The Effect of the Canine ABCB1-1Δ Mutation on Sedation after Intravenous Administration of Acepromazine.

BACKGROUND: Dog breeds with the ABCB1-1Δ mutation have substantially truncated nonfunctional P-glycoprotein. Dogs homozygous for this mutation (mut/mut) are susceptible to the toxic adverse effects of ivermectin, loperamide, and vincristine. Anecdotal reports suggested ABCB1 mut/mut dogs showed increased depth and duration of acepromazine sedation. HYPOTHESIS/OBJECTIVES: That ABCB1 mut/mut dogs have increased depth and duration of sedation after acepromazine IV compared to normal dogs (nor/nor). ANIMALS: Twenty-nine rough-coated collies were divided into 3 groups of dogs based on their ABCB1 genotype: 10 mut/mut, 10 mut/nor, and 9 nor/nor. METHODS: Dogs were given 0.04 mg/kg of acepromazine IV. Level of sedation, heart rate, respiratory rate, and blood pressure were recorded for 6 hours after acepromazine administration. Area under the curves (AUCs) of the normalized sedation score results were calculated and compared. RESULTS: The median sedation scores for ABCB1 mut/mut dogs were higher than nor/nor dogs at all time points and were higher in mut/nor dogs for the first 2 hours. These differences were not found to be significant for any individual time point (P > .05). The median sedation score AUC for mut/mut dogs was significantly higher than nor/nor dogs (P = .028), but the AUC for mut/nor dogs was not (P = .45). There were no significant differences between groups for heart rate, respiratory rate, and blood pressure (P > .05). CONCLUSIONS AND CLINICAL IMPORTANCE: In ABCB1 mut/mut dogs acepromazine dose rates should be reduced and careful monitoring performed during sedation.

The pharmacokinetics of methimazole in a novel lipophilic formulation administered transdermally to healthy cats.

AIM: To determine the pharmacokinetics of a novel lipophilic formulation of transdermal methimazole compared to oral carbimazole. METHODS: Healthy cats received 5 mg carbimazole orally every 12 hours for 13 treatments (n=6), then received transdermal methimazole (n=5) at a dose of 5 mg, then 10 mg, once daily on the pinna for 7 days, with 21 days between treatments. Concentrations of methimazole in serum over 24 hours and at 148 hours were determined by high performance liquid chromatography. RESULTS: Concentrations of methimazole in serum for the first 24 hours were not reliably detected in all cats treated with 5 mg methimazole transdermally, while for those receiving 5 mg carbimazole orally and 10 mg methimazole transdermally all cats had detectable concentrations of methimazole in serum. The maximum concentration and area under the curve were lower in cats receiving 10 mg methimazole transdermally (108 (SD 25) ng/mL and 2544 (SD 216) mg-hour/mL, respectively) than those receiving 5 mg oral carbimazole (355 (SD 113) ng/mL and 31,866 (SD 439) ng-hour/mL, respectively) (p<0.05). The time at maximal concentration and elimination half-life were longer for 10 mg transdermal methimazole (5.2 (SD 1.1) hours and 13 (SD 3) hours, respectively) compared to 5 mg oral carbimazole (2.1 (SD 1.6) hours and 5.1 (SD 1.2) hours, respectively). At 148 hours, mean concentrations of methimazole in serum were higher in cats receiving 10 mg methimazole transdermally (506 (SD 165) ng/mL) than for 5 mg oral carbimazole (255 (SD 28) ng/mL) or 5 mg transdermally (204 (SD 76) ng/mL). The mean relative bioavailability of 10 mg transdermal methimazole compared to oral carbimazole was 48 (min 43, max 55)%. CONCLUSION: Transdermal methimazole at a dose of 10 mg administered to the pinnae of healthy cats once daily in a novel lipophilic formulation has half the relative bioavailablity compared to 5 mg oral carbimazole. CLINICAL RELEVANCE: Transdermal methimazole can be absorbed from the skin of healthy cats.

The efficacy and safety of a novel lipophilic formulation of methimazole for the once daily transdermal treatment of cats with hyperthyroidism.

BACKGROUND: Previous studies on transdermal methimazole have used pluronic lecithin organogel as the vehicle. This might not be the most suitable vehicle for a lipophilic drug, such as methimazole. HYPOTHESIS/OBJECTIVES: Once daily transdermal administration of a novel lipophilic formulation of methimazole is as safe and effective as oral carbimazole in treating hyperthyroidism in cats. ANIMALS: Forty-five client-owned cats diagnosed with hyperthyroidism. METHODS: Prospective study. Cats with newly diagnosed, untreated hyperthyroidism were treated with carbimazole (5 mg p.o., q12h) or methimazole (10 mg) applied to the inner pinnae q24h. Cats were examined after 0, 1, 4, 8, and 12 weeks of treatment. Clinical signs, body weight, systolic blood pressure, hematologic, serum biochemical and urine parameters, total serum thyroxine concentrations (TT4), and serum methimazole concentrations were recorded. RESULTS: No significant differences between groups were detected at day 0. Both formulations were effective in treating hyperthyroidism. No significant differences were detected in thyroxine concentrations, body weight, blood pressure, heart rate, alkaline phosphatase, alanine aminotransferase, creatinine, urea, and urine specific gravity (USG) between groups. The serum methimazole concentrations correlated poorly with TT4-concentrations in both groups. CONCLUSIONS AND CLINICAL IMPORTANCE: In this 12-week trial, once daily application of a novel formulation of transdermal methimazole applied to the pinnae was as effective and safe as twice daily oral carbimazole in the treatment of cats with hyperthyroidism. This novel formulation and transdermal application could have practical advantages to some pet owners.

