Open-Label, Dose-Escalation, Phase 1 Study of Safety and Single and Multiple-Dose Pharmacokinetics of Dichlorphenamide in Healthy Volunteers

Single‐and multiple‐dose pharmacokinetics and safety were investigated in this phase 1 study of dichlorphenamide, a carbonic anhydrase inhibitor approved in the United States for treatment of primary periodic paralysis. Dichlorphenamide was administered to 6 cohorts (n = 6 each) of healthy adults. Cohorts A through E received single doses of 25–400 mg followed by 50–800 mg/day in divided doses for 10 total doses. Cohort F (safety analysis only) received up to 28 titrated doses from 100–800 mg/day. Plasma for pharmacokinetics sampling was obtained predose and up to 48 hours postdose. Twenty‐five of 36 enrolled subjects completed. Median time to maximum plasma concentration ranged from 1.5–3 hours, and mean half‐life from 32–68 hours. Mean area under the concentration‐time curve from time 0 to tau (length of the dosing interval estimated using the trapezoidal method) and maximum observed plasma concentration increased dose‐proportionally after multiple doses. The incidence and severity of adverse events (AEs) were dose‐related, with at least one mild AE reported among 17%, 17%, and 67% of patients in cohorts A, B, and C, respectively; and at least one mild‐to‐moderate AE among 100% of subjects in cohorts D, E, and F. One serious AE of rash was reported in cohort F. Eleven subjects discontinued; 10 due to AEs at 400 or 800 mg/day (cohorts E and F), including 100% of cohort F. Hypokalemia contributed to 5 of 6 discontinuations in cohort F (all 800 mg/day).

Review of the Diagnosis and Treatment of Periodic Paralysis

Periodic paralyses (PPs) are rare neuromuscular disorders caused by mutations in skeletal muscle sodium, calcium, and potassium channel genes. PPs include hypokalemic paralysis, hyperkalemic paralysis, and Andersen‐Tawil syndrome. Common features of PP include autosomal dominant inheritance, onset typically in the first or second decades, episodic attacks of flaccid weakness, which are often triggered by diet or rest after exercise. Diagnosis is based on the characteristic clinic presentation then confirmed by genetic testing. In the absence of an identified genetic mutation, documented low or high potassium levels during attacks or a decrement on long exercise testing support diagnosis. The treatment approach should include both management of acute attacks and prevention of attacks. Treatments include behavioral interventions directed at avoidance of triggers, modification of potassium levels, diuretics, and carbonic anhydrase inhibitors. Muscle Nerve57: 522–530, 2018

Toxicity and Physiological Actions of Carbonic Anhydrase Inhibitors to Aedes aegypti and Drosophila melanogaster

The physiological role of carbonic anhydrases in pH and ion regulation is crucial to insect survival. We examined the toxic and neurophysiological effects of five carbonic anhydrase inhibitors (CAIs) against Aedes aegypti. The 24 h larvicidal toxicities followed this rank order of potency: dichlorphenamide > methazolamide > acetazolamide = brinzolamide = dorzolamide. Larvicidal activity increased modestly in longer exposures, and affected larvae showed attenuated responses to probing without overt tremors, hyperexcitation, or convulsions. Acetazolamide and dichlorphenamide were toxic to adults when applied topically, but were of low potency and had an incomplete effect (<50% at 300 ng/mosquito) even after injection. Dichlorphenamide was also the most toxic compound when fed to adult mosquitoes, and they displayed loss of posture and occasionally prolonged fluttering of the wings. Co-exposure with 500 ng of the synergist piperonyl butoxide (PBO) increased the toxicity of dichlorphenamide ca. two-fold in feeding assays, indicating that low toxicity was not related to oxidative metabolism. Dichlorphenamide showed mild depolarizing and nerve discharge actions on insect neuromuscular and central nervous systems, respectively. These effects were increased in low buffer salines, indicating they were apparently related to loss of pH control in these tissues. Overall, sulfonamides displayed weak insecticidal properties on Aedes aegypti and are weak lead compounds.