Immunization of rats reduces nicotine distribution to brain.

The effect of active immunization against nicotine on the initial distribution of nicotine to brain was studied in anesthetized rats. Animals received nicotine 0.03 mg/kg nicotine (equivalent to the nicotine dose absorbed by a human smoking two cigarettes) as a rapid injection in the jugular vein. In control animals, the arterial serum nicotine concentration initially exceeded the venous concentration 4.6-fold, similar to the initial arteriovenous difference produced by cigarette smoking in humans. Animals immunized with the nicotine analog CMUNic maintained this arteriovenous gradient, but with both arterial and venous nicotine concentrations several times higher than in controls. The arterial nicotine concentration was higher in immunized animals even at the first (7.5 s) sampling time. The brain nicotine concentration at 3 min was 36% lower in the immunized animals. The time course of nicotine distribution to brain was studied in a second group of animals. Brain nicotine concentration was reduced in rats immunized with CMUNic over the entire 6-min sampling period immediately following nicotine dosing (mean reduction 38%). A reduction was found at the earliest sampling time (30 s) and was maximal at 1 min (48%). Nicotine protein binding in serum was markedly increased in animals immunized with CMUNic compared to controls (91.2 versus 10.9%), and the unbound nicotine concentration in serum was lower (10.0 versus 13.4 ng/ml). The reduction in brain nicotine concentration correlated with antibody affinity for nicotine, and the percentage of nicotine bound in serum. These data demonstrate that nicotine-specific antibodies produced by active immunization rapidly bind nicotine in arterial blood, reduce the unbound nicotine concentration, and reduce the early distribution of nicotine to brain. Effects were observed using a clinically relevant nicotine dose and route of administration. These data suggest that the use of immunization to modify the behavioral effects of nicotine may be possible.

Monitoring blood levels of selected drugs. Remember to factor in the many confounding variables.

Appropriate use of various pharmacologic agents involves not only awareness of therapeutic indications and side effects but also familiarity with clinical use and timing of blood level monitoring. The effective as well as the toxic level of antiepileptic drugs varies widely among patients, so the patient's response is more important than the serum drug level. These agents may interact with other disease states, other drugs, and even other antiepileptic agents. Because of digoxin's long half-life and the effect of physical exercise on serum concentration, the timing of serum collection is important. The usefulness of measuring amiodarone serum concentrations is controversial, but findings may help identify patients at risk for side effects related to the drug. Procainamide has a very short half-life and concentrations change over a short period, so blood levels of this agent should be measured before administration of a dose. The dose of levothyroxine required to restore a normal thyroid hormone level varies with age, coexistent conditions, and use of other medications. After the appropriate dose is determined, follow-up monitoring yearly is necessary (more often in the elderly). Efficacy and toxicity of theophylline are directly related to serum concentrations, and a reduced target level of 5 to 15 micrograms/mL has recently been suggested. Proper monitoring is important, because metabolic changes and drug interactions can cause either subtherapeutic or toxic levels.

Copperhead envenomations: clinical profiles of three different subspecies.

Copperhead envenomation cases reported in the literature frequently lack identification of the subspecies of copperhead responsible for the envenomation. Whether subspecific identity would be useful in predicting possible different toxicity profiles may have clinical relevance. We report here the clinical profiles from envenomations involving 3 different subspecies of captive adult copperhead snakes--the southern copperhead (Agkistrodon contortrix contortrix), the northern copperhead (Agkistrodon contortrix mokasen), and the broad-banded copperhead (Agkistrodon contortrix laticinctus). The bites occurred in the north-central region of the US where none of these subspecies are endemic and involved a professional and 2 amateur herpetologists. The victims were adult males with no previous history of venomous snake bite, and all bites were evidenced by fang puncture marks to their index finger or thumb. Envenomations from the broad-banded and northern copperhead subspecies caused localized symptoms of pain, edema and ecchymosis. In addition to these symptoms, southern copperhead envenomation resulted in a more severe clinical toxicity profile as evidenced by propulsive emesis, diarrhea and hematuria. Whether these differences in observed clinical toxicity were the result of unique subspecific venom pharmacological actions is an interesting question. However, independent of the copperhead subspecies involved, conservative medical management was effective in each case.

Active immunization alters the plasma nicotine concentration in rats.

The ability of active immunization to alter nicotine distribution was studied in rats. Animals were immunized with 6-(carboxymethylureido)-(+/-)-nicotine (CMUNic) linked to keyhole limpet hemocyanin (KLH). Antibody titers determined by ELISA, using CMUNic coupled to albumin as the coating antigen, were greater than 1:10,000. Antibody binding was inhibited by neither of the nicotine metabolites cotinine and nicotine-N-oxide but was inhibited to a greater extent by CMUNic than by nicotine; this suggests the presence of antibodies to the linker structure as well as antibodies to nicotine. Antibody affinity for nicotine measured by soluble radioimmunoassay was 2.4 +/- 1.6 x 10(7) M-1, and binding capacity was 1.3 +/- 0.7 x 10(-6) M, which corresponds to 0.1 +/- 0.05 mg/ml of nicotine-specific IgG per milliliter of serum. One week after their second boost, groups of eight anesthetized rats immunized with either CMUNic-KLH or KLH alone received nicotine 0.03 mg/kg (equivalent to two cigarettes in a human) via the jugular vein over 10 sec. This dosing regimen was shown to mimic the arterio-venous nicotine concentration gradient typical of nicotine delivered by cigarette smoking in humans. Plasma nicotine concentrations at 10 to 40 min were 4 to 6-fold higher in the CMUNic-KLH rats than in controls (P < .001). Nicotine binding in plasma determined by equilibrium dialysis was markedly increased in the CMUNic-KLH group (83.4 +/- 6.8% vs. 16.4 +/- 14.2%), but brain nicotine concentrations at 40 min did not differ (37.9 +/- 4.5 vs. 44.0 +/- 8. 4 ng/g, CMUNic-KLH vs. KLH, P = .1). The amount of nicotine bound to antibody in plasma, estimated from the in vivo data, was 9% of the administered dose. These data demonstrate that active immunization can bind a significant fraction of a clinically relevant nicotine dose in plasma. Observing this effect with antibodies of modest affinity and titer is encouraging, but better immunogens may be needed to alter nicotine distribution to brain and modify nicotine's behavioral effects.