Non-linear pharmacokinetics of high-dose intravenous verapamil

Aims In an attempt to reverse multidrug resistance, in a recent trial of verapamil in association with doxorubicin, we used escalating doses of continuous intravenous (i.v.) verapamil under close haemodynamic monitoring. We report the pharmacokinetics of escalating doses of verapamil. Methods We studied nine patients [ seven males, two females; median age 46 years (range, 31–57)] with advanced adenocarcinoma of the colon and normal renal, hepatic, and cardiac functions. After a loading dose (0.15 mg kg⁻¹ followed by 12 h continuous i.v. infusion at 0.20 mg kg⁻¹ h⁻¹ ), the infusion rate (ko) of verapamil was increased every 24 h (0.25, 0.30, 0.35, and 0.40 mg kg⁻¹ h⁻¹ ). The highest rate was maintained for 48 h. Doxorubicin was given as a continuous i.v. infusion from 12 to 108 h (n=4) or 60 to 108 h (n=5). Blood samples and urine collections were taken every 12 h. Verapamil and nor-verapamil were assayed by high performance liquid chromatography. We calculated systemic clearance of verapamil (CL=ko/C_ss ) and renal clearance (CLr) of verapamil and nor-verapamil. The C_ssvs rate relationship was fitted to a Michaelis-Menten equation: C_ss=ko(K_m+C_ss )/(V V_m ). Results CL was dose-dependent and in all nine patients a significant reduction in CL was observed over the dose range (mean CL±s.d. were 0.51±0.31, 0.38±0.16, 0.32±0.18, and 0.27±0.11 l h⁻¹ kg⁻¹, respectively, at 0.25, 0.30, 0.35, and 0.40 mg kg⁻¹ h⁻¹; P=0.0001). C_ss increased more than proportionally to the dose rate and the C_ssvs rate relationship was best defined by a Michaelis-Menten equation (K_m=730 μg l⁻¹; V V_m=0.55 mg kg⁻¹ h⁻¹ ), (r=0.994; P=0.006). CLr of verapamil and nor-verapamil was not saturable but the contribution to the elimination was only 2 to 4% of the dose. Conclusions These findings suggest a non-linear, capacity-limited metabolic clearance of high-dose verapamil. Using escalating infusion rates, high verapamil concentrations (1500–2500 ng ml⁻¹ ) were achieved without major toxicity. Saturable clearance may cause higher bioavailability and slower elimination of verapamil after acute oral overdoses.     

Characterization of purinoceptors mediating depolarization of rat isolated vagus nerve.

1. As part of a broader study to characterize neuronal purinoceptors, the effects of adenosine 5'-triphosphate (ATP) and a range of ATP analogues were investigated on the extracellularly recorded membrane potential of the rat isolated vagus nerve, using a 'grease-gap' technique. 2. ATP evoked depolarization of the rat vagus nerve. The concentration-effect curve to ATP was not monophasic: at the lower concentrations (1 x 10(-5)-1 x 10(-3) M) the curve was shallow (< 50% of the near maximal response to 5-hydroxytryptamine (5-HT)) whilst at higher concentrations the relationship between concentration and amplitude of depolarization was steeper (> 135% of the response to 5-HT at the highest concentration tested, 1 x 10(-2) M). On washout of the high drug concentrations large after-hyperpolarizations were often observed. 3. alpha,beta-methylene ATP (1 x 10(-6)-3 x 10(-4) M), beta,gamma-methylene ATP (1 x 10(-6)-1 x 10(-3) M), and 5'-adenylylimidodiphosphate (beta,gamma-imido ATP; 1 x 10(-6)-1 x 10(-3) M) were all more potent than ATP and produced large depolarizations of the rat vagus nerve at the highest concentrations tested (> 150% of the response to 5-HT). The overall rank order of potency was alpha,beta-methylene ATP > beta,gamma-methylene ATP = beta,gamma-imido ATP > ATP. 4. In contrast, 2-methylthio ATP (1 x 10(-6)-1 x 10(-3) M) produced relatively small depolarizations (< 100% of the response to 5-HT). As was the case with low concentrations of ATP, the concentration-effect curve to 2-methylthio ATP was very shallow.(ABSTRACT TRUNCATED AT 250 WORDS)     