Evidence for epidermal growth factor receptor-enhanced chemosensitivity in combinations of cisplatin and the new irreversible tyrosine kinase inhibitor CI-1033.

Irreversible inhibitors of the epidermal growth factor receptor (EGFR) are showing promise in clinical trials. This report is the first to show that inhibition of the EGFR tyrosine kinase by an irreversible binder synergizes with cisplatin, at least in EGFR-overexpressing tissue culture cell lines in vitro. Unlike previous synergies demonstrated between ErbB2 blockade and DNA-damaging drugs, the synergy between the irreversible EGFR inhibitor and cisplatin does not appear to involve the repair of DNA-cisplatin adducts. Given the current clinical data, this combination may be of more than theoretical interest.

Cytotoxicity and DNA interaction of the enantiomers of 6-amino-3-(chloromethyl)-1-[(5,6,7-trimethoxyindol-2-yl)carbonyl]indo- line (amino-seco-CI-TMI).

The enantiomers of the previously reported racemic 6-amino-3-(chloromethyl)-1-[(5,6,7-trimethoxyindol-2-yl)carbonyl] indoline (amino-seco-CI-TMI) were prepared via resolution of a precursor by chiral HPLC. The only detectable product isolated from reaction of the racemic compound with calf thymus DNA, followed by thermal cleavage, was shown by mass spectrometry and two-dimensional NMR spectroscopy to be the adenine N3 adduct. Polyacrylamide gel electrophoresis assays with the racemate and with each enantiomer also showed adenine to be the only site of alkylation. While the racemic amino compound exhibited sequence selectivity identical to that of the previously characterized phenol analogue, the enantiomers exhibited distinctly different sequence selectivities, allowing the (+) enantiomer to be assigned the "natural" S configuration. The (+)-(S) enantiomer is 3-fold more cytotoxic than the (-)-(R) enantiomer (IC(50) values of 240 and 700 nM, respectively, in AA8 cells, after exposure for 4 h).

Comparison of the patterns of DNA alkylation by phenol and amino seco-CBI-TMI compounds: use of a PCR method for the facile preparation of single end-labelled double-stranded DNA.

Both 5-hydroxy- and 5-amino-seco-CBI-TMI minor groove alkylators are very potent cytotoxins. The patterns of alkylation of the two enantiomers of both compounds were compared on a section of the gpt gene. All of the compounds alkylated only at adenines, with the amino compounds being slightly more selective. Consensus alkylation sequences for both S (natural) enantiomers were identical, but for the R (unnatural) enantiomers these varied slightly. The consensus sequences suggest that the S enantiomers bind lying in the 3'-->5' direction from the alkylated adenine, but there was no clear indication of which direction the R enantiomers lie on the DNA. Both S enantiomers were 10- to 100-fold more efficient alkylators than the R enantiomers, and the amino compounds were somewhat more efficient than the corresponding phenols. The S enantiomers were more cytotoxic then the R in both the phenol and amino series. The large amounts of end-labelled DNA required for this work was obtained by first end-labelling appropriate primer oligonucleotides, then amplifying by PCR. Compared with other methods in use, this is a simple and flexible one-step procedure for the preparation of labelled DNA of any sequence. An improvement in the synthesis of 5-hydroxy-seco-CBI-TMI is reported.

Elephantfish proinsulin possesses a monobasic processing site.

Total pancreatic RNA from the holocephalan species Callorhyncus milii (elephantfish) was used to make cDNA as a template for the polymerase chain reaction. Three redundant primers based on the known amino acid sequence of elephantfish insulin were used to amplify a fragment of proinsulin comprising truncated B-chain, complete C-peptide, and complete A-chain. Whereas the C-peptide/A-chain junction contained the expected dibasic cleavage site (-Lys-Arg-), the B-chain/C-peptide junction was found to contain only a single Arg, the first such site to be unequivocally associated with the proteolytic processing of a proinsulin to insulin. Examination of the flanking sequences around this site shows that a typical endocrine/neuroendocrine PC3 conversion enzyme should still be able to cleave, as the general requirements for precursor processing at a monobasic site are satisfied, notably a basic residue (Lys) at the -4 position. An acidic residue (in this case Asp) at the +1 position, which is seen in all known proinsulins, is maintained. The corresponding genomic DNA fragment of elephantfish proinsulin was also amplified by PCR, revealing a 402-bp intron at the conserved IVS-2 position within the C7 codon.