decreased activity CYP3A4*22 allele and the loss of function CYP3A5*3 allele have been described as potential factors that could help to explain the inter-patient variability in tamoxifen metabolism. The aim of this study is to investigate the effect of CYP3A4*22, CYP3A5*3, and CYP3A combined genotypes on tamoxifen metabolism.

Methods

DNA from 667 women enrolled in the CYPTAM study (NTR1509) was genotyped (CYP2D6, CYP3A4*22, and CYP3A5*3). Tamoxifen and metabolite concentrations were measured in serum, and metabolic ratios were calculated. The effect of the CYP3A4*22, CYP3A5*3, and CYP3A combined genotypes in addition to the CYP2D6 genotypes was examined by multiple linear regression analysis.

Results

CYP3A4*22 carriers reached significant higher concentrations of tamoxifen, N-desmethyl-tamoxifen, and 4-hydroxy-tamoxifen compared to non-carriers, whereas a tendency toward increased endoxifen levels was observed (p = 0.088). The metabolic ratio tamoxifen/N-desmethyl-tamoxifen was significantly higher in CYP3A4*22 individuals (0.59 vs. 0.52, p < 0.001). At the same time, CYP3A4*22 genotype contributed to improving the inter-variability [R² of the (log-transformed) metabolic ratio tamoxifen/N-desmethyl-tamoxifen improved from 21.8 to 23.9%, p < 0.001]. CYP3A5*3 marginally improved the explained variability of the (log transformed) metabolic ratio 4-hydroxy-tamoxifen/endoxifen (from 44.9 to 46.2%, p < 0.038).

Conclusion

Our data demonstrate that CYP3A genotype has a minor effect to explaining the variability between patients in tamoxifen metabolism and has no added value in addition to CYP2D6 genotype.

Electronic supplementary material

The online version of this article (10.1007/s00228-017-2323-2) contains supplementary material, which is available to authorized users.

Population Modeling Integrating Pharmacokinetics, Pharmacodynamics, Pharmacogenetics, and Clinical Outcome in Patients With Sunitinib-Treated Cancer

The tyrosine kinase inhibitor sunitinib is used as first‐line therapy in patients with metastasized renal cell carcinoma (mRCC), given in fixed‐dose regimens despite its high variability in pharmacokinetics (PKs). Interindividual variability of drug exposure may be responsible for differences in response. Therefore, dosing strategies based on pharmacokinetic/pharmacodynamic (PK/PD) models may be useful to optimize treatment. Plasma concentrations of sunitinib, its active metabolite SU12662, and the soluble vascular endothelial growth factor receptors sVEGFR‐2 and sVEGFR‐3, were measured in 26 patients with mRCC within the EuroTARGET project and 21 patients with metastasized colorectal cancer (mCRC) from the C‐II‐005 study. Based on these observations, PK/PD models with potential influence of genetic predictors were developed and linked to time‐to‐event (TTE) models. Baseline sVEGFR‐2 levels were associated with clinical outcome in patients with mRCC, whereas active drug PKs seemed to be more predictive in patients with mCRC. The models provide the basis of PK/PD‐guided strategies for the individualization of anti‐angiogenic therapies.

Abstract P3-07-54: Insulin-like growth factor 1 receptor expression and polymorphism are associated with response to neoadjuvant chemotherapy in breast cancer patients: Results from the NEOZOTAC trial (BOOG 2010-01)

Background

The insulin-like growth factor 1 (IGF-1) pathway is involved in cell growth, proliferation and cell cycle progression and associated with tumor genesis and therapy resistance. This study aims to elucidate whether variation in the IGF-1 pathway is predictive for pathologic response in early breast cancer (BC) patients taking part in the phase III NEOZOTAC trial, randomizing between 6 cycles of neoadjuvant TAC chemotherapy with or without zoledronic acid.