The avidity of specific IgM detected in primary rubella and reinfection

An IgM capture enzyme-linked immunosorbent assay for rubella-specific IgM was used to assess the avidity of specific IgM by comparing the results obtained with and without a mild protein denaturant in the washing fluid used after incubation of IgM with rubella haemagglutinating antigen. An avidity index (AI) was calculated with AIs less than 50% considered to indicate low avidity. Sera from recent primary rubella, rubella reinfection and from patients persistently reactive for specific IgM were tested. Urea and diethylamine (DEA) were compared as the protein denaturants. Twenty-six of 28 sera from cases of primary rubella gave an AI less than 50% with DEA, compared with 25 of 28 with urea. Seventeen of 20 sera from cases of reinfection gave an AI greater than 50% with DEA whereas only 14 of 20 had a similarly high avidity with urea. Eight of 10 sera from 4 cases of persistent specific IgM reactivity gave AIs greater than 50% with DEA, although this was reduced to 5 when urea was used. Thus a difference has been demonstrated between the avidity of specific IgM in primary infection from that demonstrated after a secondary antigenic challenge (reinfection). This may help in serologically distinguishing primary infection from reinfection.     

Retinoblastoma. The relationship of proliferating cells to blood vessels

In 150 retinoblastomas the authors found a uniform thickness of the cuff of viable retinoblastoma cells that surrounds blood vessels. The mean thickness was 98.7 microns with a standard deviation of 11.9 microns. The cross-sectional area of the cuff was negatively correlated with the mitotic activity in the cuff and positively correlated with the diameter of the central vessel. The mitotic activity in the cuff of cells was inversely related to the distance from the central blood vessel. When the cuff was divided into three concentric rings, the inner ring contained a mean of 6.2 mitotic figures, the middle ring contained a mean of 2.9 mitotic figures, and the outer ring contained a mean of 0.6 mitotic figures. This pattern of growth is similar to that observed in other rapidly growing neoplasms in humans and experimental animals. In these tumors this pattern results from reduction in oxygen tension with increased distance from the central blood vessel.     

Down-regulation of muscarinic receptors in the striatum of organophosphate-treated swine

Subacute (daily) administration of diisopropylfluorophosphate (DFP) to male swine (Yorkshire white) resulted in a 97% inhibition of cholinesterase and a decrease of [3H]quinuclidinyl benzilate [( 3H]QNB) binding sites in homogenates of striata by approximately 50% after 14 days. The maximal density of receptors (Bmax) decreased from 2.1 +/- 0.3 to 1.0 +/- 0.2 pmole/mg protein. There was no significant change in the dissociation constant (Kd) for [3H]QNB binding (control: 52.6 +/- 10.7 pM; 7-day: 57 +/- 2.8 pM). Carbachol displacement of [3H]QNB binding yielded data best fit by a two-binding site model. The dissociation constants were KiL = 115 +/- 62 microM (55 +/- 3%) and KiH = 1.8 +/- 0.7 microM (45 +/- 3%), respectively, for the low- and high-affinity states. Seven-Day treatment with DFP reduced the percentage of high-affinity receptors to 22 +/- 8.6%, but affected neither the low- nor the high-affinity Kd (100 +/- 20 and 2 +/- 0.6 microM). With the addition of Mg2+, striatal homogenates had low- and high-affinity receptors in the proportion of approximately 1 to 1. In the presence of Gpp(NH)p + Mg2+ the ratio of high- to low-affinity receptors was 3:1 in homogenates of control tissue (to 26 +/- 5%). This treatment had no effect on this ratio in homogenates of tissue from 7-day DFP-treated swine (3:1) since it was already 3:1. Pirenzepine displacement of [3H]QNB binding was best described by a two-binding site model, with Ki values of 38 +/- 14 and 201 +/- 78 nM, which represent 74 and 26% of the binding sites, respectively. The high affinity Kd value was unchanged following 7 days of DFP treatment (24 +/- 5 nM). There appears to be little change in the displacement curves for pirenzepine inhibition of [3H]QNB binding. This suggests that about 75% of the receptors are of the M1 subtype. Thus, subacute administration of DFP causes not only a decrease in the number of receptors, but also a change in the proportion of agonist affinity states which is related to the interaction of the guanine nucleotide binding protein and the muscarinic receptor.     

