Pre-clinical and preliminary dose-finding and safety studies to identify candidate antivenoms for treatment of envenoming by saw-scaled or carpet vipers (Echis ocellatus) in northern Nigeria.

The aim of this study was to identify candidate antivenoms with specific activity against the venom of the saw-scaled or carpet viper (Echis ocellatus) in northern Nigeria, where bites by this species cause great morbidity and mortality but where effective antivenoms have become scarce and unaffordable. Selected antivenoms were destined to be compared by randomised controlled clinical trials (RCTs). Standard pre-clinical neutralisation assays were carried out in rodents. We included two licensed antivenoms of established clinical efficacy and 6 candidate antivenoms. Although 6 of the tested antivenoms showed promising efficacy, all but 3 were excluded from further study because of inadequate pre-clinical efficacy or because they were unavailable or unaffordable for the anticipated RCTs. Median effective doses (ED(50)) of the remaining three candidate antivenoms suggested that the following doses might neutralise the maximum observed venom yield of 24.8 mg (dry weight) of venom milked from captive E. ocellatus: 10 ml of MicroPharm "EchiTAb G" (ET-G) antivenom; 30 ml of Instituto Clodomiro Picado "EchiTAb-Plus-ICP" (ET-Plus) antivenom; 50 ml of VacSera, Cairo "EgyVac" antivenom. A preliminary clinical dose-finding and safety study of these three antivenoms was carried out in 24 patients with incoagulable blood after E. ocellatus bites who were not severely envenomed. A 3+3 dose escalation design was employed. Initial doses of 10 ml ET-G and 30 ml ET-Plus restored blood coagulability in groups of 6 patients with early mild reactions (pruritus only) in not more than one third of them. EgyVac antivenom did not fulfil efficacy or safety criteria in 12 patients. On the basis of these results, ET-G and ET-Plus were selected for comparison in a RCT.

Effect of quinine on electroshock and pentylenetetrazol-induced seizures in mice.

1. Effect of quinine on electroshock and pentylenetetrazol (leptazol)-induced seizures was investigated in mice. 2. Quinine (0.1-100 mg/kg, ip) did not protect mice against electroshock seizure. 3. 25-100 mg/kg, ip of quinine reduced the incidence of leptazol (80-90 mg/kg, sc)-induced seizure and significantly prolonged the onset of both myoclonic and tonic phases. 4. d-Amphetamine (2.5 mg/kg, ip), inhibited the protective effect of quinine (100 mg/kg, ip) against leptazol (80-90 mg/kg, sc)-induced seizure and significantly shortened the onset of both myoclonic and tonic phases of the seizure. 5. Pimozide (4 mg/kg, ip) significantly potentiated the protective effect of quinine (50-100 mg/kg, ip) against leptazol (80-90 mg/kg, sc)-induced seizure. 6. These results suggest that quinine in moderate doses, may have slight anticonvulsant properties and that dopaminergic mechanism may be involved in the protective influence of quinine against leptazol-induced seizure in mice.

Some behavioural effects of quinine in mice.