Method

Formalin-fixed paraffin-embedded (FFPE) tissue samples of pre-chemotherapy biopsies and operation specimens were collected for analysis of IGF-1 receptor (IGF-1R) expression using IHC (n=216) and for analysis of 8 candidate SNPs in genes of the IGF-1 pathway (n=184) using OpenArray® RealTime PCR. Optionally, blood samples were collected immediately before chemotherapy for determination of glucose, insulin, IGF-1, IGF-2 and IGF-BP3. Associations with patient and tumor characteristics and chemotherapy response according to Miller and Payne (MP) pathologic response were performed using chi square and logistic regression analyses.

Results

High IGF-1R expression was associated with estrogen receptor expression (P=0.001). During chemotherapy, a significant number of the tumors (47.2%) showed a decrease in IGF-1R expression, while in a small number of the tumors an upregulation was seen (15.1%). IGF-1R expression before treatment was not associated with pathological response, however absence of IGF-1R expression after treatment was associated with a better response in multivariate analyses (P=0.012) and patients with a decrease in expression during treatment showed a better response to chemotherapy as well (P=0.008). Moreover, the variant T allele of 3129G&gt;T in IGF-1R (rs2016347) was associated with a better pathological response in multivariate analyses (P=0.032). In addition, high glucose and insulin levels were associated with positive lymph node status before chemotherapy in multivariate analysis (P=0.019) and (P=0.031), respectively.

Conclusion

Neoadjuvant chemotherapy induced changes in the IGF-1R expression in most of the tumors. Absence or diminished expression of IGF-1R after treatment was associated with a better pathological response. Additionally, we found a SNP (rs2016347) in IGF-1R as a potential predictive marker for chemotherapy efficacy in BC patients treated with TAC. These findings may help to select patients who might benefit from (co-)treatment with an IGF-1 pathway inhibitor.

Citation Format: de Groot S, Charehbili A, van Laarhoven HWM, Mooyaart AL, Dekker-Ensink NG, van de Ven S, Janssen LGM, Swen JJ, Smit VTHBM, Heijns JB, Kessels LW, van der Straaten RJHM, Bhringer S, Gelderblom AJ, van der Hoeven JJM, Guchelaar HJ, Pijl H, Kroep JR. Insulin-like growth factor 1 receptor expression and polymorphism are associated with response to neoadjuvant chemotherapy in breast cancer patients: Results from the NEOZOTAC trial (BOOG 2010-01). [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-07-54.

Exploratory analysis of candidate germline gene polymorphisms in breast cancer patients treated with neoadjuvant anthracycline-containing chemotherapy and associations with febrile neutropenia

AIM

SNPs may be associated with (side) effects of chemotherapy and may be useful as biomarkers to predict febrile neutropenia.

PATIENTS & METHODS

187 DNA samples extracted from formalin-fixed paraffin-embedded tissue from patients with stage II/III HER2-negative breast cancer were genotyped.

RESULTS

Candidate SNPs were selected and explored for association with febrile neutropenia and/or pathological complete response. TT genotype of 388 C>T in FGFR4 (rs351855) had a tendency toward higher incidence of febrile neutropenia during neoadjuvant chemotherapy, compared with the CT (p = 0.383) genotype and compared with the CC genotype (p = 0.068).

CONCLUSION

The TT genotype of 388 C>T FGFR4 may be related to incidence of febrile neutropenia during neoadjuvant TAC (docetaxel, doxorubicin, cyclophosphamide) chemotherapy and is possibly useful as a patient-related risk factor when assessing febrile neutropenia risk. Original submitted 23 January 2015; Revision submitted 26 May 2015.

Clinical Pharmacogenetics Implementation Consortium (CPIC) Guidelines for CYP3A5 Genotype and Tacrolimus Dosing

Tacrolimus is the mainstay immunosuppressant drug used after solid organ and hematopoietic stem cell transplantation. Individuals who express CYP3A5 (extensive and intermediate metabolizers) generally have decreased dose-adjusted trough concentrations of tacrolimus as compared with those who are CYP3A5 nonexpressers (poor metabolizers), possibly delaying achievement of target blood concentrations. We summarize evidence from the published literature supporting this association and provide dosing recommendations for tacrolimus based on CYP3A5 genotype when known (updates at www.pharmgkb.org).