Patterns of referral to Red Cross War Memorial Children's Hospital, Cape Town

Patterns of referral to Red Cross War Memorial Children's Hospital were studied to assess the appropriateness of referrals. From 1 July to 31 December 1987 all 9,288 referral letters presented to the hospital were collected and a sample (4,662 letters) analysed. It emerged that the patients were similar to those attending the outpatient department without referral, except that relatively fewer referred patients were black. The private sector, i.e. general practitioners, was the largest referral agency, followed by day hospitals. Most patients were referred to the outpatient department without an appointment. Of the specialist clinics, the surgical clinics (i.e. ophthalmology and ear, nose and throat) had the highest number of referrals. The majority of patients (84.9%) were not admitted. Only in 30.3% of referred cases did the hospital make contact with referral agents. Referral rates were highest from the predominantly coloured areas of the Cape Peninsula. The hospital cannot isolate itself from the community it serves and needs to support and guide referral agents in order to improve the utilisation of the hospital. Training of health professionals in order to increase expertise is a priority. A study of the total patient population would facilitate the understanding of hospital utilisation. Similar studies could be beneficial at other hospitals.     

The management of patients with an intrinsic supratentorial brain tumour

The management of patients presenting with supratentorial glioma between 1978 and 1986 is reviewed. Complete follow-up in 517 cases was obtained. One hundred and fifty eight patients were not submitted to any form of surgery, 299 patients were biopsied and 60 patients underwent craniotomy and internal decompression. The no surgery group contained a higher proportion of patients with poor prognostic indicators than either the biopsy or craniotomy groups. The craniotomy group consisted of patients with better prognostic indicators than the biopsy group, in particular, younger age and more favourable site, type and grade of tumour. This was reflected in the difference in outcome between the groups. Median survival was 14 months in the craniotomy group, four months in the biopsy group and 2.2 months in the no surgery group. The outcome in patients with histologically proven malignant gliomas was best in those patients who received radiotherapy. The craniotomy group had a median survival of 18.5 months, a two year survival of 48% and a five year survival of 9%. The median survival following radiotherapy of those patients with proven malignant gliomas who had a biopsy was 9.5 months with a two year survival of 16% and a five year survival of 2%. These results compare favourably with studies which have adopted a more aggressive approach, suggesting that outcome is determined as much by patient selection using favourable prognostic indicators as by the treatment itself. The need for prospective trials of the management of unselected consecutive glioma patients randomizing them to conservative and radical treatment groups in order to define the role of both conventional therapy and radical therapy is discussed.     

Planning the aesthetic foreheadplasty

Different approaches to aesthetic foreheadplasty have been thoroughly described and well documented. However, there has been a paucity of information in the literature describing indications for the various approaches. We detail our approach to planning the foreheadplasty; most commonly, we opt for the anterior forehead-hairline approach. We believe that proper patient selection with regard to anatomical, aesthetic, and physiological factors is of the greatest importance in planning an aesthetic foreheadplasty.     

Growth of melanocytes in human epidermal cell cultures

Epidermal cell cultures were grown in keratinocyte-conditioned medium for use as burn wound grafts; the melanocyte composition of the grafts was studied under a variety of conditions. Melanocytes were identified by immunohistochemistry based on a monoclonal antibody (MEL-5) that has previously been shown to react specifically with melanocytes. During the first 7 days of growth in primary culture, the total number of melanocytes in the epidermal cultures decreased to 10% of the number present in normal skin. Beginning on day 2 of culture, bipolar melanocytes were present at a mean cell density of 116 +/- 2/mm2; the keratinocyte to melanocyte ratio was preserved during further primary culture and through three subpassages. Moreover, exposure of cultures to mild UVB irradiation stimulated the melanocytes to proliferate, suggesting that the melanocytes growing in culture maintained their responsiveness to external stimuli. When the sheets of cultured cells were enzymatically detached from the plastic culture flasks before grafting, melanocytes remained in the basal layer of cells as part of the graft applied to the patient.