Gingival sequestration of nifedipine in nifedipine-induced gingival overgrowth

The mechanism of gingival overgrowth associated with long-term use of nifedipine and of other drugs that affect calcium homoeostasis, such as cyclosporin and phenytoin, is unknown. With an ultrasensitive assay, we measured the pharmacokinetics of nifedipine in plasma and gingival crevicular fluid (GCF) of nine patients receiving this drug for angina and hypertension. In seven patients, the maximum nifedipine concentration was in the range 15-316 (mean 84 [SD 105]) times greater in GCF than in plasma. The two patients with low (undetectable) GCF nifedipine did not have overgrowth. We propose that gingival tissues sequester nifedipine and that the very high nifedipine concentrations predispose the tissues to overgrowth.

The incidence and severity of nifedipine-induced gingival overgrowth

The gingival health of 19 patients with cardiovascular problems who were medicated with nifedipine was compared with a similar cohort treated with atenolol and a control group of healthy patients. In the nifedipine and atenolol groups, patients had been taking their respective medication for a minimum period of 6 months. Plaque scores were similar for all three groups. However, patients medicated with nifedipine had a significantly higher gingival index (P less than 0.005), gingival overgrowth scores (P less than 0.02) and probing sites greater than 3 mm (P less than 0.005) when compared with the atenolol and control groups. 4 patients in the nifedipine group experienced clinically significant gingival overgrowth which required surgical excision. Gingival changes in the nifedipine patients were not related to drug dosage or plaque scores. It is concluded that nifedipine therapy results in significant gingival changes, an effect which may be mediated by the drug's action on calcium transport.

Mutant debrisoquine hydroxylation genes in Parkinson's disease

The frequency of fifteen genotypes of CYP2D6 (debrisoquine 4-hydroxylase) in 53 patients with Parkinson's disease was determined by the polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analyses and compared with the findings in 72 healthy controls. The commonest mutant allele, CYP2D6B, was twice as frequent among patients as in controls, with an approximate relative risk ratio of 2.70 (95% confidence interval 1.14-6.41; p = 0.0063) for subjects homozygous or heterozygous for this allele.

Comparison of a novel thin-layer chromatographic-fluorescence detection method with a spectrofluorometric method for the determination of 7-hydroxycoumarin in human urine

A novel method for the determination of 7-hydroxycoumarin in human urine which combines thin-layer chromatography (TLC) with fluorescence detection (FD) has been devised. The limit of detection (1 ng/ml) enables determination of 7-hydroxycoumarin after both administration of coumarin and environmental exposure to this fragrance material. When compared to a spectrofluorometric method of analysis, the TLC-FD method proved to be more selective for the analysis of 7-hydroxycoumarin in human urine.

Combined thin-layer chromatography-photography-densitometry for the quantification of ifosfamide and its principal metabolites in urine, cerebrospinal fluid and plasma

A method has been devised for the determination of the anticancer drug ifosfamide and its principal metabolites in urine, plasma and cerebrospinal fluid (CSF). The urine and CSF samples are absorbed onto Amberlite XAD-2 eluting the compounds of interest with methanol. Plasma is deproteinated using cold acetonitrile and centrifuged to yield a clear supernatant. The eluate and supernatant are analyzed by thin-layer chromatography, with spot visualization using 4-(4-nitrobenzyl)pyridine. The plates are photographed for subsequent densitometeric analysis. The intra-assay coefficient of variation for each compound in both urine and plasma was less than 10% and the lower limit of detection was 1 microgram/ml. The method provides a means of determining the full spectrum of metabolic products of ifosfamide in patients and will allow detailed investigation of variability in metabolism and pharmacokinetics of this drug.

Deficient nifedipine oxidation: a rare inherited trait associated with cystic fibrosis kindreds

Previous studies have indicated that there is weak genetic linkage between the defective gene in cystic fibrosis (CFTR) and the gene encoding the nifedipine metabolizing enzyme P4503A4 which are both located on chromosome 7. To examine further this possible association, nifedipine metabolism was investigated in a group of 59 volunteers, and 17 adult cystic fibrosis patients and 37 of their relatives. In agreement with the majority of previous studies, the volunteer group showed a unimodal distribution of recoveries for the major metabolite M-II ranging from 33 to 78% excretion in 8 h. In the case of both the cystic fibrosis patients and their parents, the distribution of recoveries was shifted to the left with five out of 20 parents and three out of 11 unrelated cystic fibrosis patients showing recoveries below the range observed in the volunteer group. This poor metabolism appeared to be both reproducible and heritable and did not appear to be a consequence of mutations in the CFTR gene.