Association analysis of genetic polymorphisms in genes related to sunitinib pharmacokinetics, specifically clearance of sunitinib and SU12662

Interpatient variability in the pharmacokinetics (PK) of sunitinib is high. Single nucleotide polymorphisms (SNPs) in PK candidate genes have been associated with the efficacy and toxicity of sunitinib, but whether these SNPs truly affect the PK of sunitinib remains to be elucidated. This multicenter study involving 114 patients investigated whether these SNPs and haplotypes in genes encoding metabolizing enzymes or efflux transporters are associated with the clearance of sunitinib and its active metabolite SU12662. SNPs were tested as covariates in a population PK model. From univariate analysis, we found that the SNPs in CYP3A4, CYP3A5, and ABCB1 were associated with the clearance of both sunitinib and SU12662. In multivariate analysis, CYP3A4*22 was found to be eliminated last with an effect size of -22.5% on clearance. Observed effect sizes are below the interindividual variability in clearance and are therefore too limited to directly guide individual dosing of sunitinib.

Clinical Pharmacogenetics Implementation Consortium guidelines for dihydropyrimidine dehydrogenase genotype and fluoropyrimidine dosing

The fluoropyrimidines are the mainstay chemotherapeutic agents for the treatment of many types of cancers. Detoxifying metabolism of fluoropyrimidines requires dihydropyrimidine dehydrogenase (DPD, encoded by the DPYD gene), and reduced or absent activity of this enzyme can result in severe, and sometimes fatal, toxicity. We summarize evidence from the published literature supporting this association and provide dosing recommendations for fluoropyrimidines based on DPYD genotype (updates at http://www.pharmgkb.org).

Pharmacogenetics: from bench to byte--an update of guidelines

Currently, there are very few guidelines linking the results of pharmacogenetic tests to specific therapeutic recommendations. Therefore, the Royal Dutch Association for the Advancement of Pharmacy established the Pharmacogenetics Working Group with the objective of developing pharmacogenetics-based therapeutic (dose) recommendations. After systematic review of the literature, recommendations were developed for 53 drugs associated with genes coding for CYP2D6, CYP2C19, CYP2C9, thiopurine-S-methyltransferase (TPMT), dihydropyrimidine dehydrogenase (DPD), vitamin K epoxide reductase (VKORC1), uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1), HLA-B44, HLA-B*5701, CYP3A5, and factor V Leiden (FVL).

Interaction between nondepolarizing neuromuscular blocking agents and inhalational anesthetics

Although many studies have presented data based on administration of nondepolarizing neuromuscular blocking agents to patients given inhalation anesthesia for 30-45 min, no data exist on the interaction in a clinical situation where the relaxant is administered immediately after the start of anesthesia. We therefore studied the effect of the commonly used inhalation anesthetics, halothane and enflurane, on the clinical pharmacology of atracurium, vecuronium, pipecuronium, and pancuronium. No significant influence of the anesthetic technique on the onset time of the various neuromuscular blocking agents was observed. The duration of action of atracurium, pipecuronium, and pancuronium was significantly prolonged during enflurane anesthesia as compared with the other two anesthetic techniques. The duration of vecuronium blockade was not significantly influenced by enflurane. Halothane, in contrast to enflurane, did not significantly prolong the blockade induced by these agents. The prolongation of atracurium blockade was clinically irrelevant. A fact that is statistically significant but clinically irrelevant is that a cumulative effect with atracurium and vecuronium was only seen during enflurane anesthesia and after the fourth maintenance dose. We conclude that there is no clinical indication that the dosage of atracurium and vecuronium during inhalation anesthesia should be reduced, but the doses of pipecuronium and pancuronium should be reduced when prolonged paralysis is not desired.

