Galenical source none pure synthetic drug class

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Galenical Source None (Pure Synthetic) Drug Class Benzodiazepine (chemical class). Anxiolytic (use). Related Drugs Other benzodiazepines: chlordiazepoxide, oxazepam, lorazepam, triazolam. Note: except for the first (chlordiazepoxide), all the names end in “pam” or “am”. Actions Binds to GABA-A related chloride channel and enhances GABA-mediated chloride flux. (Enhances GABA-mediated inhibition in the brain.) pKa 3.3 It’s a base, with a lower pKa than ASA. Mean Vd 1.1 L/kg. This works out to be 77 liters in a 70 K male (typical subject) - more than the actual size of the body. Factors: high protein binding is more than compensated for by entry into fat stores. Plasma Protein Binding 98-99% Oral Bioavailability 100% (Low extraction drug with no first pass effect.) Note: i.m. bioavailability is poor.
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Half-Life 40 hours (some books say less, but it’s definitely long). It also has two active metabolites with long half lives. Therapeutic effect can be very long due to active metabolites, which is good for chronic anxiety, but not for use as a sleeping pill. (Note: diazepam’s active metabolites are sold as “drugs” in some countries.) Prolonged in the elderly and in patients with liver disease. Absorption Rapid (30-60 minutes), probably because it has a high Po/w. Distribution The drug probably goes into the whole body water. It crosses the BBB. Fat is a significant reservoir. Elimination Undergoes phase 1 biotransformation, which produces active metabolites. Eventually, a metabolite is conjugated (phase 2) and usually becomes a glucuronide or sulfate, which is eliminated in the urine. Biotransformation may be slow in the elderly, neonates and patients with hepatic disease. ADR’s Major problems are drowsiness, ataxia, confusion. High doses may cause memory loss. There can be paradoxical irritability and hostility (and even increased anxiety). There is functional tolerance that can results in an abstinence (“withdrawal”) syndrome (anxiety, insomnia) and even withdrawal seizures (more likely in congeners with shorter half-lives). Interactions Major problem is supra-additive pharmacodynamic interaction with other CNS depressants (e.g., ethanol). Digoxin (= “non-proprietary name” = “official name”) Galenical Source Foxglove. Brand Names (= “proprietary names”): Lanoxin, Novodigoxin. Drug Class Cardiac glycoside. Related Drugs Digitoxin Actions Complex. Affects cardiac Na+ / K+ ATPase. Improves cardiac function. pKa None. It’s not an acid or a base. Mean Vd 5.3 L/kg. Largest Vd of your example drugs. Reasons? It distributes into muscle.
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Plasma Protein Binding 30%. Oral Bioavailability 75%. (Better in solution.) Poor i.m bioavailability. Half-Life 20-50 hours. Why so long? Muscle reservoir? Strongly dependent on renal function. Absorption Varies from 40-90% depending on dosage form. (Remember solution – 90-100%.) Peak plasma concentrations in 2-3 hours (slower than diazepam).
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