A phase I study on the reversal of multidrug resistance (MDR) in vivo: nifedipine plus etoposide

Multidrug resistance (MDR) is one of the mechanisms of resistance to multiple cytotoxic drugs and is mediated by the expression of a membrane pump called the P-glycoprotein. Nifedipine is one of the calcium channel blocking agents which reverses MDR in vitro. Fifteen patients with various malignancies received nifedipine at three dose levels: 40 mg, 60 mg and 80 mg orally twice daily for 6 days. Etoposide was administered intravenously on day 2 in a dose of 150-250 mg m-2 and orally 150-300 mg twice daily on days 3 and 4. Cardiovascular effects of nifedipine were dose limiting and the maximum tolerated dose was 60 mg bid. Mean area under the plasma concentration curve (AUC0-00) and plasma half-life (beta) of nifedipine and its major metabolite MI at the highest dose level were 7.87 microM.h, 7.97 h and 4.97 microM.h, 14.0 h respectively. Nifedipine did not interfere with the pharmacokinetics of etoposide.

Pharmacokinetics and metabolism of cyclophosphamide in paediatric patients

The pharmacokinetics and metabolism of cyclophosphamide were studied in nine paediatric patients. Plasma samples were obtained from eight subjects and urine was collected from six children during a 24-h period after drug administration. Cyclophosphamide and its major metabolites phosphoramide mustard (PM), carboxyphosphamide (CX), dechloroethylcyclophosphamide (DCCP) and 4-ketocyclophosphamide (KETO) were determined in plasma and urine using high-performance thin-layer chromatography-photographic densitometry (HPTLC-PD). Cyclophosphamide (CP) was nearly, if not completely, cleared from plasma by 24 h after its administration. The plasma half-life of CP ranged from 2.15 to 8.15 h; it decreased following higher doses and was shorter than that previously reported for adult patients. Both the apparent volume of distribution (0.49 +/- 1.4 l/kg) and the total body clearance (2.14 +/- 1.4 l m-2 h-1) increased with increasing dose. Renal clearance ranged between 0.12 and 0.58 l/h (mean, 0.43 +/- 0.19 l/h). Between 5.4% and 86.1% of the total delivered dose was recovered as unchanged drug in the urine. The major metabolites identified in plasma and urine were PM and CX. One patient appeared to be deficient in CX formation. This study suggests that there is interpatient variability in the pharmacokinetics and metabolism of CP in paediatric patients. The shorter half-life and higher clearance as compared with adult values indicate faster CP metabolism in children.

Genetic and metabolic criteria for the assignment of debrisoquine 4-hydroxylation (cytochrome P4502D6) phenotypes

A randomly selected population of 73 volunteers, together with 22 previously established poor metabolisers of debrisoquine, were phenotyped for their ability to 4-hydroxylate debrisoquine and were also analysed for a number of mutations in the CYP2D6 gene. Genotyping was performed using both restriction fragment length polymorphism with the restriction enzyme Xba I, together with two separate polymerase chain reaction assays. Together, these assays detected 98% of mutant alleles in the poor metaboliser group which corresponded to positive identification of 95% of this group. The most common mutant allele detected as the 29B which comprised 75% of total alleles in the poor metaboliser group, whereas the 29A had a frequency of 0.11. Two other allelic variants, which were detectable by restriction fragment length polymorphism analysis occurred at frequencies of 0.07 and 0.05. In the volunteer group, 2.7% of subjects were genotypically poor metabolisers, 35.6% heterozygous extensive metabolisers and 61.7% homozygous extensive metabolisers, on the basis of the genotyping assays used. A good correlation between debrisoquine metabolic ratio and genotype was obtained particularly for subjects genotyped as homozygous extensive metabolisers.

Is environmental carcinogenesis modulated by host polymorphism?

It is now clear that tobacco smoking, alcohol consumption, dietary factors and occupation can all interact with genetic host factors to place one individual at a greater or lesser risk of a particular cancer than another. Phenotypes which confer significantly elevated risks arise from the human CYP1A1. CYP2D6, GST1 and NAT (N-acetyltransferase) genes. The last is the only one remaining to be cloned. It is envisaged that several of these genes may interact in a given circumstance cooperatively to increase susceptibility. For example CYP1A1, CYP2D6 and GST1 genotypes may have additive or multiplicative risks of bronchogenic carcinoma in cigarette smokers. CYP2D6 and NAT genotypes may interact in bladder cancer. The advent of molecular genetics brings us closer to the day when, for example, factory workers in potentially hazardous environments might be screened using PCR methodology on skin scrapings or buccal swabs for their innate susceptibility to combined workplace and lifestyle cancer risks.