Vecuronium infusion dose requirements during fentanyl and halothane anesthesia in humans

Steady-state infusion rate requirements of vecuronium were determined in 29 patients during either halothane-nitrous oxide or fentanyl-nitrous oxide anesthesia at different levels of neuromuscular block. During N2O-halothane anesthesia (end-tidal concentration, 0.5%), the infusion rate necessary for a steady-state (defined as unchanging twitch height and infusion rate for at least 20 min) 50% depression of twitch force was 28.8 +/- 5.4 (mean +/- SD) (n = 8) and 47.6 +/- 9.7 micrograms . kg-1 . hr-1 (n = 6) at 90% reduction of twitch force. During N2O-fentanyl anesthesia, the steady-state infusion rate required for 50 and 90% decrease of twitch force was 56.3 +/- 20.0 (n = 9) and 74.8 +/- 16.0 micrograms . kg-1 . hr-1 (n = 6), respectively. The variances of vecuronium steady-state infusion dose requirements were smaller in the halothane groups than in the fentanyl anesthesia groups. The steady-state vecuronium infusion dose requirements during fentanyl anesthesia were greater than the mean infusion dose requirements during halothane anesthesia at equivalent levels of twitch depression.

Hypocarbia and spontaneous recovery from vecuronium neuromuscular blockade in anesthetized patients

The effect of hypocarbia on the recovery from the neuromuscular blockade produced by vecuronium was studied in 20 anesthetized patients. Vecuronium was administered until twitch tension was reduced to between 0-15% of control. Neuromuscular function was then allowed to spontaneously recover during continued normocarbia (end-tidal PCO2 5.5 kPa [41 mm Hg]) in half the patients, and in the other half of the patients hyperventilation producing hypocarbia (mean end-tidal PCO2 of 3.1 +/- 0.4 kPa SD [23 +/- 3 mm Hg] at the completion of twitch force recovery) was initiated at the beginning of spontaneous recovery from neuromuscular blockade. The mean vecuronium recovery index (time for spontaneous recovery from 25-75% of control twitch tension) was slightly but not significantly shorter in the hyperventilated patients (8.4 +/- 1.8 min SD) than in the normally ventilated patients (10.4 +/- 3.4 min SD). We conclude the vecuronium recovery index in anesthetized patients is not significantly changed by hyperventilation with hypocarbia when induced at the beginning of recovery from neuromuscular blockade.

The effects of hypercarbia and hypocarbia on pancuronium and vecuronium neuromuscular blockades in anesthetized humans

To determine the effects of hypercarbia and hypocarbia on a pancuronium or vecuronium neuromuscular blockade, 54 patients were anesthetized with halothane and 60% nitrous oxide in oxygen. In 30 patients, end-tidal PCO2 was maintained at either 25 mmHg (3.5 kPa, N = 10), 41 mmHg (5.5 kPa, N = 10), or 56 mmHg (7.5 kPa, N = 10). Five patients in each group then were given pancuronium or vecuronium 0.022 mg/kg iv. Neither maximal depressions of twitch tension nor recovery indexes (time for spontaneous recovery of twitch tension from 25 to 75% of control) were altered by hypercarbia or hypocarbia. The remaining 24 patients were divided into three equal groups. Either pancuronium (N = 8) or vecuronium (N = 8) was administered iv as continuous infusion at a rate sufficient to produce a 50% depression of twitch tension. In the remaining eight patients, no muscle relaxant was given. After twitch tension was stable, half of the patients in each group had hypercarbia induced, which depressed twitch tension in all three groups. The patients who received vecuronium had a significantly larger decrease in twitch tension than those who received pancuronium or no muscle relaxant. Conversely, in the remaining patients, hypocarbia produced a significant increase in twitch tension. There was no difference in the magnitude of the increases in twitch tension among the three groups. The authors conclude that pre-muscle relaxant administration-induced hypercarbia or hypocarbia has no effect on a subsequent neuromuscular blockade from pancuronium or vecuronium.(ABSTRACT TRUNCATED AT 250 WORDS)