The effects of quinine on motor activity, pentobarbitone-induced sleep and gross behaviour were examined in mice. Low doses of quinine (0.1-0.5 mg/kg intraperitoneally) increased locomotor activity in mice; this effect was potentiated by L-dopa (25 mg/kg sub cutaneously), L-dopa (25 mg/kg subcutaneously) plus benserazide (12.5 mg/kg subcutaneously) and pargyline (50 mg/kg intraperitoneally) and antagonized by α-methyl- p-tyrosine (50 mg/kg intraperitoneally), pimozide (0.2 mg/kg intraperitoneally), L-sulpiride (40 mg/kg intraperitoneally) and SCH 23390 (0.2 mg/kg subcutaneously). Similarly, D-amphet amine (2.5 mg/kg intraperitoneally)-induced locomotor activity in mice was blocked by pimo zide (0.2 mg/kg intraperitoneally). On the other hand, pimozide (0.2 mg/kg intraperitoneally), L-sulpiride (40 mg/kg intraperitoneally and SCH 23390 (0.2 mg/kg subcutaneously) potentiated the locomotor depressant effect of high doses of quinine (1-5 mg/kg) intraperitoneally). Furthermore, the onset and duration of pentobarbitone (30 mg/kg intraperitoneally)-induced sleep were respectively shortened and prolonged in a dose-dependent manner. D-Amphet amine (25 mg/kg intraperitoneally) significantly delayed the onset and shortened the duration of sleep induced by the interaction of quinine (100 mg/kg intraperitoneally) with pen tobarbitone (30 mg/kg intraperitoneally). L-sulpiride (40 mg/kg intraperitoneally) and pimozide (4 mg/kg intraperitoneally), on the other hand, significantly shortened the onset and prolonged the duration of sleep resulting from the interaction of quinine with pentobarbitone. The antagonism of pentobarbitone (30 mg/kg intraperitoneally)-induced sleep by D-amphetamine (2.5 mg/kg intraperitoneally) was prevented by pimozide (4 mg/kg intraperitoneally). Quinine (0.1 mg/kg intraperitoneally) desynchronized the EEG and antagonized pentobarbitone (20 mg/kg intraperitoneally)-induced EEG synchronization while 100 mg/kg intraperitoneally of quinine desynchronized the hyperstriatum with marked decrease in EMG activity in chicks and potentiated pentobarbitone (20 mg/kg intraperitoneally)-induced EEG synchronization with profound reduction in EMG activity. Quinine (0.01-5 mg/kg intraperitoneally) exhibited a biphasic dose-related increase in circling. The stereotyped circling induced by D-amphetamine (4 mg/kg intraperitoneally) was dose-dependently reduced by quinine (0.5-25 mg/kg intra peritoneally) while 0.05-0.1 mg/kg intraperitoneally of quinine weakly potentiated this activity. Pimozide (4 mg/kg intraperitoneally) and L-sulpiride (40 mg/kg intraperitoneally) antagonized both the circling and increase in locomotor activity induced by quinine (0.1 mg/kg intra peritoneally) and D-amphetamine (4 mg/kg intraperitoneally) respectively. These results indi cate that quinine exhibits both excitatory and inhibitory effects on the gross behaviour of mice; these biphasic effects were dose-related. Since pimozide, L-sulpiride and SCH 23390 influenced both effects, both D( 1) and D(2) receptors may be involved in the behavioural effects of quinine.

Concurrent monitoring of central carbamazepine and transmitter amine metabolism and motor activity in individual unrestrained rats using repetitive withdrawal of cerebrospinal fluid.

A method for repeated withdrawal of cerebrospinal fluid (CSF) from the cisterna magna was used in a pharmacokinetic and behavioural study of conscious, freely-moving rats, given the antiepileptic drug carbamazepine (35 mg/kg i.p.). Pharmacokinetic constants (i.e. time to peak concentration, peak concentration, area under the curve and t 1/2) for the drug and its primary metabolite carbamazepine-10,11-epoxide and also concentrations of acidic metabolites of 5-hydroxytryptamine and dopamine were obtained for the CSF of individual rats. A pharmacodynamic constant, the effective concentration of drug in CSF for 50% inhibition of motor activity was also determined for each animal. The above data provides good indices of the corresponding values for carbamazepine and its metabolite in brain insofar as a separate experiment showed good correlations between CSF and brain for concentrations of both the drug and its metabolite. Carbamazepine appeared to be largely responsible for the depression of motor activity as the metabolite, at the levels attained, seemed to have little effect. The changes in motor activity were not associated with altered concentrations of the metabolites of 5-hydroxytryptamine or dopamine in the CSF. While the investigation did not reveal major advantages in monitoring the drug under study in CSF rather than in serum it illustrates the potential of the CSF method as a simple way to obtain neuropharmacokinetic and neuropharmacodynamic profiles of the action of drugs in individual rats.

Preliminary phytochemical, pharmacological and antibacterial studies of the alkaloidal extracts of the leaves of Synclisia scabrida Miers.