Comparative effects of the diastereoisomers, quinine and quinidine in producing phenocopy debrisoquine poor metabolisers (PMs) in healthy volunteers

1. A single oral dose (50 mg) of quinidine significantly increased the debrisoquine metabolic ratio in six healthy volunteers. For four of the volunteers the metabolic ratio changed to that typical of the poor metaboliser (PM) phenotype. 2. The effect of quinidine in producing debrisoquine oxidation "poor metaboliser" phenocopies persisted for at least 3 days but had disappeared by 1 week. 3. The debrisoquine metabolic ratios for the same six subjects were not significantly altered by the oral administration of quinine (200 or 400 mg), the diastereoisomer of quinidine. 4. The plasma pharmacokinetic parameters of both nortriptyline and desipramine in healthy volunteers were all changed to those more typical of the debrisoquine PM phenotype following the concomitant administration of quinidine (50 mg). 5. It is concluded that quinidine, but not its diastereoisomer quinine, is a potent selective inhibitor of the in vivo oxidation of debrisoquine and can produce an artifactual PM phenocopy in persons who are phenotypically extensive metaboliser (EM) phenotype status. The clinical implications of this observation are discussed.

Lack of effect of co-trimoxazole on the pharmacokinetics and pharmacodynamics of nifedipine

The pharmacokinetics of nifedipine and its primary oxidised metabolite, M-I were studied in nine healthy volunteers following a single oral dose of 20 mg nifedipine alone or after pretreatment with oral co-trimoxazole. Following pretreatment with co-trimoxazole, no significant effect was detected on maximum plasma concentration, elimination half-life, or area under the plasma concentration-time curve of either nifedipine or M-I, nor on the blood pressure response to nifedipine.

Pharmacokinetics and toxic effects of nifedipine in massive overdose

A 57-year-old man took 30 x 20 mg nifedipine retarded release tablets. He developed hypotension, tachycardia and flushing, but remained in sinus rhythm. The concentration of nifedipine 10 h after overdose was 604 micrograms 1-1, and of the M-I metabolite 110 micrograms 1-1. Log concentration time curves were linear from 10-72 h for nifedipine, with a half-life of 7.5 h; and for M-I with a half-life of 8.2 h. On this evidence, oral absorption of nifedipine retarded release is complete by 10 h. There was no evidence of saturation of nifedipine or M-I metabolism, even at concentrations ten times above the therapeutic concentration.

The effect of route of administration and fractionation of dose on the metabolism of ifosfamide

The measurement of urinary ifosfamide, isophosphoramide mustard, dechloroethyl ifosfamide and carboxyifosfamide using high-performance thin-layer chromatography with photographic densitometry (TLC-PD) is described. This technique was also used to demonstrate the large inter-individual variation in the ifosfamide metabolic profile of patients receiving the drug as single-agent therapy for non-small-cell lung cancer. In addition, oral administration was shown to result in higher levels of these metabolites in the urine. Fractionation of the ifosfamide dose over several days resulted in increasing levels of metabolites in the urine, consistent with auto-induction of ifosfamide metabolism.

Cytochrome P450dbl phenotypes in malignant and benign breast disease

129 female patients with breast cancer and 79 controls undergoing biopsy for benign breast conditions had debrisoquine hydroxylator phenotype established. 129 female hospital patients with known hydroxylator phenotype were used as another control group. The breast cancer cases differed significantly from the benign controls in their debrisoquine phenotype, with 10% being poor metabolisers compared with none of the controls (P less than 0.01). However, while a comparison of the distributions of metabolic ratio (an inverse measure of debrisoquine metabolism) of breast cancer patients and hospital controls showed a significant difference by rank, there was no significant difference in the proportion of poor metabolisers in these two groups. The cases with benign disease differed from the hospital controls in both metabolic ratio distribution (P less than 0.001) and frequency of poor metabolisers (P less than 0.05). Although there was a shift in metabolic ratio distribution, debrisoquine hydroxylator phenotype was not a genetic marker for breast cancer. Why no patients undergoing biopsies for benign conditions were poor metabolisers is unknown.

The influence of food on the pharmacokinetics of 'biphasic' nifedipine at steady state in normal subjects

Previous studies following single dose administration have suggested that the pharmacokinetics of various nifedipine formulations could be influenced by the timing of associated food consumption. In order more closely to reflect the clinical situation we have carried out a study at steady state using a 'biphasic' formulation comprising 'rapid' and 'retarded' drug release components. Fifteen normal subjects took 20 mg 'biphasic' nifedipine 12 hourly for 10 days. Studies were carried out on days 4, 7 and 10. On these days the nifedipine was taken 2 h or 1 h before or immediately following a light breakfast. A light breakfast influenced neither the rate nor the extent of nifedipine absorption nor the rate or extent of major metabolite appearance. We conclude that at steady state the timing of a light meal is unlikely to alter in any clinically important manner the pharmacokinetics of nifedipine released from 'biphasic' tablets.