Preliminary phytochemical investigation of the leaves of Synclisia scabrida indicated the presence of two alkaloids in the water extracts and five alkaloids in the ethanol extracts. The alkaloidal fraction obtained from the cold ethanol extract furnished on column-chromatography, a homogeneous amorphous solid which has been designated as alkaloid C. Alkaloid C showed positive test for alkaloids. The UV and IR spectra and colour reactions of alkaloid C indicated that the compound may be a phenolic bisbenzylisoquinoline alkaloid. All the extracts delayed the onset and shortened the duration of apomorphine-induced stereotyped behaviour in chicks. In addition, 40 mg kg-1 i.p. of the ethanolic extract induced catalepsy in rats. The cold water extract (CWE) synchronized the EEG of the hyperstriatum, optic tectum and the reticular formation while the EMG activity was slightly enhanced. The hot ethanol alkaloidal extract (HEE) inhibited the growth of Pseudomonas aeruginosa and Staphylococcus aureus. The minimum inhibitory concentration of HEE on Pseudomonas aeruginosa strains I and II were 5 and 2.5 micrograms/ml while for Staphylococcus aureus strains I and II were 5 and 10 micrograms/ml, respectively. Up to 1 g kg-1 i.p. of the extract failed to induce any lethal effect in chicks and rats. These effects of the leaf extracts of Synclisia scabrida Miers support some of the local uses of the plant by traditional medical practitioners.

Some behavioural and EEG effects of ascorbic acid in rats.

Ascorbic acid (50-200 mg/kg IP) activated gross behaviour and EEG of rats. The behavioural excitation induced by d-amphetamine (2.5 mg/kg SC) was significantly potentiated by ascorbic acid (100-200 mg/kg IP). Catalepsy induced by haloperidol (0.25 mg/kg IP) was attenuated by ascorbic acid (50-200 mg/kg IP) while pentobarbitone (20 mg/kg IP)-induced sleep in rats was dose-dependently antagonised by ascorbic acid (50-400 mg/kg IP). Ascorbic acid (50-400 mg/kg IP) desynchronized the EEG of the frontal cortex and optic cortex while the EMG activity was slightly enhanced in the rat. Ascorbic acid (100 mg/kg IP) potentiated d-amphetamine (2.5 mg/kg SC)-induced EEG desynchronization and EMG activation in the rat. These results indicate that ascorbic acid exerts stimulatory effects in rats. The results also suggest that dopaminergic mechanism may contribute indirectly or directly to the observed behavioural and EEG effects of ascorbic acid.

Influence of acute and chronic administration of ethanol on photic-evoked response in rats.

The effect of acute and chronic administration of ethanol on photic-evoked response was studied in rats. Acute administration of ethanol (1-3 g/kg, i.p.) produced behavioural depression, EEG synchronization and a biphasic effect on the amplitude of the photic evoked responses (PER) recorded from the frontal cortex (FC) and optic cortex (OC), while a reduction in amplitude was observed in the midbrain reticular formation (MBRF). The amplitude of the averaged PER in the FC and OC was increased in chronic ethanol-treated rats, while in the MBRF, a reduction in amplitude was observed. Abrupt discontinuation of ethanol produced behavioural excitation and increase in amplitude of the averaged evoked responses recorded from the three brain areas studied. These observations suggest that the neural hyperexcitability that characterizes ethanol withdrawal may affect both cortical and subcortical structures.

Behavioural effects of beta,beta'-iminodipropionitrile (IDPN) in the domestic fowl (Gallus domesticus).

The behavioural effects of beta,beta'-iminodipropionitrile (IDPN) were studied in chicks and adult fowls. Repeated administration of IDPN (75 mg/kg) for 5 days induced behavioural changes in chicks and adult fowls characterized by excitation, choreiform head and neck movements and circling (ECC-syndrome). Both acute and chronic administration of IDPN induced EEG desynchronization, EMG activation and enhancement of photic-evoked response (PER) in the hyperstriatum and pontine reticular formation while a decrease in PER was observed in the optic tectum. d-Amphetamine (2.5-5 mg/kg), apomorphine (0.1-0.25 mg/kg), piribedil (2.5-5 mg/kg), atropine (2.5-5 mg/kg), hyoscine (2.5-5 mg/kg) and cyproheptadine (0.5 mg/kg) potentiated the circling and choreiform head and neck movements. These activities were antagonized by pimozide (1 mg/kg), physostigmine (0.5 mg/kg) and quipazine (2.5-5 mg/kg). The results suggest that dopaminergic, serotoninergic and cholinergic mechanisms may be involved in IDPN-induced behavioural effects in chicks.